Nervous System - The Iris Reflex + Accommodation

Question 1

What is the role of the iris and pupil?

Answer 1

To regulate the light intensity that reaches the retina

Question 2

How can the retina be damaged and how does the body prevent it?

Answer 2

• very bright light
• iris reflex protects it

Question 3

Are radial muscles circular or like spokes of a wheel?

Answer 3

They run outward form the pupil like spokes on a wheel

Question 4

radial and circular muscles are …………….
What does the missing term mean

Answer 4

agnostic
Work in opposition to eachother

Question 5

When there is a high light intensity how do the radial and circular muscles react and what state does the pupil become?

Answer 5

Radial muscles: Relax
Circular muscles: contract
State of pupil: contracts

Question 6

Describe the reflex arc of the iris reflex.

Answer 6

• receptor cells on the retina detect the intensity of light reaching it
• impulses are sent along the sensory neurones in the optic nerve which are processed and coordinated by the brain
• brain sends impulse along the motor neurone to the iris muscles which respond accordingly

Question 7

Accommodation -

Answer 7

The process of changing the shape of thelens to focus on near or distant objects

Question 8

Light rats must be …………. so they hit the ………. the most sensitive part of the retina

Answer 8

Refracted
Fovea

Question 9

Describe accommodation when the eye is focusing on a object that is close up.

Answer 9

• widely diverging light rays enter the eye
• cornea refracts light rays
• ciliary muscles contract
• suspensory ligaments slacken
• lens: thicker, more convex** - to refract light rays more strongly
• light rays focused on fovea

Question 10

Describe how the contract of the ciliary muscles effect the suspensory ligaments and lens

Answer 10

• when ciliary muscle contract —> contracts inwards towards lens
• suspensory ligaments slacken —> distance is shorter
• lens becomes thicker —> suspensory ligaments no longer pulling it taught

Question 11

Describe the actions within the eye when focusing on a distant object

Answer 11

• light rays enter the eye parallel
• cornea refracts light rays
• ciliary muscles relax
• suspensory ligaments pulled tight
• lens: thinner - only have to refract light rays slightly onto fovea

Question 12

How do light rays enter the eye from a distance object

Answer 12

parallel light rays

Question 13

Describe how focusing on distant object effects the ciliary muscles and the suspensory ligaments and lens in detail.

Answer 13

• ciliary muscles relax - moves away from lens —> pulls suspensory ligaments taught
• taught ligaments —> stretched lens
• lens thinner