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ABOUT "TRIGEMINAL
NERVE ANATOMY"
INTRODUCTION
ANATOMY
SENSORY COMPONENT OF THE TRIGEMINAL NERVE - BLUE LABELS
BRANCHIAL MOTOR COMPONENT OF THE TRIGEMINAL NERVE - LIGHT
ORANGE LABELS
VISCERAL MOTOR COMPONENT OF THE TRIGEMINAL NERVE - DARK ORANGE
LABELS
Early in my fourth year of medical school, I scheduled a month of independent study in medical illustration. During that time, I completed a set of trigeminal nerve posters to be used as learning aides in the first year gross anatomy class. My goal was to create a single illustration for students that would showcase all major branches of the trigeminal nerve, their relationship to one another, and the skull. This web site represents an interactive version of that illustration with the addition of descriptive text as well as gross anatomical and clinical correlation. The illustration and text were created with a level of detail aimed at medical and dental students studying the trigeminal nerve for the first time. I hope they will also be useful for clinicians looking for a quick review. Good luck with your studies! Jeremy S. Melker, MS IV
The trigeminal nerve is the fifth of the twelve cranial nerves. Often referred to as "the great sensory nerve of the head and neck", it is named for its three major sensory branches. The ophthalmic nerve (V1), maxillary nerve (V2), and mandibular nerve (V3) are literally "three twins" carrying information about light touch, temperature, pain, and proprioception (position sense) from the face and scalp to the brainstem. It is important to note that the commonly used terms "V1", "V2", and "V3" (pronounced "vee one", "vee two", and "vee three") are simply shorthand notation for cranial nerve five (V being the Roman numeral five), branches one, two, and three respectively. In addition to nerves carrying incoming sensory information, certain branches of the trigeminal nerve also contain nerves carrying outgoing signals. These outgoing motor components include branchial motor nerves ("branchial" refers to nerves innervating muscles derived embryologically from the branchial arches) as well as "hitchhiking" visceral motor nerves ("visceral" refers to nerves innervating viscera, including smooth muscle and glands). Each of these trigeminal nerve components will be discussed individually below. Structures labeled in the illustration are shown in bold.
The ophthalmic nerve (V1) enters the middle cranial fossa through the superior orbital fissure and courses within the lateral wall of the cavernous sinus (part of the venous system that returns blood from the brain to systemic circulation - dissected away in the illustration) on its way to the trigeminal ganglion. The maxillary nerve (V2) enters the middle cranial fossa through foramen rotundum and may or may not pass through the cavernous sinus en route to the trigeminal ganglion. The mandibular nerve (V3) enters the middle cranial fossa through foramen ovale, coursing directly into the trigeminal ganglion. The trigeminal ganglion (a.k.a. semilunar ganglion in reference to its sometimes "half moon" shape) lies in a depression known as the trigeminal cave (or Meckel's cave). The trigeminal nerve exits the trigeminal ganglion and courses "backward" to enter the mid-lateral aspect of the pons (a division of the brainstem - shown in faded yellow).
Branchial motor nerves exit the mid-lateral aspect of the pons, course within the trigeminal nerve, pass through the trigeminal ganglion, and exit the middle cranial fossa within the mandibular nerve through foramen ovale. Branchial motor nerves can not be distinguished from sensory nerves on gross dissection and are therefore described as "within" the trigeminal and mandibular nerves. Therefore, these grossly named nerves carry bi-directional signals. Branchial motor nerves convey outgoing information while the majority of nerves contained in the mandibular nerve and in the main trunk of the trigeminal nerve proximal to the trigeminal ganglion convey incoming sensory information.
Visceral motor nerves are not a true component of the trigeminal nerve, but are important "hitchhikers" along its branches. These hitchhiking fibers originate centrally as part of other cranial nerves and travel along sensory branches of the trigeminal nerve en route to glands within the head and neck. Again, this creates trigeminal nerve branches that carry bi-directional signals.
The trigeminal nerve is divided into the ophthalmic nerve (V1), maxillary nerve (V2), and mandibular nerve (V3), each of which will be discussed individually below.
The frontal nerve arises from the supraorbital nerve and supratrochlear nerve. The supraorbital nerve courses from the forehead through the supraorbital notch (foramen) to join the supratrochlear nerve. The supratrochlear nerve carries information from the medial forehead, medial portion of the upper eyelid, and bridge of the nose.
The nasocilary nerve arises from the infratrochlear nerve, anterior ethmoidal nerve, and posterior ethmoidal nerve. The infratrochlear nerve carries information from the medial eyelid and lateral aspect of the nose. The external branches of the anterior ethmoidal nerve convey sensation from the apex of the nose and ala (nostril). The anterior ethmoidal nerve also carries information from the ethmoidal air cells along with the posterior ethmoidal nerve.
The lacrimal nerve conveys sensation from the lateral portion of the upper eyelid and conjuctiva. In addition, post-ganglionic visceral motor fibers (see visceral motor component of the trigeminal nerve below) hitchhike along the lacrimal nerve en route to the lacrimal gland.
The zygomatic nerve arises from the zygomaticofacial nerve and zygomaticotemporal nerve. The zygomaticofacial nerve courses from the lateral cheek through the zygomaticofacial foramen to join the zygomaticotemporal nerve. The zygomaticotemporal nerve carries information from the lateral cheek posterior to the zygomatic process.
The infraorbital nerve conveys sensory information from the lateral aspect of the nose, lower eyelid, medial cheek, and upper lip as it courses through the infraorbital foramen. It is then joined by superior alveolar branches from the upper teeth which play an important role in transmitting dental pain.
The buccal nerve carries information from the lower cheek, gums, and mucous membranes of the mouth.
The lingual nerve conveys sensation from the anterior two-thirds of the tongue. In addition, pre-ganglionic visceral motor fibers (see visceral motor component of the trigeminal nerve below) hitchhike along the lingual nerve en route to the sublingual gland and submandibular gland.
The inferior alveolar nerve arises from the mental nerve and inferior alveolar plexus. The mental nerve courses from the chin and lower lip through the mental foramen to join the inferior alveolar plexus. The inferior alveolar plexus carries primarily painful sensation from the lower teeth and plays an important role in dental anesthesia.
The auriculotemporal nerve carries information from the lateral scalp (via superficial temporal branches) as well as from skin anterior to the ear and jaw (auricular and articular branches). In addition, post-ganglionic visceral motor fibers (see visceral motor component of the trigeminal nerve below) hitchhike along the auriculotemporal nerve en route to the parotid gland. Interestingly, the auriculotemporal nerve splits around the middle meningeal artery just before it merges with other major branches of V3.
The term "branchial" refers to structures embryologically derived from the branchial arches. The branchial motor component of the trigeminal nerve consists of lower motor neurons whose cell bodies are located in the motor nucleus of the trigeminal nerve in the brainstem. These nerves exit the mid-lateral aspect of the pons, course within the trigeminal nerve, pass through the trigeminal ganglion, and within the mandibular nerve before branching. The muscles innervated by the branchial motor component can be remembered as "the muscles of mastication (chewing) plus two tensors." That is, the temporalis, masseter, medial and lateral pterygoids, tensor veli palatini, and tensor tympani.
The facial nerve (cranial nerve VII) gives rise to two important trigeminal hitchhikers - the Vidian nerve and the chorda tympani nerve. The Vidian nerve (a.k.a. nerve of the pterygoid canal) emerges from the pterygoid canal (not labeled) carrying pre-ganglionic fibers to the pterygopalatine ganglion. After synapse, post-ganglionic fibers exit the ganglion and hitchhike along trigeminal nerve branches en route to the lacrimal gland and minor salivary glands of the palate and mouth. The chorda tympani exits the skull through the petrotympanic fissure (not labeled) and courses extracranially to join the lingual nerve. It carries pre-ganglionic fibers to the submandibular ganglion which "hangs" from the lingual nerve. After synapse, post-ganglionic fibers exit the ganglion to innervate the submandibular gland and sublingual gland. The intracranial course of the facial nerve (cranial nerve VII) prior to the emergence of the Vidian and chorda tympani nerves is complex and non-essential for understanding basic trigeminal nerve anatomy.
The glossopharyngeal nerve (cranial nerve IX) also contributes an important trigeminal hitchhiker - the lesser petrosal nerve. The lesser petrosal nerve has a complicated intracranial course, eventually exiting the skull through or near the foramen ovale. It carries pre-ganglionic fibers to the otic ganglion. After synapse, post-ganglionic fibers exit the ganglion, hitchhiking along the auriculotemporal nerve to innervate the parotid gland.