参考答案:
Explanation:
1.The diagram must include three of the following labels and correctly drawn corresponding structures:
→ dendrites 1
→ axon 1
→ myelin sheath 1
→ nodes of ranvier 1
→ cell body 1
→ nucleus 1
→ axon terminal 1
2.Any four of the following:
→ myelin sheath is composed of proteins and lipids OR myelin is made up of Schwann cells, OR oligodendrocytes
myelin acts as an insulator
→ there are gaps OR nodes of Ranvier between Schwann cells on the axon
→ (myelin) allows for nerve impulses to jump from node to node OR saltatory conduction
→ sodium ions diffuse from node to node without leaking out of the axon OR local currents stimulate downstream nodes
→ sodium and potassium channels are concentrated at the nodes (increasing the speed of neurotransmission)
3.Any eight of the following:
→ an action potential is the depolarisation and repolarisation of a neuron due to the movement of positive ions
→ inside the neuron, there is a high concentration of $K^+$ ions and a low concentration of $Na^+$ ions
→ depolarisation is due to $Na^+$ ions diffusing into the neuron
→ $Na^+$ ions diffuse in through ligand-gated channels on dendrites, OR cell body, OR synaptic transmission, causes initial $Na^+$ ion influx
→ if threshold potential is reached, OR at -55mV, voltage-gated $Na^+$ channels open
→ the voltage-gated influx of $Na^+$ ions makes the inside more positive compared to the outside, OR raising the membrane potential up to +30mV
→ (at +30mV) voltage-gated sodium channels close
→ (at +30mV) voltage-gated potassium channels open
→ repolarization happens due to $K^+$ ions diffusing out of the neuron
→ cell interior becomes more negative compared to the outside of the cell OR reaches -75mV OR hyperpolarisation
→ (after -75mV) voltage-gated K++ channels close
→ $Na^+$–$K^+$ pump restores the relative concentrations of $Na^+$ and $K^+$ in the cell
ample Answer:
An action potential is the depolarisation and repolarisation of a neuron due to the movement of positive ions (✓).
The initial depolarisation occurs on the cell body or on dendrites at synapses. Here neurotransmitters cause sodium channels to open and $Na^+$ ions diffuse into the neuron (✓).
There is an ion imbalance in the neuron where the concentration of $Na^+$ is higher outside the neuron and the concentration of $K^+$ is higher inside the neuron (✓).
The resting potential of a neuron is about -70 mV.
If the initial depolarisation reaches the threshold potential, an action potential is generated and voltage-gated $Na^+$ channels open (✓).
$Na^+$ ions diffuse into the neuron, leading to the membrane potential rising to +30mV (✓).
At +30mV, voltage-gated sodium channels close (✓),
and voltage-gated potassium channels open (✓).
This is followed by repolarisation, where $K^+$ ions diffuse out of the neuron.
A quality mark is awarded if each part of the question (a, b, c) is answered to earn at least half of the points available, answers do not require re-reading to be understood, and there are almost no errors and little irrelevant information.
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