8.1.6 - Detection Of Light

Question 1

Describe Receptors
(2 Points)

Answer 1

~ Specialised cells, which generate an electrical impulse in a sensory neurone.

~ When stimulated by a particular stimulus by rods and cones.

Question 2

Describe The Process Of How Light Enters The Eye
(4 Points)

Answer 2

~ Through the pupil, and is focused onto a region of the retina called the fovea.

~ Amount of light, which enters the eye is controlled by the iris.

~ Nerve impulses from the photoreceptor cells, are carried from the retina to the brain via the optic nerve.

~ The optic nerve leaves the back from the blind spot, which contains no photoreceptors.

Question 3

What Does The Fovea Contain?

Answer 3

Many photoreceptors.

Question 4

What Types Of Photoreceptors, Does The Retina Contain?
(2 Points)

Answer 4

~ Rod cells.

~ Cone cells.

Question 5

Describe Rod Cells
(3 Points)

Answer 5

~ Located on the outer retina.

~ Sensitive to light intensity.

~ Images are generated are in black and white.

Question 6

Describe Cone Cells
(4 Points)

Answer 6

~ Group together in the fovea.

~ Sensitive to different wavelengths, they detect colour.

~ Can be red-sensitive, green-sensitive or blue-sensitive.

~ The numbers of sensitive cone cells, will determine the colours seen.

Question 7

Describe The Process Of Bleaching
(4 Points)

Answer 7

~ Rod cells contain a light-sensitive pigment called rhodopsin.

~ When light hits rhodopsin, it breaks apart into retinal and opsin.

~ Causing a chemical change in the photoreceptor, generating a nerve impulse.

~ These impulses travel along the bipolar neurone to the optic nerve, then to the brain.

Question 8

How Do Rod Cells Initiate An Action Potential?

Answer 8

When they are hyperpolarised, an action potential is initiated in the neighbouring bipolar neurones.

Question 9

Describe The Role Of Rod Cells, During Darkness
(5 Points)

Answer 9

~ Sodium ions (Cations) are pumped out rod cells via active transport, generating a concentration gradient.

~ Sodium diffuse back into rod cells, via sodium ion channels.

~ This causes the rod cell to become depolarised.

~ Triggering the release of neurotransmitters, which diffuse across a synapse to a bipolar neurone.

~ The neurotransmitter inhibits the action potential, preventing a nerve impulse from being sent to the optic nerve.

Question 10

Describe The Role Of Rod Cells, During Light
(6 Points)

Answer 10

~ Light bleaches rhodopsin, causing it to break down into retinal and opsin.

~ Causing sodium ion channels to close, preventing sodium ions from diffusing back into the rod cell.

~ Sodium ions are still being transported into the cell, but they can’t leave.

~ Rod cell interior becomes more negative and reaches a hyper polarised state.

~ The rod cell then stops releasing the neurotransmitter, the action potential is not inhibited in the bipolar neurone.

~ Depolarisation occurs, and the action potential in the bipolar neurone, is transmitted via the optic nerve.