Select the correct statements regarding mechanism of muscle contraction.
A. It is initiated by a signal sent by CNS via sensory neuron.
B. Neurotransmitter generates action potential in the sarcolemma.
C. Increased Ca++ level leads to the binding of calcium with troponin on action filaments.
D. Masking of active site for actin is activated.
E. Utilising the energy from ATP hydrolysis to form cross bridge.
Choose the most appropriate answer from the options given below:
A. It is initiated by a signal sent by CNS via sensory neuron.
B. Neurotransmitter generates action potential in the sarcolemma.
C. Increased Ca++ level leads to the binding of calcium with troponin on action filaments.
D. Masking of active site for actin is activated.
E. Utilising the energy from ATP hydrolysis to form cross bridge.
Choose the most appropriate answer from the options given below:
- B, C and E only
- C, D and E only
- A and D only
- B, D and E only
The Correct Option is A
Solution and Explanation
Analysis of muscle contraction steps:
A. Initiation: CNS signals initiate muscle contraction via motor neurons, not sensory neurons. Sensory neurons transmit signals from the periphery to the CNS. Statement A is incorrect.
B. Neurotransmitter and action potential: Motor neuron neurotransmitters (e.g., acetylcholine) bind to muscle cell membrane receptors, generating an action potential that propagates across the sarcolemma and into T-tubules. Statement B is correct.
C. Calcium binding to troponin: The action potential triggers calcium release from the sarcoplasmic reticulum. Increased cytoplasmic calcium binds to troponin on actin filaments, causing a conformational change in tropomyosin and exposing myosin-binding sites on actin. Statement C is correct.
D. Masking of active site for actin: Tropomyosin initially masks actin's active sites. Increased calcium binding to troponin shifts tropomyosin, unmasking these sites. Statement D is incorrect.
E. ATP hydrolysis and cross-bridge formation: ATP hydrolysis energizes myosin heads to bind to exposed actin sites, forming cross-bridges. The myosin power stroke pulls actin filaments, causing muscle shortening. Statement E is correct.