My name is Dr.Medicine and today i will be teaching you about muscle contractions.
First, the nervous system sends a signal that stimulates the muscle. Each muscle fiber has axon terminals. The axon terminals and muscle fibers are separated by a thin wall called the synaptic cleft. That's where the muscle produces junctional folds in the postsynaptic membrane.
Then the axon terminal will release acetylcholine into the synaptic cleft. Acetylcholine is a neurotransmitter that is located in the synaptic vessels. When sodium ions enter, depolarization will happen.
When depolarization happens, it will cause other sodium channels to open. The sodium will go anywhere along the membrane. Next, an enzyme will break down acetylcholine and then muscle wont be able to contract anymore unless there is another impulse.
The action potential will then multiply along the sarcolemma. One protein that is important in muscle contraction is myofilaments. Myofilaments are constructed of myosin or actin. They are in muscles and help contract them. When there is a rise in calcium, the actin filaments slide, which causes the myosin heads to move and pull the actin filament along. This process uses ATP.
When the calcium levels go down, the tropin go back to their normal shape. Tropomyosin blocks actin binding sites. In the end the muscle fiber relaxes. And that's how a muscle contracts! See you next lesson!