Contraction of Skeletal Muscle

Resistance

passive force that opposes resistence

The order of events in muscle contraction is:

1. Activation by neurons

2. Action potential in sarcolemma and T tubules

3. Release of calcium from SR

4. filament sliding

Neuromuscular junctions (NMJs)

where motor neurons communicate with skeletal muscle fibers

synaptic terminals

contains vesicles of acetylcholine which tells muscle fiber to contract

synaptic cleft

gap that separates the synaptic terminal and motor end plate of fiber; contains acetylcholinesterase

Transmission of action potentials at NMJ

1. Action potentials cause Ca to enter synaptic terminal which triggers the release of ACh

2. ACh diffuses across synaptic cleft and binds to receptors at motor end plate

3. This causes sodium ion channels to open and triggers another action potenti

Acetylcholinesterase

breaks down ACh so muscle doesn’t contract forever

The steps of the contraction cycle:

1. ATP hydrolysis and formation of crossbridge

2. power stroke (myosin heads release ADP and phosphate, then pivot)

3. binding to new ATP and detachment of cross bridges

isometric contration

when you are working against an immovable force

The duration of muscle contraction is controlled by:

the duration of stimulation at NMJ and the availability of free Ca and ATP

Events which end a contraction:

1. ACh is broken down

2. Ca is pumped back to SR

3. troponin releases calcium and tropomyosin recovers active sites

4. all cross bridges are disrupted

Passive relaxation

filaments don’t always slide back after contraction on there own