5th L

Question 1

explain Vestibulocochlear (CN VIII)

Answer 1

-Auditory stimuli activate hair cells in the organ of Corti. Nerve fibers supplying the hair cells are the peripheral processes of the bipolar neurons that make up the spiral ganglion lying in the center of the cochlea. The central processes of these neurons form the auditory nerve, which follows a direct course through the internal auditory canal and across the CPA, enters the brainstem at the pontomedullary junction, and synapses in the cochlear nuclei.
-PATHWAY: The vestibular nerve arises from the vestibular (Scarpa’s) ganglion. The peripheral processes of its bipolar neurons receive impulses from the utricle, saccule, and three semicircular canals; the central processes convey these impulses through the vestibular portion of CN VIII.
-Clinical:
Hypakusis
Anakusis
Hyperakusis.
-Vestibular disorders
Dizziness
Tendency to fall to the side of the lesion
Nausea and vomiting
Nystagmus

Question 2

explain Glossopharyngeal (CN IX)

Answer 2

-pathway :The nucleus ambiguus sends axons via CN IX to innervate the pharyngeal plexus. The functions of CNs IX and X are virtually inseparable in this regard.
-The only muscle innervated solely by CN IX is the stylopharyngeus. In company with CNs X and XI, the nerve exits the skull through the jugular foramen.
-CN IX also conveys taste fibers from the posterior third of the tongue and supplies parasympathetics to the parotid gland.
—The clinical syndrome of a IX nerve lesion is characterized by:
1-Impairment or loss of taste (ageusia) on the posterior third of the tongue
2-Diminution or absence of the gag and palatal reflexes
3-Anesthesia and analgesia in the upper portion of the pharynx and in the area of the tonsils and the base of the tongue
4-A mild disturbance of swallowing (dysphagia)
5-Impaired salivation from the parotid gland

Question 3

explain Vagus (CN X)

Answer 3

-pathway :CN X carries motor fibers from the nucleus ambiguus to the palate, pharynx, and larynx. In addition, a heavy input arises from the dorsal motor nucleus of the vagus, which conveys parasympathetic fibers to innervate viscera of the thorax and abdomen. The vagus also carries visceral afferents and taste fibers.
-Clinical:
Complete bilateral transection of vagus nerves → fatal.
Syndrome of a Unilateral Lesion of the Vagus Nerve^
1-The soft palate hangs down on the side of the lesion, the gag reflex is diminished, and the patient’s speech is nasal.
2-Paresis of the pharyngeal constrictor muscle causes the palatal veil to be pulled over to the normal side when the patient phonates.
3-Hoarseness
4-dysphagia and occasionally tachycardia, and cardiac arrhythmia

Question 4

explain Accessory (CN XI)

Answer 4

-The accessory nerve has two parts.
1-The spinal portion arises from lower motor neurons in the upper cervical cord. Because of its branchial arch origin, it exits laterally, runs upward to enter the skull through the foramen magnum, and ascends to the jugular foramen. These fibers ultimately innervate the sternomastoid and trapezius muscles.
2-The cranial portion of CN XI arises from the nucleus ambiguus, exits laterally, joins the spinal root briefly, and then quickly turns off to join IX and X. Its functions are not separable from those of the vagus.
-Clinical:
Paralysis of SCM → inability to rotate head to contralateral side.
Paralysis of upper portion of trapezius muscle → winglike scapula and inability to shrug ipsilateral shoulder.

Question 5

explain Hypoglossal (CN XII)

Answer 5

-pathway :CN XII arises from motor neurons in the hypoglossal nucleus, exits the medulla anteriorly in the groove between the pyramid and the olive, leaves the skull through the hypoglossal foramen, and runs forward to innervate the tongue.
-Clinical
1-Hypoglossal nerve palsy.
- In unilateral hypoglossal nerve palsy, the tongue usually deviates a little toward the paretic side when it is protruded.
-dysarthria
-swallowing is not impaired.
2-Bilateral supranuclear palsy produces severe dysarthria and dysphagia (pseudobulbar palsy).
3-Nuclear lesions
- bilateral flaccid paralysis of the tongue with atrophy and fasciculations.
-speech and swallowing are profoundly impaired.