muscle contraction

a shortening of the muscle fibers in response to electrical stimulation from a motor neuron by which a muscle exerts force on the tissues to which it is attached. This stimulation initiates an electrochemical sequence in which myosin filaments, powered by ATP (adenosine triphosphate), detach from a nearby actin filament, swing forward to reattach further along the actin filament, and then swing back causing the actin and myosin filaments to slide in opposite directions. When this process is repeated in many muscle fibers, the overall muscle becomes shorter but thicker. See isometric contraction; isotonic contraction.

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Psychology term of the day

September 8th 2024

NMDA receptor

a type of glutamate receptor that binds NMDA as well as glutamate. NMDA receptors are coupled to ligand-gated ion channels and are also voltage-sensitive, which enables them to participate in a variety of information-processing operations at synapses where glutamate is the neurotransmitter. The drugs of abuse ketamine and PCP are antagonists at NMDA receptors, preventing the influx of calcium ions at calcium channels, which may cause the hallucinogenic effects of these drugs. Excessive flow of calcium ions into the presynaptic neuron via the NMDA receptor is thought to contribute to glutamate toxicity. A hypothesis on the etiology of schizophrenia involves dysfunction of the NMDA glutamate receptor (see glutamate hypothesis). Compare AMPA receptor.