4d: Communication And Signalling

Question 1

What is the resting membrane potential

Answer 1

The state where there is no net flow of ions across the membrane

Question 2

What does the transmission of a nerve impulse require

Answer 2

Changes in the membrane potential of the neurone’s plasma membrane

Question 3

What is depolarisation

Answer 3

A change in the membrane potential to a less negative value inside

Question 4

if the change in membrane potential caused by depolarisation is big enough it may trigger an _________

Answer 4

Action potential

Question 5

What is an action potential

Answer 5

Aa wave of electrical excitation (or wave of depolarisation) along a neurones’s plasma membrane

Question 6

How do neurotransmitters initiate a response

Answer 6

By binding to their receptors at a synapse.

Neurotransmitter receptors are ligand gated channels

Question 7

what happens after the binding of a neurotransmitter

Answer 7

Triggers the opening of a ligand gated ion channels at the synapse

Ion movement occurs and the depolarisation of the plasma membrane.

Question 8

What causes depolarisation

Answer 8

Entry of sodium ions

Question 9

What causes repolarisation

Answer 9

Exit of potassium ions

Question 10

What happens if the membrane is depolarised past the threshold value

Answer 10

The opening of voltage-gated sodium channels is triggered, and sodium ions enter the cell down their electrochemical gradient.

It’s huge influx of sodium ions causes the cell to be much more negative and triggers the potassium gated channels to open, and the K+ can leave the cell.

Question 11

What re-establishes the resting potential of a nerve cell after depolarisation?

Answer 11

Voltage gated potassium channels open to allow K+ to move out of cell

Question 12

What is the area within the cell that detects light

Answer 12

The retina

Question 13

The retina contains 2 types of photoreceptor cells, ______ and _________

Answer 13

Rods and cones

Question 14

What are rods (photoreceptor)

Answer 14

Rods function in dim light but do not allow for colour perception.

Useful for vision in areas of low light intensity. Nocturnal animals have a greater proportion.

Question 15

What are cones (photoreceptor)

Answer 15

Cones are responsible for colour vision and only function in bright light

Not as sensitive to light as rods. They are particularly sensitive to specific colours: green, red, blue and in some animals, UV.

Question 16

In animals, what does retinal combine with to form the photoreceptors in the eye

Answer 16

Membrane protein opsin

Question 17

In rod cells the retinal-opsin complex is called _________

Answer 17

Rhodopsin

Question 18

In cone cells, different forms of opsin combine with retinal to…

Answer 18

Give different photoreceptor proteins, each with a maximal sensitivity to specific wavelengths: red, green, blue or UV

Question 19

How does the retina respond to light

Answer 19

Retinal absorbs a photon of light and rhodopsin changes conformation to photoexcited rhodopsin.

A cascade of proteins amplifies the signal.

Question 20

What does a photoexcited rhodopsin activate.

Answer 20

G-protein called transducin.

A single photoexcited rhodopsin activates hundred of molecules of G-protein

Question 21

What does transducin activate

Answer 21

The enzyme phosphodiesterase (PDE).

Each activated G-protein only activates one molecule of PDE

Question 22

What does phosphdiesterase (PDE) do.

Answer 22

Catalyses the hydrolysis of a molecule called cyclic GMP (cGMP). Each active PDE molecule breaks down thousands of cGMP molecules per second.

Question 23

What does the reduction in cGMP concentration as the result of hydrolysis (catalysed by PDE) do.

Answer 23

It affects the function of ion channels in the membrane of rod cells.

Consequently, it results in the closure of ion channels in the membrane of the rod cells, which triggers nerve impulses in neurons in the retina.

Question 24

Why are rod cells more sensitive than cone cells at low light intensities

Answer 24

A higher degree of amplification (in dim light)