Question

Which of the following is the correct sequence of events for muscle contractions?a) motor neuron action potential, meurotransmitter release, muscle cell action potential, release of calcium ions from SR, AtP-driven power stroke, sliding of myofilamentsb) neurotransmitter release, muscle cell action potential, motor reuron action potential, release of calcium ions from SR, sliding of myofilaments, ATP-driven power strokec) muslce cell action potential, neurotransmitter release, atp-driven power stroke, calcium ion release from SR, sliding of myofilamentsd) neurotransmitter rlease, motor neuron cation potential, muscle cell action potential, release of calcium ions from SR, ATP-driven power stroke

Answer 1

The answer is; A

When an impulse from the motor neuron reached the neuromuscular junction, the voltage-dependent calcium channels are activated and the neurotransmitter released from the presynaptic cleft. When the neurotransmitter binds to their receptors on the sarcolemma, the muscle fibers become depolarised; the calcium is released from their vesicles. The Ca2+ ions are important in the power stroke because they bind to troponin. Upon binding calcium, troponin moves tropomyosin away from the myosin-binding sites on actin. Powered by the energy from ATP molecule, the myosin is able to bind on the actin and slides over the actin filament.