Concept explainers
Watch this video (http://openstaxcollege.org/l/micromacro) to learn more about macro- and microstructures of skeletal muscles. (a) What are the names of the “junction points” between sarcomeres? (b) What are the names of the “subunits” within the myofibrils that run the length of skeletal muscle fibers? (c) What is the “double strand of pearlsâ€� described in the video? (d) What gives a skeletal muscle fiber its striated appearance?
(a) To write:
The names of junction points between sarcomeres.
Introduction:
Sarcomeres are the units of the skeletal muscle which are formed of muscle fibers. Many sarcomeres together form myofibrils.
Explanation of Solution
Sarcomeres are the units of muscles and junction points between sarcomeres is Z line. In between two Z lines, two sarcomere units are present. At Z line, actin filaments or the ends of sarcomere are present.
Junction points between sarcomeres is known as Z line.
(b) To write:
The name of subunits of myofibrils.
Introduction:
Myofibrils are elongated thread like structures in the skeletal muscles. Many myofibrils together form skeletal muscles.
Explanation of Solution
The subunit of myofibrils are sarcomeres. Sarcomeres are the basic units of a skeletal muscle which together form myofibrils. These myofibrils together form a skeletal muscle.
Subunits of myofibrils are sarcomeres.
(c) To write:
To determine what double strands of pearl means in the video.
Introduction:
In the given video double strands of pearl shows the arrangement of actin and myosin filament.
Explanation of Solution
In the given video, arrangement of actin filaments of skeletal muscle is shown. Actin filament is a thin filament which is formed by a double chain of many subunits. Both the chains are twisted and this resembles the structure of double strands of pearl.
Double strands of pearl resemble twisted double chain of actin filaments formed of many subunits.
(d) To write:
To determine the reason of striated appearance of skeletal muscle.
Introduction:
Skeletal muscles have striated appearance due to presence of alternating dark and light bands in them.
Explanation of Solution
Due to arrangement of myosin and actin filaments, light and dark bands are formed. This gives striated appearance to the skeletal muscle. The A bands forms the dark bands as they have both actin and myosin filaments in them giving a dark appearance. The I bands forms light bands as they have only thin actin filaments in them. This results in striated appearance of a skeletal muscle.
Striated appearance of skeletal muscle is formed by dark A bands and light I bands formed by arrangement of actin and myosin filaments of the muscle.
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