Anatomy-Cranial Nerves IX & XII Flashcards
What cranial nerves are indicated below?
1) Hypoglossal (XII) 2) Glossopharyngeal (IX) and Vagus (X)
What does the hypoglossal nerve do?
Motor innervation of the tongue (all muscles except palatoglossus, which is innervated by CN X)
The image below is a slice from the upper region of the medulla. Where would you find the lower motor neurons of CN XII? Where do its axons travel?
This is a GSE fiber. It is a midline gray matter structure seen below. Note that the axons course between the pyramid and olive. Their rootlets exit and form they hypoglossal nerve.
Does the ansa cervicalis come from the hypoglossal nerve?
No. It comes from the sympathetic trunk, the fibers just piggyback on the hypoglossal nerve.
What cranial nerve lesion does this patient have?
CN XII. You will have atrophy of the tongue muscles on the ipsilateral side of the lesion and when you stick out the tongue it will deviate toward the side that is affected.
What does the spinal accessory nerve do?
Motor “I don’t know” functions (shrug shoulders and nod head by SCM and trapezius)
Where are the lower motor neurons of CN XI located?
C1-C5 ventral horn of spinal cord. It then travels up through the foramen magnum and then leaves through the jugular foramen to innervate muscle.
A patient gets stabbed in the neck. During his physical exam he has difficulty shrugging his right shoulder and turning his head left. What cranial nerve lesion does he have?
CN XI. Lesions here present with difficulty shrugging the ipsilateral shoulder and turning head to contralateral side.
What functional components does the vagus nerve have?
SVE (pharyngeal arches 4 &6), GVE (parasympathetic from below neck to splenic flexure), SVA (epiglottis taste), GVA (organ sensory), GSA (ear & meninge pain & temperature)
The image below is a slice from the upper region of the medulla. Where would you find the lower motor neurons of CN X that go to pharyngeal arches 4 & 6 (SVE fibers)? Where do its axons travel?
LMNs are found in the nucleus ambiguus on the ventral aspect of the tegmentum.
The image below is a slice from the upper region of the medulla. Where would you find the lower motor neurons of CN X that go to supply parasympathetic innervation in the body (GVE fibers)? Where do its axons travel?
Dorsal motor nucleus of CN X (DMX).
The image below is a slice from the upper region of the medulla. Where would you find the lower motor neurons of CN X that go to supply epiglottic taste (SVA fibers)? Where do its axons travel?
Solitary nucleus. Its axons project to higher sensory centers after synapsing in the inferior ganglion
The image below is a slice from the upper region of the medulla. Where would you find the lower motor neurons of CN X that go to supply organ sensation (GVA fibers)? Where do its axons travel?
Solitary nucleus. Its axons project to higher sensory centers.
The image below is a slice from the upper region of the medulla. Where would you find the lower motor neurons of CN X that go to supply general sensation around the external ear and posterior cranial fossa meninges (GSA fibers)? Where do its axons travel?
Spinal Vth nucleus.
What branches come off of the vagus nerve as it courses through the carotid sheath?
1) Pharyngeal branch (pharyngeal motor & palate motor) 2) Superior laryngeal -> internal laryngeal (sensory to upper larynx) and external laryngeal (cricothyroid muscle motor) 3) Recurrent laryngeal (motor to larynx and sensory to lower larynx)
What would you expect to see clinically with a patient who has a unilateral lesion of the vagus nerve?
Dysphonia (hoarseness), dysarthria (slurred), dysphagia, uvula deviation to opposite side of lesion and lack of palate elevation w/gag reflex.
What functional units does the glossopharyngeal nerve have?
SVE (pharyngeal arch 3), GVE (parasympathetic for parotid), SVA (taste to posterior 1/3 tongue), GVA (organ sensory), GSA (ear & meninge pain & temperature)
Where do the fibers that innervate stylopharyngeus originate from in the medulla?
Stylopharyngeus is the only muscle that comes from arch 3. Arch 3 is innervated by CN IX, with the nucleus in the medulla is the nucleus ambiguus.
Where do the CN IX fibers that provide taste sensation to the posterior 1/3 of the tongue travel to and synapse in the medulla?
Inferior gangion -> solitary nucleus.
Where do the CN IX fibers that provide sensory input (GVA fibers) from the mucosa of the pharynx, carotid body and carotid sinus travel to and synapse in the medulla?
Inferior ganglion -> solitary nucleus.
Where do the CN IX fibers that provide general sensory input from the ear travel to and synapse in the medulla?
Superior ganglion -> Spinal Vth nucleus.
What branches comes off of the glossopharyngeal nerve?
1) Stylopharyngeal branch 2) Carotid branch
What clinical signs would you see if a patient had glossopharyngeal neuralgia?
Pain in pharynx region and around ear for a few seconds. This is thought to be caused by compression of the nerve.
You eat some ice cream. How does that sensory input get to the cortex of the brain?
Tongue taste receptors stimulate primary neuron (Anterior 2/3 = CN VII. Posterior 1/3 = CN iX. Epiglottis = CN X) -> Synapse in solitary nucleus of brainstem -> Secondary neuron travels up central tegmental tract to thalamus and synapses in the ventral posterior medial nucleus (VPN) -> Tertiary fibers go to the insula and operculum of the cortex.
What is the ascending sensory pathway to the cortex from the cardiorespiratory system?
Baro-, chemo- and stretch receptors (primary neurons) travel up to the medulla and synapse in the solitary nucleus -> Secondary neurons project to many places: reticular formation (autonomic control center), spinal cord (phrenic nucleus and IML cell column), hypothalamus, and DMX (vagus parasympathetics)
How does activation of vagus receptors in the gut induce vomiting?
Serotonin in gut activates emetic primary neurons -> synapse in solitary nucleus -> secondary neuron goes to area postrema
What cranial nerves does the gag reflex test?
CN IX (afferent limb goes to the solitary nucleus after stimulation) -> Interneuron goes to nucleus ambiguus -> CN X (efferent limb elevates palate)
