receptors

Question 1

How is a generator potential produced?

Answer 1

When a stimulus is detected, the cell membrane is excited, becomes more permeable, allowing more ions to move into or out of the cell. This alters the potential difference across the cell membrane and therefore produces a generator potential.

Question 2

What type of stimulus does the Pacinian corpuscle respond to?

Answer 2

Pressure/mechanical

Question 3

Describe the structure of the Pacinian corpuscle.

Answer 3

A Pacinian corpuscle contains the end of a sensory neurone. The sensory neurone ending is wrapped in layers of connective tissue called lamellae with viscous gel between each layer.

Question 4

How does pressure cause an action potential in the Pacinian corpuscle

Answer 4

When the corpuscle is deformed by pressure it causes deformation of stretch-mediated sodium ion channels in the cell membrane. The sodium ion channels open and sodium ions diffuse into the cell, creating the generator potential, if this reaches the threshold value, an action potential will be produced.

Question 5

. Describe the role of the gel in a Pacinian corpuscle

Answer 5

Redistributes pressure so that the receptor will only respond to changes in pressure.

Question 6

Where are rods found?

Answer 6

All over the retina except for the fovea.

Question 7

Where are cones found?

Answer 7

All over the retina but in highest concentration in the fovea.

Question 8

Why do cones have better visual acuity?

Answer 8

Each cones connects to one neurone while multiple rods connect to the same neurone so when multiple cones are stimulated, multiple action potentials reach the brain whereas when multiple rods are stimulated only one action potential reaches the brain.

Question 9

What colours are seen by rods and cones?

Answer 9

Rods - black and white, cones -red, blue and green

Question 10

Compare the sensitivity to light of rods and cones?

Answer 10

Rods are very sensitive to light because their pigment (rhodopsin) is easily bleached by light, cones are less sensitive because their pigment (iodopsin) is only bleached by high intensity light. In addition, rods converge onto one neurone so spatial summation occurs meaning threshold is more likely to be reached/overcome.

Question 11

How does light cause a response in rods and cones?

Answer 11

1. Light enters the eye and hits the photoreceptors and is absorbed by pigment inside the cell.
2. Light bleaches the pigment (causes a conformational changes) which causes a chemical reaction that causes….
3. sodium ions channels on the neurone to open and sodium ions move into the neurone
4. A generator potential is generated.
5. If threshold is reached, an action potential occurs in the neurone and the stimulus is detected.