3.6.1.2 Receptors

Question 1

What is the key feature of receptors in responding to stimuli?

Answer 1

Receptors respond only to specific stimuli.

Question 2

What happens when a receptor is stimulated?

Answer 2

Stimulation of a receptor leads to the establishment of a generator potential.

Question 3

Describe the basic structure of a Pacinian corpuscle.

Answer 3

The Pacinian corpuscle consists of a sensory neurone ending surrounded by layers of connective tissue, separated by viscous gel, all enclosed within a capsule.

Question 4

How does deformation of stretch-mediated sodium ion channels in a Pacinian corpuscle result in a generator potential?

Answer 4

Deformation of stretch-mediated sodium ion channels causes them to open, allowing sodium ions to diffuse into the neurone, leading to depolarisation and the establishment of a generator potential.

Question 5

What explains the differences in sensitivity to light between rods and cones?

Answer 5

Rods are more sensitive to light because multiple rods connect to a single bipolar neurone (spatial summation), whereas each cone connects to its own bipolar neurone.

Question 6

Why do cones provide sensitivity to colour but rods do not?

Answer 6

Cones contain three different types of optical pigments sensitive to red, green, and blue light, while rods contain only one type of optical pigment sensitive to low light intensity.

Question 7

Why do cones provide better visual acuity than rods?

Answer 7

Cones provide better visual acuity because each cone connects to its own bipolar neurone, allowing signals to be sent separately to the brain. In contrast, multiple rods converge on a single bipolar neurone, reducing resolution.

Question 8

What is the role of the optic nerve in vision?

Answer 8

The optic nerve transmits electrical impulses from the retina to the brain for visual processing.

Question 9

Suggest and explain how the interaction between the circular and radial muscles could cause the pupil to constrict (narrow)

Answer 9

1. Circular muscle contracts;
2. Radial muscle relaxes

Question 10

Explain how a fovea allows an organism to see in detail

Answer 10

1. High (visual) acuity;
2. (Each) cone is connected to a single neurone;
   Accept no retinal convergence. Accept ‘bipolar/nerve cell’ for neurone.
3. (Cones send) separate (sets of) impulses to brain;

Question 11

Explain how a high density of rod cells allows an organism to have good night vision.

Answer 11

1. High (visual) sensitivity; Accept retinal convergence.
2. Several rods connected to a single neurone;
   Accept ‘bipolar/nerve cell’ for neurone
3. Enough (neuro)transmitter to reach/overcome threshold OR Spatial summation to reach/overcome threshold; more for ‘several

Question 12

Describe how stimulation of a Pacinian corpuscle produces a generator potential

Answer 12

1. (There are) stretch-mediated sodium ion channels (in the membrane);
2. (Increased pressure) deforms/changes (sensory neurone/axon) membrane/lamella(e)
   OR
   (Increased pressure) deforms/changes sodium ion channels;
3. Sodium ion channels open;
4. Sodium ions diffuse in;
5. Depolarisation (leading to generator potential);