Question
Which of the following statements wrongly represents the nature of smooth muscle? [NEET 2021]
(a) These muscles have no striations
(b) They are involuntary muscles
(c) Communication among the cells is performed by intercalated discs
(d) These muscles are present in the wall of blood vessels
Answer/Explanation
Ans. (c)
Statement in option (c) is incorrect and can be corrected as
Intercalated discs are not found in smooth muscles these are found in cardiac muscles.
Smooth muscle cells are spindle-shaped, have a single nucleus and do not show striations. These involuntary muscles are found on the walls of internal organs such as blood vessels.
Question
36 Which of the following is not exclusively supplied with involuntary muscles? [CBSE AIPMT 1998]
(a) Muscular coats of blood vessels
(b) Muscles of the ducts of glands
(c) Muscles of iris
(d) Muscles of urethra
Answer/Explanation
Ans. (b)
Muscles of the ducts of glands are not exclusively supplied with involuntary muscles. Smooth muscles are involuntary muscles and are found in the posterior part of oesophagus, stomach, urinogenital tract, blood vessels, iris of eye and dermis of skin.
Question
Characteristics of smooth muscle fibres are [CBSE AIPMT 1990]
(a) spindle-shaped, unbranched, unstriated, uninucleate and involuntary
(b) spindle-shaped, unbranched, unstriped, multinucleate and involuntary
(c) cylindrical, unbranched, unstriped, multinucleate and involuntary
(d) cylindrical, unbranched, unstriated, multinucleate and voluntary
Answer/Explanation
Ans. (a)
Smooth muscle fibres are spindle-shaped, thick in the middle and thin at either ends, uninucleated, no sarcolemma, contraction is slow. involuntary under the control of autonomous nervous system. These muscles are also known as visceral muscles, non-striated, non-skeletal or involuntary muscles.