BIOLOGY CT-2 TEXT

Light

Electromagnetic radiation that is visible to the human eye and is responsible for the sense of sight.

Retina

A layer at the back of the eye made of cells sensitive to light that focuses an upside-down picture of an object.

Optic nerve

Nerve that transmits visual information from the retina to the brain.

Iris

The colored part of the eye that controls the size of the pupil and the amount of light entering the eye.

Pupil

The hole in the center of the iris that lets light into the eye.

Sclera

The tough, white protective layer of the eye.

Aqueous humour

A watery liquid that fills the front part of the eye.

Vitreous humour

A jelly-like substance that fills the back part of the eye.

Ciliary muscles

Muscles that change the shape of the lens to help focus on objects.

Cornea

The clear front part of the eye that helps to bend light.

Choroid

A black layer in the eye that prevents light from being reflected inside the eye.

Blind spot

The area in the retina where there are no light-sensitive cells and thus no visual perception.

Neurones

Nerve cells that transmit nerve impulses.

Sensory neurones

Nerve cells that carry impulses from sense organs to the central nervous system.

Motor neurones

Nerve cells that transmit impulses from the central nervous system to effector organs.

Impulse

An electrical signal that travels along a nerve fibre.

Synapse

The tiny gap between nerve cells where impulses are transmitted.

Stimulus

Any change in the environment that elicits a response.

Response

An action or change in behavior resulting from a stimulus.

Three-dimensional vision

The ability to perceive depth and see objects in three dimensions by integrating the slightly different views from each eye.

Rods

Light-sensitive cells in the retina that work in dim light and do not perceive color.

Cones

Light-sensitive cells in the retina that function in bright light and are responsible for color vision.