Question

Which of the following has involuntary muscles?
A. Legs
B. Arms
C. Neck
D. Intestine

Answer 1

Hint:-Involuntary muscles are the type of muscles that cannot be controlled by will i.e. it can contract or relax without conscious control of the mind. The autonomous nervous system is responsible for the stimulation of involuntary muscles. Voluntary muscles can be controlled consciously and they are stimulated by the somatic nervous system.

Complete step-by-step solution:-Involuntary muscles are also called smooth or non-striated muscles. They are found inside the lining of the walls surrounding the internal organs such as in the intestine, stomach, esophagus, and urinary bladder and also line the respiratory tract, urogenital tract, blood vessels, etc. Muscles of legs, arms, and neck can be controlled by will therefore they are voluntary muscles.
A specialized cell membrane surrounds the muscle cells called sarcolemma. It is found both in voluntary and involuntary muscles. The sarcolemma in the involuntary cells is very thin and the sarcomeres are absent. Sarcomeres are functional units of muscle fibers. The sarcomeres are made up of myofilaments that are the actin and myosin proteins and these are absent in involuntary muscles. These muscles also help in the passage of food down the food pipe in the digestive system (peristalsis), and also in the passage of body fluids as blood vessels are made up of involuntary muscles. So, the correct answer is option D.

Note:- The involuntary muscles can work continuously without fatigue like the heart muscles. The heart muscles have to pump blood continuously and therefore there is rhythmic contraction and relaxation of the involuntary muscles. The contraction of cardiac muscle is different from a skeletal or smooth muscle. An electrical stimulus is generated in the cardiac muscle which can generate action potential that can cause the release of calcium ions that helps in the contraction and excitation of the muscles. The control of the iris of the eye is also through involuntary muscles.