Q. Smooth muscle fibres are
Solution:
Non-striated muscle/Smooth muscle:
Location: They are found in walls of visceral organs like alimentary canal, genital and urinary ducts, blood vessels and urinary bladder muscles. They are also found in the dermis of the skin, iris and ciliary body of the eye.
Structure:
(i) Each muscle fibre is long, narrow and spindle-shaped with tapering ends.
(ii) Each muscle fibre maybe 0.02 to 0.05 mm in length and 5 to 10 µm in diameter. It is generally shorter than striated muscle fibre.
(iii) Myofibril is made up of actin & myosin but remarkably less than skeletal muscle but filaments are not placed in a highly ordered pattern so striation is absent. Actin is more than myosin
(iv) The non-striated muscles cannot be moved on one’s own will, they are involuntary.
(v) The non-striated muscles contract and relax slowly. They can remain contracted for a long time without getting fatigued.
They are of two types:
a) Single-unit smooth muscles: In the single unit smooth muscles, the fibres are closely joined together by abundant gap junctions. They contract simultaneously as a single unit. They are found in visceral organs of the body.
b) Multi-unit smooth muscles: In the multi-unit smooth muscles, the fibres are not closely jointed. They contract more or less independently as separate and graded contractions. They occur in iris of the eye, walls of large blood vessels and in the dermis of the skin.
Location: They are found in walls of visceral organs like alimentary canal, genital and urinary ducts, blood vessels and urinary bladder muscles. They are also found in the dermis of the skin, iris and ciliary body of the eye.
Structure:
(i) Each muscle fibre is long, narrow and spindle-shaped with tapering ends.
(ii) Each muscle fibre maybe 0.02 to 0.05 mm in length and 5 to 10 µm in diameter. It is generally shorter than striated muscle fibre.
(iii) Myofibril is made up of actin & myosin but remarkably less than skeletal muscle but filaments are not placed in a highly ordered pattern so striation is absent. Actin is more than myosin
(iv) The non-striated muscles cannot be moved on one’s own will, they are involuntary.
(v) The non-striated muscles contract and relax slowly. They can remain contracted for a long time without getting fatigued.
They are of two types:
a) Single-unit smooth muscles: In the single unit smooth muscles, the fibres are closely joined together by abundant gap junctions. They contract simultaneously as a single unit. They are found in visceral organs of the body.
b) Multi-unit smooth muscles: In the multi-unit smooth muscles, the fibres are not closely jointed. They contract more or less independently as separate and graded contractions. They occur in iris of the eye, walls of large blood vessels and in the dermis of the skin.