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Anatomy

Muscles Around the Mouth

  • The sphincter of the mouth is orbicularis oris and the dilator muscles radiate outward from the lips like the spokes of a wheel.

Orbicularis Oris Muscle

  • This muscle encircles the mouth and is the sphincter of the oral aperture
  • This muscle (1) closes the lips, (2) protrudes them and (3) compresses them against the teeth.
  • It plays an important role in articulation and mastication. Together with the buccinator muscle, it helps to hold the food between the teeth during mastication.

Zygomaticus Major Muscle

  • It extends from the zygomatic bone to the angle of the mouth.
  • It draws the corner of the moth superolaterally during smiling and laughing.

Zygomaticus Minor Muscle

  • This is a narrow slip of muscle, and passes obliquely from the zygomatic bone to the orbicularis oris.
  • It helps raise the upper lip when showing contempt or to deepen the nasolabial sulcus when showing sadness.

 

The Buccinator Muscle

  • This is a thin, flat, rectangular muscle.
  • It is attached laterally to the alveolar processes of the maxilla and mandible, opposite the molar teeth and the pterygomandibular raphe.
  • Medially, its fibres mingle with those of orbicularis oris.Innervation: the buccal branch of facial.
  • It aids mastication and swallowing by pushing the cheeks against the molar teeth during chewing.

Mesodermal Origin

Muscles

Innervation

Somitomeres 1, 2

Superior, medial and ventral recti

Oculomotor (III)

Somitomere 3

Superior oblique

Trochlear (IV)

Somitomere 4

Jaw-closing muscles

Trigeminal (V)

Somitomere 5

Lateral rectus

Abducens (VI)

Somitomere 6

Jaw-opening and other 2nd arch muscles

Facial (VII)

Somitomere 7

Stylopharyngeus

Glossopharyngeal (IX)

Somites 1, 2

Intrinsic laryngeals

Vagus (X)

Somites 2-5

Tongue muscles

Hypoglossal (XII)

  • This is the posterior curtain-like part, and has no bony support. It does, however, contain a membranous aponeurosis.
  • The soft palate, or velum palatinum (L. velum, veil), is a movable, fibromuscular fold that is attached to the posterior edge of the hard palate.
  • It extends posteroinferiorly to a curved free margin from which hangs a conical process, the uvula (L. uva, grape).
  • The soft palate separates the nasopharynx superiorly and the oropharynx inferiorly.
  • During swallowing the soft palate moves posteriorly against the wall of the pharynx, preventing the regurgitation of food into the nasal cavity.
  • Laterally, the soft palate is continuous with the wall of the pharynx and is joined to the tongue and pharynx by the palatoglossal and palatopharyngeal folds.
  • The soft palate is strengthened by the palatine aponeurosis, formed by the expanded tendon of the tensor veli palatini muscle.
  • This aponeurosis attaches to the posterior margin of the hard palate.

The Temporomandibular Joint

  • This articulation is a modified hinge type of synovial joint.
  • The articular surfaces are: (1) the head or condyle of the mandible inferiorly and (2) the articular tubercle and the mandibular fossa of the squamous part of the temporal bone.
  • An oval fibrocartilaginous articular disc divides the joint cavity into superior and inferior compartments. The disc is fused to the articular capsule surrounding the joint.
  • The articular disc is more firmly bound to the mandible than to the temporal bone.
  • Thus, when the head of the mandible slides anterior on the articular tubercle as the mouth is opened, the articular disc slides anteriorly against the posterior surface of the articular tubercle

  •  Provides a rigid support system
  • Protects delicate structures (e. g., the protection provided by the bones of the vertebral column to the spinal cord)
  • Bones supply calcium to the blood; are involved In the formation of blood cells (hemopoiesis)
  • Bones serve as the basis of attachment of muscles; form levers in the joint areas, aIlowing movement

Innervation of the Skin

  • Innervation of the skin is mainly through the three branches of the trigeminal nerve (CN V).
  • Some skin over the angle of the mandible and anterior and posterior of the auricle is supplied by the great auricular nerve from the cervical plexus.
  • Some cutaneous branches of the auricular branch of the facial nerve also supplies skin on both sides of the auricle.
  • The trigeminal nerve is the general sensory nerve to the head, particularly the face, and is the motor nerve to the muscles of mastication.

The Ophthalmic Nerve

  • This is the superior division of the trigeminal nerve, the smallest of the three branches and is wholly sensory.
  • The ophthalmic nerve divides into three branches: the nasociliary, frontal and lacrimal just before entering the orbit through the superior orbital fissure.
  • The nasociliary nerve supplies the tip of the nose through the external nasal branch of the anterior ethmoidal nerve.
  • The frontal nerve is the direct continuation of CN V1 and divides into two branches, the supraorbital and supratrochlear.
  • The supratrochlear nerve supplies the middle part of the forehead.
  • The supraorbital nerve supplies the lateral part and the front of the scalp.
  • The lacrimal nerve, the smallest of the main ophthalmic branches, emerges over the superolateral orbital margin to supply the lacrimal gland and the lateral part of the upper eyelid.

The Maxillary Nerve

  • This is the intermediate division of the trigeminal nerve.
  • It has three cutaneous branches.
  • The infraorbital nerve is the largest terminal branch of the maxillary nerve.
  • It passes through the infraorbital foramen and breaks up into branches that supplies the skin on the lateral aspect of the nose, upper lip and lower eyelid.
  • The zygomaticofacial nerve, a small branch of the maxillary, emerges from the zygomatic bone from a foramen with the same name.
  • It supplies the skin over the zygomatic bone.
  • The zygomaticotemporal nerve emerges from the zygomatic bone from foramen of the same name.
  • It supplies the skin over the temporal region.

The Mandibular Nerve

  • This is the inferior division of the trigeminal nerve.
  • Of the three division of the trigeminal nerve, CN V3 is the only one that carries motor fibres (to the muscles of mastication).
  • The main sensory branches of the mandibular nerve are the buccal, auriculotemporal, inferior alveolar and lingual nerves.
  • The buccal nerve is a small branch of the mandibular that emerges from deep to the ramus of the mandible.
  • It supplies the skin of the cheek over the buccinator muscle, the mucous membrane lining the cheek, and the buccal surface of the gingiva.
  • The auriculotemporal nerve passes medially to the neck of the mandible and then turns superiorly, posterior to its head and anterior to the auricle. It then crosses over the root of the zygomatic process of the temporal bone, deep to the superficial temporal artery.
  • It supplies the auricle, external acoustic meatus, tympanic membrane, and the skin in the temporal region.
  • The inferior alveolar nerve is the large terminal branch of the posterior division of the mandibular nerve (the lingual nerve is the other terminal branch).
  • It enters the mandible through the mandibular foramen to the mandibular canal. In the canal, it gives branches to the mandibular teeth.
  • Opposite the mental foramen, this nerve divides into the mental nerve and the incisive nerve.
  • The incisive nerve supplies the incisor teeth, the adjacent gingiva and the mucosa of the lower lip.
  • The mental nerve emerges from the mental foramen and supplies the skin of the chin and the skin and mucous membrane of the lower lip and gingiva.
  • The lingual nerve is the smaller terminal branch of the mandibular nerve.
  • It supplies the general sensory fibres to the anterior two-thirds of the tongue, the floor of the mouth and the gingivae of the mandibular teeth.

  • Skull 
    Cranium
    o    Superior portion formed by the frontal. parietal, and occipital bones
    o    Lateral portions formed by the temporal and sphenoid bones
    o    Cranial base formed by the temporal. sphenoid, and ethmoid bones
    o    Fontanels-soft spots in which ossification is incomplete at birth

    Frontal bone
    o    Forms the forehead
    o    Contains the frontal sinuses
    o    Forms the roof of the orbits
    o    Union with the parietal bones forms the coronal suture

    Parietal bones
    o    Union with the occipital bone forms the lambdoid suture
    o    Union with the temporal bone forms the squamous suture
    o    Union with the sphenoid bone forms the coronal suture

    Temporal bones
    o    Contains the external auditory meatus and middle and inner ear structures
    o    Squamous portion-above the meatus: zygomatic process-articulates with the zygoma
    o    to form the zygomatic arch 

    •    Petrous portion
    o    Contains organs of hearing and equilibrium 
    o    Prominent elevation on the floor of the cranium

    •    Mastoid portion
    o    Protuberance behind the ear

    o    Mastoid process
    •    Glenoid fossa-articulates with the condyle on the mandible
    •    Styloid process-anterior to the mastoid process; several neck muscles attach here
    •    Stylomastoid foramen-located between the styloid and mastoid processes; facial nerve emerges through this opening
    •    Jugular foramen-located between the petrous portion and the occipital bone: cranial nerves IX. X, and XI exit
     

 

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