Unit 1: Photoreception (Vision)

Question 1

Sensation:

Answer 1

-sensation occurs when neural impulses generated by the stimulation of sensory receptors arrive at the cerebral cortex.
-example:
•when a ray of sunlight hits your skin, sensory receptors send a message to the brain, which receives and processes this information, causing you to feel warmth.

Question 2

Sensory adaptation:

Answer 2

-sometimes the brain can filter out redundant sensory information to prevent over-stimulation. This is known as sensory adaptation.

Question 3

Sensory receptors- four general categories of receptors:

Answer 3

1. Photoreceptors.
2. Chemoreceptors.
3. Mechanoreceptors.
4. Thermoreceptors.

Question 4

Photoreceptors:

Answer 4

-stimulated by light (e.g. eye receptors).

Question 5

Chemoreceptors:

Answer 5

-stimulated by chemicals (e.g. nose or tongue receptors).

Question 6

Mechanoreceptors:

Answer 6

-stimulated by pressure (e.g. ear receptors).

Question 7

Thermoreceptors:

Answer 7

-stimulated by heat/cold (e.g. skin receptors).

Question 8

Photoreception (vision):

Answer 8

-vision is associated with the stimulation of photoreceptors at the back of the eye by light energy. Rods and cones in the retina convert this light energy into electrochemical impulses which the brain uses to form an image.

Question 9

Photo:

Answer 9

Light.

Question 10

Anatomy of the eye & vision:

Answer 10

-the eye is made of three layers:
1. Sclera.
2. Choroid.
3. Retina.

Question 11

1. Sclera:

Answer 11

•(tough outer layer).
•cornea: front of sclera.
-protective layer (transparent).
•light enters the eye and is bent (refracted) through the cornea.

Question 12

Astigmatism:

Answer 12

-unequal curvature of the cornea.

Question 13

2. Choroid:

Answer 13

-(middle layer).
-contains blood vessels to nourish eye.
-dark in colour to absorb light.

Question 14

Ciliary body:

Answer 14

-(muscle).
-attached to the lens for focusing.

Question 15

Iris:

Answer 15

-pigmented muscle. Controls the amount of light entering the eye.

Question 16

3. Retina:

Answer 16

•(inner layer).
•ganglion layer: forms optic nerve that exits back of eye (blind spot).
•photoreceptor layer.

-rods: located on periphery.
->night vision.

-cones: concentrated near center.
->fovea centralis: most acute vision.
->colour vision.

Question 17

Pupil:

Answer 17

-(opening in front of eye).
-adaptation: pupil dilates or constricts.

Question 18

Lens:

Answer 18

-(focuses light on retina).
-aqueous humour: lens changes shape if objects are near or far.

Question 19

Aqueous humour:

Answer 19

-maintains cornea shape.

Question 20

Vitreous humour:

Answer 20

-maintains eyeball shape.

Question 21

Aqueous and vitreous humour are:

Answer 21

Liquids.

Question 22

Vision pathway:

Answer 22

•light enters the eye through the cornea, past the pupil and through the lens which helps focus light.
•the light strikes photoreceptors in the retina.
•photoreceptors relay sensory impulses to the occipital lobe of the brain via the optic nerve.

Question 23

Conditions affecting the lens:

Answer 23

-myopia.
-hyperopia.

Question 24

Myopia:

Answer 24

•(nearsightedness):
-the inability to see objects at a distance.
-eyeball is elongated (too long), so focused light falls in front of the retina.

Question 25

Hyperopia:

Answer 25

•(farsightedness):
-the inability to see close objects.
-eyeball is shortened, so focused light falls behind the retina.

Question 26

Conditions affecting the cones:

Answer 26

•colour blindness is a genetic condition caused by a lack of specific cones or colour receptors.
-most colour blind individuals lack the cones which respond to red-green wavelengths, so they cannot perceive those colours (see them as shades of brown).