y4.1 eye 👀

Question 1

what are the three layers of the eye and their functions?

Answer 1

1) sclera (continuous with cornea)
- protects eyeball from mechanical damage
2) choroid
- contains black pigments to prevent internal reflection of light
- contains blood vessels that bring oxygen and nutrients to eye and removes metabolic products
3) retina
- contains photoreceptors, where images are formed

Question 2

other structures of the eye and their functions

Answer 2

1) cornea
- refracts light towards the lens
2) iris (light intensity)
- adjusts the amount of light entering the eye
3) lens (distance)
- changes curvature or thickness to refract light onto retina
4) ciliary muscles (distance)
5) suspensory ligaments (distance)
- transfer the effect of ciliary muscle to lens
6) aqueous humour
- refracts light onto lens
- medium for diffusion of oxygen and nutrients
7) vitreous humour
- refracts light onto retina
- keeps eyeball firm
8) fovea / yellow spot
- greatest concentration of cones but no rods
- detailed colour vision in bright light
9) blind spot (found over optic nerve)
- neurones leave the eye
10) optic nerve
- transmits nerve impulses from sensory neurone to brain

Question 3

what are the two types of photoreceptors and their functions + characteristics?

Answer 3

1) COnes
- allow us to see in COlour in bright light
- present in the greatest concentration at the fovea
3) rods
- allow us to see in black and white in dim light
- contain visual purple (rhodopsin), which is bleached when the eye is exposed to bright light from a dimly light room

Question 4

what is accomodation?

Answer 4

accomodation is the adjustment of the lens to change curvature or thickness so that clear images at different distances are formed on the retina

Question 5

describe the process focusing on a near object

Answer 5

1) ciliary muscles contract, reducing pull on suspensory ligaments
2) suspensory ligaments slacken
3) lens becomes thicker and more convex, decreasing its focal length
4) light rays from the near object are brought to focus on the retina
5) photoreceptors are stimulated and nerve impulse is transmitted to the brain via the optic nerve

Question 6

describe the process of focusing on a distant object

Answer 6

1) ciliary muscles relax, pulling on suspensory ligaments
2) suspensory ligaments become taut
3) lens becomes thinner and less convex, increasing its focal length
4) light rays from the distant object are brought to focus on the retina
5) photoreceptors are stimulated and nerve impulses are transmitted to the brain

Question 7

what are the 3 cranial eye reflexes?

Answer 7

1) pupil reflex - controlling the amount of light entering the eye
2) blink reflex
3) tearing reflex
all have protective function!

Question 8

describe the pupil reflex in bright light

Answer 8

1) photoreceptors in the retina detect an increase in light intensity and transmits nerve impulses to the brain via the sensory neurone in the optic nerve
2) the brain returns nerve impulses along the motor neurone to the circular and radial muscles in the iris
3) circular muscles are stimulated to contract, radial muscles relax
4) diameter of the pupil decreases, allowing less light to enter

Question 9

describe the pupil reflex in dim light

Answer 9

1) photoreceptors in the retina detect a decrease in light intensity and transmit nerve impulses to the brain via the sensory neurone in the optic nerve
2) brain returns nerve impulses along the motor neurone to the circular and radial muscles of the iris
3) circular muscles are stimulated to relax, radial muscles contract
4) diameter of the pupil increases, allowing more light to enter