FC: Steps to Muscle Contraction By: Jordan Waldhart Maggie Huiting Maggie Schuh
1: Brain sends nerve impulse down motor unit (which is composed of neurons) to the axon terminal.
2: This impulse triggers the calcium gates to open. | Calcium ions rush in which stimulates ACh to be released into the synaptic cleft.
4: ACh then binds to protein channels on the sarcolemma, which causes the protein channels to open.
5: Sodium ions then rush into the cell, which causes Potassium ions to rush out.
7: As a result, depolarization occurs and action potential is created. | Action potential allows the sarcoplasmic reticulum to let go of the calcium ions.
8: Calcium ions bind to troponin (on the thin filaments), which changes shape and opens up the active actin sites, which makes these sites available for myosin heads to bind to.
9: An ATP molecule is bound to the myosin head, which activates the head to stand up. Now, this head will bind to a site on the actin. Then, myosin tugs the thin filament. | This shortens the sarcomere.This action allows the A bands and I bands to overlap.The myosin head is attatched to actin until a new ATP molecule binds on it. | After this new binding occurs, myosin releases the actin.This whole process, called the Sliding Filament Theory, is now able to repeat itself.
10: The stimulation stops, which causes the action potential to stop. ACh is then broken down by acetylocholi-nesterase.
11: The Sodium Potassium pump repolarizes the ions, where it puts them back into regular position. Calcium is then reabsorbed by the sarcoplasmic reticulum. Myosin heads can no longer bind, which causes the muscle to relax.