Question

Contraction and relaxation of the heart is controlled by the
A.Cardiac muscle
B.Smooth muscle
C.Striated muscle
D.None of the above

Answer 1

Hint: Under a microscope when different types of muscles are viewed post staining with appropriate stains (such as haematoxylin phloxine and saffron) some muscles appear to have striations. These are called striated muscles and are characterised by the presence of a large number of mitochondria to meet the energy needs. The heart pumps continuously throughout the lifetime of an organism and requires a lot of energy to carry out its function.

Complete answer:
1.The striations seen in certain types of muscles (namely skeletal and cardiac muscle) is due to the presence of sarcomere. Thus, sarcomere is the building block, the contractile unit of striated muscle.
2.When viewed under polarised light different parts of the sarcomere diffract light differently and this property of differential light diffraction has been utilised to name different parts of sarcomere. The names are derived from German words
3.The band is composed of thin filaments made up of actin and has tropomyosin, troponin along with other regulatory proteins. I band is an abbreviation of ‘isotropic’ since more light can pass through.
4.Besides the I band sarcomere has A band derived from the first letter of the word anisotropic. A bands are made up of thin actin filaments and thick myosin filaments.
5.The I bands are interrupted by dark Z bands in the mid zone and the A bands are interrupted by clear zone H bands.
6.Striated muscles can be two types: cardiac muscle and skeletal muscle. Cardiac muscle is responsible for contraction of heart. Striated muscles have tubular cells and are often multinucleate.
7.Smooth muscles are made of cell that taper towards both ends. These muscles are devoid of striations when stained and viewed under a light microscope. Generally, these muscles are uninucleate and are involuntary in nature i.e., their action cannot be controlled by us at will. 8.These muscles are found in ureters, eyes, digestive tract and bronchi of the lungs.

Hence the correct answer is OPTION(A)

Note: Cardiac muscles are a type of striated muscle but are found only in the heart. These muscles are also involuntary in nature despite not being smooth muscles. Though some simpler vertebrates like certain fishes have the ability to regenerate cardiac muscles, adult humans cannot regenerate cardiac muscles post myocardial infarction( heart attack, which restricts blood flow and kill of cardiac cells).