1
The electrical signal comes from the brain, travels down the axon to the synaptic knob opening voltage- gated calcium channels
2
Calcium diffuses into synaptic knob forcing acetylcholine (Ach) filled vesicles to move down to bottom of synaptic knob
3
Vesicles release Ach into the synaptic cleft via exocytosis.
Ach binds to the Ach receptors on
the motor endplate.
4
Ach opens the Ach receptors allowing sodium to diffuse into the cell and potassium to diffuse out generating an end plate potential at motor endplate.
5
The resulting action potential travels along sarcolemma opening additional voltage gated sodium and potassium channels
1-5
excitation
6
The electrical signal travels down into the transverse tubules (T-tubule)
7
Signals open voltage gated calcium channels on the terminal cisterna allowing calcium to diffuse into the myofilaments
8
Calcium binds to troponin causing tropomyosin to rotate medial (toward the middle)
9
Myosin binding sites are exposed on the actin filament
10
Myosin ATPase hydrolyzes (breaks) an ATP molecule and cocks the myosin head back (using an
ATP molecule).
11
The myosin-actin cross- bridge forms
6-11
Excitation Contraction coupling
12
Power stroke occurs pulling the actin filament over top of the myosin filament; the muscle shortens
13
An additional ATP binds, breaking the crossbridge
12-13
contraction
14
Nervous stimulation stops and Ach released.
15
Acetylcholinesterase removes Ach from receptors and the synaptic cleft.
16
Calcium is pumped back into the terminal cisterna using active transport (requires ATP)
17
Loss of calcium ion from troponin
18
Tropomyosin covers the actin binding site returning the muscle to its resting length
14-18
relaxation
