1. A nerve to a muscle contains many motor neurones.

Fig. 21.1 shows two motor neurones supplying a muscle that moves the fingers. Fig. 21.2 shows the force of contraction of the muscle when the neurones are stimulated separately or both together.

Fig. 21.1

Fig. 21.2

(i) Suggest how the brain can finely control the force of contraction in the muscles controlling the fingers.

[2]

(ii) Fig. 21.3 shows a motor neurone supplying a muscle that moves the leg.

Fig. 21.3

Explain the reason for the difference in the neurone supplying this muscle compared to the neurones supplying the muscle that moves the fingers.

[3]