Question

The ions that always keeps the cardiac muscle unit in a contracting state is
A. Sodium
B. Potassium
C. Calcium
D. Magnesium

Answer 1

Cardiac muscle which is also called as myocardium or heart muscle is one of the types of muscles found in vertebrates. Cardiac muscles are present only in the heart. It constitutes the main tissue that surrounds the wall of the heart.

Complete answer: The soft tissue which is found in most of the animals is called muscles. Protein filaments called actin and myosin are responsible for the contraction and relaxation of the muscle. Muscles regulate the function of producing force and motion. Three types of muscles are found in vertebrates. They are smooth muscle, skeletal muscle, and cardiac muscle. The muscles found in the heart are known as cardiac muscles. Cardiac muscles are involuntary muscles. Cardiac muscles are branched and cylindrical in shape. They are uninucleate cells. The contraction of cardiac muscles is due to the calcium ions which induce an action potential in the cell. Heart muscles may experience a prolonged state of contraction if more influx of calcium ions takes place. This will lead to an abnormal increase in the heart rate. The contraction and relaxation of the cardiac muscle are due to the calcium-induced calcium release. The contraction and relaxation of the muscle can be explained with the help of the sliding filament model of contraction. The pacemaker cells in the sinoatrial (SA) and atrioventricular (AV) nodes induce action potentials which is conducted to contractile cardiomyocytes. The calcium channels in the T-tubules are activated As the action potential travels between sarcomeres. This results in the influx of calcium ions into the cardiomyocyte. Calcium ions present in the cytoplasm binds with the cardiac troponin-C, which then moves the troponin complex away from the actin-binding site. contraction of the muscle is due to the binding of the myosin head to the ATP and pulls the actin filaments toward the center of the sarcomere. intracellular calcium concentration is dropped as the Intracellular calcium is removed by the sarcoplasmic reticulum which results in the relaxation of the muscle.

So, option C is the correct option.

Note: The contraction and relaxation of the cardiac muscle is similar to that of the skeletal muscles but has some differences. The cardiac cells of the heart are specialized excitable cells that are able to induce electrical impulses and give rise to an action potential. Cardiac muscle cells are also called cardiomyocytes.