10 Steps of Muscle Contraction

Step 1 - Nerve Impulse reaches Neuromuscular Junction

Nerve signal from brain arrives at neuromuscular junction & axon terminal of motor neuron

Step 2 - Acetylcholine (ACH) Released by Motor Neuron

Motor neuron releases neurotransmitter Acetylcholine (Ach) into synaptic gap between nerve & muscle cells

Step 3 - ACH binds to Muscle Receptor Sites

ACH (key) binds to receptors on the muscle cell

Step 4 - Sodium Channels in muscle OPEN

Receptors stimulated by ACH allow sodium (Na+) channels in muscle cell to open

Step 5 - Na+ Ion rush causes change in cell charge

Na+ influx into muscle cell causes polarity change, creates electrical current called an Action Potential

Step 6 - Action Potential charge travels down muscle cell

Action Potential impulse travels down the sarcolemma membrane and all over the muscle cell

Step 7 - Release of Ca+ into cell

Action potenial impulse causes the sarcoplasmic reticulum web to release stored Ca++ into the cell and around sarcomere contraction units

Step 8 - Ca+ influx causes Myosin & Actin to bind

Inside sarcomeres, Ca++ ions allow myosin heads to fit onto actin filaments

Step 9- CONTRACTION

Myosin & Actin move, Sacromere shortens

Myosin heads "pull" Actin filaments toward center, allowing filaments to slide past each other in opposite directions, shortens sacromere

Step 10 - RELAXATION

When action potential ends, Ca++ is reabsorbed by sacroplasmic reticulum, myosin & actin return to orginal position, and muscle relaxes