Uncal herniation leads to paralysis of which cranial nerve-

Ans. is 'a' i.e., 3rd nerve o Uncal herniation is a common subtype of transtentorial herniation in which the innermost part of the temporal lobe, the uncus, can be squeezed so much that it moves towards the tentorium and puts pressure on the brainstem, most notably the midbrain.o The uncus can squeeze the oculomotor nerve or the 3rd nerve which may affect the parasympathetic input to the eye on the side of the affected nerve, causing the pupil of the affected eye to dilate and fail to constrict in response to light as it should.o Pupillary dilatation often precedes the somatic motor effects of cranial nerve 3rd compression called oculomotor nerve palsy or 3rd nerve palsy. This palsy presents as deviation of the eye to a 'down and out'position due to loss of innervations to all ocular motility muscles except for the lateral rectus (innervated by CN 6th) and superior oblique (innervated by CN 4th)o These symptoms occur in order because the parasympathetic fibres surround the motor fibres of CN 3 and hence compressed first.