3.6.2.1 - NERVOUS COORDINATION

Question 1

explain how a resting potential is maintained across the axon membrane in a neurone (3)

Answer 1

1. higher concentration of potassium ions inside the neurone and higher concentration of sodium ions outside OR potassium ions diffuse out OR sodium ions diffuse in
2. membrane is more permeable to potassium ions leaving than sodium ions entering because the sodium channels are closed
3. three sodium ions are actively transported out and two potassium ions are transported in (maintains concentration/electrochemical gradient)

Question 2

a scientist investigates the effect of inhibitors on neurones. she added a respiratory inhibitor to a neurone. the resting potential of the neurone changed from -70mV to 0mV

explain why. (3)

Answer 2

1. no/less ATP produced
2. no/less active transport OR sodium potassium pump inhibited
3. electrochemical gradient is not maintained OR results in same concentration of sodium and potassium ions on either side of the membrane

Question 3

explain why the speed of transmission of impulses is faster along a myelinated axon than along a non-myelinated axon (3)

Answer 3

1. myelination provides electrical insulation
2. in myelinated axon saltatory conduction OR in myelinated axon depolarisation occurs at nodes of Ranvier
3. in non-myelinated depolarisation occurs along length/whole of axon

Question 4

multiple sclerosis is a disease that involves damage to the myelin sheaths of neurones. movement in sufferers may be jerky or slow.

damage to the myelin sheathes of neurones can lead to problems controlling the contraction of muscles.

suggest one reason why (2)

Answer 4

ANY PAIR:

1. action potentials travel more slowly/don’t travel
2. so delay in muscle contraction/muscles don’t contract/muscles contract slower

OR

3. action potentials/depolarisation leaks to adjacent neurones/neurones not insulated
4. so wrong muscle fibres contract

Question 5

cannabinoids are hydrophobic molecules. in the body, they easily pass into neurones.

explain why (1)

Answer 5

1. lipid soluble/pass through phospholipid bilayer

Question 6

explain how the resting potential of -70mV is maintained in the sensory neurone (2)

Answer 6

1. membrane more permeable to potassium ions and less permeable to sodium ions
2. sodium ions actively transported/pumped out and potassium ions in

Question 7

the membrane potential at Q was the same whether medium or heavy pressure was applied to the finger tip.

explain why (2)

Answer 7

1. threshold potential has been reached
2. threshold or above causes maximal response/all or nothing principle

Question 8

multiple sclerosis is a disease in which parts of the myelin sheaths surrounding neurones are destroyed.

explain how this results in much slower responses to stimuli (2)

Answer 8

1. less/no saltatory conduction/action potential/impulse unable to ‘jump’ from node to node
2. more depolarisation over the length of a membrane

Question 9

when DDT binds to a sodium ion channel, the channel remains open all the time. use this information to suggest how DDT kills insects. (2)

Answer 9

1. neurones remain depolarised
2. so no action potentials/no impulse transmission

Question 10

a myelinated axon conducts impulses faster than a non-myelinated axon.

explain this difference (3)

Answer 10

1. in myelinated, action potential/depolarisation only at nodes
2. in M, nerve impulse jumps from node to node/saltatory
3. in M, action potential/impulse does not travel along whole length

Question 11

during an action potential, the membrane potential rises to +40mV and then falls.

explain why. (3)

Answer 11

1. potassium channels open
2. potassium out
3. sodium channels close

Question 12

after exercise, some ATP is used to restablish the resting potential in axons.

explain how the resting potential is re-established (2)

Answer 12

1. pump/active transport/transport against concentration gradient
2. of sodium from axon/sodium out/potassium in

Question 13

serotonin is a neurotransmitter releasd in some synapses in the brain. it is transported back out of the synaptic cleft by a transport protein in the pre-synaptic membrane.

serotonin diffuses across the synaptic gap and binds to a receptor on the post-synaptic membrane.

describe how this causes depolarisation of the post-synaptic membrane (2)

Answer 13

1. causes sodium ion channels to open
2. sodium ions enter cell and cause depolarisation

Question 14

the membrane potential at Q was the same whether medium or heavy pressure was applied to the finger tip.

explain why (2)

Answer 14

1. threshold potential has been reached
2. theres hold causes maximal response / all or nothing principle

Question 15

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 (2)

Answer 15

1. less / no saltatory conduction / action potential / the impulse is unable to jump from node to node
2. so depolarisation occurs over the length of the axon membrane

Question 16

explain how a lower temperature leads to slower nerve impulse conduction (2)

Answer 16

1. slower diffusion
2. of ions / Na+ / K+

Question 17

other than temperature, give two factors that affect the speed of nerve impulse conduction (2)

Answer 17

1. myelination/saltatory condition
2. axon diameter

Question 18

after exercise, some ATP is used to re-establish the resting potential in axons.

explain how the resting potential is re-established (2)

Answer 18

1. pump / active transport against concentration gradient
2. of sodium from axon / sodium out / potassium in