Structure and Function of the Human Eye - WordPress.com

Structure and Function of the Human Eye - WordPress.com

Bell work: 3/13/13 Fill in the blank with the correct work: The eye is an example of a group of _______ cells. (effector or receptor) Structure and Function of the Human Eye

The Human Eye ~ Sense Organ Fig. 49.9 Cornea Description: Front part of the tough outer coat, the sclera. It is convex and transparent. Function: refracts light - bends it as it enters

the eye Iris Description: Pigmented - decides the color of your eyes - so light cannot pass through. Its muscles contract and relax to alter the size of its central hole or pupil. Function: controls how much light enters the pupil

Lens Description: Transparent, bi-convex, flexible disc behind the iris attached by the suspension ligaments to the ciliary muscles. Function: focuses light onto the retina Retina

Description: The lining of the back of eye containing two types of photoreceptor cells rods - sensitive to dim light and black and white - and cones sensitive to color. Function: contains the light receptors

Optic Nerve Description: bundle of sensory neurons at back of eye. Function: carries impulses from the eye to the brain Pathway of Light Light passes through the eyeball to the retina.

It is refracted (its rays are bent) by the cornea and lens, so that the light is brought to a focus on the retina. Reflex Actions 1. Receptor detects a stimulus - change in the environment 2. Sensory neuron sends signal to relay neuron 3. Motor neuron sends signal to effector

4. Effector produces a response Example: The way the iris in our eye adjusts the size of the pupil in response to bright or dim light is a reflex action. Reflex Actions of our EYES In bright light:

Radial muscles of the iris relax. Circular muscles of the iris contract. Less light enters the eye through the contracted pupil. In dim light: Radial muscles of the iris

contract. Circular muscles of the iris relax. More light enters the eye through the dilated pupil. Focusing Light Accommodation is the focusing of light

in the retina. Mammals focus by changing the shape of the lens. The lens is flattened for distant objects. The lens is rounded for near objects.

Accommodation of the Lens How the shape of the lens is changed Distant Object Flat/thin lens Muscles relax Near Object Thick/fat lens

Muscles contract

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