Fourth cranial nerve

Fourth Cranial Nerve

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The fourth cranial nerve, also known as the trochlear nerve, as illustrated in Gray's Anatomy.

The Fourth Cranial Nerve or Trochlear Nerve is one of the twelve Cranial nerves that originate from the brain. It is the smallest nerve in terms of the number of axons it contains, and the only cranial nerve to emerge from the back of the brainstem.

Anatomy

The fourth cranial nerve is unique among the cranial nerves in several respects:

• It is the smallest nerve in terms of the number of axons it contains.
• It has the greatest intracranial length.
• It is the only cranial nerve that exits from the dorsal (rear) aspect of the brainstem.

Function

The fourth cranial nerve controls the Superior oblique muscle, which is a muscle of the eye responsible for downward and inward eye movements.

Clinical significance

Damage to the fourth cranial nerve can result in Trochlear nerve palsy, which is characterized by the eye drifting upward and slightly outward. This condition can cause double vision and difficulty in looking down, especially when walking down stairs or reading.

See also

• Cranial nerves
• Superior oblique muscle
• Trochlear nerve palsy