muscle contraction steps Flashcards
Excitation step 1
nerve signal arrives at the synaptic knob
Excitation step 2
Calcium stimulates vesicles to release ACh via excytosis
Excitation step 3
ACh binds to ACh receptors on sarcolemma
Excitation step 4
Receptors open, Na+ to quickly flow into the cell and K+ to flow out. Forms an End Plate Potential (EPP) rapid change in polarity at the motor end plate
Excitation step 5
Action potential created, muscle is now excited
Excitation-Contraction Coupling step 1
Wave of action potential spread down into cell interior via T-Tubules
Excitation-Contraction Coupling step 2
Action potential in the terminal cisternae, causes SR to diffuse Ca+ into the cytosol
Excitation-Contraction Coupling step 3
Calcium binds to troponin
Excitation-Contraction Coupling step 4
Troponin-Tropomyosin complex exposes active site on actin
Contraction step 1
Myosin must have ATP bound to is. Myosin ATPase hydrolyzes this ATP to ADP and phosphate. Activates head into high energy position (extended)
Contraction step 2
Extended myosin binds to active site on actin forming a cross bridge
Contraction step 3
Myosin released ADP and phosphate, flexes into bent (low energy) position, tugging thin filament along with it, called the power stroke
Contraction step 4
ATP binds to myosin and destabilizes myosin/actin bond breaking cross bridge. Myosin repeats the whole process, and performs recovery stroke (myosin attaches to new actin site further down thin filament.)
Relaxation step 1
Nerve signals stop arriving at neuromuscular junction
Relaxation step 2
ACh dissociated from receptors, AChE breaks it down into fragments
