S5 Learning Objectives

1. Describe the significant bony landmarks delineate the temporal fossa and infratemporal fossa. Which bony structures and openings relate to mastication, the temporomandibular joint (TMJ), and passages for key neurovasculature? What are the pterygoid plates, which muscles attach here, and what function does the pterygoid hamulus serve?

Temporal fossa

The temporal fossa is a depression on the lateral cranium that houses the temporalis muscle and the deep temporal aa. and nn. The temporalis m. passes deep to the zygomatic arch to insert on the mandible.


Boundaries:

Infratemporal fossa

The infratemporal fossa is a funnel-shaped space deep to the mandibular ramus that houses three of the muscles of mastication – temporalis m., lateral pterygoid m., and medial pterygoid m. Branches of the mandibular n., the maxillary a., and the pterygoid venous plexus are also found here. The superior portion of the fossa includes the mandibular fossa of the temporal bone, which forms the superior aspect of the temporomandibular joint surface.

Boundaries:

Communications

The infratemporal fossa has communications with the middle cranial fossa, orbit, pterygopalatine fossa, and middle ear.

Pterygoid plates

The medial and lateral pterygoid plates are inferior projections of the sphenoid bone that act as attachment points for muscles. The lateral pterygoid plate marks the medial boundary of the infratemporal fossa. The inferoposterior corner of the medial pterygoid plate narrows into a hook, or hamulus, around which the tendon of the tensor veli palatini m. wraps medially before meeting its contralateral partner in a midline raphe.



2. Describe the temporomandibular joint (TMJ). What type of joint is the TMJ? What actions occur here? What major ligaments and other connective tissues limit its range of motion?

The temporomandibular joint is a synovial joint between the mandibular fossa and articular tubercle of the temporal bone superiorly and the condylar process of the mandible inferiorly. The articulating portions of the bones are separated by an intracapsular, fibrocartilaginous articular disc, which divides the joint into superior and inferior compartments.

The actions produced at the TMJ move the mandible into different positions. The mandible can be elevated or depressed, and protracted (pulled anteriorly onto the articular tubercle) or retracted (pulled posteriorly into the mandibular fossa). These movements are accomplished within the separate compartments of the joint: gliding movements (protraction and retraction) occur in the upper synovial cavity, and hinge movements (elevation and depression) occur in the lower synovial cavity.


Several structures serve to reinforce the TMJ. The lateral ligament is an extracapsular ligament that forms part of the lateral joint capsule. It restricts posterior and lateral movements of the condylar process. The sphenomandibular ligament from the spine of the sphenoid to the ramus of the mandible and is tense when the TMJ is in an intermediate position. The stylomandibular ligament runs from the styloid process of the temporal bone to the mandibular ramus. It does not limit motion, per se, but reinforces the joint.

3. Describe the muscles of mastication. What are their attachments, innervation, and actions? What muscles comprise the masticatory (pterygomasseteric) sling?

The muscles of mastication are a group of four muscles with attachments to the cranium and mandible that move the mandible into different positions, especially during chewing or mastication. As a group these muscles are supplied by branches of the mandibular n. (CN V3), the maxillary a., and the pterygoid venous plexus.

The pterygomasseteric sling (masticatory sling) is composed of the masseter m. and the medial pterygoid m. Both of these have a superior attachment to the cranium and an inferior attachment to the mandibular ramus and angle, but attach to opposite sides (i.e.: the masseter attaches on the lateral surface of the mandibular ramus, and the medial pterygoid attaches to the medial surface). In this way, they form a sling that supports the weight of the mandible against the pull of gravity, much like one might use a sling to support their upper limb after injury. This acts as an additional stabilizer for the temporomandibular joint.

4. What are temporomandibular disorders (TMD)? What occurs with dislocation of the jaw (subluxation of the temporomandibular joint)?

Temporomandibular disorder (TMD) is very broadly defined as “pain around the temporomandibular joint.” This pain can be caused by any number of pathologies, but most commonly is related to inflammation of joint components including the bony articular surfaces, the articular disc, the retrodiscal tissue and neurovasculature, and the muscles of mastication.


Dislocation or subluxation of the TMJ is a specific condition wherein hyper-protraction of the mandible results in the condylar process moving anterior to the articular tubercle. While contraction of the lateral pterygoid muscle can be sufficient to dislocate the mandible, external applied force is often required to move the condyle back into the mandibular fossa.

5. Describe the divisions and terminal branches of V3 (mandibular n.). What modalities do they carry and what do they innervate? Which branches are affected by an inferior alveolar nerve block? What bony opening(s) do fibers of V3 use to exit the skull? What key autonomic ganglia and pathways are associated with the mandibular n. (V3)?

The mandibular n. (CN V3) is the only division of the trigeminal n. (CN V) to carry somatic motor fibers in addition to somatic sensory. It exits the middle cranial fossa via the foramen ovale and emerges in the infratemporal fossa. Once there, it first branches into anterior and posterior divisions before giving rise to individually named branches. In general, most somatic motor branches to the muscles of mastication (with the exception of the nerve to mylohyoid) arise from the anterior division, and somatic sensory branches arise from the posterior division (with the exception of the (long) buccal n.). 

The mandibular n. communicates with the otic ganglion near the foramen ovale, and picks up hitchhiking postganglionic parasympathetic fibers that are then carried along the auriculotemporal n. to the parotid gland.

The chorda tympani carries special taste sensory and preganglionic parasympathetic fibers that originate with the facial n. (CN VII). It courses through infratemporal fossa to join and hitchhike along with the lingual n. branch of V3 into the oral cavity, where it distributes parasympathetic fibers to the submandibular ganglion and special sensory fibers to the anterior tongue.

Trigeminal n. (CN V)

6. Describe the pathway of special sensory (taste) and somatic sensory information from the tongue to the brain. 

Sensory innervation of the tongue includes both somatic and special taste sensory, and separate nerves innervate the root and body of the tongue for each. For the root of the tongue, both somatic and special sensation is carried primarily by the glossopharyngeal n. (CN IX), with a small region near the epiglottic vallecula receiving somatic sensation from the vagus n. (CN X). Somatic sensation from the body of the tongue is carried by the lingual n. (a branch of V3), and special sensory input is carried by the chorda tympani (a branch of the facial nerve that hitchhikes with the lingual n.).



Special sensory (taste):


Somatic sensory

7. Define the three divisions of the maxillary a. What are the major branches of the maxillary a. that supply the muscles of mastication, the meninges, and TMJ? What are the major branches of the maxillary artery associated with the pterygopalatine fossa? What general areas to do these arteries supply?

The maxillary a. is divided into three regions based on its spatial relationship to the lateral pterygoid m. The proximal 1st part is also known as the mandibular part, as it sits deep to the mandibular ramus. The 2nd, or pterygoid part, begins as the artery crosses superficial to the lateral pterygoid m. The distal 3rd part, or pterygopalatine part, begins as the artery moves anterior to the lateral pterygoid m. to dive anteromedially into the pterygopalatine fossa via the pterygomaxillary fissure.


Maxillary a.

Inferior alveolar a.: Mandibular teeth, lower lip

8. What is the pterygoid venous plexus?

The pterygoid venous plexus is a network of smaller veins that sit within the infratemporal fossa and drain the regions typically supplied by the maxillary a. Its major tributaries include:



In addition to draining venous blood from these territories, the pterygoid venous plexus also participates in several anastomoses with other regions of the head. The include:



Posteriorly, this network condenses to form a short maxillary v. that drains into the retromandibular v. From there blood can then either drain through the anterior division to the facial v. and into the internal jugular v., or it may drain through the posterior division, which joins the posterior auricular v. to form the external jugular v.