What causes muscles to contract

Excitation contraction coupling is the

Sequence of events that converts an action potential to a muscle contraction

As the action potential reaches the end of the axon

Voltage gated calcium channels open and calcium enters the synaptic bulb

If the threshold voltage is reached

Voltage gated sodium channels initiate the action potential that travels down the T tubules and triggers the release of calcium ions from the sarcoplasmic reticulum

Skeletal muscle contracts

Voluntarily

Eventually the acetylcholine will be removed from the synaptic cleft and when this occurs calcium will be

Transported back to the sarcoplasmic reticulum via active transport and tropomyosin will once again block the music binding sites and the cross bridges will detach

1st step of muscle contraction

A motor neuron sends an electrical signal

Calcium causes the vesicles in the motor neuron containing neurotransmitter called acetylcholine to

Fuse with the presynaptic membrane causing the release of ACh into the synaptic cleft of the neuromuscular junction via exocytosis

The acetylcholine molecules bind to

Ligand gated channels on the motor end plate allowing sodium to enter the muscle which triggers a strong excitatory postsynaptic potential along the membrane

Calcium then binds to troponin and initiates a muscle contraction

The signal to contract is an action potential because muscle cells are big and the signal has to move quickly

T tubules help bring the action potential from the

Outside of the muscle cell to the myofibrils that lie deep inside the muscle cell and that the sarcoplasmic reticulum surrounding the myofibrils realeases calcium to initiate a muscle contraction

The contractor unit of skeletal muscle is

Sarcomere