Flashcards in H&N 4.1 cranial nerves Deck (87)
How many cranial nerves are there?
12 pairs (24)
Where do they arise from?
Mainly the brainstem, some directly off the brain
What's a difference between the arrangement of the spinal nerves and the cranial nerves?
Spinal nerves arise at regular intervals, cranial nerves do not
Are the cranial nerves part of the central or peripheral nervous system?
What are the different types of fibres that cranial nerves carry?
What are the parts of the brain stem?
How many cranial nerves come from each part of the brain stem?
What nerve is CN1?
What is the course of the olfactory nerve?
-from the nasal mucosa
-through the cribriform plate of the ethmoid bone
-to the olfactory bulb
-along the olfactory tracts
-to the forebrain
What fibres does CN1 carry?
Therefore, what is it's function?
Special sensory- conveys the sense of smell.
How would you test CN1?
test one nostril at a time, to see if the patient could smell certain smells, such as coffee.
Not formally tested
What is the result of damage to the olfactory nerve?
What are some different causes of anosmia?
-temporary eg due to a virus
-degenerative- for example alzhaemiers
-permanent (eg if there has been trauma which has damaged the olfactory nerve)
-congenital (eg Kallman's syndrome)
What is Kallmann's syndrome?
a chromosomal abnormality leading to malformation of the hypothalamus which leads to lack of GnRH release, and also anosmia.
How can trauma lead to damage of the olfactory nerve?
blunt trauma will cause movement of the brain within the cranial cavity, which may cause the cribriform plate to shear the olfactory nerves, leading to anosmia.
What nerve is CN2?
What is the route of the optic nerve?
From the retina
through the optic chiasm
What's anatomically important about the optic chiasm?
It lies very close to the pituitary gland, so any tumour etc can compress the optic chiasm and affect sight.
What nerve fibres are contained in CN2?
What is its function?
How would you test the optic nerve?
Visual acuity (letter charts)
Describe the pupillary reflex.
When bright light is shone in the eye, the optic nerve conveys this to the brain, this stimulates the parasympathetic nerve fibres on the occulomotor nerve to carry a signal to cause pupilalry constriction.
Why do patients with meningitis suffer from photobia?
meningitis causes inflammation of the meninges, the covering of the brain.
The optic nerve is a direct extension of the brain, so the inflammation will cause impingement of the nerve, so sight will be affected. light causes irritation, becuase the signals have to travel down an injured nerve.
How can you visually see the optic nerve?
Via a fundoscope, seen as the optic disc.
What nerve is CN3?
What is the route of CN3?
arises from the midbrain
through the cavernous sinus
travels through the superior orbital fissue to enter the orbit.
What nerve fibres does the occulomotor nerve carry?
What's its function?
movement of the eyeball (and constriction of the pupil in response to light)
What muscles are innervated by the occulomotor nerve?
-levator palpabrae superioris
How can you test the occulomotor nerve?
Test eye movement asking the patient to follow a H shape.
Also test the pupillary light reflex.
ask patient to open eyes against resistance.
What's the function of levator palpabrae superioris?
to elevate the superior eyelid.