the nervous system

Question 1

Why is it important that a neurotransmitter eg seretonin is transported back out of the synapse and explain why

Answer 1

if not removed, it will keep binding to the receptors on the post synaptic membrane and so would keep causing action potentials.

Question 2

suggests how cocaine leads to feelings of pleasure`

Answer 2

cocaine binding will lead to the shape of transporter changing so dopamine can not be removed. this builds up in the synapses leading to pressure

Question 3

Cannabinoid receptors are found in the pre-synaptic membrane of neuromuscular
junctions. When a cannabinoid binds to its receptor, it closes calcium ion channels.
Suggest how cannabinoids could prevent muscle contraction.

Answer 3

Prevents influx of calcium ions (into pre-synaptic membrane);
Need idea of moving into pre-synaptic membrane / synaptic
knob
Accept Ca++ / Ca2+
2. (Synaptic) vesicles don’t fuse with membrane / vesicles don’t release
neurotransmitter;
Accept vesicles don’t release acetylcholine
3. Neurotransmitter does not diffuse across synapse / does not bind to
receptors (on post-synaptic membrane);
Accept: sarcolemma / muscle membrane for post-synaptic
membrane
4. No action potential

Question 4

how is a resting potential maintained

Answer 4

the membrane is more permeable to potassium ions less permeable to sodium ions
sodium ions are actively transported out and potassium in

Question 5

Explain how applying pressure to the Pacinian corpuscle produces the changes in
membrane potential recorded by microelectrode P

Answer 5

pressure causes membranes to become stretched
sodium ion channels in membrane open
greater pressure means more channels open

Question 6

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

Answer 6

threshold has been reached so all or nothing principle causes maximal response as no aps generated.

Question 7

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 7

Less / no saltatory conduction / action potential / impulse unable to
‘jump’ from node to node;
2. More depolarisation over length / area of membranes.

Question 8

When DDT binds to a sodium ion channel, the channel remains open all the time.
Use this information to suggest how DDT kills insects.

Suggest how the KDR minus allele gives resistance to DDT

Answer 8

neurones remain depolarised
so not action potentials

(Mutation) changes shape of sodium ion channel (protein) / of receptor

(protein) ;
2. DDT no longer complementary / no longer able to bind

Question 9

speed of myelinated vs non

Answer 9

(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

remember- say ap not impulse or depolarisation.

Question 10

Why isn’t the whole length of the axon covered from beginning to end with myelin?

Answer 10

The axon has nodes on it that cause the electrical impulse to “jump,” if you will, from one node to another. This speeds up conductivity and allows impulses to travel faster. Most of the axon is covered in myelin anyway, but only a number of small portions on the axon have these nodes. They’re called nodes of Ranvier.

Question 11

The doctors used a statistical test to compare the results for AD and LD.
They obtained a value for P of 0.047.
What does this result show about the difference between the means for AD and LD?
Use the words probability and chance in your answer.

Answer 11

Probability of obtaining this difference by chance;
Reject ‘results’ once only
2. Is less than 5% / less than 0.05 / less than one in twenty;
Accept is 4.7% / 0.047 but reject less than 4.7% / 0.047
Accept correct greater than 95% / greater than 0.95
arguments
3. Difference is significant;

Question 12

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 12

Causes sodium ion channels to open;

2. Sodium ions enter (cell and cause depolarisation);

Question 13

Give one similarity and one difference between a taxis and a tropism.
Similarity
Difference .

Answer 13

Similarity − directional response (to a stimulus) / movement
towards / away from a stimulus;
2. Difference − taxis (whole) organism moves and tropism a growth
(response).

Question 14

In each experiment, the biologist exposed the surfaces to light that was dim and
even, so he could see where the worms went.
Apart from seeing where the worms went, suggest two reasons why it was
important that the light was dim and even.

Answer 14

(Dim) worms live in soil / dark / affected by bright light / dim light is like
normal environment / what they are used to;
2. (Even) because worms might move towards / away from bright light / to
avoid creating light gradient / prevent worms showing phototaxis / all
parts of surface exposed to same light;
Accept to avoid kinesis due to light
3. (Dim light) ensures heat from light not a variable / heat from lamp could
kill / dry out worms;

Question 15

describe na ions and releasing them sybapses

Answer 15

once released, it diffuses across the synaptic cleft and it binds to receptors ont the sodium ion channels and this causes sodium ions to diffuse into the post synaptic neuonr depolarising the membrane causing the initiation of an ap

Question 16

GABA is a neurotransmitter released in some inhibitory synpapses int he brain, GABA causes negatively charged chloride ions to enter the post synatic neurone, explain how this inhibts post synaptic neurones

Answer 16

adding more negative= hyperpolarisation, lower than resting potential

cl- entering the post synaptic neurone causes hyperpolarisation, this means that more sodium ions have to enter the post synaptic neurone in order for the voltage to reach the threshold potential in order for depolarisation of the membrane initiating an ap

Question 17

How does temperature affect the speed of a nerve impulse? (5)

Answer 17

1. The higher the temperature the faster the nerve impulse;
2. Sodium-potassium pump uses active transport;
3. Which requires energy from ATP from respiration;
4. Respiration is enzyme-controlled;
5. More kinetic energy so more enzyme-substrate complexes formed and faster diffusion

Question 18

how is the resting potential manintained

Answer 18

sodium potassium pump, k+ diffuses out whilst na+ diffuses in= actively transporte.d membrane is more permeable to k+.

Question 19

why is aps faster in myelinated neurone

Answer 19

nodes, aps do not need to be generated at all the nodes, non myelination across the entire length of the axon,
also say that
myelination provides electrical insulation

Question 20

why does an inhibitor result in an overall potential of 0

Answer 20

as there is less atp less active transport, electrochemical gradient is not maintained, same conc of na+ and k+ on either side

Question 21

pacinian corpuscle

Answer 21

membrane becomes deformed or stretched
sodium ion channels in membranes open and sodium ions move in
increase of channels open

Question 22

myelination depolarisation

Answer 22

only at nodes, jumps from node to node= saltatory conductionn.