Skeletal Muscle Contraction

Step one

Action potential flows down axon of neuron

Step two

Motor neuron will synapse with sarcolemma of muscle fibre

Step three

Triggers vesicles containing ACh, calcium ions come into axon terminal and vesicles move down towards synapse, ACh released into synaptic cleft

Step four

ACh binds to receptors on sarcolemma and opens gated sodium channels, sodium ions enter cell and triggers action potential down length of muscle fibre

Step five

Action potential travels down t tubes and triggers sarcoplasmic reticulum to release calcium ions

Step six

Calcium binds to regulatory proteins on actin, troponin exposes active sites on actin

Step seven

Myosin binds to active sites on actin and forms cross bridges, creates contractions and therefore, movement

Step eight

Action potential stops, stops triggers and stops contractions

What energy source is required for muscle contraction

atp

How does myosin bind to actin in the presence of calcium

Tropomyosin covers active sites on actin and troponin holds tropomyosin in place, calcium binds to troponin and releases it, tropomyosin rolls off actin to expose active sites, myosin heads bind to active sites on actin

Sliding filament theory

Myosin binds to actin, pulls then releases

Myofilaments shorten, sarcomere shortens, myofibril shortens, muscle cell shortens, muscle organ shortens = contractions

Contraction cycle

Myosin head already energised by adp and p attached

Calcium ion binds to troponin, tropomyosin rolls off actin binding sites

Myosin forms cross bridges with actin

adp and p is released from myosin and myosin head moves the actin chain towards m line of sarcomere

atp attaches to myosin head and releases it from actin to expose active sites

myosin becomes reenergised by adp and p and forms another cross bridge down the actin chain