For each of the functional characteristics of heart muscle A–E, select the most appropriate option from the types of heart muscle listed below

A. Option 2 The Purkinje system. The modified heart muscle fibres in the Purkinje system can conduct the impulse at about 8 metres/second.

B. Option 3 The AV node. The slow conduction of the impulse through the AV node allows the atrial muscle to contract before ventricular contraction begins.

C. Option 1 The sinoatrial node. The sinoatrial node normally generates impulse faster than any other cardiac pacemaker and so in responsible for the normal heart rate.

D. Option 4 Atrial muscle. The P wave results from the spread of excitation from the sinoatrial node over the atria.

E. Option 5 The longest action potentials. Ventricular muscle action potentials are much longer than those in atrial muscle