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Optic Nerve

A bundle of more than 1 million nerve fibers that carries visual messages from the retina to the brain.

PubMed Health Glossary
(Source: NIH - National Eye Institute)

Terms to know

Body Fiber
In the body, fiber refers to tissue made of long threadlike cells, such as muscle fiber or nerve fiber.
Brain
The part of the central nervous system that is contained within the skull (cranium).
Brain Stem
The part of the brain that is connected to the spinal cord.
Central Nervous System
The brain and spinal cord. Also called CNS.
Cerebellum
The portion of the brain in the back of the head between the cerebrum and the brain stem. The cerebellum controls balance for walking and standing, and other complex motor functions.
Cerebral Ventricles (Brain Ventricles)
A series of interconnected, fluid-filled cavities found within the brain. These cavities are the ventricles of the brain, and the fluid is cerebrospinal fluid.
Cerebrum
The largest part of the brain. It is divided into two hemispheres, or halves, called the cerebral hemispheres. Areas within the cerebrum control muscle functions and also control speech, thought, emotions, reading, writing, and learning.
Choroid
A thin layer of tissue that is part of the middle layer of the wall of the eye, between the sclera (white outer layer of the eye) and the retina (the inner layer of nerve tissue at the back of the eye). The choroid is filled with blood vessels that bring oxygen and nutrients to the eye.
Choroid Plexus
A network of blood vessels and cells in the ventricles (fluid-filled spaces) of the brain. The blood vessels are covered by a thin layer of cells that make cerebrospinal fluid.
Ciliary Body
A part of the middle layer of the wall of the eye. The ciliary body includes the ring-shaped muscle that changes the size of the pupil and the shape of the lens when the eye focuses. It also makes the fluid that fills the eye.
Cornea
The transparent part of the eye that covers the iris and the pupil and allows light to enter the inside.
Eye
Eyes are the organs of vision. They detect light and convert it.
Eyelid
An eyelid is a thin fold of skin that covers and protects the eye.
Hypothalamus
The area of the brain that controls body temperature, hunger, and thirst.
Iris
The colored tissue at the front of the eye that contains the pupil in the center. The iris helps control the size of the pupil to let more or less light into the eye.
Lens in the Eye
A clear disk that focuses light, as in a camera or microscope. In the eye, the lens is a clear, curved structure at the front of the eye behind the pupil. It focuses light rays that enter the eye through the pupil, making an image on the retina (light-sensitive layers of nerve tissue at the back of the eye).
Medulla Oblongata (Brain Medulla)
The medulla oblongata is the lower half of the brainstem. It is often referred to simply as the medulla. The medulla deals with the autonomic (involuntary) functions of breathing, heart rate and blood pressure.
Nerves
A bundle of fibers that receives and sends messages between the body and the brain. The messages are sent by chemical and electrical changes in the cells that make up the nerves.
Pineal Gland
A tiny organ in the cerebrum that produces melatonin. Also called pineal body and pineal organ.
Pituitary Gland
A pea-sized gland at the base of the brain that regulates the body's balance of hormones.
Pons
Part of the central nervous system, located at the base of the brain, between the medulla oblongata and the midbrain. It is part of the brain stem.
Pupil
The opening at the center of the iris. The iris adjusts the size of the pupil and controls the amount of light that can enter the eye.
Retina
The light-sensitive tissue lining at the back of the eye. The retina converts light into electrical impulses that are sent to the brain through the optic nerve.
Sclera (White of the Eye)
The white layer of the eye that covers most of the outside of the eyeball.
Spinal Cord
A column of nerve tissue that runs from the base of the skull down the back. It is surrounded by three protective membranes, and is enclosed within the vertebrae (back bones). The spinal cord and the brain make up the central nervous system, and spinal cord nerves carry most messages between the brain and the rest of the body.
Vitreous Humor (Vitreous Body)
The clear jelly-like substance that fills the inside of the eyeball. As a person ages, the vitreous humor becomes more liquid.

Related conditions

Terms to know

Body Fiber
In the body, fiber refers to tissue made of long threadlike cells, such as muscle fiber or nerve fiber....
Brain
The part of the central nervous system that is contained within the skull (cranium)....
Brain Stem
The part of the brain that is connected to the spinal cord....
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