Tag: muscle contraction

Questions Related to muscle contraction

During muscle contraction

muscle contraction locomotion and movements biology

  1. Size of A-bands remains the same

  2. Size of H-zone becomes smaller

  3. Size of I-bands decreases

  4. All of the above

Show answer
Correct Option: D
Explanation:
  • Active sites for myosin(Thick filament) are present on actin which are masked by troponin in resting state. when  Ca++ level increases it leads to the binding of calcium with a subunit of troponin on actin(thin) filaments and thereby remove the masking of active sites for myosin.
  • Utilizing the energy from ATP hydrolysis, the myosin head now binds to the exposed active sites on actin to form a cross bridge. 
  • This pulls the attached actin filaments towards the centre of ‘A’ band.
  •  The ‘Z’ line attached to these actins are also pulled inwards thereby causing a shortening of the sarcomere, i.e., contraction. Hence Size of A-bands remains the same, the Size of H-zone becomes smaller and Size of I-bands decreases.
  • So, the correct answer is 'All the above'

Which is true of muscle contraction

muscle contraction locomotion and movements biology

  1. Sarcolemma becomes permeable to $Ca^{2+}$ ions

  2. Sarcolemma becomes permeable $Na^+$ ions

  3. Sarcolemma becomes nonpermeable to $Na^+$ ions

  4. Concentration of $Ca^{2+}$ ions is reduced in myoplasm

Show answer
Correct Option: B
Explanation:

Acetylcholine release from synaptic vesicles and travels across synaptic cleft and binds with protein receptors in sarcolemma. This causes the sarcolemma to become more permeable to sodium ions which causes them enter. Now sarcolemma is elctro positive inside and negative outside. This new potential difference is called action potential and sarcolemma now is called as depolarised. So the correct answer is 'Sarcolemma becomes permeable Na+ ions'.

Correct order of stages of muscle contraction is

muscle contraction locomotion and movements biology

  1. Stimuli Neurotransmitter secretion $\rightarrow$ Release of calcium $\rightarrow$ Cross-bridges formation $\rightarrow$ Excitation of T-system $\rightarrow$ Sliding of actin filament

  2. Stimuli Neurotransmitter secretion $\rightarrow$ Excitation of T-system $\rightarrow$ Release of C$a^{2+}$ $\rightarrow$ Cross-bridges formation $\rightarrow$ Sliding of actin filaments $\rightarrow$ H band diminishes

  3. Stimuli Excitation of T-system $\rightarrow$ Neurotransmitter secretion $\rightarrow$ Crossbridges formation $\rightarrow$ Sliding of actin filaments $\rightarrow$ H band diminishes

  4. Stimuli $\rightarrow$ Neurotransmitter secretion $\rightarrow$ Cross-bridges formation $\rightarrow$ Excitation of T-system $\rightarrow$ Sliding of actin filaments

Show answer
Correct Option: B
Explanation:

  • Active sites for myosin(Thick filament) are present on actin which are masked by troponin-C in resting state. when  Ca++ level increases it leads to the binding of calcium with a subunit of troponin i.e Troponin-C on actin(thin) filaments and thereby remove the masking of active sites for myosin.
  • Utilizing the energy from ATP hydrolysis, the myosin head now binds to the exposed active sites on actin to form a cross bridge. 
  • This pulls the attached actin filaments towards the center of ‘A’ band.
  •  The ‘Z’ line attached to these actins are also pulled inwards thereby causing a shortening of the sarcomere, i.e., contraction. Hence the ‘I’ band and 'H' band get reduced, whereas the ‘A’ bands retain the length.

So, Correct answer is 'Stimuli Neurotransmitter secretion →→ Excitation of T-system →→ Release of $Ca^2+$ →→ Cross-bridges formation →→ Sliding of actin filaments →→ H band diminishes'

Involuntary muscular contraction is called

muscle contraction locomotion and movements biology

  1. Muscle sprain

  2. Muscle fatigue

  3. Muscle spasm

  4. Muscle twitch

Show answer
Correct Option: C
Explanation:
  • Muscle is a  bundle of fibrous tissue in a body that has the ability to contract, producing movement in or maintaining the position of parts of the body.
  • The total number of muscles in the human body comes in the range of 640-850.
  • Involuntary muscular contraction is called muscle spasm. Spasms of skeletal muscles are most common and are often due to overuse and muscle fatigue, dehydration, and electrolyte abnormalities.
  • So, the correct answer is 'Muscle spasm'.

Identify the events occurring in muscular contraction;

(i) H-zone disappears
(ii) A band widens
(iii) I-band reduces in width
(iv) The width of A band is unaffected
(v) M-line and Z-line come closer

muscle contraction locomotion and movements biology

  1. i, ii, v

  2. i, ii, iii

  3. i, iii, iv, v

  4. ii, iv, v

Show answer
Correct Option: C
Explanation:
  • Each myofibril has alternate dark and light bands on it. The light bands contain actin and are called I-band or Isotropic band, whereas the dark band called ‘A’ or Anisotropic band contains myosin.
  •  In the centre of each ‘I’ band is an elastic fibre called ‘Z’ line which bisects it. The thin filaments are firmly attached to the ‘Z’ line. The thick filaments in the ‘A’ band are also held together in the middle of this band by a thin fibrous membrane called’ line.
  •  Utilizing the energy from ATP hydrolysis, the myosin head now binds to the exposed active sites on actin to form a cross bridge. 
  • This pulls the attached actin filaments towards the centre of ‘A’ band.
  •  The ‘Z’ line attached to these actions are also pulled inwards thereby causing a shortening of the sarcomere, i.e., contraction.
  • Hence the events occurring in muscular contraction are  H-zone disappears, I-band reduces in width, The width of A band is unaffected and M-line and Z-line come closer.
  • So, the correct answer is 'i, iii, iv, v

Contraction period for a skeletal muscle is

muscle contraction locomotion and movements biology

  1. 4 sec

  2. 0.04 sec

  3. 0.2 sec

  4. 20 sec

Show answer
Correct Option: A
Explanation:

  • When an impulse reaches the muscle fibres of a motor unit, it stimulates a reaction in each sarcomere between the actin and myosin filaments. 
  • This reaction results in the start of a contraction and the sliding filament theory. And the Contraction period for a skeletal muscle is 4 sec.

    Hence, Contraction period for a skeletal muscle is 4 sec.
    So, the correct answer is '4 sec'.

Muscular and nervous excitability is reduced by

muscle contraction locomotion and movements biology

  1. $Na^+$

  2. $K^+$

  3. $Ca^{2+}$

  4. $Mg^{2+}$

Show answer
Correct Option: B
Explanation:

  • Potassium is an important mineral that functions as an electrolyte. 
  • It helps regulate fluid balance, nerve signals and muscle contractions and nervous excitability. 
  • Increased extracellular potassium levels result in depolarization of the membrane potentials of cells due to the increase in the equilibrium potential of potassium.
  •  This depolarization opens some voltage-gated sodium channels but also increases the inactivation at the same time. Hence, Muscular and nervous excitability is reduced by K+. 
So, the correct answer is 'K+'.

Which one of the following sets of ions is necessary for chemical events for muscle contraction?

muscle contraction locomotion and movements biology

  1. $Ca^+ \, and \, Mg^{++}$

  2. $K^+ \, and \, Na^+$

  3. $K^+ \, and \, Ca^+$

  4. $Na^+ \, and \, Fe^{+++}$

Show answer
Correct Option: A
Explanation:

  • The muscle contraction cycle is triggered by calcium ions binding to the protein complex troponin, exposing the active-binding sites on the actin.
  • ATP then binds to myosin, moving the myosin to its high-energy state, releasing the myosin head from the actin active site.
So, the correct option is '$Ca _+$ and $Mg++$'.

Which of the following is a source of energy for muscle contraction ?

muscle contraction locomotion and movements biology

  1. Actin

  2. ATP

  3. Myosin

  4. Actomyosin

Show answer
Correct Option: B
Explanation:

'ATP' is the source of energy for muscle contraction.

So the correct answer is 'ATP'.

Following is given a randomly arranged list of events that occur at neuromuscular junction to trigger muscle contraction.
(i) Receptor sites on sarcolemma
(ii) Nerve impulse
(iii) Release of $Ca^{+2}$ from sarcoplasmic reticulum
(iv) The neurotransmitter acetylcholine is released (v) Sarcomere shorten
(vi) Synaptic cleft 
(vii) Spread of impulses over sarcolemma on T-tubules
Which of the following gives the correct sequence of these steps ?

muscle contraction locomotion and movements biology

  1. (ii) $\rightarrow$ (iv) $\rightarrow$ (i) $\rightarrow$ (vi) $\rightarrow$ (vii) $\rightarrow$ (v)

  2. (ii) $\rightarrow$ (iv) $\rightarrow$ (vi) $\rightarrow$ (i) $\rightarrow$ (vii) $\rightarrow$(iii) $\rightarrow$ (v)

  3. (i) $\rightarrow$ (ii) $\rightarrow$ (iii) $\rightarrow$ (iv) $\rightarrow$ (v) $\rightarrow$ (vi) $\rightarrow$ (vii)

  4. (vii) $\rightarrow$ (vi) $\rightarrow$ (v) $\rightarrow$ (iv) $\rightarrow$ (iii) $\rightarrow$ (i)

Show answer
Correct Option: B
Explanation:

Muscle contraction:

a. As a nerve impulse( action potential) from a motor neuron arrives via its axon at the neuromuscular junction, the vesicles in the end plate release a neurotransmitter, the acetylcholine, into the nerve-muscle gap (synaptic cleft). 
b. Acetylcholine depolarises the postsynaptic muscle cell's sarcolemma and set up an action potential in the latter.
c. The action potential spreads deep into the interior of the muscle fibre via T- tubules and Z lines.
d. The incoming action potential changes the permeability of the SR, causing to release calcium ions.
e. The calcium ions bind to troponin molecules. 
f. The latter change shape and shift position.
So, the correct answer is '(ii) $\rightarrow$(iv)$\rightarrow$(vi)$\rightarrow$(i)$\rightarrow$(vii)$\rightarrow$(iii)$\rightarrow$(v)'.