10 steps of Muscle Contraction

step 5

Na+ rush creates an electrical current: action potential

step 6

electrical current travels all over the muscle cell and down T-tubule

step 2

motoneuron releases acetylcholine (Ach) which is a neurotransmitter

step 4

muscle cell membrane is permeable to Na+ at that moment only

step 1

signal from motoneuron gets to synapse

step 7 (now inside the muscle instead of at motor neuron)

the action potential causes Ca2+ from the sarcoplasmic reticulum to be released into the cell

step 9 (contraction)

the myosin heads immediately "pull" on the actin causing the muscle fiber to shorten, needs ATP to detach myosin from actin

step 10

when action potential ends, Ca2+ is reabsorbed and everything goes back to its original state and the muscle relaxes

step 8

Ca2+ ions allow the myosin heads to fit onto the actin

step 3

Ach meets its receptor on the muscle cell