10/4 Cranial Nerves I-VI

Question 1

• Define the 6 classifications of cranial nerve nuclei and list the nuclei that belong to each classification.

Answer 1

• General somatic efferent (body): 3,4,6,11,12
• Special visceral efferent (striped muscles brachial): 5,7,9,10
• General visceral efferent (autonomic, involuntary): 3,7,9,10
• General and special visceral afferent (taste, gut): 7,9,10
• General somatic afferent: 5
• Special somatic afferent: 8

Question 2

• Describe why olfactory sensory neuron are not vulnerable to COVID-19 infection, and why this infection still leads to anosmia.

Answer 2

• Olfactory sensory neurons do not express the surface receptors that covid uses to get into the neuron. Supporting neurons in the olfactory (like SUS) do, and their function of support is disrupted. Loss is temporary because these neurons regenerate and turn over quickly

Question 3

• Define the loss of visual field resulting from a lesion is the following locations: optic nerve, optic chiasm, optic tract, Meyers loop, Baums loop

Answer 3

• Optic nerve: whichever eye nerve was from. Outside fiber=inside field inside fiber=outside field. Chiasm: loss of peripheral visual field for opposite eye. Optic tract: internal field for ipsi eye peripheral field for contra eye. Meyers loop: upper visual field inside for ipsi outside for contra. Baums: lower visual field (not middle) inside for ipsi outside for contra.

Question 4

• Describe the pupillary reflex. Describe why muscarinic antagonism leads to pupil dilatation.

Answer 4

• Retinal ganglion cells act as luminance detectors and project to pretectal n. at junction of midbrain and thalamus. Neurons in pretectal n. project bilaterally through posterior commissure to parasympathetic preganglionic cells (Ach) in Edinger Westphal nucleus. Exit CN3 and contact ciliary ganglion cells that constrict muscle in iris (mAch). Constriction is bilateral. Antagonism causes the Ach receptors not to work in the muscle responsible for constriction.

Question 5

• Describe how one would distinguish between damage to CN3, 4 or 6.

Answer 5

• III: pupil down and out because lateral rectus and superior oblique are intact. Aneurysms, uncle herniation, meningitis, ischemia of CN3
• IV: eye cannot look down as far as it should, head is tilted towards opposite shoulder. Head trauma, congenital nerve palsy
• VI: Affected eye cannot look laterally (crosseyed). Caused by trauma.

Question 6

• Explain the nerves, nuclei and tracts that support the jaw jerk reflex.

Answer 6

• Sensory information from neuromuscular spindles in muscles of mastication responding to stretch, conveyed by mandibular nerve to mesencephalic nucleus. Bilateral. Mesencephalic nucleus motor nuclei of V (bilateral. Somatomotor part of CN5 to mandibular nerve to muscles causing jaw to close. Jerk sign of UMN injury

Question 7

• Compare and contrast the spinal nucleus versus the chief sensory nucleus of 5.

Answer 7

• Similar to ASL and DCML tracts. Spinal nucleus is at level of V and below, receives pain and temp from face. Sensory at level of V touch and vibration from face. Both have input from trigeminal ganglion (ipsi) and output contra VTTT to VPM

Question 8

• Describe the clinical correlates of CN5 damage.

Answer 8

• Ipsilateral loss of sensation, ipsi paresis to muscles of mastication. Episodes of severe pain in unilateral face (trigeminal neuroalgia or tic douloureux). Treatment is carbamazepine (anticonvulsant) or surgery. Tic convulsive (hemifacial spasm) cluster headache.