nerve impulses

Question 1

where are sodium ion channels found

Answer 1

post synaptic membrane

Question 2

where are voltage gates found

Answer 2

on the axon tp maintain resting potential;

Question 3

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.

Answer 3

sodium ion channels open
causes sodium ions to enter neurone by facilitated diffusion and make more positive/ depolarisation.

Question 4

It is important that a neurotransmitter such as serotonin is transported back out of
synapses. Explain why.

Answer 4

1. (If not removed) keeps binding (to receptors);
   2.2. Keeps causing action potentials / depolarisation (in post-synaptic
   membrane);

Question 5

how do u write frequency using Hardy vein berg

Answer 5

-decimal ( only percentage if it asks)

Question 6

what is selection pressure?

Answer 6

an organism is more likely to survive and reproduce in response to a change in envrironment

Question 7

what is selective advantage

Answer 7

better chance of surviving and reproducing

Question 8

The KDR plus allele codes for the sodium ion channels found in neurones.
(c) When DDT binds to a sodium ion channel, the channel remains open all the time.
Use this information to suggest how DDT kills insects.

Answer 8

1. Neurones remain depolarised;
2. So no action potentials / no impulse transmission.

Question 9

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

Explain this difference.

Answer 9

1. (In myelinated) action potential / depolarisation only at node(s);
2. (In myelinated, nerve impulse) jumps from node to node / saltatory;
3. (In myelinated) action potential / impulse does not travel along whole
   length;

Question 10

how is resting potential formed

Answer 10

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

Question 11

(b) Explain how applying pressure to the Pacinian corpuscle produces the changes in
membrane potential

Answer 11

1. (Pressure causes) membrane / lamellae to become deformed /

stretched;
2. Sodium ion channels in membrane open and sodium ions move in;
3. Greater pressure more channels open / sodium ions enter.

Question 12

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

Answer 12

• threshold is reached
• all or nothing principle

Question 13

(d) 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 13

Less / no saltatory conduction
More depolarisation over length / area of membranes.

Question 14

Damage to the myelin sheaths of neurones can lead to problems controlling the
contraction of muscles.
Suggest one reason why.

Answer 14

1. Action potentials travel more slowly
2. So delay in muscle contraction

Question 15

what happens of calcium ions are inhibited in the presynaptic membrane for muscle contraction

Answer 15

1. Prevents influx of calcium ions in presynaptic knob
2. 2. (Synaptic) vesicles don’t fuse with membrane / vesicles don’t release
      neurotransmitter;
3. Neurotransmitter does not diffuse across synapse / does not bind to
   receptors (on post-synaptic membrane);\
4. No action potential / depolarisation (of post-synaptic membrane) /
   sodium (ion) channels do not open / prevents influx of sodium ions.

Question 16

One reason that reaction time is slower when body temperature falls is
because nerve impulse conduction is slower. Explain how a lower temperature
leads to slower nerve impulse conduction.

Answer 16

1. Slower diffusion less kinetic energy of sodium ions and potassium ions

Question 17

Other than temperature, give two factors that affect the speed of nerve
impulse conduction.

Answer 17

axon diameter
saltatory conduction

Question 18

if you are measuring things at different temperatures what. would be the control temperature

Answer 18

room temperature

Question 19

if you are given a separate column which says standard error what do u do

Answer 19

add or minus values given to see if figures overlap

Question 20

Explain how a resting potential is maintained across the axon membrane in
a neurone.

Answer 20

3. Sodium ions (actively) transported out and potassium ions in;
   Higher concentration of potassium ions inside and higher
   concentration of sodium ions outside (the neurone)
   (Membrane) more permeable to potassium ions (leaving
   than sodium ions entering)

Question 21

Explain why the speed of transmission of impulses is faster along a
myelinated axon than along a non-myelinated axon.

Answer 21

1. Myelination provides (electrical) INSULATION
2. (In myelinated) saltatory (conduction)
3. In non-myelinated depolarisation occurs along whole/length (of axon);

Question 22

A scientist investigated the effect of inhibitors on neurones. She added a
respiratory inhibitor to a neurone. The resting potential of the neurone
changed from –70 mV to 0 mV.
Explain why.

Answer 22

Resting potential not maintained as no ATP for active transport of sodium ions out of the neurone and potassium ions into the neurones
electrochemical gradient not maintained

Question 23

GABA is a neurotransmitter released in some inhibitory synapses in the
brain. GABA causes negatively charged chloride ions to enter postsynaptic
neurones.
Explain how this inhibits postsynaptic neurones.

Answer 23

(Inside of postsynaptic) neurone becomes more negative
2. More sodium ions required (to reach threshold)
3. For depolarisation/action potential;

Question 24

what happens if you inhibiting acetyl choline esterase?

Answer 24

Less acetylcholine is hydrolysed so more bind to postsynaptic membrane complimentary receptors causing sodium ions to enter an depolarise post synaptic neurone