GA Infratemporal Fossa and Oral Cavity

LMN Lesion of TONGUE

* A lesion of the hypoglossal nerve on one side will cause the tip of the tongue to move toward the side of the lesion. The genioglossus on the affected side is not working; it can't pull the tongue forward on that side. Sticking the tongue out can check on the integrity of the hypoglossal nerve. Fasciculations and atrophy of the tongue can occur on the side that is de-innervated. A lower motor lesion of the hypoglossal nerve affects the muscle on the same side (ipsilateral side).

TMJ - Capsule and Ligaments

1. The stable position of the TMJ is when the jaw is elevated. 2. A capsule surrounds the joint. 3. There are ligaments that strengthen the joint -Lateral temporomandibular- Part of the capsule that prevents excessive side to side movements and some depression. Next page also: -Stylomandibular ligament (2)- Prevents excessive protrusion and depression. -Sphenomandibular ligament (3)- Prevents excessive depression

Oral Cavity-TongueSummary of Cranial nerves related to tongue.

1.Anterior two thirds of the tongue. - general sensation- CNV V3 Lingual nerve branch. - special sensation- taste is from CN VII chorda tympani branch 2.Posterior one third of the tongue. - general sensation- CN IX glossopharyngeal nerve - special sensation-CN IX glossopharyngeal nerve. 3. Motor to the tongue is the Hypoglossal Nerve, CN XII

Summary slide

1.Lateral Pterygoids- main action is to protract (protrude) and depress. 2.The Posterior Fibers of Temporalis retract the jaw. 3.Medial Pterygoid, Masseter and Anterior Fibers of Temporalis elevate the jaw. 4.Mylohyoid and Anterior Digastric assist in more forceful opening. A lesion of CN V affecting the muscles of mastication would cause the jaw to deviate toward the side of the lesion. The Lateral Pterygoid muscles protrude the jaw and if for example one side was not contracting the jaw would deviate to the side of the lesion as the unaffected muscle protrudes the jaw.

Auriculotemporal Nerve in Detail

A classic anatomical landmark especially important for lab id, is the auriculotemporal nerve and middle meningeal artery relationships in the infratemporal fossa. The auriculotemporal nerve divides into two parts that circle around ("hugs") the middle meningeal artery as the middle meningeal artery enters into the foramen spinosum. The auriculotemporal nerve is a sensory branch of the V3 Mandibular nerve from Trigeminal but it also contains postganglionic parasympathetic fibers from the otic ganglia located in the infratemporal fossa that are secretomotor to the parotid gland. The preganglionic parasympathetic fibers come from the glossopharyngeal nerve along the lesser petrosal nerve to the otic ganglia.

Development of the Tongue

Develops from the 1st to fourth pharyngeal arches. For innervation: the anterior two thirds of the tongue develops from the 1st arch and is then related to CN V3. The second arch is also involved with the anterior two thirds of the tongue with innervation of taste provided by the chord tympani, a branch of CN VII. CN VII is associated with structures derived from the second arch. The posterior one third of the tongue develops from the third arch which is associated with CN IX and thus the posterior third of the tongue is innervated by CN IX Glossopharyngeal nerve. 1. Anterior two thirds of tongue a. Develop from one median lingual swelling (tuberculum impar) and two lateral swellings (tongue buds) that are found in the first pharyngeal arch. The lateral swellings grow over the median and form the anterior two thirds of the tongue b. Somatic sensory-pain carried on lingual nerve from CN V3. Taste carried on the chorda tympani nerve, a branch of CN VII. 2. Posterior one third of the tongue- Develops primarily from pharyngeal arch 3, and innervation is from the nerve associated with arch three, CN IX. A smaller portion of the tongue, the base, is derived from pharyngeal arch 4 and is innervated by arch 4 nerve, CN X. 3. Tongue muscles are formed by myoblasts that migrated to the tongue region from somites. Motor innervation to the tongue muscles is from CN XII, except for the palatoglossus.

Motor to the Tongue is the Hypoglossal nerve CN XII.

Hypoglossal nerve exits the skull through the hypoglossal canal. The next it can be localized in lab is in the neck. That dissection was moved by unit directors request to unit 5. But it is still important to know the innervation and action of the hypoglossal nerve and the tongue in this unit. It is important for both gross and neuroanatomy for diagnosis of upper or lower motor lesions.

INCISAL CHEWING - BITING

Incisal chewing is when the condyles rotate forward on both sides and depress the mandible symmetrically. To return to stable position, the mandibular condyles rotate and the condyles are elevated.

Lateral Pterygoid

Lateral Pterygoid- Origin from greater wing of the sphenoid bone and the pterygoid plate. Insertion onto the condyle and the articular disc. Actions- Protracts the mandible and depresses. Has and upper and lower head. The lingual or other branches of the mandibular nerve can pass between the heads and can be impinged with resultant sensory symptoms. The upper head from the sphenoid bone is sometimes referred to as the" sphenomeniscal muscle"

MASSETER

Masseter- Origin from the zygomatic bone and the zygomatic process of the temporal bone. Insertion onto the ramus and angle of the mandible. Elevates the mandible.

Medial Pterygoid

Medial Pterygoid- Origin on Pterygoid plate. Insertion on inside of the angle of the mandible. Elevates the mandible.

Bones and TMJ

Modified hinge joint between mandibular condyle (1) and mandibular fossa of zygomatic process (2).

Hypoglossal nerve

Motor to the tongue is the Hypoglossal nerve. CN XII. Hypoglossal nerve arises from the medulla. There are two hypoglossal nerves. When the tongue is "stuck out", the genioglossus muscles on both sides pull the tongue forward. Hypoglossal nerve is commonly said to innervate the genioglossus, hyoglossus, styloglossus and the intrinsic muscles of the tongue. There is some variability in the literature if it innervates other muscles. The primary one to remember for clinical cases is the genioglossus.

TMJ - PROPERTIES 2

Movements-three types. Rotation- depression and elevation Translational- Protrusion (Protraction) and retraction. Side to side movements.

MUSCLES OF MASTICATION

Muscles of Mastication: Temporalis, Masseter, Lateral Pterygoid, Medial Pterygoid. Accessory muscles of Mastication: Mylohyoid, Anterior digastric muscle are the primary accessory muscles to know for this session. Other muscles associated with mastication or the hyoid bone and covered in multiple sessions are the geniohyoid and stylohyoid. Infrahyoid muscles covered in the neck session are sternohyoid, thyrohyoid, omohyoid, and sternohyoid. A primary function of these muscles related to mastication is stabilization of the hyoid bone. "Muscles of Mastication". Innervated by motor branches of the mandibular nerve.

MYLOHYOID & ANTERIOR DIGASTRIC

Mylohyoid and Anterior belly of the Digastric muscle. Mylohyoid. Origin from deep surface of the mandible. Insertion onto the hyoid bone. Anterior digastric- origin from inner surface of mandible. Inserts onto the hyoid bone. These muscles are innervated by the nerve to the mylohyoid a motor branch of V3. These muscles depress the mandible.

Oral Cavity

Oral Cavity- Oral Vestibule- area bounded by the cheeks externally and the teeth and gums internally. Parotid duct empties here by upper second molar. Oral Cavity Proper- bounded by the teeth and gums anteriorly and laterally, the roof is the palate, the floor is the tongue and mucosa supported by the geniohyoid and mylohyoid muscles. Connects posteriorly with the oropharynx. Sublingual (paralingual) space- space between mylohyoid inferiorly and the tongue and mucosa superiorly.

TMJ - MOVEMENTS -3

Second step-Open wider. The mylohyoid and anterior digastric can depress the mandible further. This is very unstable and the jaw can be dislocated in front of the articular process. The ligaments can become stretched. This contributes to the development of TMJ syndrome which is a common pathology and could include pain and clicking at the joint.

Sensory Nerves of Trigeminal V3 in the Infratemporal Fossa.

Sensory Branches of the Trigeminal nerve in the infratemporal fossa. The Mandibular nerve or the third branch of the Trigeminal nerve enters the Infratemporal Fossa through the Foramen ovale. Branches: Auriculotemporal nerve-Sensory from the auricle of the ear and the skin of the temporal region. Sends fibers to the TMJ. Postganglionic Parasympathetic fibers are carried on this nerve from the otic ganglia to the Parotid gland. These fibers are secretomotor to the gland and the preganglionic fibers originate with the glossopharyngeal nerve. Buccal Nerve- Somatic sensory from the mucosa and skin of the cheek. (do not confuse this nerve with the Buccal branch of the facial nerve which innervates the Buccinator muscle, a muscle of facial expression) Lingual Nerve-Somatic sensory from the anterior two thirds of the tongue. Special sensation-taste to the anterior two thirds of the tongue with fibers from the chorda tympani nerve which is a branch of the facial nerve in the infratemporal fossa. The facial nerve is the origination of the special sensory fibers for taste to the anterior two thirds of the tongue. Inferior Alveolar nerve- Somatic sensory from the lower jaw and teeth. Terminates as the mental nerve that innervates the skin at the front of the mandible. Motor fibers run with this nerve until they are given off in a motor nerve, the nerve to the mylohyoid.

Tongue Innervation Overview

Sensory: Anterior two thirds of tongue- general sensation from Lingual nerve, a branch of Mandibular (V3). These sensory cell bodies are in the trigeminal ganglia. Taste or special sensation from VII or Facial. These cell bodies are in the geniculate ganglia. (board review question) Posterior one third of the tongue- general sensation and taste from CN IX Glossopharyngeal nerve. Motor: To the intrinsic muscles of the tongue- Hypoglossal nerve CN XII.

TMJ - MOVEMENTS 1.

Slide 1 for First Step. First step is to move the mandibular condyle forward onto the articular process (tubercle) of the temporal bone. The lateral pterygoid protracts the mandible. It is attached to the condyle and the articular disc. This movement is rotation and translation. The condyle is depressed (rotation) and then protruded (translation).

Sublingual space

Sublingual (paralingual) space- space between mylohyoid inferiorly and the tongue and mucosa superiorly. Contents include Hypoglossal nerve, Lingual nerve and artery, Glossopharyngeal nerve, Sublingual gland, Deep lobe of submandibular gland, submandibular gland duct. (board review question). During surgery of the submandibular duct, the lingual nerve can ne damaged because of it's proximity.

TEMPORALIS

Temporalis muscle- Origin from squamous portion of the temporal bone. Insertion onto the coronoid process of mandible. The anterior fibers elevate the mandible and the posterior fibers retract the mandible.

TMJ - PROPERTIES 1

Temporomandibular Joint "TMJ". The condyle of the mandible fits into the mandibular fossa of the temporal bone. An articular process is present anteriorly to the fossa. A modified hinge joint. There is an articular disc of connective tissue between the two bones, this disc is slightly movable.

Blood Supply Arteries

The maxillary artery supplies the blood to the infratemporal fossa and surrounding structures. This artery ends in the nasal cavity. This artery branches from the external carotid artery and lies medial to the condyle in the infratemporal fossa. (common board question). Branches to identify in the infratemporal fossa: Middle meningeal artery- this artery enters the foramen spinosum to the cranial cavity. The auriculotemporal nerve branches around the artery or hugs the artery in it's path to the temporal region of the skin. The middle meningeal artery is the primary blood supply to the dura. Inferior alveolar artery- Runs with the inferior alveolar nerve into the mandible and supplies the lower jaw and teeth. It terminates with the mental nerve as the mental artery.

TRIGEMINAL NERVE

The nerve to the mylohyoid is a named motor branch that comes off the inferior alveolar nerve before it heads into the mandibular foramen of the mandible. The nerve to the mylohyoid provides motor innervation to the mylohyoid and anterior digastric muscles. These two muscles are accessory muscles of mastication. Other muscles that are innervated by the Trigeminal nerve are the muscles of Mastication; Masseter, Lateral Pterygoid, Medial Pterygoid, and Temporalis. They are innervated by motor branches of V3, Mandibular nerve. The mandibular branch of trigeminal also has motor branches to the tensor tympani and tensor palatini muscles.

TMJ - MOVEMENTS 4. Two parts.

To return to stable position- The anterior temporalis, masseter, and medial pterygoid elevate the mandible. These muscles also are involved with elevation of the mandible while chewing occurs with the condyle located on the articular process. The posterior temporalis is the retractor. The jaw returns to the stable position in the mandibular fossa. Elevation (rotation) and retraction (translation).

Trigeminal has a sensory root and motor root from Pons. V3 is associated with the motor root.

Trigeminal Nerve The Trigeminal nerve has three major branches that all include somatic sensory innervation. The Trigeminal nerve also has a motor component that is innervation for the muscles of mastication. The Mandibular nerve branch of the Trigeminal Nerve provides motor innervation to the muscles of mastication. We will not ask you to specifically identify all the motor branches. A motor branch that we ask you to know is the nerve to the mylohyoid. It is a named motor branch that comes off the inferior alveolar nerve before it heads into the mandibular foramen of the mandible. The nerve to the mylohyoid provides motor innervation to the mylohyoid and anterior digastric muscles. These two muscles are accessory muscles of mastication.

Blood Supply-Veins of the Infratemporal Fossa

Veins- There is a large interlocking plexus of veins in this area called the pterygoid venous plexus. This plexus surround the medial and lateral pterygoid muscles. The plexus can drain anteriorly into the facial vein through a deep facial vein. It mostly drains posteriorly into the maxillary vein and then the retromandibular vein. The retromandibular vein is located just behind the mandible.

There are two hypoglossal nerves, one on each side.

When the tongue is "stuck out". The genioglossus muscles on both sides pull the tongue forward by their attachment to the mandible and genial tubercles. If there is a lesion of the hypoglossal the tongue will turn toward the side of the lesion because the muscles on that side are not working. A "lower motor lesion" of hypoglossal means it affects the nerve or nuclei in the medulla. This will eventually cause fasciculations and atrophy of that side.

SIDE TO SIDE CHEWING

chewing-one condyle is forward on articular process and the other is not. Asymmetrical.