Question
Choose the correct statements regarding muscle contraction. A. A motor neuron carries a signal sent by the Central Nervous System (CNS) to the sarcolemma of the muscle fibre. B. The neural signal generates an action potential which causes the release of Ca ^ ++ into sarcoplasm. C. Increase in Ca ^ ++ inactivates the actin for breaking cross bridges. D. Actin binds to the myosin head to form a cross bridge. E. Shortening of sarcomere takes place, by pulling actin filaments towards the centre of 'A' band. Choose the correct answer from the options given below :
Step-by-step solution
Statement A is correct: Muscle contraction is initiated by a signal sent by the Central Nervous System (CNS) via a motor neuron to the neuromuscular junction, which is the junction between a motor neuron and the sarcolemma of the muscle fibre. Statement B is correct: The neural signal releases a neurotransmitter (acetylcholine) which generates an action potential in the sarcolemma. This action potential spreads through the muscle fibre and causes the release of Ca ^ ++ ions into the sarcoplasm. Statement C is incorrect: An increase in Ca ^ ++ level leads to the binding of calcium with a subunit of troponin on actin filaments, which removes the masking of active sites for myosin. It does not inactivate actin. Statement D is correct: Utilising the energy from ATP hydrolysis, the myosin head binds to the exposed active sites on actin to form a cross bridge. Statement E is correct: The formation of cross bridges pulls the attached actin filaments towards the centre of the 'A' band. The 'Z' lines attached to these actins are also pulled inwards, causing a shortening of the sarcomere, which is muscle contraction. Therefore, statements A, B, D, and E are correct. Answer: A, B, D and E only