Home / Topic 1: Skeletal Muscle and its Contraction NEET Style Questions

Question

 During muscular contraction, which of the following events occur? [NEET 2021]

I. ‘H’zone disappears

II. ‘A’ band widens

III. ‘I’ band reduces in width

IV. Myosine hydrolyses ATP, releasing the ADP and $\mathrm{Pi}$

V. Z-lines attached to actins are pulled inwards.
Choose the correct answer from the options given below.
(a) I, III, IV and V

(b) I, II, III and IV

(c) II, III, IV and V

(d) II, IV, V and I

Answer/Explanation

Ans. (a)
Statements I, III, IV, and V are correct and statement $I \mathrm{is}$ incorrect and can be corrected as During muscular
contraction by utilising energy from ATP hydrolysis the myosin head binds to the exposed active sites on actins to form a cross bridge.
This pulls the attached actin filaments towards the center of A band. This movement contricts ‘A’ band.

Question

 Calcium is important in skeletal muscle contraction because it [NEET 2018]

(a) detaches the myosin head from the actin filament

(b) activates the myosin ATPase by binding to it

(c) binds to troponin to remove the masking of active sites on actin for myosin

(d) prevents the formation of bonds between the myosin cross bridges and the actin filament

Answer/Explanation

Ans. (c)
Calcium plays a key regulatory role in muscle contraction. $\mathrm{Ca}^{2+}$ ions bind to troponin and changes its shape and position. This in turn, alter the shape and position of tropomyosin and hence, the active sites on $\mathrm{F}$-actin are exposed. Due to this, myosin cross-bridges are able to bind to these active sites and muscle contraction occurs.

Question

 Lack of relaxation between successive stimuli in sustained muscle contraction is known as [NEET 2016, Phase I]

(a) fatigue

(b) tetanus

(c) tonus

(d) spasm

Answer/Explanation

Ans. (b)

Sustained muscle contraction due to repeated stimulus is known as tetanus. This results due to muscle fatigue.

Question

 Name the ion responsible for unmasking of active sites for myosin for cross-bridge activity during muscle contraction. [NEET 2016, Phase II]

(a) Calcium

(b) Magnesium

(c) Sodium

(d) Potassium

Answer/Explanation

Ans. (a)
$\mathrm{Ca}^{++}$ions bind with $\mathrm{Tp}_{\mathrm{c}}$ unit of troponin which is responsible for masking of active sites for myosin through tropomyosin. The event initiates cross-bridge activity during muscle contraction mechanism.

Question

 Smooth muscles are [NEET 2016, Phase II]

(a) involuntary, fusiform, non-striated

(b) voluntary, multinucleate, cylindrical

(c) involuntary, cylindrical, striated

(d) voluntary, spindle-shaped, uninucleate

Answer/Explanation

Ans. (a)

Smooth muscles are involuntary, fusiform and non-striated. These muscles are located in the inner walls of hollow visceral organs of the body like alimentary canal, reproductive tract, etc.
They do not exhibit any striation and are smooth in appearance. Their activities are under autonomic and hormonal control and thus they are also known as involuntary muscles.
Hence, option (a) is correct.

Question

 The $\mathrm{H}$-zone in the skeletal muscle fibre is due to [NEET 2013]
(a) the absence of myofibrils in the central portion of A-band

(b) the central gap between myosin filaments in the A-band

(c) the central gap between actin filaments extending through myosin filaments in the A-band

(d) extension of myosin filaments in the central portion of the $\mathrm{A}$-band

Answer/Explanation

Ans. (c)
$\mathrm{H}$-zone in skeletal muscle is due to the central gap between actin filaments extending through myosin filaments in the A-band. Alternate arrangement of dark and light bands gives the striated appearance to a skeletal muscle. At the centre of A-band, a comparatively less dark zone called $\mathrm{H}$-zone is present.In the centre of $\mathrm{H}$-zone, $\mathrm{M}$-line is present, formed by the threats that connect the myofilaments.

Question

 Which one of the following is the correct pairing of a body part and the kind of muscle tissue that moves it? [CBSE AIPMT 2009]

(a) Heart wall – Involuntary unstriated muscle

(b) Biceps of – Smooth muscle fibres upper arm

(c) Abdominal – Smooth muscle wall

(d) Iris $\quad-$ Involuntary smooth muscle

Answer/Explanation

Ans. (d)
Smooth muscles are plain, non-striated, involuntary or unstriped muscles due to the absence of striations. These occur in the walls of hollow internal organs, in capsules of lymph glands, spleen, etc., in iris and ciliary body of eyes, skin dermis, penis and other accessory genitalia, etc.

Question

 The contractile protein of skeletal muscle involving ATPase activity is [CBSE AIPMT 2006]

(a) myosin

(b) a-actinin

(c) troponin

(d) tropomyosin

Answer/Explanation

Ans. (a)

The kinesin, myosin and dynein proteins of skeletal muscle involve ATPase activity. This activity cause the contraction of skeletal muscles, propelling action of cilia and flagella and the intracellular transport of organelles.

Question

 ATPase enzyme needed for muscle contraction is located in [CBSE AIPMT 2004]

(a) actinin

(b) troponin

(c) myosin

(d) actin

Answer/Explanation

Ans. (c)
During muscular contraction myosin cross bridges heads. Myosin is not only an actin binding protein, it is also an ATPase (an enzyme) which is activated by $\mathrm{Ca}^{2+}$ and $\mathrm{Mg}^{2+}$ ions. Hence, ATPase enzyme is located in myosin.

Question

 Which statement is correct for muscle contraction? [CBSE AIPMT 2001]

(a) Length of $\mathrm{H}$-zone decrease

(b) Length of A-band remains constant

(c) Length of I-band increases

(d) Length of two Z-line increases

Answer/Explanation

Ans. (b)
When $\mathrm{Ca}^{+}$ions combine with troponin then in consequence muscle contraction will initiates.
During contraction, the Z-lines come closer together and the sarcomere becomes shorter. The length of A-band remains constant. I-bands shortens and $\mathrm{H}$-zone narrows.

Question

What is sarcomere? [CBSE AIPMT 2001]

(a) Part between two $\mathrm{H}$-lines

(b) Part between two A-lines

(c) Part between two I-bands

(d) Part between two Z-lines

Answer/Explanation

Ans. (d)

Huxley reported the fine structure of striated muscle fibre or myofibril. Each myofibril is made up of A-bands (dark band anisotropic) and I-bands = isotropic (light bands isotropic). These two bands are made up of myosin and actin filament respectively. Each I-band is divided into two equal halves by a thin, fibrous and transverse zig-zag partition, called Z-band or Z-disc or Krause’s membrane.
The part of the myofibril between two successive Z-lines functions as a contractile unit called sarcomere.

Question

 The functional unit of contractile system in striated muscle is [CBSE AIPMT 1998]

(a) myofibril

(b) sarcomere

(c) Z-lines

(d) cross bridges

Answer/Explanation

Ans. (b)

Skeletal muscle is also called striated muscle because the regular arrangement of the myofilaments creates as repeating pattern of light and dark bands. Each repeating unit is a sarcomere, the basic functional unit of the muscle.

Question

 Which of the following is the contractile protein of a muscle? [CBSE AIPMT 1998]

(a) Myosin

(b) Tropomyosin

(c) Actin

(d) Tubulin

Answer/Explanation

Ans. (a)

Myosin-II, a two-headed tailed variety of myosin is involved in muscle contraction.

Question

 Which ion is essential for muscle contraction? [CBSE AIPMT 1994]

(a) $\mathrm{Na}$

(b) $\mathrm{K}$

(c) $\mathrm{Ca}$

(d) $\mathrm{Cl}$

Answer/Explanation

Ans. (c)
Calcium is an essential element required for the contraction of muscles. Release of calcium ions from sarcoplasmic reticulum trigger the muscle contraction process. In fact, calcium ions and ATP, actin and myosin interact forming actomyosin, which causes the muscles to contract.

Question

Intercostal muscles occur in [CBSE AIPMT 1988]

(a) abdomen

(b) thigh

(c) ribs

(d) diaphragm

Answer/Explanation

Ans. (c)
Intercostal muscles, i.e. internal intercostal and external intercostal are attached with the ribs, these are the main muscles for normal quite breathing. External intercostal muscle and diaphragm contract during inspiration and relax during expiration.

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