Skull

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Introduction[edit | edit source]

The skull (also known as cranium) consists of 22 bones which can be subdivided into 8 cranial bones and 14 facial bones.

The main function of the bones of the skull along with the surrounded meninges, is to provide protection and structure.[1] Protection to the brain (cerebellum, cerebrum, brainstem) and orbits of the eyes. Structurally it provides an anchor for tendinous and muscular attachments of the muscles of the scalp and face. The skull also protects various nerves and vessels that feed and innervate the brain, facial muscles, and skin.

Human skull side.png.png

Cranial Bones Sutures Facial Bones
  • Fontal Bone
  • Parietal Bone (2)
  • Temporal Bone (2)
  • Occipital Bone
  • Sphenoid Bone
  • Ethmoid Bone [1]
 Strong, fibrous, elastic bands of tissues that binds/connect the cranial bones together.
  • Coronal Suture: Junction between the frontal and two parietal bones. The coronal suture lies in the coronal plane.
  • Sagittal Suture: Junction between two parietal bones. The sagittal suture lies in the sagittal plane.
  • Squamous Suture: Junction between the temporal and parietal bones.
  • Lambdoid Suture: Junction between the parietal bones and the occipital bones.
  • Pterion: Junction of the frontal, parietal and temporal bones in the lateral aspect of the skull.
  • Nasal Conchae (2)
  • Nasal Bones (2)
  • Maxilla Bones (2)
  • Palatine Bones (2)
  • Lacrimal Bones (2)
  • Zygomatic Bones (2)
  • Mandible
  • Vomer [2]

Blood Supply[edit | edit source]

The skull and its contents are mainly supplied with oxygenated blood from the common carotid artery. The remainder of blood supply comes from the vertebral artery.

Nerve Supply[edit | edit source]

The base of skull has numerous foramina that allow the entry lot of vessels and nerves, including the cranial nerves.

  • The Optic Nerve and Ophthalmic Artery passes through the Optic Nerve Canal.
  • Superior orbital fissure transmits the Oculomotor Nerve, Trochlear Nerve, Ophthalmic branch of the Trigeminal Nerve and the Abducens Nerve.
  • Internal Carotid Artery enters through the Carotid Canal.
  • The Mandibular Branch of the Trigeminal Nerve exits the skull through the Foramen Rotunda.
  • The Middle Meningeal Artery passes through the Foramina Spinosum.
  • Foramina Magnum: allows the Spinal Cord through the base of skull into the Spinal Canal of the Vertebral Column.[2]

Resources[edit | edit source]

[3]
[4]

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Equine Spine and Head Anatomy - Physiopedia Introduction Equine anatomy refers to the gross and microscopic anatomy of horses and other equids (donkeys, and zebras). This page introduces the Anatomy of Equine Spine and Head. Axial Skeleton[edit | edit source] The axial skeleton consists of the skull, vertebral column, sternum, and ribs. Multiple sternebrae fuse to form one bone, attached to the 8 "true" pairs of ribs, out of a total of 18.[1] The vertebral column contains 54 bones: 7 cervical vertebrae: includes the atlas (C1) and axis (C2) 18-19 thoracic vertebrae 5-6 lumbar vertebrae 5 sacral vertebrae 15-25 caudal vertebrae[2] In certain breeds, there may be variations in these numbers.[3] Skull[edit | edit source] The skull contains the brain and the most important organs of sense. Cranium[edit | edit source] The Roof of the cranium is made up of frontal and parietal bones. The Floor is made up of sphenoid bone. The cranium consists of 5 orbital regions: Frontal Lacrimal Palatine Sphenoid Zygomatic Interparietal bone: only found in horse and cat. The orbit is complete in horse and ruminants while it is incomplete in carnivores but completed by the orbital ligament. The lacrimal fossa collects tears and sends them through lacrimal canal into the nasal cavity. Bones in the Equine Skull[edit | edit source] There are 34 bones and most of them are flat. During the birth process, these bones overlap and allow the skull to compress as much as possible to allow for parturition. The 14 major bones are:[1] Incisive bone (premaxillary): part of the upper jaw; where the incisors attach Nasal bone: covers the nasal cavity Maxillary bone: a large bone that contains the roots of the molars Mandible: lower portion of the jaw; largest bone in the skull Lacrimal bone: contains the nasolacrimal duct, which carries fluid from the surface of the eye, to the nose Frontal bone: creates the forehead of the horse Parietal bone: extends from the forehead to the back of the skull Occipital bone: forms the joint between the skull and the first vertebrae of the neck (the atlas) Temporal bone: contains the eternal acoustic meatus, which transmits sound from the ear to the cochlea (eardrum) Zygomatic bone: attaches to the temporal bone to form the zygomatic arch (cheekbone) Palatine bone: forms the back of the hard palate Sphenoid: formed by fusion of the foetal basisphenoid and presphenoid bones, at the base of the skull. Can become fractured in horses that rear over backwards Vomer: forms the top of the inside of the nasal cavity Pterygoid: small bone attached to the sphenoid that extends downward Cavities[edit | edit source] The equine skull consists of 4 cavities: The cranial cavity: Protects and encloses the brain, supports sense organs. The cranium consists of a roof made up of the frontal and parietal bones and a floor made up of the sphenoid bone The orbital cavity: Has 5 orbits: frontal, lacrimal, palatine, sphenoid and zygomatic. It protects and surrounds the eye.[4] Horses have both monocular and binocular vision: Monocular vision: The horse can see objects with one eye. This means that the brain receives two images simultaneously Binocular vision: The horse can focus with both eyes just like humans and the brain receives only one signal The oral cavity: A passage into the respiratory and digestive system The nasal cavity: Contains bone that protects the mucous membrane from inspired warm air Foramina of the Skull and the Structures Passing Through[edit | edit source] Foramina Structures passing through Infra-orbital foramen Infra-orbital nerve. CNV Maxillary foramen Cribriform foramen Olfactory nerve. CNI Optic canal Optic nerve. CNII Orbital fissure CNVII, IV, V and VI (ophthalmic division) Round foramen CNV (maxillary division) Oval foramen CNV (mandibular division) Foramen lacerum Internal carotid artery CN V3 (horse and pig) Internal acoustic meatus CNVIII Jugular foramen CNIX, X, XI Stylomastoid foramen CNVII Mandibular foramen CNV (mandibular alveolar nerve) Mental foramen Joints and Ligaments[edit | edit source] Joints and Ligaments of the Skull[edit | edit source] The temporo-mandibular joint - a condylar joint between the mandibular condyles and the mandibular fossae of the temporal bones. It has a loose joint capsule with thickenings that form a lateral ligament, as well as an articular disc[1] Mandibular symphysis Hyoid apparatus - consists of three joints: Tympanohyoid cartilage- skull (syndesmosis) Interhyoid joints (synovial) Thyrohyoid bone- cranial cornu of thyroid cartilage (synovial)[1] [5] Cervical Spine[edit | edit source] Joints[edit | edit source] Atlanto-Occipital Joint[edit | edit source] A condylar, modified synovial hinge joint. The articulating surfaces are the occipital condyles and the cranial articular surfaces of the atlas (C1). There are three thickenings that strengthen the spacious joint capsule: Dorsal, Ventral, Lateral. The transverse atlantal ligament holds the dens of the axis against the ventral arch of the atlas.[1] Atlanto-Axial Joint[edit | edit source] A pivot joint between the atlas and the saddle shaped surface of the axis (C2), which extends upon the dens. It has a loose joint capsule. The apical ligament of dens connects the apex of the dens to the occipital bone. Motion at this joint includes rotation of the atlas and head upon the axis and some accessory lateral flexion.[1] Rotation at this joint makes up 73 percent of cervical rotation.[6] Cervical Spine C3-C4[edit | edit source] A planar, extensive, oval shaped joint that is obliquely oriented in transverse plane. The cranial articular processes face dorsomedially and the caudal articular processes face ventrolaterally. Spinous process height increases caudally from C6. Lateral flexion is the primary motion at these joints (25-45 degrees each joint - C1/C2 only has 3.9 degrees of lateral flexion).[6] Ligaments[edit | edit source] Dorsal longitudinal ligament Ventral longitudinal ligament Ligamentum flavum Nuchal ligament: This ligament connects the thoracic vertebra to the head and assists in supporting its weight. It consists of two paired parts:[1] Funicular (cord) part - extends from the poll to +/- the second to the fourth thoracic spinous process Lamellar part - arises from the second and third thoracic spinous processes and the funicular part, and inserts on the C2-C6 spinous processes. The first digitation going to the axis is very strong, but it decreases in strength caudally Thoracic Spine (T1-T18)[edit | edit source] Articular processes[edit | edit source] Caudal articular processes face ventrally and are positioned at the base of the spinous process. The cranial articular processes are oval facets on the arch of the vertebra and face dorsally. Each thoracic vertebrae has a pair of costal facets on the dorsal body (except the last) forming the costal fovea.[1] Anticlinal vertebrae: This is the point in the caudal thoracic vertebral column at which the anatomic features of the vertebra start to change.[7] This usually occurs at the 13th vertebra in horses. Motion: Flexion - most flexion occurs at T17/T18; least flexion occurs at T3-T9 Extension - most extension occurs at T14-T18; least extension occurs at T2-9[1] Rib Neck[edit | edit source] Has 2 converse facets: Cranial and Caudal Rib 1 attaches to C7, T1 and the associated IV disc Motion: rotation of the rib, which is greater caudally Costovertebral Joint[edit | edit source] Joints[edit | edit source] The costovertebral joints have two distinct articulations between most ribs and the vertebral column:[1] Head of the rib: Cranial and caudal costal facets of adjacent vertebrae; a ball and socket synovial joint Tubercle of the rib: Transverse process of vertebrae; a plane synovial joint Ligaments[edit | edit source] Radiate longitudinal ligament Intercapital ligament Costotransverse ligament Ligament of the neck Lumbar Spine[edit | edit source] Joints[edit | edit source] Horses usually have 6 lumbar vertebrae (L1-L6), but some arabian horses only have 5 (L1-L5).[1] Articular processes[edit | edit source] Cranial articular processes are fused with mammillary processes. They are concave dorsally and mostly in sagittal alignment. Caudal processes are convex ventrally and correspond with the convexity of the cranial articular processes. They are differentiated from the last thoracic vertebra by the lack of costal facets.[1] Motion: The lumbar spine and caudal thoracic spine are the least mobile regions of a horse's back.[8] Lateral flexion and rotation is very limited especially at L4-L6 due to intertransverse joints.[1] Ligaments of Thoraco-Lumbar Spine[edit | edit source] Supraspinous ligament: A heavy band of connective tissue running over the top of spinous processes ( T2/T3 caudally). It prevents abnormal separation of spinous processes during flexion Ventral longitudinal ligament: Marks the ventral surface of vertebrae from the axis to the sacrum. It is strongest and widest caudally. It plays a major role in preventing overextension of the spine Dorsal longitudinal ligament: Extends from the floor of the vertebral canal from the axis to sacrum and helps to prevent spine hyper-flexion Annulus fibrosis of IVD: Thick ventrally Intertransverse ligament Interarcuate ligament/ yellow ligament/ ligamentum flavum: An elastic ligament that fills the dorsal space between the arch of the adjacent vertebra[1] Lumbosacral Joint[edit | edit source] The cranial articular process of the first sacral vertebra are concave and face dorsomedially. Motion: Flexion and Extension - 23.4 degrees[9] Sacrum[edit | edit source] The sacrum consists of fused sacral vertebrae and has dorsal and ventral sacral foramina. [10] Myology and Neurology[edit | edit source] Muscles of the Head[edit | edit source] Muscles of the Face[edit | edit source] The muscles of facial expressions are innervated by the motor fibers of CNVII (facial nerve).[1] Muscle Origin Insertion Action M. Levator labii maxillaris Lacrimal, Zygomatic and Maxillary bones The maxillary lip Elevates the Maxillary lip M. Levator nasolabialis Nasal and Frontal bones The lateral wing of nostril The maxillary lip Elevates and retracts the angle of the mouth M. Zygomaticus The fascia covering the Masseter The commissure of the lips M. Buccinator Maxilla and Mandible Flattens the cheeks and thus presses food between the teeth M. Depressor labii mandibulars The alveolar border of the Mandible The mandibular lip Depresses and retracts the mandibular lip M. Orbicularis oris The sphincter muscle of the skin and the muscles of the lips Corner of the mouth Into the lips as it surrounds the mouth Closes the mouth M. Risorius Part of M. cutaneous faciei The angle of the mouth Retracts the angle of the mouth M. Dilator naris Alar cartillage Alar cartillage Dilates the nostril M. Lateralis nasi Dorsal part Nasal bone Parietal cartilage Dilates the nostril and nasal vestibule Ventral part Nasal process of Incisive bone Lateral wall of the Nasal vestibule M. Caninus Maxilla close to the rostral extremity of the facial crest Lateral wing of the nostril Dilates the nostril laterally M. Levator nasolabialis Frontal and Nasal bones Lateral wing of the nostril Elevates the maxillary lip and the commissure of the mouth Dilates the nostril Ear[edit | edit source] The ear is an organ of hearing and balance. It consists of the outer, middle, and inner ear. Outer Ear[edit | edit source] The outer ear includes:[1] Pinna: mobile and can move independently - can hear multiple sounds at the same time[11] Ear canal Cartilage: Cartilages of the ear collect and transmit sound to the essential organ of hearing within the temporal bone. In order to achieve this, they (especially the concha) need to move.[1] The muscles of outer ear:[1] Rostral Dorsal Caudal Ventral There are 3 cartilages:[1] Conchal: Forms the framework of the portion of the ear which stands erect. It has a large vertical opening on one side to receive sound, and is attached below to the annular cartilage Annular: A small ring of gristle connected to the auditory process of the petrous temporal bone Scutiform: A small, flat and somewhat triangular cartilaginous plate situated in front of the base of concha, to which it is attached Middle Ear[edit | edit source] The middle ear includes:[1] Eardrum Small, air-filled chamber containing 3 tiny bones: the hammer, anvil, and stirrup. It also includes 2 muscles: the oval window, and the eustachian tube. Inner Ear[edit | edit source] The inner ear is a complex structure that includes the cochlea and the vestibular system.[11] Muscles of Mastication[edit | edit source] The muscles of mastication are innervated by the mandibular branch of trigeminal nerve CNV.[1] Muscle Origin Insertion Action M. Masseter The zygomatic arch and the facial crest The lateral border of the ramus of the mandible Closes the mouth M. Temporalis The temporal fossa and the temporal crest The coronoid process of the mandible Closes the mouth (to raise the mandible) M. Pterygoideus medialis The crest formed by the pterygoid processes of the basisphenoid and the palatine bones The medial surface of the ramus of the mandible M. Pterygoideus lateralis The pterygoid process of the sphenoid bone Rostral border of the condyle of the mandible Draws and moves the mandible rostrally M. Digastricus The jugular process of occipital bone Medial surface of the ventral border of the molar part of the body of the mandible Opens the mouth M. Occipitomandibularis The jugular process The caudal border of the ramus of the mandible Muscles of the Eyes[edit | edit source] M. Orbicularis oculi - innervated by palpebral branch of CN VII M. Levator palpebrae superioris - originates from the posterior orbit and inserts at orbicularis oculi fibers of the lower eyelid. It elevates the upper eyelid and is innervated by CN III (oculomotor nerve) M. Malaris - lowers the ventral eyelid. It is innervated by CN VII (facial nerve) Muller's muscle - innervated by sympathetic nerves Ciliary muscles M. Retractor anguli - retracts and anchors the lateral canthus M. Levator anguli oculi medialis and M. Frontalis - slightly elevates of the upper eyelid[12][13] Muscles of the Tongue[edit | edit source] The equine tongue is made up of twelve different muscles[14] including styloglossus, genioglossus and hyoglossus. These muscles are covered by mucosa on the sides and underneath.[1] Action: prehension, mastication (i.e. chewing) Innervation: Hypoglossus (CNXII) Muscles of Pharynx and Soft palate.[edit | edit source] [15][16] Muscle Origin Insertion Action Innervation INTRINSIC MUSCLES M. Tensor veli palatini Muscular process of the petrous part of the temporal bone, pterygoid bone, and lateral lamina of the auditory tube Palatine aponeurosis Retracts the soft palate away from the dorsal pharyngeal wall, expanding the nasopharynx and slightly depressing it ventrad during inspiration Mandibular branch of the trigeminal nerve M. Levator veli palatini Muscular process of the petrous part of the temporal bone and the lateral lamina of the Auditory tube and passes along the lateral wall of the nasopharynx Soft palate dorsal to the glandular layer Elevates the soft palate during swallowing Pharyngeal branch of the Vagus nerve M. Palatinus Caudal aspect of the palatine aponeurosis Caudal free margin of the soft palate Shortens the soft palate and depresses it towards the tongue M. Palatopharyngeus Palatine aponeurosis and from the palatine and pterygoid bones Upper edge of the thyroid cartilage M. Stylopharyngeus Rostral Medial surface of the rostral end of the Stylohyoid bone Pharyngeal raphe Pharyngeal constrictor Glossopharyngeal nerve Caudal Medial aspect of the caudal third of the Stylohyoid bone Dorsolateral wall of the pharynx Pharyngeal dilator EXTRINSIC MUSCLES M. Genioglossus Median plane of the Tongue Oral surface of the Mandible Protracts the tongue Hypoglossal nerve M. Geniohyoideus Medial surface of the Mandible Basihyoid bone Protrudes the tongue M. Thyrohyoideus Lateral lamina of the Thyroid cartilage Caudal aspect of the thyrohyoid bone Moves the larynx rostrad M. Hyoglossus Hyoid bones Median plane of the dorsum of the tongue Retracts and depresses the base of the tongue M. Hyoepiglotticus M. Styloglossus Lateral aspect of the stylohyoid bone Tip of the tongue Retraction of the tongue M. Sternohyoideus Sternal manubrium Basihyoid bone and lingual process of the hyoid apparatus Caudal traction Branches of the first and second cervical nerves M. Sternothyroideus Caudolateral aspect of the thyroid cartilage Muscles of the Hyoid Apparatus and Larynx[edit | edit source] Muscles of the hyoid apparatus and larynx are innervated by CNX. Hyoid Apparatus[edit | edit source] The hyoid apparatus has muscular connections from the throat to the forelimbs, shoulder, and sternum. Sternohyoid and omohyoid provide a direct connection from the hyoid apparatus to the shoulder of the horse via the ventral neck. The tongue connects to the hyoid apparatus. Small muscles of the hyoid apparatus connect to the TMJ and the poll and the TMJ articulates with the hyoid apparatus.[17][18] Larynx[edit | edit source] Intrinsic muscles: Cricoarytenoideus dorsalis - abduction of arytenoids and tensing of vocal cords Thyroarytenoideus - adduction of arytenoids Arytenoideus transversus - adduction of arytenoids Cricoarytenoideus lateralis - adduction of arytenoids[19] Muscles of Cervical spine[edit | edit source] [20][21] Muscle Origin Insertion Action Innervation M. Omotransversarius Fascia of shoulder Scapular cartilage and transverse processes of C2-4 Advances limb Adducts limb Moves neck laterally Ventral branch of local cervical spinal nerve M. Brachiocephalicus Mastoid process of temporal bone and first cervical vertebra Deltoid tuberosity and crest of the humerus Shoulder extension Protraction Flexion of the neck towards the side of the protracting limb Accessory nerve M. Cleidobrachialis Inscription of clavicle Crest of the humerus Advances limb Adducts limb Axillary nerve M. Cleidomastoideus Clavicular intersection Mastoid process of temporal bone Advances limb Flexes neck Turns head Ventral branch of Accessory nerve (cranial nerve XI) M. Sternocephalicus (Sternomandibularis) Manubrium of the sternum Caudal border of mandible Turns head Opens mouth M. Omohyoideus Subscapular fascia Lingual process of basihyoid bone Retracts basihyoid bone and tongue Spinal nerve C1 M. Trapezius Nuchal ligament and Supraspinous ligaments of C2-10 Cervical part: Entire scapular spine Advances thoracic limb Abducts thoracic limb Elevates shoulder Dorsal branch of Accessory nerve (cranial nerve XI) Thoracic part: Dorsal third of Scapular spine M. Rhomboideus (cervicis and thoracis) Nuchal ligament and dorsoscapular ligaments of C2-T8 Scapular cartilage Elevates neck Draws scapula cranially and dorsally Local thoracic nerve and Local cervical nerve M. Serratus ventralis (cervicis) Transverse processes of C4-7 Scapular cartilage and medial scapula Supports trunk between forelimbs Raises neck when the limb is fixed Ventral branch of local cervical nerve M. Splenius (capitus and cervicis) Nuchal ligament and spinous processes of T3-T5 Nuchal crest and mastoid process of temporal bone Extends neck Elevates neck Bends neck laterally Dorsal branch of Accessory nerve and dorsal branch of local spinal nerve M. Longissimus (cervicis, capitus, atlantis) Transverse processes of cervical and thoracic vertebrae Wing of atlas and mastoid process of temporal bone Elevates head and neck Bends head and neck laterally Stabilizes and extends vertebral column Dorsal branch of local spinal nerve M. Semispinalis capitis Articular processes of C2/3-7 and transverse processes of T1-6/7 Occipital bone Elevates head and neck Bends head and neck laterally M. Longus capitis Transverse processes of C3-5 Base of skull Bends head and neck Ventral branch of local spinal nerve M. Longus colli Cervical part Transverse processes of C3-7 Ventral tubercle of atlas and bodies of cervical vertebrae Flexes head Thoracic part Bodies of T1-6 Transverse processes of C6-7 Flexes head Bends head laterally M. Obliqus capitis caudalis Spinous process of the axis Wing of the Atlas Rotates atlas and Head Dorsal branch of C2 M. Rectus capitis dorsalis Major Nuchal crest Elevates head Dorsal branch of C1 Minor Dorsal arch of the atlas Occipital bone M. Scalenes Transverse processes of the last 4 cervical vertebrae Anterior border and Outer surface of the first rib Assists inspiration by drawing the first rib forward. With the rib fixed, draws the neck downward and to one side. Cervical nerves Muscles of Trunk[edit | edit source] Muscles Origin Insertion Action Innervation M. Latissimus dorsi Supraspinous ligaments from T3 and thoracolumbar fascia Teres major tuberosity of humerus Flexes shoulder and draws limb caudally. Draws trunk cranially when the limb is flexed. Thoracodorsal nerve M. Serratus ventralis (thoracis) Ribs 1-8/9 Scapular cartilage and Medial scapula Supports trunk between forelimbs. Raises neck when the limb is flexed. Long thoracic nerve M. Serratus dorsalis Cranialis Supraspinous ligament Cranial border of ribs 5-11 Inspiration Intercostal nerve Caudalis Thoracolumbar fascia Caudal borders of ribs 11-18 Expiration M. External intercostal Muscles run caudodorsally in the intercostal spaces Inspiration Intercostal nerve M. Internal intercostal Muscles run cranioventrally in the intercostal spaces Expiration M. External abdominal oblique Thoracolumbar fascia and lateral aspect of ribs 4-18 Linea alba Prepubic tendon Pelvic tendon Coxal tendon Inguinal ligament Flexes the trunk Ventral branch of lumbar nerve and local intercostal nerve M. Internal abdominal oblique Coxal tuber and inguinal ligament Linea alba Prepubic tendon Last rib Cartilages of ribs 14-18 Flexes the trunk Ventral branches of lumbar nerve and local intercostal nerve M. Transversus abdominis Medial surface of Costal cartilage 7-18 and transverse processes of lumbar vertebrae Linea alba M. Rectus abdominis Lateral surface of costal cartilages 4-9 Prepubic tendon and the head of the femur Flexes the trunk Flexes lumbar spine and lumbosacral joint M. Longissimus thoracis et lumborum Spinous processes of thoracic, lumbar and sacral vertebrae and wing of ilium Transverse processes of vertebrae and tubercles of ribs Stabilizes and extends vertebral column Dorsal branch of local spinal nerve M. Semispinalis thoracis and lumborum Sacrum, the articular processes of the lumbar vertebrae and the transverse processes of the dorsa vertebrae Spinous processes of third or fourth vertebra in front of the one from which it arises Fixes the bone during the action of the large spinal muscle, and assists in spine extension M. Iliocostalis thoracis and lumborum Transverse processes of vertebrae Bodies of the adjacent vertebrae and/or the tuberosities of the ribs Expiration Thoracolumbar extension M. Cutaneous trunci Superficial trunk fascia Superficial shoulder fascia and medial surface of humerus Moves the skin of the abdomen Lateral thoracic nerve and intercostobrachial nerve M. Multifidus lumborum Articular processes of each vertebra from C2 to sacrum Spinous process of the preceding vertebrae Stabilizes and rotates vertebral column Dorsal branches of local spinal nerve M. Psoas major Lumbar transverse processes and ventral surface of the last two ribs Lesser trochanter of Femur Rotates pelvic limb outward Flexed hip Advances limb Stabilizes vertebral column when limb is fixed Ventral branches of lumbar and local intercostal nerve and lumbar plexus [22] Brain Anatomy - Physiopedia Introduction The brain, contained in and protected by the skull and suspended in cerebrospinal fluid, is one of the most important and complex organs in the body. It is the central organ of the nervous system, and with the spinal cord makes up the central nervous system, which controls most of the activities of the body, processing, integrating, and coordinating the information it receives from the sense organs and determining the signals or instructions sent back to the rest of the body. [1] At birth, the average brain weighs about 350 - 400grams, approximately 25% of the final adult brain weight of 1.4 - 1.45 kg and accounting for only 2% of overall body mass, which is reached between 10 and 15 years of age. Fastest growth occurs during the first 3 years of life, with almost 90% of the adult value reached by the age of 5 years. Its average width is about 140 mm, the average length is about 167 mm, and average height about 93 mm. While the brain continues to change throughout our life span, changes in brain morphology during childhood, adolescence and adulthood are much more subtle than those in the first 4 years of life.[2][3][4] The rate and amount of growth that occurs in the brain after birth is neither constant nor pre-determined, nor is it protected from outside influences, both positive and negative, and as such can be speeded up and increased, or slowed down and decreased. [3] Gross Anatomy[edit | edit source] Main brain regions The brain consists of three main structural divisions The cerebrum (outer layer is the cerebral cortex) The cerebellum, The brain stem at the base of the brain (which extends from the upper cervical spinal cord to the diencephalon of the cerebrum). [5][6] Cerebrum[edit | edit source] Cerebrum The cerebrum is the largest part of the brain. The surface of the cerebrum is composed of depressions or grooves (sulci) and ridges or raised areas (gyri), which increase the surface area of the cerebrum without an increase in the size of the brain. Grey matter, approximately 2 to 4 mm thick, forms the outer surface of the cerebrum, which processes and integrates information from white matter fibre tracts, which form the inner surface of the cerebrum. [7] The cerebrum consists of two cerebral hemispheres, the right hemisphere and the left hemisphere, connected by the corpus callosum which facilitates communication between both sides of the brain, with each hemisphere in the main connection to the contralateral side of the body i.e. the left hemisphere of the cerebrum receives information from the right side of the body resulting in motor control of the right side of the body and vice versa. The Hemispheres are then further divided into four lobes. [1][7][5] Frontal Lobe[edit | edit source] The frontal lobe is located at the front of the brain, occupying the area anterior to the central sulcus and superior to the lateral sulcus. It is associated with reasoning, motor skills, higher-level cognition and expressive language. At the back of the frontal lobe, near the central sulcus, lies the motor cortex. This area of the brain receives information from various lobes of the brain and utilises this information to carry out body movements. Damage to the frontal lobe can lead to changes in sexual habits, socialisation, and attention as well as increased risk-taking. [1][5][6] Area Function Dysfunction Primary Motor Cortex Voluntary Control of Movement Altered Muscle Tone Poor Motor Control Pre Motor Area Selection of movement based on external events Dyspraxia Supplementary Motor Area Selection of movement based on stored plans specified by internal cues. Involved in planning of motor actions. Pre-Supplementary Motor Area Acquiring new sequences Dyspraxia Broca's Area Left Hemisphere - Expression of Speech Expressive Dysphasia Right Hemisphere - Non-Verbal Communication Pre-frontal Cortex Personality and Behaviour Changes in Character Inappropriate Behaviour Higher executive function - problem solving, initiation, moderation and termination of bevaiour. Dysexecutive Syndrome Parietal Lobe[edit | edit source] The parietal lobe is located in the middle section of the brain, occupying an area posterior to the central sulcus and superior to the lateral sulcus, extending posteriorly as far as the parieto-occipital sulcus. It is associated with processing tactile sensory information such as pressure, touch, and pain. A portion of the brain known as the somatosensory cortex is located in this lobe and is essential to the processing of the body's senses. [1][5][6] Area Function Dysfunction Primary Somatosensory Cortex Receives Sensory Information from Whole Body Altered Sensation Homunculus Representation Sensory Association Area Integrates Sensory Information based on sensory inputs Inferior Parietal Lobe Left Hemisphere - Attention to Right Side Only Inability to Perceive and Attend to Objects, Space or Own Body despite vision, somatosensation and motor ability being intact. Right Hemisphere - Attention to both Left and Right Contralateral Neglect Visual Association Area Processing of Visual Information for perception of motor and spatial relationships Visuospatial Dysfnction Temporal Lobe[edit | edit source] The temporal lobe is located on the bottom section of the brain, occupying the area inferior to the lateral sulcus. This lobe is also the location of the primary auditory cortex, which is important for interpreting sounds and the language we hear. The hippocampus is also located in the temporal lobe, which is why this portion of the brain is also heavily associated with the formation of memories. Damage to the temporal lobe can lead to problems with memory, speech perception, and language skills. [1][5][6] Area Function Dysfunction Primary Auditory Cortex Loudness Deafness Pitch Localisation of Basic Sound Temporal Association Areas: Recognition and Identification fo Stimuli Agnosia - Acknowledge the existence of a stimulus but unable to recognize what it is Right Inferior Temporal Lobe Face and Object Recognition Prosopagnosia Superior Temporal Lobe - Auditory Association Area Processing Complex Sound Left Inferior Temporal Lobe - Wernicke's Area Recognize Spoken Word Receptive Dysphasia Interpret the meaning of Speech Visual Association Area Process Visual Information related to form recognition and object representation Visuoperceptual Dysfuncton Linked to the storage of Long Term Memory Pyriform Cortex Processing Olfactory Sensations Olfactory Dysfunction Insula Cortex Process Taste Sensation Taste Dysfunction Occipital Lobe[edit | edit source] The occipital lobe is located at the back portion of the brain, occupying the small area behind the parietal-occipital sulcus. It is associated with interpreting visual stimuli and information. The primary visual cortex, which receives and interprets information from the retinas of the eyes, is located in the occipital lobe. Damage to this lobe can cause visual problems such as difficulty recognizing objects, an inability to identify colors, and trouble recognizing words. [1][5][6] Area Function Dysfunction Primary Visual Cortex Determines basic attributes of Vision Light Shape Colour Soze Direction Binocular Vision Diplopia (Double Vision) Blindness Visual Association Area Respond to Visual Stimuli within Receptive Fields Modulated by Attention & Working Memory Cerebellum[edit | edit source] Cerebellum The cerebellum, sometimes referred to as the "Little Brain", is found inferior to the tentorium cerebella or tentorial membrane in the posterior cranial fossa, posterior to the fourth ventricle, the pons and the medulla oblongata. The cerebellum accounts for approximately 10 % of the brain's total size but has for more than 50 % of the total number of neurones located in the entire brain. It is the largest part of the hindbrain forming the Deep Cerebellar Nuclei, which consists of an outer layer cortical region with an inner subcortical mass of cells. It consists of two cerebellar hemispheres joined by a narrow median vermis and is connected to the posterior aspect of the brainstem by 3 cerebellar peduncles, which are symmetrical bundles of nerve fibres. The cerebellum is divided into three small lobes; anterior, middle and flocculonodular lobes, which receive information from the balance system of the inner ear, sensory nerves, and the auditory and visual systems. [1][6] The cerebellum is primarily involved in the coordination of movements as well as the learning of movements (motor learning) and has ipsilateral control of movement i.e. the left hemisphere of the cerebellum controls the left side of the body and vice versa. It regulates initiation, timing, sequencing, and force generation of muscle contractions, sequencing the order of muscle firing when a group of muscles work together to perform a movement and assists with balance and posture maintenance. While the cerebellum is associated with motor movement and control, motor commands do not originate here, rather the cerebellum serves to modify these motor commands it receives from sensory systems of the spinal cord and from other parts of the brain, and integrates these inputs to fine-tune motor activity in order to make motor movements accurate and useful. The cerebellum compares the intended movement originating from the motor cortex areas with the actual movement relayed back by the afferent systems and interneurons in the spinal cord. The main functions of the cerebellum are to; [1][5] To act as a comparator: comparing descending supraspinal signals with ascending afferent feedback. If there is any discrepancy, this is then fine-tuned to produce the actual movement desired via descending pathways. This helps to achieve smoothness and accuracy in movement. To act as a timing device: it converts descending motor signals into a sequence of motor activation. This helps the movement achieve smoothness and coordination, maintaining posture and balance. (receiving input from the vestibular system). To initiate and store movement: has the ability to store and update motor information. there is a significant role played inaccurate learned movement. This is due to a modifiable synapse at the purkinje cell. Cerebellar damage produces disorders in fine movement, equilibrium, posture, and motor learning depending on the part of the cerebellum involved and how it is damaged. Dysfunction may result in; Hypotonia (reduced muscle tone), Ataxia, Dysarthria (the inability to articulate words properly), Nystagmus (rapid jerky eye movements) and Palatal Tremor / Myoclunus (tremor of the palate) [5][6] Watch this 10 minute video on the Cerebellum [8] Brainstem[edit | edit source] The brainstem evolutionarily is the most ancient part of the brain beginning at the foramen magnum occupying the posterior cranial fossa of the skull and is divided into three regions; the medulla oblongata, the pons and the midbrain. It connects the narrow spinal cord with the forebrain. [1][5][6] Watch this 15 minute video on the brainstem. Medulla Oblongata: Located directly above the spinal cord at the level of the foramen magnum forming the base of the brain stem, and connecting the pons superiorly to the spinal cord inferiorly. The medulla oblongata is oblong in shape, approximately 3cm long with the descending tracts passing through it from two pyramids on the ventral surface of the medulla between the anterior median fissure, which is disrupted where the tracts cross the midline at the decussation of the pyramids. Cranial Nerves IX (Glossopharyngeal), X (Vagus), XI (Accessory) and XII (Hypoglossal) emerge form the Medulla Oblongata. [1][5][6] The Medulla Oblongata controls many vital autonomic functions such as heart rate, breathing, and blood pressure, with the following three main functions; to serve as a conduit for the ascending and descending tracts to connect the spinal cord to the higher centers in the forebrain, to contains reflex centres associated with control of respiration, the cardiovascular system and consciousness, to contains nuclei of Cranial Nerves III and XII. Pons: Located anterior to the cerebellum, the Pons connects the medulla oblongata to the midbrain. It is approximately 2.5cm long, composed of transverse fibres forming a ridge or bridge across the anterior surface area connecting the right and left cerebellar hemispheres, from which the pons gets its name. These fibres are the pontocerebellar fibers that are in turn projections from the corticopontine fibers. They cross to enter the contralateral middle cerebellar peduncle and thus enter the cerebellum. Cranial Nerves V (Trigeminal), VI (Abducens), VII (Facial) and VIII (Vestibulocochlear) emerge from the pons. [1][5][6] The Pons serves a number of important functions including playing a role in several autonomic functions including stimulation of breathing and controlling sleep cycles. Midbrain: Extending from the Pons to the Mamillary Body, the midbrain also termed the mesencephalon is the superior most aspect of the brainstem and considered the smallest region of the brain. The substantia nigra is closely associated with motor system pathways of the basal ganglia producing Dopamine which plays a role in the movement, movement planning, excitation, motivation. Cranial Nerves II (Optic), III (Oculomotor) and IV (Trochlear) emerge form the midbrain. The midbrain is associated with vision, hearing, motor control, sleep/wake, arousal (alertness), and temperature regulation, acting as a sort of relay station for auditory and visual information. It contains the following: [1][5][6] Nuclei for 10 of 12 Pairs of Cranial Nerves (All except the Olfactory and Optic Nerves) Apparatus for Controlling Eye Movements (Cranial Nerves III, IV and VI ) Monoaminergic Nuclei that project widely in the CNS Vital Respiration and Cardiovascular Centres Autonomic Centres Areas important for Consciousness Ascending and Descending Pathways, linking Brain to the Spinal Cord Diencephalon[edit | edit source] Diencephalon The diencephalon can be found just above the brainstem between the cerebral hemispheres. Although it is a relatively small part of the central nervous system in terms of mass, the diencephalon has a number of critical roles in healthy brain and bodily function. It contains a collection of structures with differing functions, all complex. The following is a brief summary of its contents.[9] [1] Thalamus[edit | edit source] Roatating: Brainstem and Thalamus (yellow) The thalamus consist of two oval collections of nuclei that make up most of the mass of the diencephalon. The thalamus is often described as a relay station because almost all sensory information (with the exception of smell) that proceeds to the cortex first stops in the thalamus before being sent on to its destination. It is hypothesised that the thalamus serves a gating function in filtering information. The thalamus also plays an important role in regulating states of sleep and wakefulness [5][6] Epithalamus[edit | edit source] Epithalamus: red The epithalamus consists primarily of the pineal gland and the habenulae. The pineal gland is an endocrine gland that secretes the hormone melatonin, which is thought to play an important role in the regulation of circadian rhythms. The habenulae (more often referred to with the singular: habenula) are two small areas near the pineal gland. The functions of the habenula are poorly understood, but it is thought to potentially be involved with reward processing and has been implicated in depression. [9] The function of the epithalamus is to connect the limbic system to other parts of the brain. Some functions of its components include the secretion of melatonin and secretion of hormones from the pituitary gland by the pineal gland circadian rhythms), and regulation of motor pathways and emotions. [5][6] Hypothalamus[edit | edit source] Hypothalamus-Pituitary Complex The hypothalamus is a small (about the size of an almond) region located directly above the brainstem. It also is made up of a collection of nuclei that are involved in a variety of functions. It receives a large input from limbic structures[9]. It has a significantly large efferent output to the ANS and has a highly significant role in the control of pituitary endocrine function. [5][6] The hypothalamus as well as inputting the ANS also has a large part to play in the homeostasis of many physiological systems such as hunger, thirst, water and sodium balance and temperature regulation. It also plays a role in memory and emotional responses, providing autonomic and endocrine responses. It also plays a role in the control of circadian rhythms via retinal input to suprachiasmatic nucleus. There may also be hypothalamus input into sexual and emotional behaviour independent of its endocrine role. [5] Subthalamus[edit | edit source] A portion of the subthalamus is made up of tissue from the midbrain extending into the diencephalon, hence parts of midbrain regions eg substantia nigra and red nucleus are found in the diencephalon. Also contains the subthalamic nucleus (densely interconnected with the basal ganglia) and the zona incerta (many connections throughout the cortex and spinal cord) Several collections of important fibers (e.g. somatosensory fibers) also pass through the subthalamus.[9] Limbic System[edit | edit source] The limbic system is not defined by strict anatomic boundaries but incorporates several important structures. The limbic structures conventionally include the amygdala, the hippocampus, the fornix, the mammillary bodies, the cingulate gyrus, and the parahippocampal gyrus, which lie mainly on the medial side of the temporal lobe. These structures form connections between the limbic system and the hypothalamus, thalamus and cerebral cortex. [1][6] The limbic system has been traditionally associated with our emotional behaviour. The hippocampus is important in memory and learning, while the limbic system itself is central in the control of emotional responses and provides high-level processing of sensory information. The main outflow of the limbic system is to the prefrontal cortex and the hypothalamus as well as to cortical areas. It appears to have a role in attaching behavioural significance and response to a given stimulus. Damage to this area has profound effects on emotional responses. [1][5][6] While a full understanding of the limbic system is far from complete, advances in neurosciences have still given a better understanding of the role the individual components of the limbic system play, and some insight into their many connections.[10]Watch this 10 minute video titled Hypothalamus and Limbic System Basal Ganglia[edit | edit source] Basal ganglia anatomy The basal ganglia are a group of large nuclei, which consist of the Neostratum (Caudate and Putamen), Internal and External segments of Globus Pallidus, the Pars Reticulata, the subthalamic nucleus and the compacta of Substantia Nigra, that partially surround the thalamus, which is important in the control of movement. The red nucleus and substantia nigra of the midbrain have connections with the basal ganglia.[6] The basal ganglia are closely integrated with the motor cortex, premotor cortex, and motor nuclei of the thalamus and play a crucial role in modulation of movements. The Neostratum is the main area of signal reception for the basal ganglia and receives information from the whole cortex in a somatotopic fashion. It relays signals to the thalamus, which projects to the premotor cortex, supplementary motor cortex and prefrontal cortex. There is also a projection to the brainstem (pedunclopontine nucleus- involved in locomotion, and superior colliculus - eye movement). [1][5] Watch this 15 minute video on the basal ganglia. Cranial Nerves[edit | edit source] There are 12 pairs of cranial nerves, numbered according to the position where they originate in the inferior surface of the brain, that function mainly to convey motor signals to and sensory information from the head and neck. The lower cranial nerves have somewhat more complex visceral functions that are not strictly limited to the head and neck. The names of the Cranial Nerves (CN) are: [1][5][6] CN I Olfactory CN II Optic CN III Oculomotor CN IV Trochlear CN V Trigeminal CN VI Abducens CN VII Facial CN VIII Vestibulocochlear CN IX Glossopharyngeal CN X Vagus CN XI Accessory CN XII Hypoglossal Ventricles and Cerebrospinal Fluid[edit | edit source] The ventricles are a system of cavities/space within the cerebral hemispheres, which produce and circulate cerebrospinal fluid, which is continuously produced and absorbed. The cerebrospinal fluid is produced, at a rate of about 450 mL/day, by the choroid plexuses within the lateral ventricles, and circulates through the ventricular system ultimately entering the subarachnoid space, which surrounds the cerebrum, cerebellum, brain stem and spinal cord down to the level of the second sacral vertebrae. At any given time there is approximately 150 mL of cerebrospinal fluid, thus, the volume of CSF in most adults is turned over about 3 times per day. [1][6] The brain has 4 ventricles, which is a series of interconnected spaces in the core of the brain. The lateral ventricles are within the cerebral hemispheres, which are connected to each other and to the third ventricle through a pathway called the Interventricular Foramen of Monro. The third ventricle lies in the midline, separating deeper brain structures such as the left and right thalami. The third ventricle communicates with the fourth ventricle through the Cerebral Aqueduct of Sylvius, which is a long narrow tube. [1][5] Blood Supply[edit | edit source] An adequate supply of oxygen and nutrients is vital for the normal function of the brain, which is achieved through a dense network of blood vessels. Arterial blood supply to the brain comes from four vessels the right and left Internal Carotid and the right and left Vertebral Arteries, which join at the base of the brain to form the basilar artery. The Anterior Circulation is composed of the carotid arteries and their branches, while the Posterior Circulation is composed of the Vertobrobasilar arteries. [1][5][6] Watch these 15 minute videos on the blood supply of the brain. [11] [12] Internal Carotid Arteries[edit | edit source] Traverse the skull within the carotid canal and cavernous sinus. They then pierce the dura and enter the middle cranial fossa lateral to the optic chiasm. They then divide to supply the anterior and middle sections of the cerebral hemispheres, anterior and middle cerebral arteries. The internal carotid artery on each side terminates into the anterior cerebral artery, the middle cerebral artery, and the posterior communicating artery.[5] Vertebral Arteries[edit | edit source] Arising from the sub-clavian artery these two arteries enter the skull through foramen magnum after passing through foramina in the transverse processes of the upper cervical vertebra. They unite in the brainstem to form the basilar artery which ascends to form the two posterior cerebral arteries at the superior border of the Pons. This is the posterior cerebral hemisphere blood supply. This network is termed the posterior circulation. On its journey to becoming the basilar artery, the vertebral arteries give off a number of branches, including the posterior spinal artery, posterior inferior cerebral artery and the anterior spinal artery. These constitute the blood supply to the upper cervical cord. The posterior inferior cerebral artery supplies the lateral medulla and cerebellum. Damage to these blood vessels can result in motor loss or sensory loss. [5][6] Basilar Artery[edit | edit source] Formed by the two vertebral arteries. This has a number of branches: anterior and inferior cerebellar artery, artery to the labyrinth, pontine branches and superior cerebellar artery which supply the brain stem and cerebellum. [5] Anterior Cerebral Arteries[edit | edit source] The anterior cerebral artery arises from the internal carotid, at the medial extremity of the lateral cerebral fissure. It passes forward and medialward across the anterior perforated substance, above the optic nerve, to the commencement of longitudinal fissure. Is one of a pair of arteries on the brain that supplies oxygenated blood to most midline portions of the frontal lobes and superior medial parietal lobes. [5][6] Middle Cerebral Arteries[edit | edit source] These supply parts of the frontal, temporal, occipital and parietal lobes bilaterally, with branches also supplying the basal ganglia and posterior limb of the internal capsule. Posterior Cerebral Arteries[edit | edit source] These supply blood to the posterior parietal cortex, occipital lobe and inferior temporal lobe. There are several branches of this artery that supply the midbrain, thalamus, subthalamus, posterior internal capsule, optic radiation and cerebral peduncle. Circle of Willis[edit | edit source] The basilar artery, the posterior cerebral arteries, the posterior communicating arteries, and the anterior cerebral arteries, along with the anterior communication artery, form an important collateral circulation, the Anterior and Posterior Circulation anastomose at the base of the brain, termed the Circle of Willis. These vessels lie within the subarachnoid space and are a common location for cerebral aneurysms to form. [5][6] Watch this 10 minute video on the circle of Willis. [13] Venous Drainage[edit | edit source] The venous circulation of the brain is very different from that of the rest of the body. Usually arteries and veins run together as they supply and drain specific areas of the body, however, this is not the case in the brain. The major vein collectors are integrated into the dura to form venous sinuses, which are adjacent to the posterior cranial fossa. The venous sinuses collect the blood from the brain and pass it to the internal jugular veins. The superior and inferior sagittal sinuses drain the cerebrum, the cavernous sinuses drains the anterior skull base. All sinuses eventually drain to the sigmoid sinuses, which exit the skull and form the jugular veins. These two jugular veins are essentially the only drainage of the brain. If occlusion of either of these venous systems then raised intracranial pressure can develop. [1][5][6] Viewing[edit | edit source] Watch these videos for a more in-depth look parts of the brain (18 minutes). Facial Muscles - Upper Group - Physiopedia Search Search Search Toggle navigation pPhysiopedia pPhysiopedia About News Contribute Courses Resources Contact Donate Login pPhysiopedia About News Contribute Courses Resources Shop Contact Donate p o + Contents Editors Categories Share Cite Contents loading... Editors loading... Categories loading... When refering to evidence in academic writing, you should always try to reference the primary (original) source. That is usually the journal article where the information was first stated. In most cases Physiopedia articles are a secondary source and so should not be used as references. Physiopedia articles are best used to find the original sources of information (see the references list at the bottom of the article). 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Cite article Facial Muscles - Upper Group Jump to:navigation, search Original Editor - Wendy Walker One Page Owner - Wendy Walker as part of the One Page Project  Top Contributors - Wendy Walker and Kim Jackson Contents 1 Introduction and Overview 2 Description 3 Orbital Facial Muscles 3.1 Occipitofrontalis 3.1.1 Origin and insertion 3.1.2 Nerve and blood supply 3.1.3 Function 3.1.4 Clinical Relevance 3.2 Orbicularis Oculi 3.2.1 Origin and Insertion 3.2.2 Nerve and blood supply 3.2.3 Function 3.2.4 Clinical relevance 3.3 Corrugator Supercilii 3.3.1 Origin and Insertion 3.3.2 Nerve and blood supply 3.3.3 Function 3.3.4 Clinical relevance 4 Nasal Facial Muscles 4.1 Procerus 4.1.1 Origin and insertion 4.1.2 Nerve and blood supply 4.1.3 Function 4.1.4 Clinical relevance 5 Nasalis 5.1 Origin and insertion 5.2 Nerve and blood supply 5.3 Function 5.4 Clinical relevance 6 Depressor Septi Nasi 6.1 Origin and insertion 6.2 Nerve and Blood Supply 6.3 Function 6.4 Clinical Relevance 7 Assessment 8 Resources Introduction and Overview[edit | edit source] The muscles of the face are striated muscles which originate from bones of the skull or the face, and are used in functions of eating and drinking, speech and non-verbal communication. The facial muscles have different characteristics compared to muscles in the trunk and limbs: They have a more complex pattern of innervation of extrafusal fibres They have a larger percentage of slow-type nerve fibres Many facial muscles insert not into bone or fascia, but into the skin Many facial muscles are very thin in structure and are poorly differentiated, merging with other facial muscles Description[edit | edit source] The muscles of the upper portion of the face can be divided into 2 groups: Orbital Facial Muscles Nasal Facial Muscles We will examine the 2 groups separately. Orbital Facial Muscles[edit | edit source] There are 3 Orbital Facial Muscles: Occipitofrontalis (often referred to simply as Frontalis) Orbicularis Oculi Corrugator Supercilii Occipitofrontalis[edit | edit source] Origin and insertion[edit | edit source] Occipitofrontalis is one of the muscles of the scalp. It consists of 2 separate bellies: Occipital part - which originates from occipital bone (lateral part of the upper nuchal line) and from the mastoid aspect of the temporal bone. Frontal part - originates from the superior fibres of the other upper facial muscles (ie. orbicularis oculi, corrugator supercilii and procerus Both parts insert into the galea aponeurotica in the scalp Revolving image of the Frontalis muscle Nerve and blood supply[edit | edit source] Nerve supply is the Facial Nerve (CN VII), with the occipital belly supplied by the posterior auricular branch, and the frontal belly by the temporal branch. Blood supply of the occipital portion is from the occipital artery, and the frontal segment is supplied by the supraorbital and supratrochlear arteries. Function[edit | edit source] The frontalis portion elevates the eyebrows, which causes the horizontal wrinkles in the forehead. It also weakly moves the skin of the scalp anteriorly The occiptal part weakly moves the scalp skin posteriorly. Clinical Relevance[edit | edit source] In facial palsy, paralysis of the frontalis muscle[1] results in lack of ability to raise the ipsilateral eyebrow; it also results in absence of horizontal lines/wrinkles on that side of the forehead. In older patients, there may also be some descent of the affected eyebrow, which as well as producing visible asymmetry of the eyebrows can impact on vision in that eye, if the brow ptosis is sufficient to obscure the upper field of vision. Brow ptosis can also lead to a secondary misdirection of the upper eyelid lashes which can irritate/scratch the eye. Orbicularis Oculi[edit | edit source] Surrounding the eye is the orbicularis oculi[2], a sphincter muscle which consists of 3 sections: the orbital, the palpebral and the lachrymal portions. The fibres are arranged in concentric circles round the upper and lower eyelids. The palpebral fibres form the eyelids. Origin and Insertion[edit | edit source] Illustration of orbicularis oculi muscle. The fibres originate from the anterior surface of the medial orbital margin, the rim of the eye socket, and the lachrymal sac. They travel laterally, both above and below the eye, to insert into the lateral palpebral raphe. At the peripheral borders of the muscle, the fibres interdigitate (merge in an interlocking fashion) into the bordering muscles, ie. the upper fibres interdigitate with the frontalis and corrugator muscles. Nerve and blood supply[edit | edit source] The muscle is supplied by the seventh cranial nerve, Facial Nerve; the upper fibres by the temporal branch, and the lower fibres by the zygomatic branch. Function[edit | edit source] The action of the orbicularis oculi muscle is to close the eye. The palpebral fibres, which form the eyelids, are responsible for blinking. The lachrymal fibres facilitate drainage of tears by helping to empty the lachrymal sac, and the orbital section of the muscle is responsible for providing a tight eye closure/seal[2]. The action of orbicularis oculi muscle helps with distribution of the tear film over the cornea[3]. Clinical relevance[edit | edit source] Paralysis of the Orbicularis Oculi muscle results in incomplete closure of the eyelids, and this has a profound effect on the condition of the cornea of the eye. If not managed well, the lack of closure can result in drying out of the cornea, often accompanied by significant pain, scarring of the cornea, and can progress to ulceration, and in extreme cases perforation of the cornea[3][4]. This means that signs of an acute Dry Eye in patients with Facial Palsy should have urgent evaluation by an opthalmic team. There is further information on general management of the eye on the Dry Eye page. Corrugator Supercilii[edit | edit source] Lying above the orbicularis oculi muscle and below occipitofrontalis, Corrugator Supercilii is a small muscle which is located at the medial end of the eyebrow. The Latin name means "Wrinkler of the Eyebrows": Corrugator from the Latin verb to wrinkle, corrugo, and the Latin word for eyebrow is supercilium, which in the plural becomes supercilii. Origin and Insertion[edit | edit source] Revolving image of Corrugator suerpcilii muscle. It originates from the superciliary arch (a ridge on the frontal bone) and the fibres travel laterally and slightly upward to insert into the deep surface of the skin of the eyebrow. Nerve and blood supply[edit | edit source] It is supplied by the temporal branch of the Facial Nerve. Blood supply comes from the Superficial Temporal Artery and from the Opthalmic Artery. Function[edit | edit source] This muscle pulls the eyebrow downward and medially, producing the vertical lines/wrinkles of the forehead. Clinical relevance[edit | edit source] This muscle acts when producing the facial expressions of sadness and puzzlement; it creates a "frown". It also acts to help shield the eye from strong light. Nasal Facial Muscles[edit | edit source] There are 2 major Nasal Facial Muscles: Procerus Nasalis Plus 2 minor Nasal Facial Muscles: Depressor Septi Nasi Myrtiformis Procerus[edit | edit source] Origin and insertion[edit | edit source] Procerus, AKA Pryamidalis Nasi) runs between the nose and the forehead. The term procerus means tall or extended in Latin. It arises from the superior surface of the nasal bones, and the upper lateral nasal cartilages. Revolving image of the Procerus muscle. The fibres travel upwards to insert into the skin of the inferomedial forehead, its fibres at this point merge with those of frontalis, in between the 2 eyebrows. Nerve and blood supply[edit | edit source] It derives its nerve supply from the temporal branch of the Facial Nerve. Blood supply is via the Facial Artery. Function[edit | edit source] This muscle pulls down the medial parts of the eyebrows, causing transverse wrinkles in the skin above the nose and between the eyebrows (this area is sometimes referred to as the glabella area). Clinical relevance[edit | edit source] Contraction of Procerus causes the facial gesture of a frown, along with Corrugator Supercilii. Procerus is responsible for producing horizontal lines over the bridge of the nose. Its main action is involved with facial expressions of sadness, bewilderment or anger. Nasalis[edit | edit source] Origin and insertion[edit | edit source] Nasalis is split into two sections: alar (AKA Dilator Naris) and transverse (AKA Compressor Naris). Both sections of the muscle originate from the frontal part of the maxilla. The fibres of the alar section travel medially to insert into the ipsilateral alar cartilages Revolving image of the Nasalis muscle. The transverse fibres insert into an aponeurosis on the dorsum of the nose Nerve and blood supply[edit | edit source] The buccal branch of the Facial Nerve supplies both sections of this muscle. Blood supply is porvided by the superior labial, septal and lateral nasal branches of the Facial Artery, and the infraorbital branch of the Maxillary Artery. Function[edit | edit source] The two sections of this muscle have opposing actions: the alar section of Nasalis brings about widening of the nostril, and the transverse fibres compress the nostril. Clinical relevance[edit | edit source] Nasalis is an accessory muscle of respiration, being particularly active during deep breathing and times of respiratory distress; it also acts in emotional states such as anger. Depressor Septi Nasi[edit | edit source] AKA Depressor Alae Nasi, this muscle is sometimes absent or present only in rudimentary form. Origin and insertion[edit | edit source] Revolving image of Depressor septi muscle. Historically this muscle has been said to originate from the maxilla (superior to the central incisor), but some more recent studies report it originates from the fibres of orbicularis oris[5]. It inserts into the nasal septum. Nerve and Blood Supply[edit | edit source] This muscle derives its nerve supply from the buccal branch of the Facial Nerve (Cranial Nerve VII). Blood supply is from the Facial Artery. Function[edit | edit source] Its action is to pull the nasal septum and the tip of the nose downward. Clinical Relevance[edit | edit source] Although this muscle (when present) is active during inspiration and also during movements of the upper lip when talking, it does not seem to have any direct clinical relevance to facial rehabilitation. Indeed, one of the most comprehensive text books on the subject, "The Facial Nerve"[6] does not mention Depressor Nasi Septi. Assessment[edit | edit source] Evaluation of the activity of the upper facial muscle group forms part of the assessment of Facial Palsy, which may be caused by Bell's Palsy, nerve damage in brain tumours such as Acoustic Neuroma (AKA Vestibular Schwannoma), Ramsay Hunt Syndrome, and other less common conditions. The primary muscle to examine initially is the action of the Orbicularis Oculi, as this is the muscle responsible for producing eye closure, and thus maintaining the healthy condition of the cornea of the eye. As the facial nerve is responsible for lubrication of the eye, providing the lacrimal glands with a portion of their parasympathetic nerve supply, a common feature of inability (or reduced ability) to close the eye in facial palsy is reduction in tear production causing a Dry Eye. As Dry Eye can lead to development of a corneal ulcer, which in turn can cause severe damage to eyesight, it is essential that a physiotherapist assessing and treating someone with this is aware of the dangers, and provides appropriate advice and education to the patient, as detailed on the Dry Eye page. Resources[edit | edit source] ↑ Bérzin F. Occipitofrontalis muscle: functional analysis revealed by electromyography.  Electromyogr Clin Neurophysiol. 1989;29(6):355‐358. ↑ 2.0 2.1 Tong J, Lopez MJ, Patel BC. Anatomy, Head and Neck, Eye Orbicularis Oculi Muscle. [Updated 2020 Apr 29]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2020 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK441907/ ↑ 3.0 3.1 Choi Y, Kang HG, Nam YS, Kang JG, Kim IB. Facial Nerve Supply to the Orbicularis Oculi around the Lower Eyelid: Anatomy and Its Clinical Implications.  Plast. Reconstr. Surg. 2017 Aug;140(2):261-271. [PubMed] ↑ Hollander MHJ, Contini M, Pott JW, Vissink A, Schepers RH, Jansma J. Functional outcomes of upper eyelid blepharoplasty: A systematic review.  J Plast Reconstr Aesthet Surg. 2019 Feb;72(2):294-309. [PubMed] ↑ Daniel RK, Glasz T, Molnar G, Palhazi P, Saban Y, Journel B. The lower nasal base: an anatomical study Aesthet Surg J. 2013;33(2):222-232. ↑ May, M & Schiatkin, BM. (2000) The Facial Nerve, 2nd edition. Thieme Medical Publishers Retrieved from "https://www.physio-pedia.com/index.php?title=Facial_Muscles_-_Upper_Group&oldid=293204" Categories: Anatomy Muscles Facial Palsy Head Head - Anatomy Head - Muscles Get Top Tips Tuesday and The Latest Physiopedia updates Email Address I give my consent to Physiopedia to be in touch with me via email using the information I have provided in this form for the purpose of news, updates and marketing. HP Yes please Our Partners The content on or accessible through Physiopedia is for informational purposes only. Physiopedia is not a substitute for professional advice or expert medical services from a qualified healthcare provider. Read more pPhysiopedia oPhysiospot +Plus   Physiopedia About News Courses Contribute Shop Contact Content Articles Categories Presentations Research Resources Projects Legal Disclaimer Terms Privacy Cookies © Physiopedia 2023 | Physiopedia is a registered charity in the UK, no. 1173185 Back to top Anatomy of the Canine Spine - Physiopedia Canine Skull Cranium[edit | edit source] Cranial skull- canine The Roof of the cranium is made up of frontal and parietal bones. The Floor is made up of sphenoid bone. The cranium consists of 5 orbital regions: Frontal Lacrimal Palatine Sphenoid Zygomatic The orbit is complete in horse and ruminants while it is incomplete in carnivores but completed by the orbital ligament. The lacrimal fossa collects tears and sends them through lacrimal canal into the nasal cavity. Joints and Ligaments of the Skull[edit | edit source] Temporo-mandibular joint:[1] A condylar joint, with an articular disc, that sits between the mandibular condyles and the mandibular fossa of the temporal bones It has a loose joint capsule with thickening, which forms a lateral ligament The temporalis muscle closes the jaw and the joint is innervated by cranial nerve V Mandibular symphysis Joints of the hyoid apparatus:[1] Tympanohyoid cartilage - skull (a syndesmosis joint) Interhyoid joints (synovial joints) Thyrohyoid bone - cranial cornu of thyroid cartilage (synovial joint) [2] Canine Spine[edit | edit source] Figure 1. The Canine Skeleton The anatomy of the canine skull and spine is quite similar to the human spine. Like in people, the canine spine supports weight and encloses the spinal cord. The spine is located along the dorsal / top side of the canine's body and runs from the base of the head to the end of the tail.[3] The canine spine is divided into five regions: cervical, thoracic, lumbar, sacral, and caudal. There are 7 cervical vertebrae, 13 thoracic vertebrae, 7 lumbar vertebrae and 3 sacral vertebrae. The number of caudal vertebrae varies according to the species.[4] Cervical vertebrae[edit | edit source] The atlas and axis are cervical vertebrae 1 and 2. Canine cervical spine The atlanto-occipital joint is a condylar modified synovial hinge joint. The capsule of the joint is strengthened by three thickenings: dorsal, ventral, and lateral.[1] The transverse process of the atlas is the wing that allows the articulation of the occipital condyles and the spine.The atlas and axis are fused in embryonic life.[4] The transverse atlantal ligament holds the dens of the axis against the ventral arch of the atlas.[1] The axis is the second and longest cervical vertebra. The atlantoaxial joint is a pivot joint and has a loose joint capsule. The dens of the axis is connected to the occipital bone through the apical ligament.[1] The cervical vertebrae are obliquely oriented in the transverse plane. The cranial articular processes face dorsomedially whereas the caudal articular processes face ventrolaterally. [1] The nuchal ligament is a paired band of connective tissue that connects the spinous processes of cervical vertebrae to the spinous processes of thoracic vertebra (from C1 to T1).[4][1] The canine ligamentum flavum, dorsal longitudinal ligament and, ventral longitudinal ligament are similar to those in people: The ligamentum flavum connects the lamina of adjacent lamina The anterior longitudinal ligament attaches to the front of each vertebra The posterior longitudinal ligament runs along the posterior aspect of spine and inside of the spinal cord[1] Muscles of the Cervical Spine[edit | edit source] Canine superficial cervical muscles Muscles of the cervical spine (table extracted from a presentation of Ansi Van Der Walt )[1] Muscle Origin Insertion Innervation Action Omotransversarius Lower spine of scapula Wing of atlas Ventral branches of local cervical spinal nerve Advances limb Moves neck laterally Brachiocephalicus [The clavicle divides the muscle into two: cleidobrachialis and cleidomastoideus] Cleidobrachialis Clavicular intersection Crest of the humerus Axillary nerve Advances limb Adducts Limb Cleidomastoideus Clavicular intersection Mastoid process of the temporal bone Ventral branch of the accessory nerve (cranial nerve XI) Forms dorsal border of jugular groove Advances limb Flexes neck Turns head Sternocephalicus (sternomandibularis) Manubrium of the sternum Mastoid part of temporal bone Nuchal crest Forms ventral border of jugular groove Flexes neck Turns head Opens mouth Omohyoideus Subscapular Fascia Lingual process of basihyoid bone Spinal nerve C1 Forms medial border of jugular groove Retracts basihyoid bone and tongue Trapezius (cervical and thoracic parts) Nuchal ligament and supraspinous ligament of C2-10 Cervical part: entire scapular spine Thoracic part: dorsal third of scapular spine Dorsal branch of accessory nerve (cranial nerve XI) Advances thoracic limb Abducts thoracic limb Elevates shoulder Rhomboiudeus muscle (cervical and thoracic) Nuchal ligament and dorsoscapular ligaments of C2-T8 Scapular cartilage Local thoracic nerve Local cervical nerve Elevates neck Draws scapula cranially and dorsally Serratus ventralis cervicis Transverse processes of C4-7 Scapular cartilage and medial scapula Ventral branches of local cervical nerve Supports trunk between forelimbs Raises neck when the limb is fixed Splenius (capitis and cervicis) Nuchal ligament and spinous processes of T3-5 via the thoracolumbar fascia Nuchal crest and the mastoid process of temporal bone Dorsal branch of accessory nerve (cranial nerve XI) and dorsal branch of local spinal nerve Extends neck Elevates neck Bends neck laterally Longissimus (cervicis,capitis, atlantis) Transverse processes of cervical and thoracic vertebrae Wing of atlas and mastoid process of temporal bone Dorsal branches of local spinal nerve Elevates head and neck Bends head and neck laterally Stabilizes and extends vertebral column Semispinalis capitis Articular processes of C2/3-7 and transverse processes of T1-6/7 Occipital bone Elevates head and neck Bends head and neck laterally Longus capitis Transverse processes of C3-5 Mastoid process Ventral branch of local spinal nerve Flexes head Bends head laterally Longus colli thoracic part Bodies of T1-6 Transverse processes of C6-7 cervical part Transverse processes of C3-7 Ventral tubercle of atlas and bodies of cervical vertebrae Flexes head Obliquus capitis caudalis Spinous process of the axis Wings of the atlas Dorsal branch of C2 Rotates atlas and head Rectus capitis dorsalis muscle minor Dorsal arch of the atlas Occipital bone Dorsal branch of C1 Elevates head major Spinous process of the axis Nuchal crest Scalenes (composed of two unequal parts and the lower one is larger) From the transverse process of the last four cervical vertebrae Into the anterior border and outer surface of the first rib Assists inspiration by drawing the first rib forward With rib fixed draws the neck downward and to one side Thoracic Vertebrae[edit | edit source] The thoracic vertebrae differ from other vertebrae in a number of ways. The thoracic vertebrae articulate with the corresponding rib (i.e. T1 to rib 1). Each thoracic vertebra has a short body, flattened extremities, short articular processes and a long spinous process. The caudal articular processes of the thoracic vertebrae face ventrally and are at the base of the spinous process. The cranial articular processes of the thoracic vertebrae are oval facets on the arch of vertebrae and face dorsally. All thoracic vertebrae have a pair of costal facets on the dorsal body (except T13) forming costal fovea. There are costal facets on the transverse processes of the vertebrae and cranial and caudal fovea on the extremities of the vertebral bodies.[5] The 11th thoracic vertebra is also known as the anticlinal vertebra. The anticlinal vertebra is the point at which vertebral anatomic features change and the spinous process becomes perpendicular to the body and the preceding vertebra incline caudally. [6] [7] The costovertebral joint has two articulations between the rib and the vertebral column. The head of the rib articulates with the cranial and costal facets of the adjacent vertebrae and is a ball and socket synovial joint. Similarly, the tubercle of the rib articulates with the transverse process of the vertebra and is a plane synovial joint. The ligaments of the costovertebral joint are the radiate ligament of the head, inter capital ligament (connects the head of the pair of opposite rib), costotransverse ligaments and ligament of the neck.[1] Lumbar spine[edit | edit source] Lumbar vertebrae are more uniform and longer in shape than the thoracic vertebrae.[4] The cranial articular process of the lumbar spine is fused with the mamillary processes and the articular processes are concave dorsally and mostly in sagittal alignment. The caudal processes are convex ventrally and correspond with the convexity of cranial articular processes. The lumbar vertebrae are differentiated from the thoracic vertebrae by their lack of costal facets. The lumbar spine allows flexion and extension of the spine. Lateral flexion and rotation are very limited, especially at the L4-L5 due to the intertransverse joints. [1] Ligaments of the thoracolumbar joint[edit | edit source] The dorsal longitudinal ligament forms a part of the floor of the vertebral canal from the axis to the sacrum and prevents hyperflexion of the spine[1] An interspinous ligament connects the spines of adjacent vertebrae from the axis to the sacrum[1] Intertransverse ligament[1] Interarcuate ligament / ligamentum flavum / yellow ligaments are the elastic ligaments filling dorsal spaces between the arches of adjacent vertebrae[1] The supraspinous ligament is made up of heavy bands of the connective tissue that run over the top of the spinous processes (T2/T3 caudally). This ligament prevents abnormal separation of spinous processes during flexion of the spine. The supraspinous ligament is a direct continuation of the funicular part of the nuchal ligament[1] The ventral longitudinal ligament runs ventrally from axis to sacrum. It widens caudally and is strongest in the lumbar spine. This prevents hyperextension of the spine[1] Sacral vertebrae[edit | edit source] The sacrum is formed by the fusion of the sacral vertebrae and articulates with the pelvic girdle. The sacrum narrows and forms a curve caudally and forms a concave surface for the pelvic cavity.[4] Caudal vertebrae[edit | edit source] The dog caudal vertebrae may vary from eighteen to twenty-five, the number differing from species to species. [4][8] Muscles of the Trunk[edit | edit source] Muscles of the trunk (table extracted from a presentation of Ansi Van Der Walt [1] Muscle Origin Insertion Innervation Action Lattisimus dorsi Supraspinous ligament from T3 and thoracolumbar fascia Teres major tuberosity of humerus Thoracodorsal nerve Flexes shoulder and draws limb caudally Draws trunk cranially when limb is flexed Serratus ventralis thoracis Ribs 1-8/9 Scapular cartilage and medial scapula Long thoracic nerve Supports trunk between forelimbs Raises neck when limb is flexed Serratus dorsalis cranialis Supraspinous ligament Cranial border of ribs 5-11 Intercostal nerve Muscle of inspiration caudalis Thoracolumbar fascia Caudal border of ribs 11-13 Muscle of expiration External intercostal muscles Muscles run caudodorsally in the intercostal spaces Muscles of inspiration Internal intercostal muscles Muscles of expiration External abdominal oblique muscle Thoracolumbar fascia and lateral aspect of ribs 4-13 Linea alba Prepubic tendon Pelvic tendon Coxal tuber Inguinal ligament Ventral branches of lumbar nerve and local intercostal nerve Abdominal press Flexes the trunk Internal abdominal oblique muscle Coxal tuber and inguinal ligament Linea alba, Prepubic tendon last rib Cartilages of ribs 14-18 Ventral branches of lumbar nerve and local intercostal nerve Abdominal press Flexes the trunk Transversus abdominis Medial surface of costal cartilages 7-18 and transverse processes of lumbar vertebrae Linea alba Ventral branches of lumbar nerve and lumbar intercostal nerve Abdominal press Flexes the trunk Rectus abdominis lateral surface of costal cartilages 4-9 Prepubic tendon and head of the femur (via accessory ligament) Ventral branches of lumbar nerve and local intercostal nerve Abdominal press Flexes the trunk Flexes lumbar spine and lumbosacral joint Longisimus thoracis and lumborum Spinous processes of thoracic, lumbar and sacral vertebrae and wings of illium Transverse processes of vertebrae and tubercles of rib Dorsal branches of lumbar nerve Stabilises and extends vertebral column Semispinalis thoracis and lumborum From the sacrum and from the articular processes of the lumbar vertebrae and from the transverse processes of the dorsal vertebrae Each slip inserts into the spinous process of the third or fourth vertebra in front of the one from which it arises Dorsal branches of local spinal nerve To fix the bones during the action of the large spinal muscles, and to assist in extending the spine Iliocostalis thoracis and lumborum Runs obliquely between the transverse processes of the vertebrae to the bodies of the adjacent vertebrae and/or the tuberosities of the rib Dorsal branches of local spinal nerves Expiration Thoracolumbar extension Cutaneous trunci Superficial trunk fascia (from the withers to the fold of the flank) Superficial shoulder fascia and medial surface of the humerus Lateral thoracic nerve and intercostobrachial nerve Moves the skin of the abdomen (and the trunk ) Longissimus thoracis and lumborum muscle are continuous from pelvis through thorax Spinous processes of thoracic, lumbar and sacral vertebrae and wings of illium Transverse processes of vertebrae and tubercles of ribs Dorsal branches of local spinal nerve Stabilises and extends vertebral column Multifidus lumborum muscle (continuous with thoracis and cervicis) Articular processes of each vertebra from C2 to sacrum Spinous process of the preceding vertebra Dorsal branches of local spinal nerve Stabilises vertebral column Rotates vertebral column Psoas major muscle Part of iliopasoas muscle Lumbar transverse processes and ventral surface of last two ribs Lesser trochanter of femur (as fused iliopsoas muscle) Ventral branches of lumbar and local intercostal nerve and lumbar plexus Rotates pelvic limb outwards Flexes hip and advances limb Stabilises vertebral column when limb is fixed Digastric Muscle - Physiopedia Description The digastric muscle (also digastricus) has two bellies[1], namely the anterior and posterior belly. It is a small, important muscle in the neck[2]. It has many variations but these variations do not necessarily produce clinical symptoms[2]. It belongs to the suprahyoid muscles group which includes the mylohyoid, geniohyoid and stylohyoid muscles[1]. Origin[edit | edit source] Anterior belly - Mandible's digastric fossa, close to the midline [2][1] Posterior belly - Notch of the mastoid process of the temporal bone[2][1] Insertion[edit | edit source] The two join, forming the intermediate tendon which inserts onto the body and greater cornu of the hyoid bone[2][1]. The intermediate tendon can sometimes penetrate the stylohyoid muscle[2]. Nerve Supply[edit | edit source] Anterior belly - mandibular division (V3) of the trigeminal (CN V) via the mylohyoid nerve[2]. In some cases, the anterior belly can be innervated by both the mylohyoid nerve and facial nerve[2]. Posterior belly - facial nerve (CN VII)[2] Blood Supply[edit | edit source] Anterior belly - submental branch of facial artery[2] Posterior belly - posterior auricular and occipital arteries[2] Function[edit | edit source] Elevates the hyoid bone to stabilize it during swallowing (protection of the airway)[2][1] Opens the jaw by depressing the mandible[2][1] Plays a role during speech and chewing[2] Structure[edit | edit source] The digastricus (digastric muscle) consists of two muscular bellies united by an intermediate rounded tendon. The two bellies of the digastric muscle have different embryological origins, and are supplied by different cranial nerves. Each person has a right and left digastric muscle. The digastric muscle stretches between the mastoid process of the cranium to the mandible at the chin, and part-way between, it becomes a tendon which passes through a tendinous pulley attached to the hyoid bone. It Posterior belly The posterior belly, longer than the anterior belly, arises from the mastoid notch which is on the inferior surface of the skull, medial to the mastoid process of the temporal bone. The mastoid notch is a deep groove between the mastoid process and the styloid process. The mastoid notch is also referred to as the digastric groove or the digastric fossa. The posterior belly is supplied by the digastric branch of the facial nerve. Anterior belly The anterior belly arises from a depression on the inner side of the lower border of the mandible called the digastric fossa of mandible, close to the symphysis, and passes downward and backward. The anterior body is supplied by the trigeminal nerve via the mylohyoid nerve, a branch of the inferior alveolar nerve, itself a branch of the mandibular division of the trigeminal nerve. It originates from the first pharyngeal arch. Intermediate tendon The two bellies end in an intermediate tendon which perforates the stylohyoideus muscle, and is held in connection with the side of the body and the greater cornu of the hyoid bone by a fibrous loop, which is sometimes lined by a mucous sheath. Triangles The digastric muscle divides the anterior triangle of the neck into three smaller triangles: The submandibular triangle (also called digastric triangle) is formed by the mandible superiorly, laterally but the digastric posterior belly and medially by the digastric anterior belly[2]. The carotid triangle is formed by the posterior belly of the digastric muscle superiorly, the sternocleidomastoid muscle laterally and medially but the superior belly of the omohyoid muscle[2]. The submental triangle is formed by the hyoid bone inferiorly and by both anterior bellies of the digastric muscles Trigger Point Referral Pattern[edit | edit source]  The anterior and posterior bellies of digastric may contain a myofascial trigger point (MTrP). The MTrP in the posterior belly may refer pain over the mastoid process and occasionally to the throat under the chin[3] . The anterior belly refers to the lower central incisors and to the alveolar ridge below.[3]                                                                                                                                                Palpation[edit | edit source] Direct external palpation of posterior digastric is difficult due to the depth of the muscle. The anterior digastric is examined by identifying the lateral margins of the hyoid, and then palpating the inferior surface of the mandible by placing the thumbs on either side of the midline. To confirm the location of the anterior digastric, the patient is requested to swallow; a prominence of the anterior belly can be palpated under the thumb tips as the hyoid is drawn superiorly.

References[edit | edit source]

  1. ↑ Jump up to: 1.0 1.1 Morton DA, Foreman K, Albertine KH. eds. 'The Big Picture: Gross Anatomy, 2e' New York, NY: McGraw-Hill. Available from:http://accessmedicine.mhmedical.com.uplib.idm.oclc.org/content.aspx?bookid=2478&sectionid=202020790 (Accessed 8 April 2019).
  2. ↑ Jump up to: 2.0 2.1 Anderson BW, Al Kharazi KA. Anatomy, Head and Neck, Skull.Treasure Island (FL): StatPearls Publishing; 2019. Available from: https://www.ncbi.nlm.nih.gov/books/NBK499834/ (accessed 8 April 2019)
  3. ↑ Gaylene Ewing. Cranial bones. Available from: https://www.youtube.com/watch?v=y1ExSUGUsU0 [last accessed 8/4/2019]
  4. ↑ Gaylene Ewing. Facial bones. Available from: https://www.youtube.com/watch?v=Q0lBvcoHJqk [last accessed 8/4/2019]
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