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Depiction of smooth muscle contraction. Muscle contraction is the activation of tension -generating sites within muscle cells. [ 1][ 2] In physiology, muscle contraction does not necessarily mean muscle shortening because muscle tension can be produced without changes in muscle length, such as when holding something heavy in the same position. [ 1]
Sliding filament theory: A sarcomere in relaxed (above) and contracted (below) positions. The sliding filament theory explains the mechanism of muscle contraction based on muscle proteins that slide past each other to generate movement. [ 1] According to the sliding filament theory, the myosin ( thick filaments) of muscle fibers slide past the ...
Neuromuscular junction. A neuromuscular junction (or myoneural junction) is a chemical synapse between a motor neuron and a muscle fiber. [ 1] It allows the motor neuron to transmit a signal to the muscle fiber, causing muscle contraction . Muscles require innervation to function—and even just to maintain muscle tone, avoiding atrophy.
The stretch reflex ( myotatic reflex ), or more accurately "muscle stretch reflex", is a muscle contraction in response to stretching a muscle. The function of the reflex is generally thought to be maintaining the muscle at a constant length but the response is often coordinated across multiple muscles and even joints. [ 1]
Smooth muscle cells. A smooth-muscle cell is a spindle-shaped myocyte with a wide middle and tapering ends, and a single nucleus. Like striated muscle, smooth muscle can tense and relax. In the relaxed state, each cell is 30–200 micrometers in length, some thousands of times shorter than a skeletal muscle cell. [ 1]
A main component in the cytoskeleton that helps show the true function of this muscle contraction is the microfilament. Microfilaments are composed of the most abundant cellular protein known as actin. [10] During contraction of a muscle, within each muscle cell, myosin molecular motors collectively exert forces on parallel actin filaments.
Electrical muscle stimulation. Electrical muscle stimulation ( EMS ), also known as neuromuscular electrical stimulation ( NMES) or electromyostimulation, is the elicitation of muscle contraction using electric impulses. EMS has received an increasing amount of attention in the last few years for many reasons: it can be utilized as a strength ...
Motor unit recruitment is a measure of how many motor neurons are activated in a particular muscle, and therefore is a measure of how many muscle fibers of that muscle are activated. The higher the recruitment the stronger the muscle contraction will be. Motor units are generally recruited in order of smallest to largest (smallest motor neurons ...