Motor/Parasympathetic Cranial Nerves - V, VII, IX, X, XI, XII (15) Flashcards
Which 5 cranial nerves are purely motor?
Occulomotor (III) Trochlear (IV) Abducens (VI) Accessory (XI) Hypoglossal (XII)
What mnemonic device can you use to remember which cranial nerves have motor, sensory, or mixed functions?
Some Say Marry Money But My Brother Says Big Business Makes Money; sensory -S, Mixed - M, both - B (duh)
Which four cranial nerves have a parasympathetic component?
Occulomotor, Facial, Glossopharyngeal, Vagus (3, 7, 9, 10)
Where do the nuclei of CN V reside?
At the mid pons level - CN V also exits the brainstem at this level, on the anterolateral surface of the pons
What nerve do motor fibers of CN V travel with? Through what foramen do they exit the calvarium?
Mandibular branch (V3) of trigeminal - exit via foramen ovale
What muscles do the motor fibers of CN V (trigeminal) innervate? (General group, two examples for bonus)
Muscles of mastication, including mastered and temporalis muscles
What mediates the afferent branch of the jaw jerk reflex? Where does it synapse?
Sensory fibers of V3 –> mesencephalon nucleus of V
Muscle spindle from masseter muscle
What nerve mediates the efferent branch of the jaw jerk reflex?
Motor division of V3 (short interneuron connects with the motor nucleus of V from the mesencephalon nucleus)
What would the symptoms of a unilateral upper motor neuron lesion (motor cortex or corticobulbar fibers) to CN V (trigeminal)?
The jaw jerk reflex may be increased
Would jaw weakness be expected with a unilateral upper motor neuron lesion to CN V?
No - there is bilateral input from upper motor neurons so weakness of jaw closing or opening would not be expected
What 3 symptoms would be expected with a unilateral lesion of CN V itself or it’s nuclei?
- Unilateral weakness of jaw closure
- Reduced jaw jerk
- Atrophy of the temporalis and masseter muscles
How can jaw strength be tested clinically?
Have pt bite down on a tongue depressor on both sides
What types of fibers does CN VII (facial) have?
Mixed - sensory and motor; also has a parasympathetic component
*sensory is covered on a separate lecture, so only motor and parasympathetic here
What is the motor nucleus of CN VII? Where is it located?
Facial nucleus - lies at the mid pons
What muscles do the motor fibers of VII innervate?
Muscles of facial expression (also stapedius)
Where does nervus intermedius synapse? What does it innervate?
Sphenopalatine and submandibular ganglia - to the lacrimal and salivary glands
Where do CN VII and nervus intermedius exit the brainstem?
At the pontomedullary junction (in a region called the cerebellopontine angle)
What do the axons leaving the facial nucleus pass over dorsal medially and loop over before exiting the brainstem?
The abducens nucleus
What is the bulge on the floor of the fourth ventricle created by facial nucleus axons called?
Facial colliculus
Via what foramen do facial nerve and nervus intermedius exit the calvarium?
Auditory canal (opening of the canal is the internal auditory meatus) *facial nerve actually bends and exits ventrally out of the auditory canal via the stylomastoid foramen
How do you test the motor component of CN VII?
Ask patient to wrinkle their forehead, close eyes tightly, and show you their teeth - look for symmetry
What would be seen with a unilateral CN VII lesion of motor fibers?
Unilateral weakness of contralateral lower facial muscles but sparing of the forehead muscles
- this is because upper motor neuron innervation is bilateral to the forehead muscles but unilateral to the muscles of the lower face
- common cause is stroke
What symptoms would a unilateral lower motor neuron lesion of CN VII cause?
Ipsilateral weakness of the lower face and forehead muscles (hyperacusis (sensitivity to sound, due to weakness of stapedius muscle) and dry eye on ipsilateral side may also be present)
*common cause is Bell’s palsy
What reflex do the motor fibers of CN VII mediate the efferent response of?
Corneal reflex (V1, ophthalmic n. mediates the afferent, via nasociliary nerve)
What is the parasympathetic nucleus of CN VII? Where is it located and what are the fibers leaving it called?
Superior salivatory nucleus - located near the midline of the upper medulla
* fibers leaving the nucleus = nervus intermedius
What kind of fibers does CN IX contain?
Mixed motor and sensory; also has parasympathetic fibers
What is the motor nucleus of CN IX? Location?
Nucleus ambiguus - located near the junction of pons and medulla (just caudal to pontomedullary junction)
((aMbiguus = motor; compare to nucleus Solitarius = sensory nucleus of 9 and 10))
What muscles does the motor component of CN IX innervate?
Stylopharyngeus (swallowing and palate elevation)
What is the parasympathetic nucleus of CN IX? Location? What are the fibers called when they leave the nucleus?
Inferior salivatory nucleus - near midline of the medulla
* axons leaving the nucleus are known as the lesser petrosal nerve
What ganglion does the lesser petrosal nerve synapse in? Eventual target?
Otic ganglion; to parotid gland
Via what foramen does CN IX exit he calvarium?
Jugular foramen
What is the best way to test the sensory function of CN IX? Why is this used instead of the motor functions?
Test the gag reflex; motor components are under control of other nerves as well, so is not particularly useful to isolate issues with CN IX only = CN X is responsible for the motor component of gag reflex, CN IX is only responsible for the sensory afferent branch of the reflex
What types of fibers do CN X contain?
Motor, sensory, and also a parasympathetic component
*only motor and parasympathetic are covered in this lecture
What is the motor nucleus of CN X? Location? What muscles does it innervate?
Nucleus ambiguus - lies near lateral medulla
- innervates soft palate, pharynx, larynx (elevates the pharynx during talking and swallowing)
- also involved in the efferent reflex of the gag reflex
What is the parasympathetic nucleus of CN X? Where does it originate?
Dorsal motor nucleus of the vagus - near the midline of the medulla
Where do fibers leaving the dorsal motor nucleus of CN X go to innervate their targets?
To intramural ganglia associated with the heart, lung, and digestive tract
Where does CN X exit the brainstem? (Between what two structures?)
On medulla, between the inferior olive and inferior cerebellar peduncle
Via what structure does CN X leave the calvarium?
Jugular foramen (w/CN IX)
What symptoms will be seen in patients with a unilateral upper motor neuron lesion of CN X?
Usually not very prominent lesions, since there is substantial bilateral upper motor neuron innervation of CN X nuclei
What three symptoms will be seen in a unilateral lesion involving The nucleus ambiguus or CN X itself (lower motor neuron lesions)?
- Dysphagia
- Hoarseness
- Inability to elevate pharynx on ipsilateral side
What are the parasympathetic functions of CN X?
Heart rate, respiration, digestion control
What is the motor nucleus for CN XI? Where is it located?
Spinal accessory nucleus - comprised of neurons that lie in the interomediolateral gray area between first 4 to 5 segments (C1-C5) of the cervical spinal cord between the dorsal and ventral horns of the spinal cord
Where do fibers from the spinal accessory nuclei exit the spinal cord?
Between the dorsal and ventral roots on the lower medulla
After going superiority and entering the calvarium through the foramen magnum, via what foramen so fibers from the spinal accessory nucleus exit the calvarium again?
Jugular foramen
What kind of fibers does CN XI contain? What muscles do they innervate?
Sternocleidomastoid muscles and trapezius muscles
*elevates the ipsilateral shoulder and rotates head in opposite direction
Unilateral lower motor neuron lesions of CN XI will cause weakness in which shoulder and turning head in which direction?
Ipsilateral shoulder weakness (can’t shrug) and difficulty turning the head AWAY from the lesion (is ipsilaterally innervated, but turns head away from side it innervates)
In a patient with a unilateral upper motor neuron lesion of CN XI, what shoulder would be affected? What difficulty in turning head would be expected?
~Weakness in contralateral shoulder elevation
~Difficulty turning head away from lesion (same as the lower, because the upper motor neurons don’t cross the midline in CN XI like they do in most other and they do for the shoulder)
What kind of fibers does CN XI have associated with it?
It is a pure motor nerve
What nucleus is the motor nucleus for CN XII? Location?
Hypoglossal nucleus–> Near the midline in the mid to posterior portion of the medulla
Where do CN XII axons exit the brainstem?
Between the inferior olives and the pyramids, at the junction of medulla and spinal cord
Via which foramen does CN XII leave the calvarium?
Hypoglossal foramen (posterior aspect of the petrous temporal bone)
Unilateral upper motor neuron lesions of CN XII will cause the tongue to protrude to which side relative to the lesion?
Tongue will protrude and deviate away from the lesion
Unilateral lesions of CN XII or its nuclei (lower motor neuron lesions) will cause the tongue to deviate to which side when protruded? What other two symptoms?
Towards the side of the lesion; also atrophy and fasciculations (like any lower motor neuron lesion)
