nervous coordination

Question 1

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 1

1. 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 the post-synaptic membrane);
   Accept: sarcolemma / muscle membrane for post-synaptic
   membrane
4. No action potential / depolarisation (of post-synaptic membrane) /
   sodium (ion) channels do not open / prevents influx of sodium ions.

Question 2

Damage to the myelin sheaths of neurones can lead to problems controlling the
contraction of muscles.

Suggest one reason why.

Answer 2

1. Less / no saltatory conduction/action potential / impulse unable to
   ‘jump’ from node to node;
2. so muscle contracts much slower

Question 3

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

Answer 3

Membrane more permeable to potassium ions and less permeable to sodium
ions;

2. Sodium ions actively transported/pumped out and potassium ions in.

Question 4

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 4

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

Question 5

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 5

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

Question 6

Use the words probability and chance in your answer.

Answer 6

1. the probablity of obtaining the results by chance
2. is less than 5%
3. therefore the results are significant

Question 7

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

Explain this difference.

Answer 7

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 8

Describe the roles of calcium ions and ATP in the contraction of a myofibril

Answer 8

1. Calcium ions diffuse into myofibrils from (sarcoplasmic) reticulum;
2. (Calcium ions) cause movement of tropomyosin (on actin);
3. (This movement causes) exposure of the binding sites on the actin;
4. Myosin heads attach to binding sites on actin;
5. Hydrolysis of ATP (on myosin heads) causes myosin heads to bend;
6. (Bending) pulling actin molecules;
7. Attachment of a new ATP molecule to each myosin head causes myosin
   heads to detach (from actin sites)

Question 9

synapses are unidirectional

Explain how acetylcholine contributes to a synapse being unidirectional;

Answer 9

acetylcholine is only released from the presynaptic neurone
they then diffuse from a higher concentration to a lower concentration
and taken up and bind to the postsynaptic receptors

Question 10

what are the characteristics of a nervous response

Answer 10

1. rapid response
2. short duration

Question 11

explain the shape of the curve for sodium ions between 0.5ms and 0.7ms

Answer 11

sodium ion channels open so sodium ions enter

threshold is reached

therefore more channels open/ positive feedback

Question 12

GABA reduces the chance of an action potential occurring at the postsynaptic membrane explains why

GABA is an inhibitory neurotransmitter and so the answer to this question can apply to all inhibitory neurotransmitters

Answer 12

1. an action potential is involved with raising potential/ depolarisation
2. with GABA, it is less likely to raise the potential threshold
3. so more sodium ions are needed

Question 13

what is the refractory period

Answer 13

the period where no NEW action potentials can be generated

Question 14

there are advantages o having both excitatory and inhibitory neurons forming synapses with the same postsynaptic neuron

Suggest one

Answer 14

controls whether the postsynaptic neuron fires or not

Question 15

what can ATP be used for in nerve impulses

Answer 15

transport of ions

• for neurotransmitter synthesis
• for vesicles movement

Question 16

explain how the length of the refractory period prevents the brain from distinguishing from the stimuli above a certain intensity

Answer 16

the higher the intensity of the stimulus it means the higher the frequency of the stimulus
as the refractory period stops any new action potentials from being generated,

above a certain intensity, the action potential triggered is the same

Question 17

what happens if a neurotransmitter continues to bind to a receptor

Answer 17

an action potential continues to be triggered/ depolarisation continues

therefore, muscles can remain contracted/ do not relax for example