Anatomy of temporal region and muscles of mastication

Dr. Mohammed Mahmoud Mosaed

Lateral side of the skull

• The lateral side ofthe skull can bedivided into anupper temporalfossa and a lowerinfratemporal fossa,separated by thezygomatic arch.

The temporal fossa • The temporal fossa is the fan shaped space on the

lateral side of the skull above the zygomatic arch

• Boundaries

• Inferiorly: by the zygomatic arch and it is continuouswith the infratemporal fossa deep to the zygomaticarch

• Superiorly and posteriorly: by the temporal lines

• Anteriorly: by the posterior surface of the frontalprocess of the zygomatic bone and the posteriorsurface of the zygomatic process of the frontal bone

• Laterally: by the temporal fascia, which is overlying thetemporalis muscle

The floor of the temporal fossa • The floor of the temporal fossa is formed by the

frontal and parietal bones superiorly and the greaterwing of the sphenoid and squamous temporalinferiorly.

• All four bones of one side meet at an H-shaped suturaljunction termed the pterion.

• This is an important anthropometric landmark as itoverlies both the anterior branch of the middlemeningeal artery and the lateral fissure of the cerebralhemisphere.

• The pterion corresponds to the site of theanterolateral (sphenoidal) fontanelle of the neonatalskull which closes in the third month after birth

Temporal lines • The superior and

inferior temporal linesarch across the skullfrom the zygomaticprocess of the frontalbone to thesupramastoid crest ofthe temporal bone.

• The superior temporalline gives attachment tothe temporal fasciawhile the inferiortemporal line providesattachment fortemporalis.

Contents of temporal fossa

• Temporalis muscle

• Zygomaticotemporalnerves

• Deep temporal nerves

• Deep temporal artery

The temporalis muscle • The temporalis muscle is a large fan-shaped muscle

that fills much of the temporal fossa.• Origin: from the bony surfaces of the fossa and the

temporal fascia.• Insertion: on the coronoid process of the mandible• The more anterior fibers are oriented vertically while

the more posterior fibers are oriented horizontally.• Action: Temporalis is a powerful elevator of the

mandible and it’s posterior fibers retracts themandible.

• Nerve supply: deep temporal branches of themandibular nerve

• Blood supply: Deep temporal arteries

Muscles of mastication

Muscles of mastication• The muscle of mastication are the muscles that

move the mandible and act on thetempromandibular joint

• There are 4 muscles of mastication:

• Temporalis muscle

• Masseter muscle

• Medial ptergoid muscle

• Lateral ptergoid muscle

Masseter muscle

• Origin: lower border andmedial surface ofzygomatic arch

• Insertion: lateral surface ofthe ramus of the mandible

• Action: elevation of themandible

• Nerve supply: nerve tomasseter from the anteriordivision of the mandibularnerve

The medial pterygoid muscle • The medial pterygoid muscle has

deep and superficial heads.• Origin: The deep head from the

medial surface of the lateralpterygoid plate.

• The superficial head from thetuberosity of the maxilla.

• Insertion: Inserted to theroughened medial surface of theramus of mandible near the angle.

• Action: it elevates the mandible,also it assists in protruding thelower jaw.

• Nerve supply: by the nerve tomedial pterygoid from themandibular nerve

The lateral pterygoid• The lateral pterygoid is a thick triangular

muscle and has two heads: upper and lowerheads

• Origin: The upper head from theinfratemporal surface of the greater wing ofsphenoid

• The lower head from the lateral surface of thelateral pterygoid plate.

• Insertion: into the pterygoid fovea of theneck of mandible and to the articular disc oftemporomandibular joint.

• Action: it open the mouth by pully themandible forward onto the articular tubercleand is therefore the major protruder of thelower jaw.

• Nerve supply: by the nerve to lateralpterygoid from the mandibular nerve

Muscles of mastication

Temporomandibular Joint

• Articulation• The articular tubercle and the anterior portion of the mandibular fossa of

the temporal bone above• The head (condyloid process) of the mandible below.• The articular surfaces are covered with fibrocartilage.• Type of Joint• It is synovial. The articular disc divides the joint into upper and lower

cavities.• Capsule• The capsule surrounds the joint and is attached above to the articular

tubercle and the margins of the mandibular fossa and below to the neckof the mandible.

• Synovial Membrane• This lines the capsule in the upper and lower cavities of the joint.• Nerve Supply• Auriculotemporal and masseteric branches of the mandibular nerve

• The articular disc

• Divides the joint into upper and lower cavities.

• It is attached circumferentially to the capsule andto the tendon of the lateral pterygoid muscle .

• The disc moves forward and backward with thehead of the mandible during protraction andretraction of the mandible.

• The upper surface of the disc is concavoconvexfrom before backward and the lower surface isconcave

Ligaments• The lateral temporomandibular ligament

• Its fibers run downward and backward from thetubercle on the root of the zygoma to the lateralsurface of the neck of the mandible.

• The sphenomandibular ligament

• lies on the medial side of the joint. It is attachedabove to the spine of the sphenoid bone and belowto the lingula of the mandibular foramen.

• The stylomandibular ligament

• It is thickened band of deep cervical fascia thatextends from the apex of the styloid process to theangle of the mandible.

Temporomandibular joint as seen from the lateral (A) and medial (B) aspects

Movements

• The mandible can be depressed or elevated,protruded or retracted. Rotation can alsooccur, as in chewing.

• In the position of rest, the teeth of theupper and lower jaws are slightly apart. Onclosure of the jaws, the teeth come intocontact.

• Depression of the Mandible• As the mouth is opened, the head of the mandible

rotates on the undersurface of the articular discaround a horizontal axis.

• Depression of the mandible is brought about bycontraction of the digastrics, the geniohyoids, andthe mylohyoids and the lateral pterygoids.

• Elevation of the Mandible• First, the head of the mandible and the disc move

backward, and then the head rotates on the lowersurface of the disc.

• Elevation of the mandible is brought about bycontraction of the temporalis, the masseter, and themedial pterygoids.

• The head of the mandible is pulled backward by theposterior fibers of the temporalis.

• Protrusion of the Mandible

• The articular disc is pulled forward onto theanterior tubercle, carrying the head of themandible with it.

• All movement thus takes place in the uppercavity of the joint.

• In protrusion, the lower teeth are drawnforward over the upper teeth, which isbrought about by contraction of the lateralpterygoid muscles of both sides, assisted byboth medial pterygoids.

• Retraction of the Mandible

• The articular disc and the head of the mandibleare pulled backward into the mandibular fossa.Retraction is brought about by contraction of theposterior fibers of the temporalis.

• Lateral Chewing Movements

• These are accomplished by alternately protrudingand retracting the mandible on each side.

• For this to take place, a certain amount of rotationoccurs, and the muscles responsible on both sideswork alternately and not in harmony.

• Important Relations of the TemporomandibularJoint

• Anteriorly: The mandibular notch and themasseteric nerve and artery.

• Posteriorly: The tympanic plate of the externalauditory meatus and the glenoid process of theparotid gland

• Laterally: The parotid gland, fascia, and skin

• Medially: The maxillary artery and vein and theauriculotemporal nerve