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.
