Biology- The eye

Question 1

Describe how a sensory receptor works.

Answer 1

1) Resting Potential: Receptor cells, like nerve fibers, maintain a resting potential.
2) Generator Potential: A stimulus causes sodium ions to move across the membrane, creating a generator potential; its size depends on stimulus strength (does not follow the all-or-nothing law).
3) Threshold & Action Potential: If the generator potential reaches the threshold, it triggers an action potential in the sensory neuron; if not, no action potential occurs.
4) All-or-Nothing Law: Action potentials follow the all-or-nothing principle—either they occur fully or not at all.

Question 2

Describe the structure of the human retina

Answer 2

The retina contains light-sensitive cells (photoreceptors), along with the neurones with which they synapse.

Question 3

What are the two main types of photoreceptors in the retina?

Answer 3

Rods and cones

Question 4

What is Retinal made from?

Answer 4

Retinal is made from Vitamin A. Retinal exists in 2 forms, cis-retinal (light) and trans-retinal (dark) .

Question 5

What happens to cis-retinal in light? and how does it affect the retina?

Answer 5

Cis-retinal gets converted to trans-retinal. This changes shape of rhodopsin and closes sodium ion channels, hyperpolarizing the cell.

Question 6

What is bleaching?

Answer 6

Bleaching is the process in which Rhodopsin is broken down into opsin and Retinal.

Question 7

What is the fovea?

Answer 7

The fovea is the region of the retina containing only cones and is responsible for the highest visual acuity