500
Create a bullet point list of the steps of muscle contraction, and how muscle contraction stops, once the electrical signal has reached the motor end plate. Minimum 6 steps.
■ The signal travels through the muscle fibers stimulating the sarcoplasmic reticulum where it releases calcium (Ca2+)
■ Calcium binds to troponin on the tropomyosin which
causes it to move and reveal the mysosin binding sites on
the actin. ATP on the Myosin head is hydrolysed to form
ADP + Phosphate
■ Cross bridge formed - myosin heads are shaped like little
golf clubs and it is the ends of the heads that attach to
the actin. Myosin head remains bound until ATP
molecule releases it. As long as there is calcium available
cross bridge formation will continue until maximum
contraction of the muscle fiber is reached.
■ The motor neuron initiates a resting potential through repolarization. Cholinesterase, an enzyme that breaks down acetylcoline, is released and cause the muscle cell to
repolarize and relax.
■ Calcium ions are removed from the cell and returned to the sarcosplasmic reticulum via the calcium pump
■ Cross bridge formation is terminated as there is no calcium which means the myosin binding sites on the actin filament are covered by tropomyosin. Myosin heads to a
resting state.