1.
It detects changes in the environment (1) Converts it into an impulse/action potential (1)
2.
A=
B=
C=
D=
E=
F=
G=
3.
Cell body (½)
Nucleus (½)
Axon (½)
Schwann cell (½)
Node of Ranvier (½)
Synaptic knob (½)
Dendrites (½)
(Max 2 marks)
(½ mark per correct label – Max 5 marks)
(i) sensory, (ii) motor, (iii) sodium, (iv) resting, (v) receptor, (vi) action potential
(1 mark per correct answer – Max 6 marks)
4.
Stage
1. Resting potential
2. Threshold value
3. Depolarisation
4. Repolarisation
5. Hyperpolarisation
Brief explanation of stage
Three sodium ions are pumped out for every two potassium ions pumped
in and potassium ions can freely diffuse back out – the inside is more
negatively charged than the outside
If stimulus is strong enough to cause membrane potential to reach this
level, action potential will happen
Sodium voltage-gated channels open / Rapid increase in number of
sodium ions inside axon
Sodium voltage-gated channels close and potassium voltage-gated
channels open, so potassium ions can move out of axon
Potassium channels close, the resting potential is slightly overshot and
enters the refractory period
(1 mark per correct label and explanation – Max 4 marks)
5.
a)
A=
Mitochondrion (½)
B=
Vesicles (containing neurotransmitter /acetylcholine) (½)
C = Synaptic gap/cleft (½)
D = Presynaptic membrane/knob (½)
(Max 2 marks)
b)
Nerve impulse arrives at synaptic knob and alters the permeability of the presynaptic
membrane to calcium ions – calcium ions enter (1). This causes synaptic vesicles to fuse with
the presynaptic membrane and release neurotransmitter (1). Neurotransmitter diffuses
across the synaptic gap/cleft and fuses with receptor molecules on the postsynaptic
membrane (1). This opens ion channels ion postsynaptic membrane allowing sodium ions to
enter and causing an action potential (1). Neurotransmitter is broken down and the
products diffuse back across the gap ready to be reformed into neurotransmitter (1).
(Max 5 marks)
6.
Gaps in the myelin sheath – nodes of Ranvier (1). Allow action potential to ‘jump’ from one node
of Ranvier to the next (1). Saltatory conduction (1). They ‘jump’ ahead of the slower
depolarisation moving along the axon membrane (1).
(Max 3 marks)
7.
Strength of stimulus is contained in the frequency of action potentials / the stronger the stimulus
the more frequent the impulses (1)
Total
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