Cranial Nerves

There are 12 pairs of cranial nerves labelled in Roman numerals. Cranial nerves I and II (the olfactory and optic nerves) are attached to the forebrain. The rest of the cranial nerves arise from the brainstem. All the cranial nerves are distributed in the head and neck except the cranial nerve X (the vagus nerve), which also supplies structures in the thorax and abdomen.

Cranial nerves have specific functions in the human body.

Popular exam question:

Why does an upper motor nerve palsy on the left spare the muscles above the eye on the right?

Answer: The facial muscles above the eyes are innervated by both right and left upper motor nerves, unlike the facial muscles below the eyes which are only innervated by the contralateral side. So a left upper facial motor nerve injury results in right facial palsy below the eyes, but spares the facial muscles above the eyes because some innervation is still available from the right upper facial nerve.

Base of Skull

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