Session 5 - Cranial Nerves I - VII Flashcards
(42 cards)
How many pairs of cranial nerves are there?
12
Where do the cranial nerves come from? What do they supply?
Relate to brain stem, arising from CNS.
Innervate structures in the head + neck.
What types of axons are carried by cranial nerves?
General sensory Special sensory Motor Autonomic (a mix of the above, or only one type)
What is the brainstem?
Brain structure connecting the brain to (continuous with) the spinal cord.
What are the brainstems main functions?
Regulation of cardio-repiratory functions, and maintaining consciousness.
Ascending sensory, and descending motor fibres run through it.
What are the cranial nerve nuclei, where are most found?
Nuclei = collections of cell bodies of nerve fibres.
In the brainstem.
How many Cranial nerves come from each part of the brainstem?
Forebrain = 2 CNs Midbrain = 2 CNs Pons = 4 CNs Medulla = 4 CNs
Name the two CNs from the forebrain.
Olfactory CN I
Optic CN II
What is the route, function and type of axons in the olfactory system?
Special Sense.
Olfactory > Cirbriform foramina > Olfactory bulbs > Olfactory tracts > forebrain
Function: Olfaction (smell)
How is olfaction tested?
Not formally tested.
“have you noticed any change in sense of smell”
Testing one nostril at a time, with salts, or any alternative etc.
What is loss of sense of smell called? What can cause it?
Anosmia
- A common cold is most common.
- Head injury (basilar skull fracture, shearing forces)
- Intracranial tumours, at base of frontal lobes, could interfere.
What is the route of the optic nerve, and its function?
Special Sense.
(complex pathway, goes through optic canal to eye)
Function: Vision
How is the optic nerve clinically tested for problems?
Test one eye at a time.
Visual test (snellen chart, visual fields)
Test pupil response/ reflexes using torch
What can cause issues with the optic nerve? How is it visualised?
Optic disc can be seen with ophthalmoscope.
- Raised intra-cranial pressure can cause nerve to swell (as they carry an extension of the meninges).
(can be seen on ophthalmoscope)
- Lesions involving retina or nerve can cause visual disturbances (affecting one eye)
What is the optic disc?
The point where the optic nerve enters the retina.
Where is vision processed in the brain? Why is the brainstem involved?
Visual pathway extends from retina towards primary visual cortex in occipital lobe.
Communication with brainstem allows reflexes, e.g. puillary reflex to light.
What are the two cranial nerves from the midbrain?
Oculomotor CN III
Trochlear CN IV
What is the route, and types of axons in the oculomotor nerve?
Motor (no sensory)
Autonomic (parasympathetic)
Route: From midbrain through cavernous sinus (sides of sella turcica) through superior orbital fissure in oribit.
What is the sella turcica?
A depression in the sphenoid bone containing the pituitary gland.
What is the function of the oculomotor nerve?
Motor
- Most extra-ocular muscles
- LPS (Levator palpebrae superioris)
Autonomic
- Sphincter pupillae (pupil)
- Ciliary muscle - lens
Why is the oculomotor nerve often compress with raised intracranial pressure?
Uncus of temporal lobe can slip/ move over tentorium cerebelli, which is in close proximity to the entry of the nerve, compressing it.
Under compression, why would autonomic function be affected first in the oculomotor? What is a sign?
Due to the autonomic (parasymp.) fibres being on the outer part of the nerve. (motor are inner).
Fixed dilated pupil (blown).
(continued compression, will compromise motor)
How is the oculomotor nerve CN III tested? What may be seen?
Inspect eyelids and pupils.
Test eye movements.
Pupillary light reflex.
Pupillary dilation and/or double vision
‘Down and out’ position of eyes, severe ptosis (eyelid droop)
Which things can cause oculomotor nerve damage?
- Raised IC pressure
- Aneurysms
- Vascular (2ndry to diabetes, hypertension/ often pupil sparing)
- Cavernous sinus thrombosis
