the neurotransmitter that is active at the neuromuscular junction is
Neuromuscular junction Muscles require innervation to functionâ€”and even just to maintain muscle tone, avoiding atrophy. Synaptic transmission at the neuromuscular junction begins when an action potential reaches the presynaptic terminal of a motor neuron, which activates voltage-dependent calcium channels to allow calcium ions to enter the neuron. Calcium ions bind to sensor proteins (synaptotagmin) on synaptic vesicles, triggering vesicle fusion with the cell membrane and subsequent neurotransmitter release from the motor neuron into the synaptic cleft. In vertebrates, motor neurons release acetylcholine (ACh), a small molecule neurotransmitter, which diffuses across the synaptic cleft and binds to nicotinic acetylcholine receptors (nAChRs) on the cell membrane of the muscle fiber, also known as the sarcolemma. nAChRs are ionotropic receptors, meaning they serve as ligand-gated ion channels. The binding of ACh to the receptor can depolarize the muscle fiber, causing a cascade that eventually results in muscle contraction.
Neuromuscular junction 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.[3] Not all species use a cholinergic neuromuscular junction; e.g. crayfish and fruit flies have a glutamatergic neuromuscular junction.[2]
Acetylcholine When a motor neuron generates an action potential, it travels rapidly along the nerve until it reaches the neuromuscular junction, where it initiates an electrochemical process that causes acetylcholine to be released into the space between the presynaptic terminal and the muscle fiber. The acetylcholine molecules then bind to nicotinic ion-channel receptors on the muscle cell membrane, causing the ion channels to open. Calcium ions then flow into the muscle cell, initiating a sequence of steps that finally produce muscle contraction.
Small intestine Food from the stomach is allowed into the duodenum through the pylorus by a muscle called the pyloric sphincter.