INFRATEMPORAL FOSSA AND MUSCLES OF MASTICATION
Learning Objectives
By the end of the course students will be able to:
1. Identify the muscles of mastication and give their functions.
2. Define the boundaries and contents of the infratemporal fossa.
3. Identify the branches of the trigeminal nerve and their functions related to
mastication and sensation from the face.
4. Identify the chorda tympani nerve and give its function.
5. Describe the structure and function of the temporomandibular joint.
6. Describe the submandibular and sublingual salivary glands and give their
innervations.
Reference: Moore, Clinically Oriented Anatomy, chapter 7
Particularly relevant Blue Boxes in Moore:
●Inferior Alveolar Nerve Block, p. 927.
●Dislocation of the TMJ, p. 927
TEMPORAL AND INFRATEMPORAL REGIONS
INFRATEMPORAL FOSSA (Moore 916-921)
Boundaries: The infratemporal fossa is the area in the skull below the zygomatic arch. It
is bounded anteriorly by the maxilla, laterally by the ramus of the mandible, medially by
the lateral pterygoid plate and superiorly by the sphenoid bone.
The major artery in the infratemporal fossa is the maxillary artery, a branch of the
external carotid (remember SALFOPSMAX).
Nerves in the Infratemporal Fossa (Moore 921; Netter 45):
Mandibular Division of Trigeminal Nerve - V3 (Netter 45)
General Description -- passes through foramen ovale to infratemporal fossa.
Motor root -- innervates the four muscles of mastication (temporalis, masseter, medial
pterygoid, lateral pterygoid), mylohyoid, anterior belly of digastric, tensor veli palatini,
and
tensor tympani.
Sensory root -- innervation to temporal region, anteriorsuperior ear, external acoustic
meatus, general sensation for anterior 2/3 of the tongue, mucous lining of cheek, lower
teeth and
gingiva, sensory to lower jaw.
Pathways of V3
After passing through foramen ovale into the infratemporal fossa, V3 forms a trunk with
the following branches:
1. Meningeal branch - returns to cranial cavity through foramen spinosum with middle
meningeal artery; distributes with this artery to the dura mater.
2. Medial pterygoid nerve -- nerve to this muscle; also branches to tensor veli palatini and
tensor tympani.
Main trunk then divides into:
A. Anterior Division - mainly motor; one sensory branch (buccal nerve).
1. Masseteric nerve - nerve to masseter muscle; also branch to temporo-mandibular
joint.
2. Deep temporal nerves -- anterior and posterior branches to temporalis muscle.
3. Nerve to lateral pterygoid -- nerve to this muscle.
4. Long Buccal nerve - pierces buccinator to provide sensory innervation to the inside
cheek, and gingiva. (NOTE: buccal branches of Facial Nerve - VII, provide motor
innervation to the buccinator muscle).
B. Posterior Division - mainly sensory; one motor branch (mylohyoid nerve.)
1. Auriculotemporal nerve -- two roots encircle the middle meningeal artery. The
nerve then passes to the temporal region accompanying the superficial temporal artery.
Its branches are: a) parotid, b) articular branches to T.M. joint, c) anterior auricular, d)
external acoustic meatus, e) terminal branch is superficial temporal.
2. Lingual nerve -- sensory innervation for anterior 2/3 of the tongue; joined high in
infratemporal fossa by chorda tympani nerve (branch of Facial Nerve VII); emerges
through petrotympanic fissure. Chorda tympani carries parasympathetic preganglionic
fibers to submandibular ganglion -- synapse with post-ganglionic fibers to submandibular
and sublingual glands. Chorda tyrnpani also carries taste fibers for the anterior 2/3 of the
tongue.
3. Inferior alveolar nerve -- enters the mandible through the mandibular foramen as it
passes along the mandibular canal; it gives inferior dental branches to inferior teeth.
Mental nerve passes out the mental foramen to supply the chin and lower lip; inferior
alveolar nerve continues in the canal to innervate the lower incisors. Mylohyoid nerve
passes along the mylohyoid groove; it supplies motor innervation to mylohyoid and
anterior belly of digastric muscles. Mylohyoid nerve arises just before the inferior
alveolar nerve passes into mandibular foramen.
MUSCLES OF MASTICATION (Moore 921)
The Primary Muscles of Mastication: All are innervated by the mandibular (motor)
division of the trigeminal nerve V3 (Netter 54, 55). The nerve to the medial pterygoid
comes off the trunk of the mandibular nerve, while the other motor nerves to the muscles
of mastication arise from the anterior division of the trunk. (Netter 45)
1. Temporalis Muscle
Innervation - Anterior and posterior deep temporal nerves.
Origin-Temporal fossa; it is a large fan-shaped muscle.
Insertion - The fibers converge to pass medial to the zygomatic arch and terminate in a
tendinous insertion onto the anterior and posterior aspects of the coronoid process. The
terminal portion of the insertion on the anterior aspect of the ramus extends inferiorly into
the retromolar triangle, extending below the occlusal plane.
Action - The fibers of the muscle may be divided into three portions: i.e., anterior fibers
(powerful elevators of the mandible); middle fibers (elevators and retractors of the
mandible); and posterior fibers (retracts the mandible).
2. Masseter Muscle
Innervation - Masseteric nerve which enters the deep side of the muscle from the
infratemporal fossa by passing through the mandibular notch.
Origin - Both superficial and deep. The superficial portion arises from the inferior border
of the zygomatic bone. If well developed, it may also arise from the zygomatic process
of the maxilla. The superficial fibers end on the zygomatic bone and do not pass the
zygomaticotemporal suture. The deep portion arises from the entire length of the
zygomatic arch -- from the zygomatic process of the maxilla to the anterior slope of the
articular eminence.
Insertion – Superficial portion inserts into the lower half of the lateral surface of the
ramus. The deep portion inserts above the superficial fibers into the lateral aspect of the
coronoid process and the upper part of the ramus.
Action - The muscle acts as a powerful elevator of the mandible. The deep fibers assist
in elevation, but also act to retract the mandible during the closing movement.
3. Medial Pterygoid
Innervation - Medial pterygoid nerve.
Origin - Medial surface of the lateral pterygoid plate, the pyramidal process of the
palatine bone and the maxillary tuberosity.
Insertion - Medial surface of the ramus and angle of the mandible. It forms a
“mandibular sling” with the masseter muscle.
Action - Assists the masseter in elevating the mandible. Alternate contraction of the
medial pterygoids may cause a “grinding” action.
4. Lateral Pterygoid
Innervation - Lateral pterygoid nerve.
Origin - Dual. Upper portion originally called the sphenomeniscus muscle. It arises from
the infratemporal crest and surface of the greater wing of the sphenoid bone.
Lower portion arises from the lateral surface of the lateral pterygoid plate.
Insertion - Upper portion has some fibers inserting into the meniscus. The bulk of these
fibers blends with the lower portion and inserts into the ptergoid fovea.
Lower portion inserts into pterygoid fovea.
Note: In many instances, no fibers of the lateral pterygoid muscle attach to the meniscus.
Action - The lower fibers protrude the mandible when acting bilaterally. Acting
unilaterally, they promote lateral movement of the mandible on the opposite side, since
the mandible is a single, horseshoeshaped bone. The lateral pterygoid muscle actually
pulls the condyle medially on its own side.
Note: The meniscus is attached to the lateral and medial poles of the condylar process,
and is carried anteriorly and posteriorly with movement of the mandible proper (see TMJ
section).
The Accessory Muscles of Mastication
These muscles assist in promoting smooth movement of the mandible upon
protrusion/retrusion and opening
1. Diagastric Muscle
Innervation - Anterior belly (mylohyoid nerve from inferior alveolar branch of V3)
Posterior belly (cranial nerve VII-facial).
Origin - Anterior belly arises from the intermediate tendon. Posterior belly arises from
the mastoid notch medial to the mastoid process.
Insertion - Anterior belly into the digastric fossa of the mandible. Posterior belly inserts
into the intermediate tendon.
Action - With the stylohyoid and infrahyoid muscles fixing the hyoid bone in postion,
contraction of the digastric muscle assists in smoothing the lowering and retrusion of the
mandible.
2. Geniohyoid Muscle
Innervation:_ C1
Origin - Inferior mental spine (gential tubercle).
Insertion - Body of the hyoid bone.
Action- Aids in retrusion of the mandible.
TEMPOROMANDIBULAR JOINT (TMJ) (Moore 916-921)
Osteology: The TMJ (Netter 18, 54, 55) is the articulation between the temporal bone
and the condyle (head) of the mandible. The temporal bone portion is divided into two
parts: the posterior part is the articular fossa (mandibular fossa) and the anterior part is
the articular tubercle (eminence). The term “condylar process” refers to the combined
head and neck portions of the mandible. At rest, the condyle is positioned in relation to
the posterior incline of the articular eminence. The condyle is not located in the roof of
the fossa, which is very thin. The translucent roof is not strong enough to withstand
pressure from the condyle.
Articular Disc (Meniscus): The disc, or
meniscus, (Netter 16, 54) lies between the
temporal bone and the mandibular condyle.
It is composed of dense fibrous connective
tissue containing nests of cartilage cell.
Therefore, it is defined as fibrous cartilage,
although fibrous connective tissue would be
more accurate. This disc separates the
articular cavity into superior and inferior
synovial cavities. The superior surface of
the disc moves on the inferior surface of the
articular fossa and eminence. The disc is
oval-shaped and biconcave (somewhat like
a “distorted erythrocyte”). It is attached to
the inner aspect of the joint capsule.
Anteriorly, the disc is fused to the capsule.
Posteriorly, the disc connects with the
retrodiscal pad of tissue (a layer of loose vascularized connective tissue). Laterally and
medially, the disc is independently bound to the lateral and medial poles of the condyles,
and has no direct relation to the capsule. It is this attachment of the disc to the condyle
that causes the disc to move in synchrony with the condyle during its excursions.
Articular Capsule: The capsule encloses the articular cavity and appears somewhat like
a sleeve or collar surrounding the articular elements. It extends from its superior
attachment at the margin of the fossa and eminence to its inferior attachment around the
neck of the mandible. The capsule consists of an outer, fibrous layer and an inner, lining
layer called the synovial membrane. The latter elaborates a lubricating and nutritional
synovial fluid. The synovial membrane is highly vascularized. It lines all areas of the
joint which are not subjected to pressure. Therefore, the synovial membrane is not
present on the articulating surfaces of the temporal bone, condyle and disc.
Classification: The TMJ is classified broadly as a diarthrodial joint. All diarthrodial
joints are characterized by a covering of cartilage on their opposing surfaces. Although
the cartilage is usually hyaline, it is fibrocartilage in the TMJ. All diarthrodial joints are
lined by a synovial membrane. Diarthrodial joints are characterized by ligments which
surround and stabilize the joint. Diarthrodial joints may or may not have a disc or
meniscus.
The specifics of classification list the lower joint cavity as ginglymus, or acting as a
hinge. This hinge motion is displayed in passive mandibular opening; e.g., during
yawning. The upper joint cavity is a freely gliding joint and so, is classified as arthrodial.
The classification of the TMJ: ginglymo-arthrodial diarthrosis (diarthrodial) or a slidinghinge
joint, which is diarthrodial.
Ligaments: There are three ligaments associated with the movements of the TMJ:
Stylomandibular - extends from the tip of the styloid process of the temporal bone
to the angle of the mandible. This is not a true ligament but merely folded
suprahyoid fascia which is a projection of the superficial investing fascia of the
neck.
Sphenomandibular - forms the spine of the sphenoid bone to the lingula of the
mandible.
Temporomandibular - a lateral thickening of the articular capsule. This lateral
reinforcement is the only major ligamentous stabilization of the TMJ.
Nerve Supply: Generally described with the aid of a modified Hilton’s Law - the nerve
supply to a joint is through branches of any nerve which courses in the vicinity. The
innervation of the TMJ most often described is through the auriculotemporal nerve. This
nerve courses deep to the neck of the mandible and then posterior to the joint structures
(in front of the ear).
The nerve supply to the TMJ, per se, is not motor since the skeletal muscles which move
the joint are innervated at locations usually far removed from the joint. The supply to the
joint, other than autonomic to blood vessels, is sensory (i.e., pain, proprioceptive), and
the receptors are mostly in the capsule and its attached structures. The masseteric nerve
often supplies a proprioceptive branch to the TMJ.
Blood Supply: The major arterial supply of the TMJ is derived from branches of the
superficial temporal and maxillary arteries:
Middle temporal and transverse facial, as well as direct branches from the
superficial temporal artery.
Deep auricular, anterior tympanic, middle meningeal and masseteric branches of
the maxillary artery.
NOTE:
The tendinous fibers of the lateral pterygoid muscle insert through the capsule
into the neck of the mandible and into the articular disc. Contraction of the lower
head of the latral ptergoid pulls the condyle with it. (See muscles of mastication
for further explanation of muscle function.)
Any movement of the single, rigid mandible always involves action in both TM
joints (double-jointed). Because of this bilateral relationship, the two joints are
often referred to as a single unit: the cranio-mandibular articulation. Each TMJ is
also “double-jointed” because each has two compartments (upper and lower) with
separate actions (arthrodial and ginglymus).
TEMPORAL AND INFRATEMPORAL FOSSA STRUCTURE LIST
Osteology
Temporal bone
Zygomatic process
Mandibular fossa
Nerves
Articular tubercle
Petrotympanic fissure
Trunk of V3
Mandible
Otic ganglion
Condyle
Auriculotemporal
Head, neck, fovea
Inferior alveolar
Mandibular fossa
Mylohyoid n.
Coronoid process
(Long) buccal
Ramus, angle, body
Anterior and posterior deep temporal
Lingula
Posterior superior alveolar (from V2)
Mandibular foramen
Lingual
Inferior alveolar canal
Mylohyoid groove
Chorda tympani (from CN VII)
Sphenoid bone
Greater wing
Pterion
Infratemporal crest
Foramen ovale
Foramen spinosum
Lateral pterygoid plate
Pterygomaxillary fissure
Maxilla
Posterior slope
Posterior superior alveolar foramina
Muscles of Mastication
Masseter
Temporalis
Lateral Pterygoid
Medial Pterygoid