trochlear nerve

anatomy

Also known as: CN 4, CN IV, fourth cranial nerve

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Last updated

June 17, 2026

Quick Summary

The trochlear nerve, also known as cranial nerve IV, is unique among the cranial nerves. It is the only one that exits the dorsal side of the brainstem. Its fibers cross in the midbrain, meaning the trochlear neurons innervate the superior oblique muscle on the opposite side of the eye. This muscle is responsible for rotating the eye downward and outward. Damage to the trochlear nerve can lead to double vision (diplopia) and a loss of this specific eye movement. Ophthalmoplegia, or paralysis of the eye muscles, often involves the trochlear nerve, resulting in double vision and vertical deviation of the affected eye.12

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human nervous system
Trochlear nerve (CN IV or 4)
The fourth cranial nerve is unique for three reasons. First, it is the only cranial nerve to exit the dorsal side of the brainstem. Second, fibers from the trochlear nucleus cross in the midbrain before they exit so that…
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The fourth cranial nerve is unique for three reasons. First, it is the only cranial nerve to exit the dorsal side of the brainstem. Second, fibers from the trochlear nucleus cross in the midbrain before they exit so that…
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nervous system disease
Oculomotor, trochlear, and abducens nerves
Compression of the oculomotor, trochlear, or abducens nerves may be caused by lesions, diabetes, vascular disease, head injury, infection, or neuropathy. In the brainstem, multiple sclerosis, stroke, Wernicke disease (see below Brainstem), and tumours are possible causes of
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Compression of the oculomotor, trochlear, or abducens nerves may be caused by lesions, diabetes, vascular disease, head injury, infection, or neuropathy. In the brainstem, multiple sclerosis, stroke, Wernicke disease (see below Brainstem), and tumours are possible causes of
Read More