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Skeletal muscles coordinate to produce movement through the contraction and relaxation of muscle fibres, controlled by the nervous system.
Skeletal muscles are responsible for all voluntary movements in the body. They are attached to bones by tendons, and when they contract, they pull on these bones to produce movement. The coordination of these movements is a complex process that involves the nervous system, specifically the motor neurons.
Motor neurons are nerve cells that originate in the spinal cord and extend to the muscles. They transmit signals from the brain to the muscles, instructing them when to contract or relax. This communication is facilitated by neurotransmitters, chemicals that transmit signals across a synapse, the gap between the neuron and the muscle fibre.
The process begins when the brain sends a signal down the spinal cord to the motor neuron. This signal is an action potential, an electrical impulse that travels along the neuron. When the action potential reaches the end of the neuron, it triggers the release of a neurotransmitter called acetylcholine.
Acetylcholine diffuses across the synapse and binds to receptors on the muscle fibre, causing it to depolarise. This depolarisation triggers a series of events that lead to the contraction of the muscle fibre. Calcium ions are released from storage sites within the muscle fibre, and these ions bind to proteins within the muscle, causing them to change shape and pull on the muscle fibres, leading to contraction.
The muscle remains contracted until the brain sends another signal to the motor neuron to stop releasing acetylcholine. The muscle fibre then repolarises, and the calcium ions are pumped back into their storage sites, causing the muscle to relax.
In this way, the nervous system and the skeletal muscles work together to coordinate movement. The precise timing and intensity of muscle contractions are controlled by the number of motor neurons that are activated and the frequency of their action potentials. This allows for a wide range of movements, from delicate tasks like threading a needle to powerful actions like lifting a heavy weight.
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