<Li> Ligand (such as acetylcholine) </Li> <P> Acetylcholine is a neurotransmitter synthesized from dietary choline and acetyl - CoA (ACoA), and is involved in the stimulation of muscle tissue in vertebrates as well as in some invertebrate animals . In vertebrate animals, the acetylcholine receptor subtype that is found at the neuromuscular junction of skeletal muscles is the nicotinic acetylcholine receptor (nAChR), which is a ligand - gated ion channel . Each subunit of this receptor has a characteristic "cys - loop", which is composed of a cysteine residue followed by 13 amino acid residues and another cysteine residue . The two cysteine residues form a disulfide linkage which results in the "cys - loop" receptor that is capable of binding acetylcholine and other ligands . These cys - loop receptors are found only in eukaryotes, but prokaryotes possess ACh receptors with similar properties . Not all species use a cholinergic neuromuscular junction; e.g. crayfish and fruit flies have a glutamatergic neuromuscular junction . </P> <P> AChRs at the skeletal neuromuscular junction form heteropentamers composed of two α, one β, one ɛ, and one δ subunits . When a single ACh ligand binds to one of the α subunits of the ACh receptor it induces a conformational change at the interface with the second AChR α subunit . This conformational change results in the increased affinity of the second α subunit for a second ACh ligand . AChRs therefore exhibit a sigmoidal dissociation curve due to this cooperative binding . The presence of the inactive, intermediate receptor structure with a single - bound ligand keeps ACh in the synapse that might otherwise be lost by cholinesterase hydrolysis or diffusion . The persistence of these ACh ligands in the synapse can cause a prolonged post-synaptic response . </P> <P> The development of the neuromuscular junction requires signaling from both the motor neuron's terminal and the muscle cell's central region . During development, muscle cells produce acetylcholine receptors (AChRs) and express them in the central regions in a process called prepatterning . Agrin, a heparin proteoglycan, and MuSK kinase are thought to help stabilize the accumulation of AChR in the central regions of the myocyte . MuSK is a receptor tyrosine kinase--meaning that it induces cellular signaling by binding phosphate molecules to self regions like tyrosines, and to other targets in the cytoplasm . Upon activation by its ligand agrin, MuSK signals via two proteins called "Dok - 7" and "rapsyn", to induce "clustering" of acetylcholine receptors . ACh release by developing motor neurons produces postsynaptic potentials in the muscle cell that positively reinforces the localization and stabilization of the developing neuromuscular junction . </P>

Difference between neuromuscular junction and motor end plate