What is the chemical substance that is released in the synapse?

Question

At the end of a neuron, there is a bit gap between Axon ending and the dendrites of the other neuron. This place is called synapse. Here, the electrical impulse are transmitted to other neuron by means of chemical signal. I want to know, what actually the chemical is and how does it carry the information.

Answer 1

acetylcholine

The release of a neurotransmitter is triggered by the arrival of a nerve impulse (or action potential) and occurs through an unusually rapid process of cellular secretion, also known as exocytosis: Within the presynaptic nerve terminal, vesicles containing neurotransmitter sit "docked" and ready at the synaptic membrane. The arriving action potential produces an influx of calcium ions through voltage-dependent, calcium-selective ion channels at the down stroke of the action potential (tail current). Calcium ions then trigger a biochemical cascade which results in vesicles fusing with the presynaptic membrane and releasing their contents to the synaptic cleft within 180µsec of calcium entry. Vesicle fusion is driven by the action of a set of proteins in the presynaptic terminal known as SNAREs. The membrane added by this fusion is later retrieved by endocytosis and recycled for the formation of fresh neurotransmitter-filled vesicles.

Receptors on the opposite side of the synaptic gap bind neurotransmitter molecules and respond by opening nearby ion channels in the postsynaptic cell membrane, causing ions to rush in or out and changing the local transmembrane potential of the cell. The resulting change in voltage is called a postsynaptic potential. In general, the result is excitatory, in the case of depolarizing currents, or inhibitory in the case of hyperpolarizing currents. Whether a synapse is excitatory or inhibitory depends on what type(s) of ion channel conduct the postsynaptic current display(s), which in turn is a function of the type of receptors and neurotransmitter employed at the synapse.

The signal is terminated by either breakdown of neurotransmitters, or reuptake, the latter is mainly in the presynaptic neuron to avail recycling of the transmitter.