CH 11: CNs of the medulla (7,9,10,11,12)

Question 1

what does the hypoglossal nerve provide?

Answer 1

motor innervation to the tongue

intrinsic musculature of the tongue as well as muscles at its base

genioglosus muscle- together draw the root of the tongue forward and cause the tip to protrude and deviate to the opposite side

Question 2

what is the functional component of CN XII?

Answer 2

GSE

Question 3

CN XII fibers arise from:

Answer 3

lower motoneuron cell bodies in the hypoglossal nucleus

this nucleus consists of a column of cells that extends nearly the entire length of the medulla in a position just under the 4th ventricle close to the midline

Question 4

what do the axons of the hypoglossal nucleus cells pass?

Answer 4

between the pyramid and the olive- exit as rootlets of the hypoglossal nerve

Question 5

what does injury to CN XII cause?

Answer 5

a LMN lesion with paralysis and atrophy of the muscles on the ipsilateral side

on voluntary protrusion, the tongue deviates to the paralyzed side

Question 6

where does the spinal portion of the accessory nerve arise and exit?

Answer 6

arises from a dorsal group of anterior horn cells (spinal accessory nucleus) in cervical segments C2-C5

exits the SC through the lateral funiculus as a series of rootlets, ascends through the foramen magnum and courses along the side of the medulla to join the cranial portion

** they will later separate again

Question 7

what is the functional component of the spinal portion of the accessory nerve?

Answer 7

SSE??

Question 8

what is the functional component of the cranial potion of the accessory nerve?

Answer 8

SVE?

Question 9

where do cranial root fibers arise from?

Answer 9

neurons in the nucleus ambiguous

Question 10

where do the cranial root fibers go? what do they innervate?

Answer 10

joins the vagus nerve and, along with the terminal branches of the vagus, innervate the branchiomeric muscles of the larynx (speech & vocalization) and the heart

Question 11

how does the spinal portion exit?

Answer 11

passes through the jugular foramen and descends into the neck to end in the SCM and trapezius muscles.

Question 12

what does into to the spinal accessory nerve result in?

Answer 12

paralysis of the SCM– causes weakness in rotating the head to the OPPOSITE side

paralysis of the upper trap– causes downward and outward rotation of the upper scapula, sagging of the shoulder, and weakness in attempts to shrug the shoulder

Question 13

what forms the vagal system?

Answer 13

nervus intermedius- sensory and parasympathetic fibers of the facial nerve

glossopharyngeal nerve

vagus nerve

cranial accessory nerve

Question 14

what is the functional component of cells in the nucleus ambiguus?

Answer 14

SVE lower motoneurons

Question 15

the nucleus ambiguus consists of ?

Answer 15

CN 9
CN 10
CN 11

Question 16

what do nerves of the nucleus ambiguus do?

Answer 16

furnish motor innervation to the striated branchiomeric musculature of the soft palate, pharynx and larynx

Question 17

a unilateral lesion of the vagus nerve leads to:

Answer 17

difficulty in coughing, clearing the throat and swallowing

frothy mucus collects in the pharynx and overflows in the larynx

palatal arch droops on the side of the lesion

during phonation, the soft palate rises only on the normal side, and the uvula deviates to the normal side

Question 18

bilateral lesions of the vagus nerve leads to:

Answer 18

difficulty swallowing (dysphagia)- with regurgitation of food into the nose on swallowing

certain vocal sounds become difficult to produce (dysphonia) and the voice develops a nasal quality

a tendency toward moth breathing

snoring at night

difficulty draining mucus from the nasal passages into the pharynx

Question 19

paralysis of both recurrent vagus nerves leads to:

Answer 19

stridor and dyspnea- may necessitate tracheotomy

Question 20

fibers of the vagus nerve arise from the:

Answer 20

dorsal motor nucleus of the vagus nerve

Question 21

stimulation of vagal parasympathetic fibers:

Answer 21

slow HR
constrict smooth muscle of the bronchial tree
stimulate the glands of the bronchial mucosa
promote peristalsis in the GI
relax pyloric and ileocolic sphincters
stimulate secretion of gastric & pancreatic juices

Question 22

what innervates taste?

Answer 22

SVA fibers of the nerves intermedius and the glossopharyngeal nerves conduct taste information to the rostral portion of the solitary nucleus

geniculate ganglion of the facial nerve– ant 2/3

inferior ganglion of the glossopharyngeal nerve- post 1/3

a few taste buds on the epiglottis from inferior ganglion of the vagus

Question 23

what are the reflexes of the vagal system?

Answer 23

salivary-taste reflex
carotid sinus reflex
carotid body reflex
cough reflex
gag reflex
vomitting reflex

Question 24

how does the salivary-taste reflex work?

Answer 24

illustrates secretory function of the vagal system

a gustatory stimulus (lemon juice) on the tongue causes salivary glands to increase saliva output

taste fibers in the facial and glossopharyngeal nerves carry the afferent stimulus to the nucleus of the solitary tract

connecting fibers project through interneurons in the adjacent RF to parasympathetic neurons in the superior and inferior salivatory nuclei

parasympathetic preganglionic neurons in the superior salivatory nuclei pass through the facial nerve to the submandibular ganglion, where a synapse occurs and postganglionic fibers connect with the submandibular and sublingual salivary glands.

parasympathetic preganglionic fibers neurons in the inferior salivatory nuclei project through the glossopharyngeal nerve to the otic ganglion to synapse and postganglionic fibers innervate the parotid salivary glands

Question 25

how does the carotid sinus reflex work?

Answer 25

increased BP stimulates special baroreceptors in the wall of the carotid sinus and sends impulses over afferent fibers of CN IX to the nucleus of the solitary tract

second order neurons in this nucleus project through RF interneruons to the dorsal motor nucleus of X and the external sub nucleus of the nucleus ambiguus.

parasympathetic fibers from these nuclei project through the vagus nerve to the sinoatrial and atrioventricular nodes and the atrial muscle itself

activating this reflex reduces HR!

simultaneously, stimulation of neurons in the rostral ventrolateral medulla activates a pathway that descends to sympathetic neurons of the SC, dilates peripheral BVs, and thereby further reduces BP

people with hypersensitive carotid sinus reflexes develop syncope after light external pressure over the carotid sinus

Question 26

how does the carotid body reflex work?

Answer 26

carotid body contains special chemoreceptors that respond to changes in the CO2 and O2 content of circulating blood.

Activation of these chemoreceptors sends impulses through the glossopharyngeal nerve to the nucleus of the solitary tract. fibers from the solitary nucleus then go to the respiratory center of the medulla, where they influence the respiratory rate.

the respiratory center consists of diffusely arranged cells of the ventrolateral reticular formation with reticulospinal fibers descending to the LMNs of the phrenic and intercostal nerves

propagation of nerve impulses over reticulospinal fibers from the reps center produces inspiration

as the lungs become inflated, stretch receptors in the walls of bronchioles discharge impulses that ascend to the medulla through the vagus nerve.

connecting neurons reach the respiratory center and, by inhibition, temporarily arrest the inspiratory phase of respiration

the respiratory center depends on impulses descending from the pons for maintenance of the rhythm

the activity of neurons in the respiratory center can be controlled voluntarily for singing and talking

Question 27

how does the cough reflex work?

Answer 27

usually occurs as a response to irritation of the larynx, trachea, or bronchial tree but can also be produced by stimulation of the vagus nerve in other locations (ext. auditory canal, tympanic membrane)

afferent impulses reach the solitary nucleus and tract by way of the vagus nerve

projections to the resp center bring about forced expiration

at the same time, fibers going to the nucleus ambiguus cause efferent impulses to the muscles of the larynx and pharynx for their participation in coughing

Question 28

how does the gag reflex work?

Answer 28

touching the posterior wall of the pharynx results in contraction of muscles in the soft palate and pharynx

sensory fibers of the glossopharyngeal nerve provide the afferent arm of this reflex

after entering the solitary tract, these fibers connect through interneurons with the nucleus ambiguus, which sends efferent fibers through the vagus nerve to the striated muscles of the pharynx

Question 29

forceful emptying of the stomach requires?

Answer 29

relaxation of the gastroesophageal spinster and contraction of the muscles of the anterior abdominal wall to expel gastric contents

simultaneous closure of the glottis prevents inspiration

Question 30

how does the vomiting reflex work?

Answer 30

the stimulus is innervated vagus nerve- evokes pulses sent to the nucleus of the solitary tract by sensory fibers of the vagus nerve.

from here, impulses project to the nucleus ambiguus to close the glottis and to neurons of the medullary RF

impulses in the RF course through the reticulospinal pathways into the SC and activate the appropriate LMNs to induce contraction of diaphragm and abdominal ms

Question 31

what can cause vomiting?

Answer 31

a general elevation of intracranial pressure- probably results from transmission of the increased pressure onto the floor of the fourth ventricle
OR
localized pressure on the medulla from a pathologic process (tumor, hemorrhage)
OR
area postrema- lies immediately rostral to the obey. contains a chemoreceptor region with connections to the nucleus solitarius, through which it can elicit vomiting in response to drugs or other emetic agents in the CSF