Question

Which of the following statements concerning cardiac muscle is correct?

• A. The force of contraction is increased by circulating adrenaline
• B. Heart muscle contracts in response to action potentials in the autonomic nerve fibres
• C. The action potential has the same duration as that of skeletal muscle
• D. All of the Ca2+required for contraction enters a myocyte during the plateau phase of the action potential

Answer 1

The correct option is A

The force of contraction is increased by circulating adrenaline

The cells of the SA node act as pacemaker cells for the heart. Their activity is modulated by the autonomic nerves. The cardiac action potential is much longer than that of skeletal muscle. Although some of the Ca²⁺ required for contraction comes from influx across the sarcolemma, the sarcoplasmic reticulum contributes significantly.