Question

Give both a teleological and mechanistic explanation of why tetany does or does not occur in cardiac and why it does or does not occur in skeletal muscle. Please specify explicitly which are your teleological and which are your mechanistic answers. What causes a compensatory pause after an extra systole?

Answer 1

Tetany is an involuntary contraction of the muscles, which may be caused due to sudden and increased action potential of the nerve cells that innervate that muscle or due to the muscle itself. It can be due to electrolyte imbalance, hypocalcemia, magnesium deficiency or any other related disorder. The symptoms are muscle cramps, spasms or tremors. The muscle contracts uncontrollably and repeatedly. It can occur in any skeletal muscle, especially those in the face, hands, and legs.

Cardiac muscles are special and are found only in the heart. They contract and relax repeatedly without getting tired. They do not need a neural stimulation to contract. This is called automaticity. As a result, cardiac muscle tissues cannot undergo tetany. This property is extremely important because a heart in tetany would not be able to pump blood to the body.

Extrasystoles are actually extra beats, or contractions, which occur when there is electrical discharge from somewhere in the heart other than the SA node. A compensatory pause is an extra and long pause after an abnormal heart during atrial fibrillation.

Usually, a premature ventricular contraction is followed by a complete compensatory pause because the sinus node timing is not interrupted.