10 Steps Of Muscle Contraction

Question: Step 1 - Nerve Impulse reaches Neuromuscular Junction

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

Question: Step 2 - Acetylcholine (ACH) Released by Motor Neuron

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

Question: Step 3 - ACH binds to Muscle Receptor Sites

Answer: ACH (key) binds to receptors on the muscle cell

Question: Step 4 - Sodium Channels in muscle OPEN

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

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

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

Question: Step 6 - Action Potential charge travels down muscle cell

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

Question: Step 7 - Release of Ca+ into cell

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

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

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

Question: Step 9- CONTRACTION

Myosin & Actin move, Sacromere shortens

Answer: Myosin heads “pull” Actin filaments toward center, allowing filaments to slide past each other in opposite directions, shortens sacromere

Question: Step 10 - RELAXATION

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