Trochlear Nerve: Function, Damage & Palsy Video

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  • 0:02 Location & Function
  • 0:41 Damage & Palsy
  • 1:30 Diploplia
  • 2:08 Lesson Summary
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Lesson Transcript
Instructor: Laszlo Vass
In this lesson, you will learn about the location and function of cranial nerve number four, the trochlear nerve. You will also learn how damaging this nerve can affect your body, and how paralysis and palsy related to this nerve effect overall nervous system function.

Location and Function

The trochlear nerve is also known as the fourth cranial nerve. It exits the brain on the dorsal side of the brain stem. The trochlear nerve is a motor nerve, and it controls the superior oblique muscle of the eye. The superior oblique muscle controls the downward movement of the eyeball and, in part, keeps the eyeball from rolling upward into the orbit (eye socket). The trochlear nerve runs through the cavernous sinus and then enters the orbit through the supraorbital fissure.

Trochlear Nerves

The diagram shows the location of the two branches of the trochlear nerve, the supratrochlear branch and the infratrochlear branch.

Damage and Palsy

Damage to the trochlear nerve that results in a loss of function is called palsy. Since the trochlear nerve functions to control the superior oblique eye muscle, palsy to this nerve involves the loss of control of this muscle, resulting in the eye drifting upward. Acute palsy is usually temporary (lasting from a week up to two months) and often results from head trauma. Initially, patients may complain of blurry vision, but more severe damage can cause double vision. Chronic palsy is normally congenital and results from the malformation or incomplete formation of the trochlear nerve. Chronic palsy can be noticed in childhood, but sometimes minor congenital defects of the trochlear nerve are not always noticed until adulthood. In some cases, congenital palsy can be repaired surgically.


Injury to the trochlear nerve can cause weakness in the ability to move the eyeball downward. This effects the vertical alignment of images resulting in double vision known formally as diplopia. To fix this, patients learn to lower their head (tuck in their chin) to bring the two eyes back to a single visual field.

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