# data[].attributes.body
Step 4: Cocking of Myosin Head - Using energy from the hydrolysis of the ATP, the myosin head “cocks” back into its high energy state. The energy will be used for the power stroke in the next cycle.

# data[].attributes.body
Step 3: Cross Bridge Detachment - ATP attaches to the myosin head. This causes the cross bridge to detach.

# data[].attributes.body
Step 2: Working (Power) Stroke - The myosin head pivots and pulls the actin filament toward the M line.

# data[].attributes.body
Step 1: Cross Bridge Formation - The myosin head, which has high energy, attaches to actin myofilaments to form a cross bridge.

# data[].attributes.body
Steps 3 and 4: The Ca2+ combines with troponin, the protein located on actin, and changes the shape of the actin. This exposes the myosin binding sites, removing the blocking action of the protein tropomyosin. The myosin binds to the actin on the binding sites, beginning contraction.

# data[].attributes.body
Step 2: As a result of the transmission of the action potential, the sarcoplasmic reticulum releases Ca2+ into the cytosol.

# data[].attributes.body
Step 1: The action potential moves down the sarcolemma and the T tubules.

# data[].attributes.body
The sarcolemma is experiencing resting membrane potential. When an action potential arrives at the axon terminal, voltage gated calcium ion channels open, allowing calcium ions to enter the neuron. The increase in calcium ions stimulates the release of acetylcholine, or ACh. The ACh goes into the cleft and binds to ACh receptor sites, activating voltage-gated Na+ ion channels. This begins the process of depolarization, in which the channels pump in Na+ ions. Depolarization causes more sodium channels to open, which eventually initiates the propagation of the action potential down the sarcolemma. This begins the process of repolarization, in which the concentration of sodium as a result of depolarization opens up voltage-gated K+ ion channels, causing K+ ions to diffuse out of the cell. This restores the resting membrane potential.