Activation of muscles Flashcards
Mo3, Ch 6, Ln 4.
How are muscles activated?
A motor neuron generates an impulse, known as an action potential, all the muscle fibers it innervates are simultaneously activated and generate force.
How is the level of control a muscle has influenced?
By the number of muscle fibers within each motor unit.
eg. muscles that require precise movements, such as the muscles controlling the eyes, may have motor units with as few as one muscle fiber per motor neuron. This small number of fibers allows for fine control and precise movement of the eyeball.
In contrast, a muscle group like the quadriceps, which is responsible for moving the leg and does not require such precise control, may have several hundred muscle fibers innervated by a single motor neuron.
How does the action potential cause the muscle fibers to contract?
It cannot directly cause muscle fibers to contract, instead, the motor neuron excites the muscle fibers it innervates through chemical transmission.
How does the chemical transmission occur?
When the action potential reaches the nerve terminal, it triggers the release of a neurotransmitter called acetylcholine. Acetylcholine then diffuses across the neuromuscular junction and excites the sarcolemma (the muscle fiber’s membrane).
If a sufficient amount of acetylcholine is released, it generates an action potential along the sarcolemma, leading to muscle contraction.
Notably, all the muscle fibers within a motor unit contract and generate force simultaneously: there is no partial activation within a motor unit.
What principle governs the activation of muscles?
the all-or-nothing principle, meaning that a motor neuron stimulus will cause all the fibers it innervates to contract fully, and a stronger action potential will not produce a stronger contraction.
