(a) A neuromuscular junction allows the transmission of an action potential from a motor neurone to a striated muscle fibre, causing it to contract. Fig. 9.1 is a graph of an action potential in a motor neurone. [Figure 9.1] Fig. 9.2 is a graph of an action potential in a striated muscle fibre. [Figure 9.2]

1. (a)With reference to Fig. 9.1 and Fig. 9.2, describe the differences between the action potential in a motor neurone and the action potential in a striated muscle fibre.[4]
2. (b)There are three phases in the contraction of a striated muscle: latent phase, contraction phase and relaxation phase. The tension in a muscle represents the degree of contraction of its fibres. Fig. 9.3 is a graph of the tension in a striated muscle during the three phases of contraction. [Figure 9.3]
3. (b)(i)With reference to Fig. 9.3, explain what is happening in the striated muscle fibre during the latent phase.[3]
4. (b)(ii)Suggest why the relaxation phase shows a gradual decrease in muscle tension.[1]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.