CN XI & CN XII Flashcards
What does CN XI innervate?
Motor: Sternocleidomastoid & Trapezius
What is the function of the sternocleidomastoid muscle?
Tilting and rotating head in opposite direction
What is the clinical exam like for the sternocleidomastoid muscle?
Looks at patient’s ability to turn the head left and right with resistance.
What is the function of the trapezius?
Shrugging shoulders
What is the clinical test for trapezius function?
Difficulty with range of motion and unilateral weakness of trapezius on one side. May be a change in posture or bilateral positioning of shoulders.
What does the hypoglossal nerve innervate?
Muscles of ipsilateral tongue (critical for eating, breathing, speech, emesis)
Where is the nucleus of XII located?
Near midline (motor) in the floor of the ventricle of the rostral medulla
Where is the nucleus of XI located?
In C1-C5, in the posteriolateral position of the anterior horn
What is the course of the spinal accessory nerve from its nucleus to when it exits the skull?
- Formed by C1-C5 lower motor neuron fibers that energy from the cervical cord.
- Does not exit the vertebral column but ascends into cranium in CSF filled sub-arachnoid space
- Exits skull through jugular foramen
- Only cranial nerve to exit and enter the skull
- Motor innervation to trapezius (shrugging) and SCM (shake head no)
What happens when there is damage to the CN XI?
Sternocleidomastoid - can’t shake head no, turn head in opposite direction of weak muscle
Trapezius - change in posture/position of shoulders, can’t push up/shrug shoulders, difficulty with range of motion, unilateral weakness
What happens if the CN XII is damaged?
Can impact chewing, swallowing and speaking
-LMN damage- ipsilateral nerve or nucleus - muscle atrophy of tongue - tongue will deviate toward lesioned side when stuck out
What happens to the tongue if there is corticobulbar damage?
Corticobulbar axons provide mostly contralateral innervation to the tongue (but some ppl vary)
-When protruded, tongue deviates away from side of the upper motor lesion.
What happens when you stick your tongue out after damage to corticobulbar tract?
Tongue deviates toward the damaged area!!
How are the SCM and trapezius innervated by upper motor neurons?
They receive bilateral innervation from UMN. [from the corticospinal input to the spinal accessory nucleus]
What side does is the motor neuron input come from for both the SCM and trapezius?
SCM - predominantly ipsilateral
Trapezius - mostly contralateral
