In: Anatomy and Physiology
Describe the process of skeletal muscle contraction starting from an action potential being sent down a motor neuron to the contraction of the sarcomere.
When the action potential reaches the axonic terminal, it causes opening of voltage gated calcium channels in the presynaptic membrane resulting in influx of calcium.
This calcium then binds to the presynaptic vesicles containing the neurotransmitter and causes their fusion with the presynaptic membrane resulting in their exocytosis.
In this way neurotransmitter are released into the synapse.
- Somatic neurons release Ach which binds to nicotinic Ach receptors on postsynaptic cell
- Action potential is produced in the postsynaptic cell and conducted along the sarcolemma to open voltage gated Ca2+ channels in the T-tubules
- Ca2+ release channels in sarcoplasmic reticulum are opened
- Ca2+ concentration in sarcoplasm increases
- Ca2+ binds to troponin and tropomyosin is removed from the binding site on the actin
- Myosin binds to actin
- The cross bridge undergoes a power stroke and ADP is released. This is called sarcomere contraction
- Phosphate is released causing a conformation change in myosin
- ATP binds to the myosin head unbinding myosin and actin
- A new ATP is hydrolyzed and the remaining ADP and P are bound to the myosin head in a cocked position ready to cycle again