10/5 Cranial Nerves VII-XII

Question 1

• Compare and contrast general visceral, special visceral, and general somatic efferents.

Answer 1

• General visceral are not processing consciously: glands and gut. Special are nerves of brachial origin and carry special senses of smell and taste. Somatic efferents are motor neurons that conduct impulses from the spinal cord to skeletal muscles.

Question 2

• Describe the following reflex arcs in the brainstem: cornea reflex, gag/pharyngeal reflex, the baroreceptor reflex, generation of breathing

Answer 2

• Cornea: involuntary blinking in response to corneal stimulation. Tests sensation via V and VII, better for V 1. Ophthalmic branch of trigeminal nerve to trigeminal ganglion and spinal trigeminal nucleus. 2. Neuron 2 in spinal trigeminal nucleus synapses bilaterally on the motor n of VII. 3. LMN in the facial n of VII innervate orbicularis oculi to close both eyes.
• Gag: n ambiguous, CN9/10. Protects airways. Afferent sensory fibers of 9 and 10 innervate spinal trigeminal nucleus whose axons project bilaterally to n ambiguous. SVE in ambigious innervate posterior pharyngeal muscles, elevates palates, constricts pharyngeal muscles to expel stimulus and closure of airway.
• Baroreceptor (helps maintain bp when moving). Receptors in the aortic arch and carotid sinuses detect changes in bp and travel through CN9 and 10 to solitary tract n. Cells in solitary project to ventral medulla lateral medulla to regulate sympathetic or parasympathetic neurons that increase or decrease heart rate. Arterial baroreceptor discharge activates NST neurons and some are tonically activated by resting bp to activate excitatory fibers to dorsal motor n of vagus, slows heart.

Question 3

• Define the dorsal and ventral respiratory groups and their role in breathing.

Answer 3

• Dorsal respiratory group is in and around n of solitary tract—receives sensory information from stretch receptors in the lungs and chemoreceptors in periphery. Hering-Breuer Reflex so lungs do not over inflate and respond to hypoxia. Chemoreceptors that innervate the NST respond to low blood o2 or acidosis from decreasing pH with CO2 increase.
• Ventral respiratory group in reticular formations of medulla in and around n ambiguous. Coordinates motor output. Axons leave through vagus nerve to innervate accessary muscles of respiration.