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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. [2] Muscles require innervation to function—and even just to maintain muscle tone, avoiding atrophy.
The neuromuscular junction is the synapse that is formed between an alpha motor neuron (α-MN) and the skeletal muscle fiber. In order for a muscle to contract, an action potential is first propagated down a nerve until it reaches the axon terminal of the motor neuron.
In some invertebrates, glutamate is the main excitatory transmitter at the neuromuscular junction. [3] [4] In the neuromuscular junction of vertebrates, EPP (end-plate potentials) are mediated by the neurotransmitter acetylcholine, which (along with glutamate) is one of the primary transmitters in the central nervous system of invertebrates. [5]
Ions can create excitatory or inhibitory potentials due to their unique reversal potentials and the membrane's permeability to each ion. The Nernst equation and Goldman equation can calculate membrane potential differences based on ion concentration, offering predictions into how ions can affect postsynaptic potentials. [3]
The neuromuscular junction (NMJ) is the most well-characterized synapse in that it provides a simple and accessible structure that allows for easy manipulation and observation. The synapse itself is composed of three cells: the motor neuron , the myofiber , and the Schwann cell .
The adult human brain is estimated to contain from 10 14 to 5 × 10 14 (100–500 trillion) synapses. [1] Every cubic millimeter of cerebral cortex contains roughly a billion (short scale, i.e. 10 9) of them. [2] The number of synapses in the human cerebral cortex has separately been estimated at 0.15 quadrillion (150 trillion) [3]
Depolarizing neuromuscular blockers: Depolarizing neuromuscular blockers directly bind to postsynaptic cholinergic receptors of the neuromuscular junction to generate a sustained action potential. This causes prolonged stimulation and desensitization of neuroreceptors, causing skeletal muscle relaxation effects such as paralysis. [ 1 ]
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.