8 Cranial Nerves I-VI Flashcards
For reference:
What is the brainstem?
Adjoins brain and spinal cord
Vital role in regulation of cardio respiratory functions + maintaining consiousness
Location of majority of cranial nerve nuclei
Ascending and descending fibres between brain and rest of body run through brainstem
How might damage to the olfactory nerve (I) present?
Difficulties/changes in sense of smell
(If tested formally, do one nostril at a time)
What is anosmia? What is the most common cause of anosmia?
Loss of sense of smell
Commonest cause: URT infection
Apart from an URT, what other causes could there be for anosmia?
(CN I Olfactory nerve)
- Head injury (basilar skull fracture/shearing forces)
- Tumours at base of frontal lobes
Explain why pituitary tumours cause bilateral visual symptoms.
Tumours compress optic chiasm
In optic chiasm: mixing of sensory fibres from right and left optic nerves
If there is pathology affecting vision involving the optic nerve and the symptoms are only present in one eye, where is the pathology (eg lesion) likely to be located?
Optic nerve or retina
Apart from pituitary tumours, give examples of other pathologies causing visual loss.
- Retinal detachment
- Optic neuritis
- Stroke
How do we test the optic nerve clinically?
Visual acuity tests eg snellen chart
Visual fields (is part of vision missing)
Pupillary light responses
Use opthalmoscope to view patient’s optic disc
What pathology is shown in the image on the right?
Papillodema (swollen optic disc)
Why would a rise in intracranial pressure impair the function of the optic nerve?
Cranial nerves I and II are extensions of forebrain
Therefore extensions of the meninges
So raised ICP may impair function of optic nerve
The visual pathway extends back from the retina towards where?
Primary visual cortex (occipital lobe)
What does the communication between the optic tracts and the brainstem allow for in the midbrain?
Allows for certain visual reflexes eg pupillary reflexes to light
What is a blown pupil after a head injury inidicative of?
Raised intracranial pressure
Oculomotor nerve (III) lies very close to edge of tentorium cerebelli
Parasympathetic fibres lie on edge of CNIII (see image)
Sphincter pupillae muscle= innervated by parasympathetic fibres on oculomotor nerve
How would you test the function of the oculomotor nerve clinically?
Inspect eyelids and pupil size
Test eye movements and pupillary reflexes (to light)
Double vision?
Ptosis (eyelid droops) and eye ‘down and out’
What can cause injury to the oculomotor nerve?
What action does the trochlear do? How would you test the function of the trochlear nerve?
Trochlear nerve= motor to superior oblique
Depresses and abducts eyeball
Test eye movements
Diplopia (double vision as eyes don’t line up
What is the sensory distribution of the trigeminal nerve supplying the skin?
How is the function of the trigeminal nerve tested?
Check dermatomes
Test muscles of mastication and corneal reflex (blink reflex)
What is trigeminal neuralgia and how does it present?
Sudden severe facial pain lasting about 2 mins (usually just one side of face)
Thought to be caused by compression of trigeminal nerve
Opthalmic shingles can be sight threatening. Explain why.
Cornea and conjunctiva also innervated by opthalmic division of trigeminal nerve. Shingles can cause scarring of eye
What is the corneal reflex?
Reflex to blink if something touches your eye as high sensory innervation density
