Tag: muscle contraction

Questions Related to muscle contraction

Name the ion responsible for masking active sites for myosin for cross-bridge activity during muscle contraction.

muscle contraction locomotion and movements biology

  1. Potassium

  2. Calcium

  3. Magnesium

  4. Sodium

Show answer
Correct Option: B
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 the ion responsible for masking active sites for myosin for cross-bridge activity during muscle contraction is calcium.
  • So, the correct answer is 'Calcium'

Sarcoplasmic reticulum of muscle fibres is the storehouse of

muscle contraction locomotion and movements biology

  1. Calcium

  2. Sodium

  3. Chloride

  4. Potassium

Show answer
Correct Option: A
Explanation:
  • The endoplasmic reticulum, i.e., sarcoplasmic reticulum of the muscle fibres is the storehouse of calcium ions.
  • A neural signal reaching this junction releases a neurotransmitter (Acetylcholine) which generates an action potential in the sarcolemma. This spreads through the muscle fibre and causes the release of calcium ions into the sarcoplasm from the sarcoplasmic reticulum and initiate the mechanism of muscle contraction.
  • Hence sarcoplasmic reticulum of muscle fibres is the storehouse of calcium.
  • So, the correct answer is 'Calcium'.

Immediate source of energy for muscle contraction is

muscle contraction locomotion and movements biology

  1. Glucose

  2. GTP

  3. Creatine phosphate

  4. ATP

Show answer
Correct Option: D
Explanation:
  •  Active sites for myosin 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. The myosin, releasing the ADP and P1 goes back to its relaxed state. Hence immediate source of energy for muscle contraction is ATP.
  • So, the correct answer is 'ATP'.

Source of $Ca^{2+}$ for muscle contraction is both sarcoplasmic (endoplasmic) reticulum as well as extracellular fluid in case of
a.  Skeletal muscles
b. Smooth muscles
c. cardiac muscles 

muscle contraction locomotion and movements biology

  1. a only

  2. b and c only

  3. a and c only

  4. b only

Show answer
Correct Option: B
Explanation:

Both smooth muscle and cardiac muscle utilise sarcoplasmic and extracellular fluid as source of calcium ion, which is in contrast to skeletal muscle which derive it from sarcoplasm only.

So, the correct option is 'b and c only'

State whether the following statements are true or false.
Cross bridges pull the actin chain as the myosin heads return to their unenergized conformation.

muscle contraction locomotion and movements biology

  1. True

  2. False

Show answer
Correct Option: A
Explanation:

  • A sarcomere is the basic unit of muscle tissue in both cardiac and skeletal muscle. Myofibril activity is required for muscle contraction on the molecular level. 
  • When ATP binds to myosin, it separates from the actin of the myofibril, which causes a contraction.
  • 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 'True'.

Which response to overcooling does not involve muscle contraction?

muscle contraction locomotion and movements biology

  1. Blood vessels narrowing

  2. Hairs standing up

  3. Shivering

  4. Reduced sweating

Show answer
Correct Option: D
Explanation:

In response to over-cooling, 

muscles allow blood vessels narrowing(circular muscles), piloerection(hair standing up by erector pili muscles), and shivering.
Reduced sweating does not involve muscle contraction or relaxation.
So, the correct answer is 'Reduced sweating'.

During skeletal muscle contractions following events can occur:
I. I-band shortens
II. A-band shortens
III. H-zone shortens
IV. Sarcomere contract
V. ATP changes to ADP and Pi
Choose the option with incorrect events.

muscle contraction locomotion and movements biology

  1. Only I

  2. Only III

  3. IV and V

  4. Only II

Show answer
Correct Option: D
Explanation:

I-band consists of only thin filaments. A-band consists of both the thin and thick filaments. H-zone is the band of thick filament only. For skeletal muscle contraction following events occur:

1. The nerve impulse is transmitted to the sarcolemma and it causes release of calcium ions from sarcoplasmic reticulum.
2. These calcium bind to the troponin and tropomyosin rotates. 
3. Then, the myosin binds to the tropomyosin. 
4. ATP is hydrolysed to detach the myosin from the tropomyosin and muscle can be relaxed.
The shortening of I-band and H-zone causes the contraction of sarcomere. 
A-band does not change.
Hence, the correct answer is 'only II'

Which responce to overcooling does not does not involve muscle contraction?

muscle contraction locomotion and movements biology

  1. Blood vessels narrowing

  2. Hairs standing up

  3. Shivering

  4. Reduced sweating

Show answer
Correct Option: D
Explanation:

Blood vessels narrowing, hairs standing up and shivering are all because of contraction of muscles. While reduced sweating is due to non-activation of sweat glands from the hypothalamus.

So, the correct option is 'reduced sweating'.

Which cell organelle is associated with muscle contraction by release and uptake of $Ca^{2+}$ ions?

muscle contraction locomotion and movements biology

  1. Golgi apparatus

  2. RER

  3. Sarcoplasmic reticulum

  4. Lysosome

Show answer
Correct Option: C
Explanation:

SER is associated with muscle contraction by release and uptake of Ca ions because SER functions as the packaging structure which stores the Ca ions until its release.

So, the correct option is 'SER'.

Match the following and mark the correct option.

Column I Column II
A. Fast muscle fibres i. Myoglobin
B. Slow muscle fibres ii. Lactic acid
C. Actin filament iii. Contractile unit
D. Sarcomere iv. I-band
muscle contraction locomotion and movements biology

  1. A-i, B-ii, C-iv, D-iii

  2. A-ii, B-i, C-iii, D-iv

  3. A-iii, B-ii, C-iv, D-i

  4. A-ii, B-i, C-iv, D-iii

Show answer
Correct Option: A
Explanation:
a) Fast muscle fibres -  They have a large amount of myoglobin which is resistant to fatigue. 
b) Slow muscles fibres - These type of fibres show a slow 'tunic' contraction characteristic of postural muscles. The lactic acid is produced during muscle contraction.
c) Actin filament - The light bands present in myofibrils contain actin and is called I-band or isotropic band.
d) Sarcomere - It is the contractile unit of muscle fibres.

So, the correct answer is 'A-i, B-ii, C-iv, D-iii'.