Question

1. Explain how a message is communicated from neurons to muscle fibers causing a contraction, include all of the components in the word bank from the matching activity. - This could be completed in a diagram as well (You will be completing this in a pre-lab as well).

Answer 1

Muscle contraction is triggered when an action potential travels along the nerves to muscle. The signal, an impulse called an action potential travels through a type of nerve cell called a motor neuron, the signal reaches neuromuscular junction called synapse where a neurotransmitter like acetyl choline is released, acetyl choline binds to the receptors on the outside of the muscle fiber, which starts a reaction within the muscle, acetyl choline causes the muscle fiber to conduct an impulse over the surface of the fiber that reaches deep within the fiber through the transverse tubules, a muscle impulse signals the sarcoplasmic reticulum to release calcium ions, the release of calcium ions initiates muscle contraction by binding to troponin, which causes tropomyosin to unmask the binding site on actin so that actin and myosin can form a cross bridge which causes muscle contraction.During muscle relaxation troponin looses its bound calcium ions and tropomyosin shifts back to its off positon.

Muscle contraction requires action potential to be generated so that there is influx of sodium ion into the cell membrane to cause depolarization, which changes the cell potential, resulting inthe outward movements of potassium ions which results in repolarization, chloride ion also diffuse into the sarcoplasma contributing to repolarization, then there is brief period of hyperpolarization, during which no action potential is generated and than the cycle begins again.