Muscle Movement

nerve impluse travels down a motor neuron axon

motor neuron terminal releases ACh (acetylcholine neurotransmitter)

ACh binds to ACh receptors on muscle fiber

sarcolemma is stimulated, muscle impulse travels surface of muscle fiber and deep into fiber through transverse tubules

*note: remember sarcomere is functional unit of skeletal mm, sarcolemma is muscle cell membrane

muscle impulse reaches sarcoplasmic reticulum and calcium channels open

Calcium ions diffuse from sarcoplasmc reticulum into sarcoplasm and bind to troponin molecules

tropomyosin molecules move and expose binding sites on actin

actin and myosin bind/link

*note: remember actin= thin filament, myosin= thick filament

thin (actin) filaments pulled toward center of sarcomere by myosin cross-bridges increasing the overlap of thick and thin filaments

muscle fiber finally contracts!

acetylocholinesterase decomposes acetylcholine (ACh), muscle fiber membrane no longer stimulated

Calcium ions actively transported into sarcoplasmic reticulum

ATP breaks linkages btw actin and myosin filaments without breakdown of ATP itself

breakdown of ATP "cocks" cross-bridges

troponin and tropomyosin molecules inhibit he interaction btw myosin and actin filaments

muscle fiber remains relaxed, ready to be stimulated