Muscle Physiology
The muscular system is an organ system composed of the muscle tissue. There are three types of muscle tissue:
- Cardiac muscle, which comprises the myocardium of the heart
- Smooth muscle, which is found in the walls of the hollow organs and blood vessels
- Skeletal muscle, which composes the skeletal muscles
All three types share a characteristic in common - the ability to contract. Only skeletal muscles contract voluntarily, enabling us to move the parts of our body. Cardiac and smooth muscles contract involuntarily, as they are under control of the autonomic nervous system.
Muscle physiology is a branch of physiology that studies the mechanism behind muscle contraction.
Muscle contraction is shortening of the muscle fibers initiated by action potentials in motor neurons which cause the release of neurotransmitters from synaptic vesicles.
Put simply, the neuronal stimulus (action potential) causes the neuron to release a chemical messenger (neurotransmitter) which excites the membrane of the muscle cell and causes it to contract.
On the molecular level, the contraction is a result of an interaction cascade between myosin and actin filaments inside a muscle fiber (muscle cell).
When enough skeletal muscle cells are excited and contract, that translates into a movement.
Learn the anatomy and functions of muscle fibers and their contraction with the interactive animations and diagrams in the topics below.
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Skeletal muscle contraction physiology
In skeletal muscle fibers, electrochemical activity triggers myofilament movement. These linked events are referred to as excitation-contraction coupling.
Excitation-Contraction Coupling
As the action potentials travel down the T tubules, calcium channels in the nearby terminal cisternae of SR open, and Ca2+ ions diffuse into the surrounding sarcoplasm. The Ca2+ ions bind to troponin proteins embedded along the thin filaments and the contraction process begins.
Acetylcholine Receptors in Muscle Fiber (Cells)
ACh receptors are embedded in the sarcolemma at the neuromuscular junction. This is the neurotransmitter that is released by the terminal branches of a motor neuron.