4. Trigeminal Nerve I. Objectives:. Understand the types of sensory information transmitted by the trigeminal system.. Describe the major peripheral divisions of the trigeminal nerve and how they innervate the head. 3. Describe the names and locations of the cell bodies and axons that transmit tactile, pain and temp, and proprioceptive information in this system. 4. Describe the somatotopic orientation for pain information on the face. 5. Describe the reflex pathways for the jaw-jerk reflex and corneal reflex and their importance in clinical testing. 6. Describe trigeminal neuralgia. 7. Describe the effects of lesions in the brainstem that interrupt the spinal trigeminal nucleus and the ventral trigeminothalamic tract. II. Case Description: A 60 year old woman develops paroxysms (i.e. sudden, periodic attacks) of sharp stabbing pain in her right cheek area, upper lips, gum, teeth with the following features: attacks last a few minutes. Electric shock-like pain of a debilitating, intense nature. Attacks are precipitated by brushing teeth or eating. Consequently, she has lost 0 lbs. over several weeks. The pain never spreads beyond the described region. Between attacks (minutes to weeks) she is symptom-free. On exam, her physician can trigger an attack by lightly rubbing her upper gum. III. Stimuli and distribution Sensory stimuli: Touch, vibration, pressure, pain, temperature, proprioception. Sensory receptors same as previous sensory systems discussed Major divisions of Trigeminal Nerve: Ophthalmic, Maxillary, Mandibular Provides sensory innervation to the face, cornea, oral cavity including tongue (General Somatic Afferents), teeth, dura, external ear, tympanic membrane V-ophthalmic V-maxillary motor V3-mandibular Modified from Neuroanatomy, JD Fix, Williams&Wilkins, 99
IV. Nuclei of CN V: Four different nuclei of the trigeminal system control: Tactile sensation - Principle (chief) sensory nucleus of V Proprioception - Mesencephalic nucleus of V Pain and Temp - Spinal trigeminal nucleus Jaw Movement - Motor nucleus of V Pathways:. Tactile Sensation First-Order Neuron Trigeminal Ganglion Cranial Nerve V/Ascend root V Second-Order Neuron Chief Sensory Nucleus V Ventral Trigeminothalamic Tract Third-Order Neuron VPM Post. Limb Internal Capsule Cortical Localization (tactile sense) Postcentral gyrus. Pain and Temperature Sensation First-Order Neuron Trigeminal Ganglion Cranial Nerve V/Spinal trigem tract Second-Order Neuron Spinal Nucleus of V Ventral Trigeminothalamic Tract Third-Order Neuron VPM Post. Limb Internal Capsule caudal medulla part of spinal trigeminal nucleus mediates pain and temp for the face
Cortical Localization Similar to distribution of pain and temp pathway for body. There are both direct and indirect routes to thalamus that project to different cortical locations: Postcentral gyrus (face area), Cingulate Gyrus, Insula Somatotopic orientation relationship between areas of the face and spinal trigeminal nucleus: perioral regions project to more rostral regions of the spinal trigeminal nucleus. Cranial nerves VII, IX, X also supply external ear, external acoustic meatus, and tympanic membrane. In the brainstem, their first order axons enter the spinal trigeminal tract and synapse in the spinal trigeminal nucleus. 3 4 pons 3 4 Spinal cord caudal medulla 3. Proprioception First-Order Neuron Mesencephalic Nucleus Cranial Nerve V/Mesenceph Root V Second-Order Neuron Motor Nucleus of V Motor Root of V Third-Order Neuron - - Pathway from mesencephalic nucleus to cortex for conscious perception of proprioception is unknown. Proprioceptive reflexes are important: initiated by ) muscle stretch during chewing, eating, talking, etc. ) tooth mechanoreceptors during chewing/eating, 3) extrinsic muscles of eye during eye movements. This information arises from tongue, jaw muscles, teeth and orbit and travels in V, V, V 3 to brainstem. V. Reflex Pathways of Clinical Importance: Jaw jerk reflex stretch reflex involving masseter; initiated by a tap on chin, which causes a weak contraction of jaw. In a normal individual, this reflex is usually too small to observe. However, in pathological conditions it can become exaggerated. Corneal reflex involves CN V and VII (see diagram). 3
CORNEAL REFLEX Spinal Trigeminal Nuc VII VII Orbicularis oculi muscle CN V When would you test the corneal reflex clinically: ) testing a patient who had sudden onset of right-sided facial paralysis, ) comatose patient : CASE: On returning home from shopping, a wife finds her 59 year-old husband unconscious on the floor. He has no pulse. After calling 9, she begins CPR. When Mr. T arrives in the ED, he is in ventricular fibrillation. Spontaneous circulation is eventually restored, but Mr. T remains comatose. After 3 days in coma, his wife asks about her husband s condition and the probability of a good outcome. How can we assess extent of CNS damage/function in unconscious patient. Somatosensory Evoked Potential Brainstem Reflexes assess functionality of pathways in brainstem. Loss of reflex indicates poor outcome; however, intact reflex does not imply cortical functionality.. Corneal reflex VI. Case Discussion Syndrome known as Trigeminal neuralgia (Tic Douloureux) Variety of causes: microvascular compression of V or V3, tumor, aneurysm, infarct, MS, idiopathic. usually observed in patients older than 50 Therapies: anticonvulsants like carbamazepine or phenytoin; surgery of trigem. nerve roots or trigem. ganglion (but loss of tactile sense and corneal reflex are complications). 4
Ventral trigeminothalamic tract mid-pons Motor nuc of V Spinal 5