Summary and Revision of the Intracranial Region, Orbit, Eye and Ear Flashcards
What is the 1st cranial nerve?
This is the olfactory nerve.
What is the 2nd cranial nerve?
This is the optic nerve.
What is the 3rd cranial nerve?
The oculomotor nerve.
What is the 4th cranial nerve?
The trochlear nerve.
What is the 5th cranial nerve?
Trigeminal nerve.
What is the 6th cranial nerve?
The abducent nerve.
What is the 7th cranial nerve?
The facial nerve.
What is the 8th cranial nerve?
The vestibulocochlear nerve.
Which cranial nerve is considered as an extension of the brain?
The olfactory nerve and the bulb.
How many olfactory nerve bundles pass to the olfactor bulb?
About 20 bundles.
How do the olfactory nerve bundles pass to the olfactory bulb?
They pass to the olfactory bulb through the cribriform plate of the ethmoid in the anterior cranial fossa from the roof of the nose.
What do the olfactory nerves innervate?
They innervate the upper part of the nasal cavity.
What is anosmia?
This is when there is loss of sensation of smell.
What can anosmis tell us?
It can tell us that there is a fracture involving the cribriform plate or it may indicate a neuroma or meningoma compressing the olfactory bulb or tract.
When is anosmia common?
It is common after a cold or upper respiratory tract infection.
How can we test the olfactory nerve?
By asking the patient to identify a strong smell such as coffee or chocolate through each nostril in turn is a way of testing the olfactory nerve.
What are the optic nerves concerned with?
They are concerned with vision.
What is the path of the optic nerve?
- pass from the back of the eye through the orbit
- pass through the optic canal in the sphenoid bone.
What is the path of nerve impulses from the lateral part of the retina?
They run to the visual cortex of the same side.
What is the path of nerve impulses from the nasal side of the retina?
They cross to the other side in the optic chiasma.
Where is the optic chiasma?
This lies in front of the pituitary stalk and between the terminal parts of both internal carotid arteries.
When do we get bitemporal hemianopia?
We can get this when a pituitary tumour presses on the centre of the optic chiasma.
What happens to the nasal parts of the retina in bitemporal hemianopia?
Thr nasal parts of the retina recieve light from the temporal fields and in this case they become insensitive to light.
When do we get nasal hemianopia?
This is when there is pressure to the side of hte optic chiasma.
What do we have to make sure that we do when there are visual field defects?
These defects need to be described and plotted with care for each eye when testing the optic nerve.
What does the oculomotor nerve supply?
It supplies most of the extrinsic muscles of the eye?
What does the oculomotor nerve not supply?
- lateral rectus
- superior oblique
- involuntary part of the levator palpebrae superioris muscle
Describe the path of the lateral rectus muscle.
- passes from front of the midbrain between posterior cerebral and superior cerebellar arteries
- into the cleft of dura between free edge of tentorium and the dura over the petroclinoid ligament
- runs forwards in the lateral wall of the cavernous sinus and through the superior orbital fissure within the tendinous ring to enter the orbit.
How can we test the muscles that are supplied the oculomotor nerve?
We can ask the subject to look from side to side and then to look up and down with the eye placed alternately medially and laterally.
Describe the trochlear nerve.
This is a small thread like nerve.
Where does the trochlear nerve arise from?
It arises from the back of the midbrain.