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A Sample Case: A 50 year old man developed an incoordination of his right hand and noticed while shaving that although he nicked the right side of his face that he felt no pain.

His general physical examination was basically normal. The principal findings of his neurologic exam revealed diminished pain and temperature sensation on the right side of his face and from the left side of his body. There was no corneal reflex closure of either eye in response to a wisp of cotton placed on the right cornea; there was a bilateral corneal response (blink) to cotton on the left cornea. The muscles of mastication were weak on the right and when asked to protrude his jaw it moved asymmetrically toward the right side. There was a diminished jaw jerk response.

Strength and muscle tone in his left arm and leg were normal but on the right side there was diminished tone, strength, and an intention tremor.

Explanation -

The loss of pain and temperature sensation on the right side of his face and left side of his body suggest injury to the spinothalamic tract on the right and the sensory division of CN 5 on the right side. The lack of a direct and consensual corneal response from stimulation of the eye on the right is also consistent with a 5th nerve sensory loss on the right. Motor weakness of the muscles of mastication, diminished jaw jerk and the pointing of the jaw to the right is consistent with injury to the motor fibers of the 5th nerve on the right; hence, both motor and sensory divisions of CN 5.

Motor examination indicated weakness and incoordination of the right arm and leg which is consistent with injury to the right cerebellar hemisphere or in this case the right middle cerebellar peduncle.

The short circumferential branches of the basilar artery at mid-pontine levels serve the middle cerebellar peduncle and in the tegmentum the motor and sensory root of the trigeminal nerve and the nearby spinothalamic tract.