Module 6 - Nervous coordination

Question 1

3 marks

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

Answer 1

1. Pressure causes membrane / lamellae to become deformed
2. Sodium ion channels in membrane open and sodium ions move in
3. Greater pressure more channels open / sodium ions enter.

Question 2

3 marks

Describe how stimulation of a Pacinian corpuscle produces a generator potential.

Answer 2

1. There are stretch-mediated sodium ion channels in the membrane
2. Increased pressure deforms (sensory neurone/axon) membrane/lamellae
3. Sodium ion channels open
4. Sodium ions diffuse in
5. Depolarisation leading to generator potential

Question 3

3 marks

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

Answer 3

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

Question 4

3 marks

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

Answer 4

1. Myelination provides electrical insulation
2. In myelinated saltatory conduction
3. In non-myelinated depolarisation occurs along whole length of axon

Question 5

3 marks

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 5

1. Less ATP produced
2. Less active transport
3. Electrochemical gradient not maintained

Question 6

4 marks

Explain how a resting potential is maintained in a neurone.

Answer 6

1. Membrane less permeable to sodium ions
2. Sodium ions actively transported out
3. By sodium ion carrier
4. 3 sodium ions out for two potassium ions in (inside is -70mV)

Question 7

2 marks

Explain how a lower body temperature leads to slower nerve impulse conduction

Answer 7

1. Slower diffusion
2. Of ions /Na+/K-

Question 8

3 marks

A myelinated axon conducts impulses faster than a non-myelinated axon. Explain the difference

Answer 8

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

Question 9

2 marks

Explain how the resting potential of-70mV is maintained in the sensory neurone

Answer 9

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 10

2 marks

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

Answer 10

1. Less / no saltatory conduction
2. Impulse unable to ‘jump’ from node to node (of ranvier)
3. More depolarisation over length / area of membranes

Question 11

3 marks

Explain how chloride ions entering the post synaptic membrane will inhibit transmission of nerve impulses by postsynaptic neurones

Answer 11

• Post synaptic membrane becomes more negatively charged / hyperpolarised
• Stimulation does not reach threshold level / action potential not produced (more Na+ required)
• Depolarisation does not occur

Question 12

2 marks

Explain how someone becomes aware of the pain if they prick their finger on a thorn

Answer 12

1. Sensory neurone synapses with another relay neurone
2. Impulses to brain

Question 13

Temporal summation

Answer 13

Several impulses in short time provide enough neurostransmitter to reach threshold

Question 14

2 marks

Explain the role of the refractory period

Answer 14

• So no impulses can be sent
• Seperates action potentials
• Ensures unidirectionality

Question 15

Compare a NMJ and synapse

Answer 15

NMJ
* Only excitatory
* Connects motor neurone to muscles
* Always acetylholine
* No concept of threshold
Synapse
* Excitatory or inhibitory
* Connects 2 neurones
* Could be any neurotransmitter
* A new action potential is generated om mext neurone

Question 16

2 marks

Give two reasons why transmission across a cholinergic synapse is unidirectional.

Answer 16

1. Only the presynaptic membrane has vesicles containing neurotransmitter/acetylcholine
   2.Only the postsynaptic membrane has receptors

Question 17

Following the release of acetylcholine into a neuromuscular junction, a muscle contraction occurs.

Describe the sequence of events, following the release of acetylcholine, that leads to stimulation of this contraction.

Do not include in your answer the events following the release of calcium ions in the myofibril. (4)

Answer 17

1. Acetylcholine diffuses across synaptic cleft
2. Acetylcholine attaches to receptors on the sarcolemma
3. Sodium ions enter, leading to depolarisation
4. Calcium (ions) released by sarcoplasmic reticulum

Question 18

2 marks

Inhibitory synapses cause hyperpolarisation in postsynaptic neurones.

Explain how this inhibits synaptic transmission.

Answer 18

1. Inside postsynaptic membrane is more negative
2. More sodium ions required for depolarisation

Question 19

5 marks

Glutamate is a neurotransmitter involved in the transmission of nerve impulses from pain receptors to the brain. Ziconotide is a drug that can reduce severe, constant pain. Ziconotide blocks the calcium ion channels at some of the synapses which use glutamate.

The transmission of glutamate at synapses is similar to that of acetylcholine.

Explain how ziconotide reduces severe, constant pain.

Answer 19

1. fewer calcium ions enter presynaptic neurone
2. fewer synaptic vesicles fuse with presynaptic membrane and less glutamate is released
   Accept neurotransmitter for glutamate.
3. less glutamate diffuses across (synaptic cleft);
4. less (glutamate attaches) to receptors on the postsynaptic membrane;
5. fewer sodium ions enter (postsynaptic neurone) so no/ fewer impulses (sent to brain);

Question 20

2 marks

Ziconotide is a polypeptide and acts on synapses in the spinal cord. Scientists investigated the effectiveness of ziconotide in reducing severe, constant pain.

Ziconotide was injected into each patient’s cerebrospinal fluid that bathes the brain and spinal cord. Patients recorded the intensity of their pain using a statistically valid scale.

Suggest two reasons why the patients had ziconotide injected into their cerebrospinal fluid rather than taking a pill containing the drug.

Answer 20

1. Quickly reaches spinal cord
2. Is broken down by enzymes

Question 21

Dopamine is a neurotransmitter released in some synapses in the brain. The transmission of dopamine is similar to that of acetylcholine.

Dopamine stimulates the production of nerve impulses in postsynaptic neurones.

Describe how.

Do not include in your answer the events leading to the release of dopamine and the events following production of nerve impulses at postsynaptic neurones. (3)

Answer 21

1. Dopamine diffuses across synapse cleft
2. Attaches to receptors on postsynaptic membrane;
3. Stimulates entry of sodium ions and depolarisation/action potential;

Question 22

2 marks

Dopamine has a role in numerous processes in the brain including pain relief. The release of dopamine can be stimulated by chemicals called endorphins produced in the brain. Endorphins attach to opioid receptors on presynaptic neurones that release dopamine.

Morphine is a drug that has a similar structure to endorphins and can provide pain relief.

Explain how.

Answer 22

1. Morphine attaches to opiod receptors
2. More dopamine is released