Understanding the intricate anatomy of the head and neck is fundamental in various medical and dental disciplines. Two critically important, yet often challenging, deep regions are the infratemporal and pterygopalatine fossae. These spaces serve as conduits and contain vital neurovascular structures that supply and innervate the face, orbit, nasal cavity, and oral cavity. Complementing this understanding is the detailed knowledge of the muscles of mastication, which are directly involved in the function of chewing and play a pivotal role in the mechanics of the temporomandibular joint (TMJ).
Boundaries and Contents of the Pterygopalatine and Infratemporal Fossae
The infratemporal and pterygopalatine fossae are interconnected deep spaces on either side of the skull, crucial for the passage of major neurovascular bundles.
1. The Infratemporal Fossa (ITF)
The infratemporal fossa is an irregularly shaped space located inferior and medial to the zygomatic arch, and posterior to the maxilla. It is a complex region, deeply situated and often difficult to access surgically, serving as a significant crossroads for structures supplying the face and oral cavity.
1.1. Boundaries of the Infratemporal Fossa:
- Superior Boundary (Roof): Formed by the inferior surface of the greater wing of the sphenoid bone, which includes the foramen ovale and foramen spinosum. A part of the temporal bone (squamous and petrous parts) also contributes superiorly.
- Inferior Boundary (Floor): There is no distinct anatomical floor; it is open inferiorly to the neck and pharynx.
- Anterior Boundary: Comprises the posterior surface of the maxilla, featuring the maxillary tuberosity and openings for the posterior superior alveolar nerves.
- Posterior Boundary: Formed by the styloid process, the carotid sheath, and the tympanic plate, as well as the mastoid process of the temporal bone.
- Medial Boundary: Primarily formed by the lateral pterygoid plate of the sphenoid bone, which separates it from the pharynx.
- Lateral Boundary: Formed by the ramus of the mandible. The zygomatic arch overlies it superiorly.
1.2. Contents of the Infratemporal Fossa:
The ITF houses a remarkable collection of muscles, nerves, arteries, and veins:
- Muscles:
- Lateral Pterygoid Muscle: Occupies a significant portion, with two heads. (Detailed below in Muscles of Mastication).
- Medial Pterygoid Muscle: Also with two heads. (Detailed below in Muscles of Mastication).
- The inferior portion of the Temporalis Muscle passes through the fossa to insert on the coronoid process and anterior border of the ramus of the mandible.
- Nerves and Ganglia: All branches of the mandibular nerve (V3) pass through or originate within the ITF.
- Mandibular Nerve (V3): Exits the skull via the foramen ovale and divides into anterior (motor with buccal sensory) and posterior (sensory with auriculotemporal, lingual, and inferior alveolar) divisions.
- Branches of V3:
- Auriculotemporal Nerve: Wraps around the middle meningeal artery, supplies sensory innervation to the temporomandibular joint, external auditory meatus, tympanic membrane, and parotid gland (parasympathetic secretomotor fibers, though these originate from cranial nerve IX via the otic ganglion).
- Inferior Alveolar Nerve: Descends to enter the mandibular foramen, supplying sensation to mandibular teeth. Gives off the mylohyoid nerve (motor to mylohyoid and anterior belly of digastric).
- Lingual Nerve: Runs anterior and medial, supplying general sensation to the anterior two-thirds of the tongue and floor of the mouth. Carries chorda tympani fibers (taste and parasympathetic).
- Buccal Nerve: Passes between the heads of the lateral pterygoid, providing sensory innervation to the skin and mucous membrane of the cheek.
- Motor Branches: To the muscles of mastication (masseteric, deep temporal, nerves to medial and lateral pterygoid), mylohyoid, and anterior belly of digastric.
- Chorda Tympani Nerve: A branch of facial nerve (CN VII), it passes through the petrotympanic fissure to join the lingual nerve in the ITF, carrying taste sensation from the anterior two-thirds of the tongue and preganglionic parasympathetic fibers to the submandibular and sublingual glands.
- Otic Ganglion: A parasympathetic ganglion associated with the mandibular nerve, located immediately inferior to the foramen ovale, medial to the mandibular nerve root. It receives preganglionic fibers from the glossopharyngeal nerve (CN IX) via the lesser petrosal nerve and relays postganglionic fibers to the parotid gland (via auriculotemporal nerve).
- Arteries:
- Maxillary Artery: A terminal branch of the external carotid artery, it enters the ITF medial to the neck of the condyle of the mandible. It gives off numerous branches here before entering the pterygopalatine fossa. Key branches include the middle meningeal artery (enters foramen spinosum), inferior alveolar artery (enters mandibular foramen), deep temporal arteries, buccal artery, and numerous muscular branches.
- Veins:
- Pterygoid Venous Plexus: A dense network of veins, often surrounding the lateral pterygoid muscle. It drains blood primarily from the maxillary artery distribution and communicates with the cavernous sinus (via emissary veins), facial vein, and pharyngeal plexus. It typically drains into the maxillary vein.
- Ligaments:
- Sphenomandibular Ligament: Extends from the spine of the sphenoid to the lingula of the mandible, important for TMJ stability.
1.3. Clinical Significance of ITF:
The ITF is a significant site for the spread of infection from dental abscesses or oral cancers. It is also a common target for nerve blocks, such as the inferior alveolar nerve block. Due to its close proximity to the skull base, tumors of the parotid gland or nasopharynx can invade this space.
2. The Pterygopalatine Fossa (PPF)
The pterygopalatine fossa is a small, inverted pyramid-shaped space, deeply situated behind the maxilla, medial to the infratemporal fossa, and inferior to the orbit. It is a critical distribution center for the maxillary nerve and artery.
2.1. Boundaries of the Pterygopalatine Fossa:
- Anterior Boundary: Formed by the posterior surface of the maxilla.
- Posterior Boundary: Formed by the anterior surface of the pterygoid process of the sphenoid bone, specifically the base of the pterygoid plates.
- Medial Boundary: Formed by the perpendicular plate of the palatine bone, which separates it from the nasal cavity.
- Lateral Boundary: Open via the pterygomaxillary fissure, linking it to the infratemporal fossa.
- Superior Boundary (Apex): Formed by the body of the sphenoid bone and the orbital process of the palatine bone.
- Inferior Boundary (Base): Tapers down to the greater palatine canal.
2.2. Contents of the Pterygopalatine Fossa:
The PPF acts as a major neurovascular relay station.
- Nerves and Ganglia:
- Maxillary Nerve (V2): A purely sensory branch of the trigeminal nerve (CN V), it enters the PPF through the foramen rotundum from the middle cranial fossa. It then gives off several important branches:
- Zygomatic Nerve: Enters the orbit via the inferior orbital fissure, divides into zygomaticofacial and zygomaticotemporal nerves.
- Infraorbital Nerve: Continues anteriorly into the orbit via the inferior orbital fissure, then enters the infraorbital canal, emerging onto the face via the infraorbital foramen. Supplies sensation to the lower eyelid, side of the nose, upper lip, and anterior maxillary teeth (via anterior superior alveolar nerve branches).
- Posterior Superior Alveolar Nerves: Descend on the posterior surface of the maxilla, supplying the molar teeth and associated gingiva.
- Ganglionic Branches: Two or three short nerves connecting V2 to the pterygopalatine ganglion.
- Pterygopalatine Ganglion: A parasympathetic ganglion suspended from V2 by its ganglionic branches. It receives preganglionic parasympathetic fibers from the facial nerve (CN VII) via the greater petrosal nerve (part of the nerve of the pterygoid canal) and postganglionic fibers are distributed with branches of V2 to the lacrimal gland, nasal glands, and palatal glands. It also receives sensory branches from V2 and sympathetic fibers from the carotid plexus.
- Nerve of the Pterygoid Canal (Vidian Nerve): Formed by the union of the greater petrosal nerve (preganglionic parasympathetic from CN VII) and the deep petrosal nerve (postganglionic sympathetic from internal carotid plexus). It courses through the pterygoid canal to reach the pterygopalatine ganglion.
- Maxillary Nerve (V2): A purely sensory branch of the trigeminal nerve (CN V), it enters the PPF through the foramen rotundum from the middle cranial fossa. It then gives off several important branches:
- Arteries:
- Terminal Part of the Maxillary Artery: Enters the PPF via the pterygomaxillary fissure and terminates here, giving off critical branches:
- Sphenopalatine Artery: The largest branch, passes through the sphenopalatine foramen into the nasal cavity, supplying much of the nasal septum and lateral nasal wall. A major source of epistaxis.
- Descending Palatine Artery: Descends through the greater palatine canal, dividing into greater and lesser palatine arteries, supplying the hard and soft palates.
- Infraorbital Artery: Accompanies the infraorbital nerve into the orbit.
- Artery of the Pterygoid Canal: Accompanies the nerve of the pterygoid canal.
- Pharyngeal Branch: Supplies the roof of the pharynx.
- Terminal Part of the Maxillary Artery: Enters the PPF via the pterygomaxillary fissure and terminates here, giving off critical branches:
- Veins:
- Veins accompanying the arterial branches, draining primarily into the pterygoid venous plexus in the ITF.
2.3. Communications of the Pterygopalatine Fossa:
The PPF is a central hub for communications with several adjacent regions:
- Pterygomaxillary Fissure: Laterally, connects to the Infratemporal Fossa.
- Foramen Rotundum: Posteriorly, connects to the Middle Cranial Fossa (for V2 entry).
- Pterygoid Canal: Posteriorly, connects to the Middle Cranial Fossa/Foramen Lacerum.
- Sphenopalatine Foramen: Medially, connects to the Nasal Cavity.
- Inferior Orbital Fissure: Superiorly, connects to the Orbit.
- Greater Palatine Canal: Inferiorly, connects to the Oral Cavity (palate).
2.4. Clinical Significance of PPF:
Due to its numerous communications, the PPF is a pathway for the spread of infections or tumors from the nasal cavity, orbit, or oral cavity to the cranial cavity. It is also a site for nerve blocks (e.g., sphenopalatine ganglion block) to manage facial pain or nasal bleeding. Trigeminal neuralgia involving V2 often presents with symptoms referable to this region.
The Muscles of Mastication
The muscles of mastication are a specialized group of four paired muscles responsible for the movements of the mandible at the temporomandibular joint (TMJ), facilitating the processes of chewing, biting, and speaking. Unlike other facial muscles, these are derived from the first pharyngeal arch and are all innervated by the mandibular division of the trigeminal nerve (V3).
1. General Characteristics:
- Innervation: All four primary muscles (Masseter, Temporalis, Medial Pterygoid, Lateral Pterygoid) are innervated by branches from the mandibular division of the trigeminal nerve (V3).
- Action: Primarily responsible for the elevation (closing), depression (opening), protrusion (forward movement), retraction (backward movement), and lateral excursion (side-to-side movement) of the mandible.
- Origin: All originate from the skull.
- Insertion: All insert onto the mandible.
2. Specific Muscles of Mastication:
2.1. Masseter Muscle:
- Description: A powerful, quadrilateral muscle located on the side of the face, superficial to the ramus of the mandible. It has a superficial and a deep head.
- Origin:
- Superficial Head: Arises from the anterior two-thirds of the inferior border of the zygomatic arch.
- Deep Head: Arises from the posterior one-third of the inferior border and the entire medial surface of the zygomatic arch.
- Insertion:
- Superficial Head: Inserts onto the angle and lower posterior half of the lateral surface of the ramus of the mandible.
- Deep Head: Inserts onto the upper part of the ramus and the coronoid process of the mandible.
- Action: Primarily a strong elevator of the mandible, closing the mouth. It also contributes to protrusion (superficial fibers).
- Innervation: Masseteric nerve (a branch of the anterior division of V3).
2.2. Temporalis Muscle:
- Description: A large, fan-shaped muscle filling the temporal fossa, it is the most powerful muscle of mastication.
- Origin: Arises from the floor of the temporal fossa and the deep surface of the temporal fascia.
- Insertion: Its fibers converge as they descend, forming a strong tendon that passes deep to the zygomatic arch and inserts onto the coronoid process and the anterior border of the ramus of the mandible.
- Action:
- Anterior and Middle Fibers: Elevate the mandible, closing the mouth.
- Posterior (Horizontal) Fibers: Retract the mandible, pulling it backward.
- Innervation: Deep temporal nerves (branches of the anterior division of V3).
2.3. Medial Pterygoid Muscle:
- Description: A quadrilateral muscle located on the medial side of the ramus of the mandible, deep to the lateral pterygoid. It mirrors the masseter in its action and orientation from an internal perspective.
- Origin:
- Deep Head (Larger): Arises from the medial surface of the lateral pterygoid plate and the pyramidal process of the palatine bone.
- Superficial Head (Smaller): Arises from the maxillary tuberosity.
- Insertion: Inserts onto the medial surface of the ramus and angle of the mandible, inferior to the mandibular foramen.
- Action: Acts synergistically with the masseter to elevate the mandible, closing the mouth. It also contributes to protrusion and grinding movements (unilateral contraction causes side-to-side movement opposite to the contracting muscle).
- Innervation: Nerve to medial pterygoid (a branch from the main trunk of V3).
2.4. Lateral Pterygoid Muscle:
- Description: A short, thick muscle with two heads, lying almost horizontally in the infratemporal fossa. It is the only muscle of mastication primarily responsible for depressing (opening) the mandible.
- Origin:
- Superior Head: Arises from the infratemporal surface and crest of the greater wing of the sphenoid bone.
- Inferior Head: Arises from the lateral surface of the lateral pterygoid plate.
- Insertion: Both heads insert into the pterygoid fovea on the neck of the condyloid process of the mandible, and into the articular capsule and articular disc of the temporomandibular joint.
- Action:
- Bilateral Contraction: Protrudes the mandible and depresses (opens) the mouth, often working with suprahyoid muscles.
- Unilateral Contraction: Produces side-to-side (lateral) movements of the mandible, crucial for grinding food.
- The superior head is particularly active in clenching, while the inferior head is more active in opening.
- Innervation: Lateral pterygoid nerve (a branch of the anterior division of V3).
3. Coordinated Actions and Clinical Significance:
The muscles of mastication work in concert to produce the complex movements required for chewing. Elevation is primarily by the masseter, temporalis, and medial pterygoid. Depression is initiated by the lateral pterygoid, assisted by gravity and suprahyoid muscles. Protrusion is mainly by the lateral pterygoids and supported by the medial pterygoids and superficial masseter. Retraction is primarily by the posterior fibers of the temporalis. Lateral excursion involves alternating unilateral contraction of the medial and lateral pterygoids.
Clinically, these muscles are highly relevant to temporomandibular joint disorders (TMJD), where dysfunction can lead to pain, clicking, and restricted jaw movement. Conditions like bruxism (teeth grinding) and trismus (restricted mouth opening) often involve spasm or hypertrophy of these muscles. Nerve damage to V3, for instance from trauma or surgery, can significantly impair masticatory function.
Conclusion
The infratemporal and pterygopalatine fossae represent intricate anatomical regions, each serving as critical junctions for neurovascular structures vital to head and neck function. Their complex boundaries and contents underscore their importance as pathways for nerve supply, arterial branches, and venous drainage, as well as potential routes for disease spread. Simultaneously, the muscles of mastication – the temporalis, masseter, medial pterygoid, and lateral pterygoid – are the chief architects of mandibular movement. Their precise actions, all orchestrated by the mandibular division of the trigeminal nerve, enable the fundamental processes of chewing and contribute significantly to oral health and speech. A thorough comprehension of these structures is indispensable for clinicians across multiple specialties, ranging from oral and maxillofacial surgery to neurology and general practice.
References
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