Reflexes and Receptors

Question 1

What is a reflex?

Answer 1

Responses to the environment that are not processed by the brain?

Question 2

Why are reflexes rapid?

Answer 2

Nervous responses, usually to increase chances of survival- avoid damage

Question 3

What neurons are involved in the reflex?

Answer 3

• Sensory neuron
• Relay neuron
• Motor neuron

Question 4

What receptors detect light?

Answer 4

Rods and cones in the retina

Question 5

What receptors detect temperature?

Answer 5

Thermoreceptors in the skin and the hypothalamus

Question 6

What receptors detect a change in pressure?

Answer 6

Pacinian corpuscle

Question 7

How is the pacinian corpuscle adapted to its function?

Answer 7

It has concentric rings of connective tissue

Question 8

How does the Pacinian corpuscle work?

Answer 8

It responds to a CHANGE in pressure as the tissue distorts and triggers an impulse in the nerve fibre

Question 9

What are rods?

Answer 9

• Photoreceptors
• Can only see in black and white (cannot distinguish different wavelengths)
• Used in the dark (low light intesity)
• May converge into one bipolar cell

Question 10

What is retinal convergence?

Answer 10

When lots of rods converge into one bipolar cell

Question 11

What happens in retinal convergence?

Answer 11

• When light hits rod cells there is the hydrolysis of rhodopsin
• this generates a generator potential
• Which travels down the rod cell
• This goes to bipolar cell via a synapse
• If bipolar cell receives a signal above the threshold value- the cell can pass

Question 12

What is the important of the generator potential threshold?

Answer 12

• If bipolar cell receives a signal above the threshold value- the cell can pass the signal to the next cell in the optic nerve
• Eventually goes to brain

Question 13

Why are lots of rods needed?

Answer 13

• Lots of rods in the bipolar cell increases the chance of more than one being stimulated
• More than one generator potential

Question 14

What is the disadvantage of pooling signals?

Answer 14

• Low visual acuity

- If lights hits receptors, the brain won’t be able to distinguish between two points

Question 15

How many types of cone cells are there

Answer 15

Three

Question 16

What are the advantage of cone cell over rod cells?

Answer 16

They are red, blue and green
They can differentiate between different wavelengths of light
One cone cell to one bipolar cell
Better visual acuity

Question 17

What is the pigment in cone cells?

Answer 17

Iodopsin- one for each type of cone cell

Question 18

Where are most cone cells in the retina?

Answer 18

There is a higher density of cone cells in the fovea

Question 19

Where are most rod cells in the retina?

Answer 19

In the periphery

Question 20

Which type of cells have better visual acuity and why?

Answer 20

Cone cells because each type of cone cell has its own connection to a single bipolar cell. High resolution. There is no retinal convergence

Question 21

What part of the eye receives the highest light intensity?

Answer 21

The fovea

Question 22

What is a stretch mediated sodium channel? (Pacinian corpuscle)

Answer 22

A special type of Na+ channel that changes its permeability to sodium ions when it is distorted

Question 23

What is the sequence of events by which the Pacinian corpuscle creates a generator potential?

Answer 23

• pressure on Pacinian corpuscle
• distorts shape
• stretches neuronal membrane
• widens stretch mediated sodium channels
• allows sodium ions to enter the neurone
• changes potential of membrane (depolarises)
• produces generator potential

Question 24

What are the advantages of simple reflexes?

Answer 24

• They prevent damage to the body

- They are quick

Question 25

Explain how applying pressure to the Pacinian corpuscle produces the changes in membrane potential.

Answer 25

• The concentric layers of connective tissue distort
• This causes the stretch-mediated sodium ion channels to open
• The greater the pressure the greater the number of sodium ions