Synaptic transmission

Question 1

When a nerve impulse arrives at a synapse, it causes the release of neurotransmitter from vesicles in the presynaptic knob.

Describe how.

Answer 1

Nerve impulse / depolarisation of membrane) causes Ca 2+ channel (proteins) to open;

2. Ca 2+ enter by (facilitated) diffusion;
3. Causes (synaptic) vesicles to fuse with (presynaptic) membrane;

Question 2

This movement of mitochondria happens when nerve impulses arrive at the synapse.

Suggest and explain one advantage of the movement of mitochondria towards the presynaptic membrane when nerve impulses arrive at the synapse.

Answer 2

Mitochondria) supply (additional) ATP / energy;

2. To move vesicles / for active transport of ions / for myosin to move past actin

OR

Re-synthesis / reabsorption of neurotransmitter / named neurotransmitter;

Question 3

When a neurone transmits a series of impulses, its rate of oxygen consumption increases. Explain why

Answer 3

More) respiration;

Reject anaerobic respiration

(More) energy supplied / (more) ATP supplied;

Reject ‘produce’ energy

For active transport of ions / ‘sodium (-potassium) pump’ / pumping
out sodium ions / for neurotransmitter synthesis / for vesicle movement;

Question 4

Figure 2 shows the results when the frequency of stimulation was 200 per second.

Figure 2

Not every stimulus in Figure 2 produced an action potential.
Explain why.

Answer 4

Ref. to ‘refractory period’;

Requires greater stimulation;
To reach threshold / threshold cannot be reached / to cause depolarisation;

K + channels are open / more negative potential than resting potential /
membrane is hyperpolarised;

Na + channels are inactive/are closed / sodium channels will not open;

Question 5

Sodium and potassium ions can only cross the axon membrane through proteins.

Explain why

Answer 5

can not pass through phospholipid bilayer;
because water soluble / not lipid soluble / charged / hydrophilic /
hydrated;

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