Which of the following statements are correct regarding skeletal muscle?
A. Muscle bundles are held together by collagenous connective tissue layer called fascicle.
B. Sarcoplasmic reticulum of muscle fibre is a store house of calcium ions.
C. Striated appearance of skeletal muscle fibre is due to distribution pattern of actin and myosin proteins.
D. M line is considered as functional unit of contraction called sarcomere.
Choose the most appropriate answer from the options given below: [2023]
A, C and D only
C and D only
A, B and C only
B and C only
(4)
Each organised skeletal muscle in our body is made of a number of muscle bundles or fascicles held together by a common collagenous connective tissue layer called fascia. The portion of the myofibril between two successive ‘Z’ lines is considered as the functional unit of contraction and is called a sarcomere.
During muscular contraction which of the following events occur?
(A) ‘H’ zone disappears.
(B) ‘A’ band widens.
(C) ‘I’ band reduces in width.
(D) Myosine hydrolyzes ATP, releasing the ADP and .
(E) Z-lines attached to actins are pulled inwards.
Choose the correct answer from the options given below: [2021]
(B), (D), (E), (A) only
(A), (C), (D), (E) only
(A), (B), (C), (D) only
(B), (C), (D), (E) only
(2)
During muscle contraction, the thin myofilaments i.e., actin slide inwards towards the H-zone. As the thin myofilaments move past the thick myofilaments, the H-zone narrows and even disappears during contraction. Utilising the energy from ATP hydrolysis, the myosin head now binds to the exposed active sites on actin to form cross bridge. The ‘Z’ line attached to these actins are pulled inwards thereby causing shortening of the sarcomere. Size of I-bands shorten, but the width of the A-band remains constant.
Calcium is important in skeletal muscle contraction because it [2018]
binds to troponin to remove the masking of active sites on actin for myosin
activates the myosin ATPase by binding to it
detaches the myosin head from the actin filament
prevents the formation of bonds between the myosin cross bridges and the actin filament
(1)
Calcium ion plays an important role in skeletal muscle contraction. Muscle contraction is initiated by signal sent by the central nervous system. The neural signal further spreads through the muscle fibre and causes the release of calcium ions. Increase in calcium ion levels lead to the binding of calcium with a subunit of troponin on actin filaments and thereby remove the masking of active sites for myosin.
Name the ion responsible for unmasking of active sites for myosin for cross-bridge activity during muscle contraction. [2016]
Calcium
Magnesium
Sodium
Potassium
(1)
Calcium ion plays an important role in muscle contraction. Calcium ions bind to troponin causing a change in its shape and position. Thus, in turn alters shape and position of tropomyosin to which troponin binds. This shift exposes the active sites on F-actin molecules. Myosin cross-bridge are then able to bind to these active sites.
Lack of relaxation between successive stimuli in sustained muscle contraction is known as [2016]
tetanus
tonus
spasm
fatigue
(1)
Tetanus refers to continued state of contraction of a muscle resulting from the summation of a series of rapid muscular contractions (twitches) that are induced by repeated stimulation of the muscle.
Sliding filament theory can be best explained as [2015]
actin and myosin filaments do not shorten but rather slide pass each other
when myofilaments slide pass each other, myosin filaments shorten while actin filaments do not shorten
when myofilaments slide pass each other actin filaments shorten while myosin filaments do not shorten
actin and myosin filaments shorten and slide pass each other
(1)
During muscle contraction, the laterally projecting heads (cross bridges) of the thick myosin myofilaments come in contact with the thin actin myofilaments and rotate on them. This pulls the thin myofilaments toward the middle of the sarcomere, past the thick myofilaments. The Z lines come closer together and the sarcomere becomes shorter. Length of the A band remains constant. Myofilaments (both actin and myosin) stay the same length. Free ends of actin myofilaments move closer to the centre of the sarcomere, bringing Z lines closer together. I bands shorten and H zone narrows. A similar action in all the sarcomeres results in shortening of the entire myofibril and thereby of the whole fibre and the whole muscle.
Stimulation of a muscle fibre by a motor neuron occurs at [2014]
the neuro-muscular junction
the transverse tubules
the myofibril
the sarcoplasmic reticulum
(1)
A neuron that transmits a stimulus to muscle tissue is called motor neuron. A motor unit consists of a single motor neuron (nerve cell) and the muscle fibres it innervates. The portion of the muscle plasma membrane (sarcolemma) that lies beneath the nerve endings (axon terminals) is called the motor end plate. The axon terminals and the motor end plate together constitute the neuro-muscular junction or neuromotor junction.
