Concept:Muscle contraction is triggered by neural signals that cause calcium release and cross-bridge formation between actin and myosin.
Key Fact:Calcium ions (
Ca++) bind to troponin, exposing active sites on actin for myosin binding, leading to sarcomere shortening.
Explanation:Statement A is correct: A motor neuron transmits the CNS signal to the sarcolemma.
Statement B is correct: The neural signal generates an action potential that releases
Ca++ into the sarcoplasm.
Statement C is incorrect:
Ca++ does not inactivate actin; instead, it activates actin by removing tropomyosin blockage, enabling cross-bridge formation.
Statement D is correct: Actin binds to the myosin head to form a cross bridge.
Statement E is correct: Shortening of the sarcomere occurs as actin filaments are pulled toward the centre of the A band.
Answer:Options A, B, D and E are correct. Therefore, the correct answer is D.
