c2 q1 science human eye

Sense organ

• receive stimuli from the
  environment.

• They help the body detect and
  respond to changes

the orbit

Each eyeball lies in a skull hollow called

Iris

Colored circular muscle that controls the pupil's size.

• Contains circular and radial muscles

Pupil

Central hole in the iris that lets light enter

Conjunctiva

Transparent membrane that keeps the
front of the eye moist

Sclera

White, tough outer layer that protects the eye.

Eyelashes

Protect eyes from dust.

Tear gland

Secretes tears to:

• Wash away dust

• Keep cornea moist

• Lubricate the conjunctiv

Eyelids

• Protect the eye

• Help with blinking and squinting

External parts of
the eye

CILIARY BODY

makes the fluid inside the eye. It also enables the lens of the eye to focus on objects at various distances.

Suspensory
Ligament

Connects lens to
ciliary body

CORNEA

is the transparent film-like part that enables the eye to focus on images so they do not look blurred

Aqueous
Chamber

Fluid-filled space
between cornea
and lens.

LENS

is a clear part that receives the light that enters the eye. It then bounces off this light to the back of the eye

Vitreous humor

is the transparent gel that gives the eye its shape.

CHOROID

is the middle layer of the wall of the eye. It is filled with blood vessels that bring oxygen and nutrients to the eye.

Fovea
(Yellow Spot)

Area of sharpest
vision; rich in cones

Blind Spot

No photoreceptors;
where optic nerve
exits.

OPTIC NERVE

transmits electrical impulses or nerve messages from the eye to the brain.

Retina

• contains rods and cones.

• Photoreceptors connect to optic nerve endings.

• Light passes through retinal layers to reach
  photoreceptors.

• Signal travels from photoreceptors → synapse →
  sensory neurones → brain

Cones

Color and
Bright Light Vision

Rods

Black and White
Vision in Dim Light

Focusing

is the adjustment of the lens to
form clear images on the retina, regardless of object
distance.

Stereoscopic Vision

• Each eye sees a slightly
  different image.

• The brain merges both to
  create a 3D view.

• Helps us judge distance and
  depth accurately

In Bright Light:

• Iris muscles contract

• Pupil becomes smaller

In Dim Light

• Iris muscles relax

• Pupil becomes larger