Lower CNs Flashcards
What obvious abnormalities might you observe in a person’s face who has a neurological condition?
Facial asymmetry eg unilateral drooping of one side of the face due to a stroke
* Eye abnormalities eg unequal pupils, nystagmus
* Abnormal facial movements eg tics
What are the three branches of the CN 5 (trigeminal nerve)?
(i)Ophthalmic (forehead), (ii) Maxillary (upper face/cheek), (iii) Mandibular (lower face/cheek)
What is the function of each of these two cranial nerves in the corneal reflex?
The sensory component is mediated by the ophthalmic branch of CN 5 and the motor component results from CN 7
innervation of orbicularis oculi muscles
What would you observe with the opening of the jaw opening with a unilateral lesion of the motor branch of CN 5?
The jaw deviates to the affected side due to weakness of the pterygoid muscle
What distinguishes an upper motor neuron and lower motor neuron defects in the facial nerve (CN 7)?
UMN defect – the upper third of the face is relatively spared because there is bilateral representation of the muscles that move
the upper third of the face muscles in the cerebral cortex eg stroke, tumour
LMN defect – all movements of one side of the face are affected eg infection (HIV), brainstem lesion (stroke, tumour, MS),
systemic disease (DM,) idiopathic LMN 7th nerve palsy = Bell’s Palsy
What are some simple bedside tests to test hearing?
After blocking one ear, test the other ear by:
a) whispering (into that ear) either numbers or letters and the patient repeats them
b) rubbing your fingers together near the external meatus and ask if the patient can hear that noise
c) portable screening audio machine that tests 500, 1000, 2000, 4000 Hz
What would a Right sided conductive deafness reveal in these tests?
Rinné negative i.e. no or little air conduction at external meatus (bone conduction better than air conduction, in this case)
Weber – sound is paradoxically louder in the abnormal ear
What are some causes of horizontal nystagmus?
a) Vestibular lesion – acute = nystagmus away from lesion, chronic = towards side of lesion
b) Cerebellar lesion – towards side of lesion
c) Toxic – phenytoin (for epilepsy) or alcohol
d) Internuclear ophthalmoplegia (nystagmus in abducting eye, failure of adduction in the other eye eg MS)
What is the purpose of looking inside the patient’s ears with an otoscope/auriscope?
You will be surprised what you may find! Hearing aid you didn’t see, tympanic membrane scarring, inflammation or perforation,
wax occluding canal and may be the reason for poor hearing, otitis media/externa, vesicles of HZV (shingles
What will happen to the eyes in a positive head impulse test?
If there is an underlying vestibular disturbance, the patient cannot keep their eyes fixed on the examiner when their head is moved
quickly, but will adjust once their head stops moving. You will therefore see the eyes flick into central position.
What is the reason for lying the patient down & with their head turned 30 degrees & downwards in a Hallpike manoeuvre?
The Hallpike manoeuvre is testing the vestibular system in the posterior semi-circular canals of the inner ear. Patients with Benign
Positional Vertigo will develop nystagmus a few seconds after lying down in the position described.
What might you see and hear in a CN 10 palsy?
When performing the ‘ah’ test, the uvula will deviate to the normal side. A hoarse voice and ‘bovine’ cough indicates a recurrent
laryngeal nerve lesion (a branch of the vagus nerve CN 10)
What is the function of each of these two cranial nerves in the gag reflex?
The sensory component is mediated by CN 9 and the motor component results from CN 10
What do you ask the patient to do when testing these muscles?
Trapezius – ‘Shrug your shoulders, hold them there and I will attempt to push them down, push against me”
SCM – “Turn your head (to one side), and push against my hand” – the opposite SCM should contract
Trapezius – ‘Shrug your shoulders, hold them there and I will attempt to push them down, push against me”
SCM – “Turn your head (to one side), and push against my hand” – the opposite SCM should contrac
LMN CN 12 causes tongue fasciculation, wasting and weakness (usually CN 12 is damaged in a group with CN 9 and CN 10)
