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Skeletal muscle (commonly referred to as muscle) is one of the three types of vertebrate muscle tissue, the other being cardiac muscle and smooth muscle. They are part of the voluntary muscular system [ 1 ] and typically are attached by tendons to bones of a skeleton .
Skeletal muscles are attached to bones and arranged in opposing groups around joints. [8] Muscles are innervated, whereby nervous signals are communicated [9] by nerves, which conduct electrical currents from the central nervous system and cause the muscles to contract. [10]
In biology, a motor unit is made up of a motor neuron and all of the skeletal muscle fibers innervated by the neuron's axon terminals, including the neuromuscular junctions between the neuron and the fibres. [1] Groups of motor units often work together as a motor pool to coordinate the contractions of a single muscle.
The nerve(s) which tell the muscle to act (innervates the muscle). The term "nerve" is included for clarity. Action The movement performed by the muscle from the standard anatomical position. In other positions, other actions may be performed. Antagonist The muscle which can 'cancel' or to some degree reverse the action of the muscle.
These neurons innervate skeletal muscle fibers through the propagation of action potentials down their axons (through ventral roots and cranial nerves), and they stimulate skeletal muscle fibers at neuromuscular junctions where they synapse with the motor end plates of muscle fibers. In humans, these axons can be as long as one meter.
The muscle fibers belonging to one motor unit can be spread throughout part, or most of the entire muscle, depending on the number of fibers and size of the muscle. [2] [3] When a motor neuron is activated, all of the muscle fibers innervated by the motor neuron are stimulated and contract. The activation of one motor neuron will result in a ...
These impulses move to the neuromuscular junction (NMJ) of skeletal muscle via peripheral axons after synapsing with the lower motor neurons through the ventral horn of the spinal cord. A signal that travels to the NMJ, which innervates muscles, is produced by the release of acetylcholine by upper motor neurons.
While their cell bodies are found in the central nervous system (CNS), α motor neurons are also considered part of the somatic nervous system—a branch of the peripheral nervous system (PNS)—because their axons extend into the periphery to innervate skeletal muscles. An alpha motor neuron and the muscle fibers it innervates comprise a motor ...