CNS and Response exam questions

Question 1

Why must organisms respond to changes in their environment

Answer 1

in order to survive

Question 2

What does an organism need to respond to changes

Answer 2

requires detection

Question 3

What is detection

Answer 3

stimulus is detected by receptor cell

Question 4

Why is ATP required to maintain the resting potential

Answer 4

The sodium-potassium pump requires ATP for the active transport of sodium ions out of the axon and potassium ions into the axon

Question 5

Explain how the refractory period ensures the unidirectional flow of a nervous impulse in a neurone

Answer 5

-Sodium channels are closed during hyperpolarisation
-depolarisation cannot occur in that region again until the resting potential has been restored
-As a result, the membrane can only be depolarised ahead of an action potential

Question 6

Three features of a neurone that influence the speed of conduction

Answer 6

-Diameter of the axon
-Myelination OR the presence of Schwann cells
-Temperature

Question 7

Why can axons with a wider diameter can transmit an action potential more quickly

Answer 7

-the axon membrane has a greater surface area (for the diffusion of ions) SO the rate of diffusion is faster
-a faster rate of depolarisation / action potential propagation
-a greater volume of cytoplasm containing ions SO there is less electrical resistance
-the action potential can move through to the next section of the axon more quickly

Question 8

How is a nerve impulse generated in the postsynaptic neurone

Answer 8

1) The neurotransmitter diffuses across the synaptic cleft
2) then binds to receptors on the postsynaptic membrane
3) Causing Na+ channel proteins to open
4) Na+ move into the postsynaptic neurone
5) causes depolarisation of the membrane
6) Leading to an action potential in the postsynaptic neurone if the threshold value is achieved

Question 9

When is the refractory period

Answer 9

Short time after action potential has been generated in axon membrane

Question 10

What happens to sodium ion channel proteins in refractory period

Answer 10

Na+ channels cant open and depolarise, so ap travels in only one direction, producing discrete impulse limiting frequency of impulses

Question 11

What happens to potassium ions in refractory period

Answer 11

axon membrane open
diffusion of potassium ions out of the axon
down their concentration gradient

Question 12

What effect do the sodium and potassium ions have

Answer 12

gradually returns the potential difference to normal (repolarisation)

Question 13

Describe whole refractory period process before and after summarisation

Answer 13

1) stimulus occurs
2) depolarisation as NA+ ions enter, voltage increases action potential occurs
3) Repolarisation as K+ exit, voltage decreases
4) As K+ exit refractory period occurs, hyperpolarisation
5) Resting state

Question 14

Why is the refractory period important

Answer 14

-ensures that action potentials are discrete events, stopping them from merging into one another
-ensures that ‘new’ action potentials are generated ahead
-impulse can only travel in one direction
-minimum time between action potentials occurring at any one place along a neurone
-length of the refractory period is key in determining the maximum frequency

Question 15

What is the refractory period definition?

Answer 15

period of hyperpolarisation in an action potential

Question 16

How does the unmyelinated neurone change the speed of impulse

Answer 16

myelin sheath is formed from Schwann cells
depolarisation cannot occur where the mylein sheath is as the myelin sheath stops the diffusion of sodium ions and potassium ions
action potentials ‘jump’ from one node to the next (saltatory conduction)
So impulse travels faster

Question 17

How does the diameter of the axon change the speed of impulse

Answer 17

Thicker axons have an axon membrane with a greater surface area over which the diffusion of ions can occur
increases the rate at which depolarisation and action potentials
AND
greater volume of cytoplasm reduces their electrical resistance so that an action potential can push into the next section faster

Question 18

Why can damage to the myelin sheaths of neurones can lead to problems controlling the
contraction of muscles

Answer 18

Action potentials travel more slowly
So delay in muscle contraction
OR
Action potentials ‘leak’ to adjacent neurones
So wrong muscle (fibres) contract

Question 19

When a cannabinoid binds to its receptor, it closes calcium ion channels.
Suggest how cannabinoids could prevent muscle contraction

Answer 19

Prevents influx of calcium ions
vesicles don’t release
neurotransmitter
Neurotransmitter does not diffuse across synapse
No action potential preventing influx of sodium ions

Question 20

Explain how the resting potential of –70 mV is maintained in the sensory neurone
when no pressure is applied.

Answer 20

Membrane more permeable to potassium ions and less permeable to sodium
ions
Sodium ions actively transported / pumped out and potassium ions in

Question 21

Multiple sclerosis is a disease in which parts of the myelin sheaths surrounding
neurones are destroyed. Explain how this results in slower responses to stimuli.

Answer 21

impulse unable to
‘jump’ from node to node
More depolarisation over length of membranes

Question 22

Why does a shoot grow to one side (other than light)

Answer 22

Tip produces IAA
IAA diffuses into shoot
(More) elongation of cells on one side (than other)