CH 11: CNs of the medulla (7,9,10,11,12) Flashcards
what does the hypoglossal nerve provide?
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
what is the functional component of CN XII?
GSE
CN XII fibers arise from:
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
what do the axons of the hypoglossal nucleus cells pass?
between the pyramid and the olive- exit as rootlets of the hypoglossal nerve
what does injury to CN XII cause?
a LMN lesion with paralysis and atrophy of the muscles on the ipsilateral side
on voluntary protrusion, the tongue deviates to the paralyzed side
where does the spinal portion of the accessory nerve arise and exit?
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
what is the functional component of the spinal portion of the accessory nerve?
SSE??
what is the functional component of the cranial potion of the accessory nerve?
SVE?
where do cranial root fibers arise from?
neurons in the nucleus ambiguous
where do the cranial root fibers go? what do they innervate?
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
how does the spinal portion exit?
passes through the jugular foramen and descends into the neck to end in the SCM and trapezius muscles.
what does into to the spinal accessory nerve result in?
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
what forms the vagal system?
nervus intermedius- sensory and parasympathetic fibers of the facial nerve
glossopharyngeal nerve
vagus nerve
cranial accessory nerve
what is the functional component of cells in the nucleus ambiguus?
SVE lower motoneurons
the nucleus ambiguus consists of ?
CN 9
CN 10
CN 11
what do nerves of the nucleus ambiguus do?
furnish motor innervation to the striated branchiomeric musculature of the soft palate, pharynx and larynx
a unilateral lesion of the vagus nerve leads to:
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
bilateral lesions of the vagus nerve leads to:
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
paralysis of both recurrent vagus nerves leads to:
stridor and dyspnea- may necessitate tracheotomy
fibers of the vagus nerve arise from the:
dorsal motor nucleus of the vagus nerve
stimulation of vagal parasympathetic fibers:
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
what innervates taste?
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
what are the reflexes of the vagal system?
salivary-taste reflex carotid sinus reflex carotid body reflex cough reflex gag reflex vomitting reflex
how does the salivary-taste reflex work?
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
how does the carotid sinus reflex work?
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
how does the carotid body reflex work?
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
how does the cough reflex work?
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
how does the gag reflex work?
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
forceful emptying of the stomach requires?
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
how does the vomiting reflex work?
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
what can cause vomiting?
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
