Draw a labelled diagram to show the structure of a sarcomere.

Outline how skeletal muscle contracts.

Explain how nerve impulses are transmitted along and between neurons.

Award [1] for each structure clearly drawn and correctly labelled.

Sarcomere – clearly indicated between Z lines;

Z lines;

actin filaments attached to Z line;

myosin filaments with heads;

(two) light bands;

dark band;

calcium ions are released from the sarcoplasmic reticulum;

they expose the myosin binding sites (on actin) / cause movement of blocking molecules/troponin;

cross-bridges form between actin and myosin molecules;

ATP provides energy;

for actin filaments to slide over the myosin filaments / for myosin to push actin;

ATP provides energy to release myosin from binding site;

action can be repeated further along the molecule;

the resting potential of cell is negative inside compared with outside;

stimulation causes depolarization/reversal of charge on each side;

due to Na⁺ channels opening / Na⁺ flowing into the cell;

which causes an action potential;

K⁺ channels open / K⁺ flows out of the cell;

sodium potassium pump restores resting potential;

transmitted between neurons across a synapse;

neurotransmitter released into synaptic cleft;

diffuse across cleft to postsynaptic membrane;

where they bind to receptors;

influx of Na⁺ into cell;

which may initiate action potential;

Most candidates who answered this question knew about the structure of the sarcomere, and the diagrams were generally good.

If the candidates could draw the sarcomere they could also explain muscle contraction.

There were many full and complete answers, although many weaker students became confused between the sodium and potassium ions, and although many remembered the -70mV, they did not mention that the inside of the axon is negative. Most were able to explain what happened at the synapse, but often failed to say what a synapse is.