HBF-III LEC 39 Neuroscience Trigeminal Complex Notes 2024 PDF

The Trigeminal Complex (L30) Page 1 of 9 Dr. Tomomi Ichinose The Trigeminal Complex Lecture Objectives At the conclusion of this session, students will demonstrate that they can effectivel...

The Trigeminal Complex (L30) Page 1 of 9 Dr. Tomomi Ichinose The Trigeminal Complex Lecture Objectives At the conclusion of this session, students will demonstrate that they can effectively: I. Describe the sensory area for three major divisions of the trigeminal nerve. II. Identify 4 trigeminal nuclei in the brainstem. III. Diagram the trigeminal nerve pathways including these 4 nuclei. III. Summarize the corneal and jaw-jerk reflexes and the clinical significance of each IV. List examples of clinical correlations regarding the trigeminal complex. Lecture Outline I. The trigeminal nerve contains sensory and motor divisions. II. Sensory division of CN V III. Ascending trigeminothalamic tracts IV. Trigeminal motor nucleus and pathways V. Trigeminal Reflexes VI. Clinical correlations Related Lectures: L20 Cranial Nerves Dr. Walker L28 Anatomy of the Brainstem Dr. Walker L29 Somatosensory Pathways Dr. Walker L60 Blood Supply of Spinal Cord & Brainstem Dr. Peduzzi-Nelson I. The trigeminal nerve is the largest cranial nerve that connects to the brainstem at the pons. The trigeminal nerve contains sensory (general somatic afferent [GSA]) and motor (special visceral efferent [SVE]) fibers. 1. Sensory modalities, which are the same as those from the body, are pain/temperature/ light touch, discriminative fine touch/vibration, conscious and unconscious proprioception. 2. Motor fiber innervates to the muscle of mastication, tensor tympani, tensor veli palatini, and anterior belly of digastric. The Trigeminal Complex (L30) Page 2 of 9 Dr. Tomomi Ichinose II. Sensory divisions of V nerve. Figure 1 shows the cutaneous innervation of the head and neck. There is no peripheral overlap between the three dermatomes of V. 1. Ophthalmic (V1): innervates the forehead, upper eyelid, cornea, orbit (cornea and C2/3 conjunctiva), dorsum of the nose, mucous membranes of the nasal vestibule, frontal and sigmoid sinuses, and cranial dura. This nerve goes through the superior orbital fissure. 2. Maxillary (V2): innervates C2/3 the upper lip and cheek, lower eyelid, lateral and posterior Figure 1 Sensory innervation of V. Note, sensory V portions of nose, anterior portion of covers exteroceptive and proprioceptive sensations. the temple, and mucous membranes of the upper mouth, nose, teeth, gums, palate, pharynx, and cranial dura. This nerve goes through the foramen rotundum. 3. Mandibular (V3): contains both sensory and motor fibers. Sensory- lower lip, chin, posterior portions of cheek and temple, external ear, and mucous membranes of the lower jaw, cheeks, and floor of the mouth, lower teeth, anterior two-thirds of the tongue, temporomandibular joint, and cranial dura. This nerve goes through the foramen ovale. Sensory innervation of the auricle is from many sources. In addition to the cervical plexus [C2/3] The dura mater is innervated by branches of and the mandibular nerve [V3], the deeper parts of all three divisions of the trigeminal nerve [V1, the auricle are supplied by the vagus nerve [X] and V2, and V3], the vagus [X], and the C1-C3. the facial nerve [VII]. The Trigeminal Complex (L30) Page 3 of 9 Dr. Tomomi Ichinose The Trigeminal Complex (L30) Page 4 of 9 Dr. Tomomi Ichinose III. Ascending trigeminothalamic tracts Pons Trigeminal N (CN V) Figure 2 An anterolateral view of the brainstem with cranial nerves. A diagram shows trigeminal pathways. Three branches of trigeminal nerve contain 3 distinct sensory signals. Mandibular V3 nerve carries motor signaling. A. Sensory pathway for pain, temperature, and light touch Peripheral nerve: V1, V2, V3 1st order neuron nucleus: located in the trigeminal ganglion 2nd order neuron nucleus: Spinal nucleus of V_ located in the spinal cord (C1-C3), medulla, and pons Projection: contralateral Ventral (anterior) trigeminothalamic tract (VTTT) 3rd order neuron nucleus: Ventral posteromedial (VPM) nucleus of the thalamus Projection: posterior limb of the internal capsule to the postcentral gyrus B. Sensory pathway for discriminative tactile and vibration Peripheral nerve: V1, V2, V3 1st order neuron nucleus: located in the trigeminal ganglion 2nd order neuron nucleus: Chief (principal) sensory nucleus of V_ located in the mid-pons Projection: contralateral VTTT and ipsilateral dorsal trigeminothalamic tract (DTTT) 3rd order neuron nucleus: Ventral posteromedial (VPM) nucleus of the thalamus Projection: posterior limb of the internal capsule to the postcentral gyrus The Trigeminal Complex (L30) Page 5 of 9 Dr. Tomomi Ichinose C. Sensory pathway for proprioception Inputs: muscle spindles joint receptors Peripheral nerve: V1… extraocular muscles V2/V3… muscles of mastication, teeth, hard palate, temporomandibular joint 1st order neuron nucleus: located in the mesencephalic nucleus (psuedounipolar neurons) Primary projection: trigeminal motor nucleus (jaw jerk reflex and regulate the force of bite) Other projections: Chief sensory nucleus of V, and cerebellum Figure 3 Trigeminal sensory pathways The Trigeminal Complex (L30) Page 6 of 9 Dr. Tomomi Ichinose IV. Trigeminal motor nucleus and pathways A. The nucleus of motor V is located in the mid pons at the level of the chief sensory nucleus of V (see Figure 3). Motor neurons in the nucleus receive inputs from corticobulbar fibers (bilateral) and the mesencephalic nucleus. B. The motor root of V exits the skull via the foramen ovale, along with V3. The root is called “Portio minor”, in contrast to “portio major” which contains trigeminal sensory afferents. C. Trigeminal motor neurons innervate the muscles of mastication (Figure 4), the tensor tympani (Figure 5), the tensor veli parlatini, the mylohyoid, and the anterior belly of the digastric (all ipsilateral). D. The oral motor system requires continual feedback during mastication. As the food is chewed, its texture and consistency are altered, changing the demands on jaw muscle tensions. The jaw-jerk reflex (below) continuously adjust the muscle tone. Also, the trigeminocerebellar connections send the proprioception via the superior cerebellar peduncle. Chewing is regulated by the cerebellum, basal ganglia, red nucleus, and cortical regions. E. The tensor tympani is one of inner ear muscle. Abnormal spasm of the tensor tympani induces hyperacusis and/or tinnitus. Lateral pterygoid Medial pterygoid Muscle Muscle temporalis masseter Medial and lateral pterygoid muscles Which muscles are closing/opening mouth? Which muscles do the jaw move side to side? Figure 4 Muscles of mastication (above) and tensor tympani (below) Tensor tympani The Trigeminal Complex (L30) Page 7 of 9 Dr. Tomomi Ichinose V. Trigeminal Reflexes A. Jaw jerk reflex (the “masseter” reflex) 1. Reflex: tap the chin in the midline with the mouth open slightly, and the mouth tends to close (a monosynaptic reflex). 2. Afferent limb: stretch receptors in muscles of mastication bilaterally. This information is conveyed by the peripheral processes of neurons in the mesencephalic nucleus of V. The central processes of these same cells send collaterals to the motor nucleus of V on the same side 3. Efferent limb: axons from the motor neurons of V bilaterally Figure 5 The jaw jerk reflex. The afferent limb is V3, and the efferent limb is the motor root that accompanies V3. 1st order sensory neurons are located in the mesencephalic nuclus. The jaw jerk reflex is a monosynaptic myotactic reflex. B. Corneal Reflex 1. Reflex: stimulate one cornea and both eyes close. The closing of the stimulated eye is called the direct response; the closing of the opposite eye is called the consensual response. 2. Afferent limb (1st order): The ophthalmic nerve V1. 3. 2nd order neuron: Neurons in spinal V (rostral two-thirds) project bilaterally and synapse in the facial motor nucleus. 4. Efferent limb (3rd order): motor axons of both facial nerves innervate orbicularis oculi muscles. Figure 6 The corneal reflex. This is a disynaptic and a consensual reflex. The afferent limb is V1. Neurons in spinal V project to both facial nuclei. The efferent limb is the motor axons of facial nerves. The Trigeminal Complex (L30) Page 8 of 9 Dr. Tomomi Ichinose VI. Clinical correlations A. Trigeminal neuralgia (tic douloureux): characterized by severe, unexpected, lancinating pain restricted to one or more of the trigeminal nerve divisions. It frequently occurs around the lip, nose, or on the cheek unilaterally. Pain attach occurs by a wide variety of stimuli, such as shaving, talking, chewing, eating, or some facial expression. Idiopathic type is caused by compression of the trigeminal nerve root by aberrant vessels, usually branches of the superior cerebellar artery. Multiple sclerosis, Charcot-Marie-Tooth disease, and others also cause this neuralgia. B. Herpes zoster (shingles): caused by a viral infection within a dermatome (unilateral). Herpes zoster may affect any sensory ganglia and its cutaneous nerve. Most of the infections affect dermatomes of t-3 to l-2, but ~10% of patients present with infections involving any of 3 branches of the trigeminal nerve. Symptoms include rash and pain (acute and chronic). If the ophthalmic nerve (V1) is affected, it may cause corneal ulceration, which may result in blindness. C. Central lesions in the medullar or pons: include tumors, vascular lesions, such as the lateral medullary syndrome (PICA or Wallenberg syndrome). Figure 7 PICA (Wallenberg) syndrome. Spinal nuc & tr V… ipsilateral loss pain & temp of face Anterolateral system (ALS)… contralateral loss pain & temp of body Posterior spinocerbellar tract… ataxia Nucleus ambiguus (root of 10) Descending autonomic tracts… Honor syndrome Sometimes include vestibular nuclei Figure 8 A central lesion caused by thrombosis of a branch of basilar artery or tumor. Ventral trigeminothalamic fibers (VTTT)… contralateral loss pain & temp of face Medial lemniscus (ML)… contralateral loss of fine touch discrimination, conscious proprioception, deep pressure of body Root of CN VI (abducens)… ipsilateral internal strabismus, diplopia. Ventral acoustic stria… bilateral hearing loses. The Trigeminal Complex (L30) Page 9 of 9 Dr. Tomomi Ichinose D. Cavernous sinus syndrome: can be caused by vascular, inflammatory, neoplastic, and infectious diseases. It causes bilateral neuropathy involving ocular motor nerves (CN III, IV, and VI), trigeminal nerve (V1 and V2), and postganglionic sympathetic fibers to the orbit. Figure 9 Cavernous sinus and cranial nerves.