Lecture 15: Motor Cranial Nerves Flashcards
CNV- Trigeminal
NUCLEI: Motor Nucleus of V
FUNCTION: Muscles of mastication and tensor tympani muscle.
CNVII- Facial and Nervus Intermedius
FACIAL NUCLEI: Facial
FACIAL FUNCTION: muscles of facial expression, stapedius muscle (dampens sound)
NI NUCLEI: Superior Salvatory
NI FUNCTION: Lacrimal and all salivary glands except parotid.
CNIX- Glossopharyngeal and Lesser Petrosal
G NUCLEI: Nucleus Ambiguous
G FUNCTION: Stylopharyngeus Muscle
LP NUCLEI: Inferior Salvatory
LP FUNCTION: Parotid Gland
CNX- Vagus
NUCLEI: Nucleus Ambiguous and Dorsal Motor Nucleus of X
FUNCTION: NA is for pharyngeal (swallow) and laryngeal (voice) muscles and DMNX is for heart, lung, and digestive tract
CNXI- Spinal Accessory
NUCLEI: Spinal Accessory
FUNCTION: SCM and Trapezius
CNXII- Hypoglossal
NUCLEI: Hypoglossal
FUNCTION: Intrinsic Tongue Muscles
Describe CNV
A mixed motor and sensory nerve.
Where are the trigeminal nuclei located?
at the mid pons level
Which branch of the trigeminal nerve carries motor fibers and where does it exit the skull?
V3 (mandibular)
**It exits via the foramen oval.
What do the motor branches of V innervate?
The muscle of mastication including the temporals and master muscles.
Describe the jaw reflex.
Tapping gently on the lower jaw triggers muscle spindles in the masseter muscle to send an impulse through the sensory fibers of the sensory cranial nerve V and synapsing in the mesencephalic nucleus of V. A short interneuron connects with the motor nucleus of V to send an impulse to the master muscle to contract.
How do you test CNV?
- Have the patient bite down on a tongue depressor and test for bilateral strength of the temporals and master muscles.
- Jaw Reflex (previously described)
What will be the result of an UMN lesion of CNV?
Because input into the trigeminal motor nuclei is largely bilateral, unilateral lesions to the motor cortex or coticobulbar fibers do not produce unilateral weakness of the jaw opening or closing but the jaw jerk may be increased.
What will be the result of a lesion to CNV or its nuclei?
Unilateral weakness of the jaw closure, reduced jaw jerk, atrophy of the temporals and masseter muscles.
Describe CNVII
a mixed motor, parasympathetic and sensory nerve
Where do CNVII and nervus intermedius exit the brainstem?
at the pontomedullary junction in a region called the cerebellopontine angle
What is the facial colliculus?
a bulge on the floor of the fourth ventricle created by the facial nucleus axons
Where does CNVII and the nervus intermedius exit the skull?
It enters the internal auditory meatus, bends ventrally to enter the facial canal and exits the skull via the sylomastoid foramen.
How do you test CNVII?
Have the patient wrinkle their forehead, close their eyes tightly, and show their teeth. Look for symmetry in these actions and also note the width of the palpebral fissure since weakness of the orbicular oculi muscle widening of the eye opening at rest.
What will be the result of an UMN lesion of CNVII?
It is largely bilateral for the forehead and unilateral for the lower face. Thus, a lesion of the UMN will cause unilateral weakness of the contralateral lower face.
**common cause is a stroke.
What will be the result of a unilateral LMN lesion?
It will cause ipsilateral weakness of the lower face and forehead muscles. Ipsilateral hyperacusis and dy eye may also occur.
**common cause is bell’s palsy
What is the association between motor nerve CNVII and the corneal reflex?
Motor VII and its nerve mediate the efferent are of the corneal reflex elicited by gently stroking the cornea and observing the eye closure.
Describe CNIX
Is a mixed motor, parasympathetic and sensory nerve.
Describe the motor component of CNIX.
It is served by the nucleus ambiguous that lies near the junction of the pons and the medulla and innervates muscles of the stylopharyngeus muscle.
Describe the parasympathetic component of CNIX.
The inferior salivatory nucleus lies near the midline of the medulla and sends preganglionic, parasympathetic fibers through CNIX to the lesser petrosal nerve to synapse on the otic ganglion with secondary innervation to the parotid gland.
Where does CNIX exit the skull?
jugular foramen
How do you test CNIX?
Since motor function of this nerve is difficult, it is not usually done. Instead, the sensory component is tested by inducing the gag reflex and watching for the motor response in the form of elevation of the soft palate.
**While the sensory component of the gag reflex is CNIX, the motor component is shared by CNIX and CNX.
How will upper and lower motor neurons lesions of CNIX appear?
may produce some dysphagia
Describe CNX
Is a mixed motor, parasympathetic, and sensory nerve.
Describe the motor component of CNX.
It is served by the nucleus ambiguous that lies near the lateral medulla and innervates the muscles of the soft palate, pharynx and larynx.
Describe the dorsal motor component of CNX.
It lies near the midline of the medulla and sends preganglionic, parasympathetic fibers to the intramural ganglia asscociated with the heart, lungs, and digestive tract.
Where does CNX exit the brainstem?
It exits as a seres of rootless between the inferior olive and inferior cerebellar peduncle.
Where does CNX exit the skull?
jugular foramen
What will be caused by unilateral lesions of the nucleus ambiguous or CNX?
Hoarseness, dysphagia, and inability to elevate the palate on the ipsilateral side.
What will be the result of a unilateral UMN lesion of CNX?
Less prominent symptoms since there is substantial bilateral UMN innervation of CNX nuclei.
What are some of the things regulated by the dorsal motor nucleus of the vagus?
heart rate, respiration and digestion
Describe CNXI
It is a pure motor nerve that controls head turning through the innervation of the SCM and shoulder elevation through the trapezius muscles.
Where does CNXI receive motor neurons from?
Both the caudal portion of the nucleus ambiguous and the spinal accessory nucleus.
What is the course of the fibers of CNXI that originate in the nucleus ambiguous?
They travel for a short distance with CNXI before joining with CNX to innervate the pharynx and larynx.
**These fibers are more appropriately considered part of the vagus nerve.
What is the spinal accessory nucleus composed of?
Neurons that lie in the interomediolateral gray horn of the first 4-5 segments of the cervical spine.
What is the course of fibers from the spinal accessory nucleus?
They exit the cord via the interomedialteral gray area and ascend alongside the spinal cord to enter the skull through the FORAMEN MAGNUM and then exit via the JUGULAR FORAMEN.
What will be the result of a unilateral lesion of either CNXI or its motor nuclei?
Produce weakness and atrophy of both muscles ipsilateral to the lesion.
What will be the result of a unilateral UMN lesion?
Weakness and atrophy of both muscles on the contralateral side of the lesion.
What direction does the left SCM turn the head?
right
Describe CNXII
It is a pure motor nerve that controls tongue movement and lies at the pontomedullary junction.
What is the nucleus that serves CNXII?
the hypoglossal nucleus that lies near the midline in the mid to posterior portion of the medulla.
Where does CNXII exit the brainstem?
Ventrally between the inferior olives and the pyramids.
Where does CNXII exit the skull?
Via the hypoglossal foramen that lies along the posterior aspect of the temporal bone.
What happens if you contract the tongue muscles on the left?
It pushes the tongue right.
What will be the result if unilateral lesions of CNXII or its nuclei?
It will produce tongue protrusion towards the side of the lesion as well as unilateral atrophy and fasciculations.
What will be the result of an UMN lesion of CNXII?
Due to the fact that coritcobulbar fibers from the motor cortex cross over to control the contralateral CNXII motor nuclei, this will cause the tongue to deviate AWAY FROM THE LESION.
