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The Sense of Sight: Motion, Nerves and Eye Movements

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  • 0:30 Optic Nerve (Cranial Nerve II)
  • 1:38 Oculomotor Nerve…
  • 2:47 Trochlear Nerve…
  • 3:13 Abducens Nerve…
  • 3:33 Lesson Summary
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Lesson Transcript
Instructor: Artem Cheprasov
Find out how cranial nerve II, cranial nerve III, cranial nerve IV, and cranial nerve VI help you see and control the movement of your eyes. You'll learn if there's a difference between those cranial nerves and that of the abducens nerve, oculomotor nerve, optic nerve, and the trochlear nerve.

Seeing With and Moving Your Eyes

The way your eyes move and the way they see have something in common. There are nerves that send signals to or from the eyes in order to accomplish this. What's different is that some nerves are involved in the sensation of light while others are involved in the movement of your eyeball left and right or up and down.

The Optic Nerve or Cranial Nerve II

Location of the two optic nerves in the brain
Optic Nerve Brain Location

When it comes to the sensation of light entering your eye, there is a large nerve connected to the back of each eyeball that transmits light information gathered by the retina to the brain; this nerve is called the optic nerve or cranial nerve (CN) II.

The two terms, cranial nerve II and the optic nerve, are completely synonymous. Do not get confused into thinking they are different nerves. Also, you should note that you have two of each cranial nerve in your body; including the optic nerve.

Again, the optic nerve is involved in the sensation of light. As light hits a structure, called the retina, at the very back of your eye, the light excites certain cells located within the retina. These cells transform information carried by light into electric impulses that travel through the optic nerve to the brain. Thereafter, the brain can interpret these electric impulses into the image you see in front of you.

The Oculomotor Nerve or Cranial Nerve III

The oculomotor nerve controls the pupils and shape of the eye lens
Oculomotor Nerve Importance

While cranial nerve II is the most important nerve in helping you interpret the information provided by light, another nerve is important not only in certain aspects of eyesight, but also in your eye's ability to move about. The most important nerve involved in the movement of the eye is called the oculomotor nerve, also referred to as cranial nerve III.

The oculomotor nerve's innervation of the muscles around your eye, the upper eyelid, and structures within the eye is critical for movement of the eye and eyesight. Cranial nerve III:

  • Opens your upper eyelid so you can see something in the first place.
  • Constricts your pupil when there is a lot of light hitting your eyes.
  • Innervates and constricts the muscles that control the shape of your eye's lens; this action helps you see objects close to you.
  • Moves your eyeballs in different directions, such as down to the ground, up towards the ceiling, or towards the nose.

The Trochlear Nerve or Cranial Nerve IV

When thinking about the third cranial nerve, cranial nerve IV, also known as the trochlear nerve, it is going to be quite a letdown. It innervates a single muscle to the eye that primarily helps you look down or towards the nose. As you can tell, the fourth cranial nerve doesn't do nearly as much as the third cranial nerve when it comes to the eyeball.

The Abducens Nerve or Cranial Nerve VI

The nerves that control eye movement
Nerves Eye Movement

Like the trochlear nerve, there is another nerve that innervates only one muscle controlling the eye's movement. This nerve innervates a muscle of the eye that allows you to look to the side, called the abducens nerve, also referred to as cranial nerve VI.

Lesson Summary

At this point, you should realize that the three main nerves involved in the movement of your eyes are cranial nerves III, IV, and VI.

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