Cranial Nerves Flashcards
Name three distinct symptoms associated with a CN III deficit
1) Severe ptosis
2) Large pupil, unreactive to light
3) Outward deviation (due to unopposed lateral rectus)
What do the eyes look like in someone with a CN VI lesion?
Busted lateral rectus –> inability to ABduct in affected eye
Which CN is responsible for mediating constriction in response to light?
CN II
What are the three components of the near reflex?
Lens accommodation
Pupillary constriction
Convergence
Selective disruption of the light reflex (when the pupil constricts as part of the near reflex but now when exposed to light) indicates a lesion in which part of the brain?
the pretectal area of the midbrain
Name two pathological processes that lead to a selective disruption of the light reflex
Disruptions of the pretectal area of the midbrain such as:
1) Argyl-Robertson pupil in neurosyphilis
2) Dorsal midbrain tumors such as pineal tumor- Parinaud’s syndrome (associated with poor upgaze)
Why does Horner’s syndrome lead to miosis?
A lesion in the sympathetic nerve –> inability for pupil to dilate
Horner’s= ptosis, miosis and anhydrosis
Describe the steps necessary for the eyes to both look left
1) Left frontal eye field of the cortex activates the left PPRF
2) PPRF activates the CN VI to contract the left lateral rectus
3) PPRF sends a signal up the right MLF pathway to the right oculomotor nucleus and activates the right CN III. Activated CN III causes the right medial rectus to contract, and both eyes are turned to the left.
Describe a left internuclear opthlamoplegia (left MLF syndrome)
a LEFT INO is seen when the left eye is unable to ADduct, but the right eye abducts with nystagmus
(Direction refers to which ascending MLF pathway is compromised)
How will the ADduction during a near reflex be affected by someone with a left INO?
It will not- the adduction will be normal because the MLF pathway is not involved
What is trigeminal neuralgia?
short-circulating nerve conduction of the trigeminal nerve leads to lightning-like jabs of pain, often in the V2/V3 area.
What causes trigeminal neuralgia?
1) Associated with young MS patients
2) Tortuous blood vessels compressing CN V in older patients
What is the tx for trigeminal neuralgia?
1) Anticonvulsants
2) Destroy nerve branch, or
3) Move blood vessel
What nerve is tested by the corneal blink test?
V1- V1 is sensory only
Describe the innervation of the muscles of mastication
bilateral UMN (corticobulbar) control
IN lower motor neuron lesions of CN5, how is the
The jaw deviates to the side of the lesion, and the masseter and temporalis muscle are atrophied
Describe the effects of left corticobulbar damage of the UM innervating the facial nerve
Weakness of the RIGHT lower face
What happens to your face where there is a LMN lesion of facial nerve or facial nerve nucleus?
weakness of entire ipsilateral face
What is Bell’s palsy?
Sudden, non-traumatic, isolated CN VII palsy
A stylomastoid lesion of the facial nerve leads to what clinical feature?
Ipsilateral facial paralysis
A petrous bone lesion of hte facial nerve leads to what clinical feature?
Loss of taste to anterior 2/3rds tongue (and facial paralysis)
Sensitivity to sound ( and facial paralysis)
A cerebellopontine angle lesion of CN VII leads to what clinical feature?
Deafness, tinnitus (and facial paralysis)
A pontine lesion of CN VII leads to what clinical feature?
Impaired lateral gaze (and facial paralysis)
Does the uvula deviate to right or left in a left sided CN X lesion?
Uvula will deviate to the RIGHT.
The uvula deviates to the unaffected side
How would an UMN lesion on the right side affect the tongue?
In most patients, an UMN lesion may not cause weakness or tongue deviation, because motor cortex controls both ipsi and contralateral hypoglossal nuclei.
In a few patients, there is unilateral control from the cortex, and the tongue deviates to the affected side.
How does a LMN lesion of CN XII affect the tongue?
atrophy, fibrillations and fasciculations of the affected side.
What is another name for Medial midbrain syndrome?
Webber Syndrome
WHat is webber syndrome?
Webber Syndrome arises from an occlusion of the posterior cerebral artery branch. It leads to ipsilateral CN III lesion and contralateral hemiplegia (due to lesion in the cerebellar peduncle)
What is another name for lateral medullary syndrome?
Wallenberg syndrome
What is wallenberg syndrome?
occlusion of vertebral or PICA
- Nystagmus (Vestibular nuclei)
- ipsilateral limb dysmetria (ICP)
- Ipsilateral horner’s syndrome (descending sympathetic fibers)
- ipsilateral palatal, vocal cord weakness (nucleus ambiguus)
- Impaired pain and temperature in the ipsilateral face and CONTRALATERAL body (descending tract CN V, Vn and Vt)
