Chemical Synapse Essay

At a chemical synapse, an electrical signal (AP) is transformed into a chemical signal (neurotransmitter) and thereafter is (re)turned back into an electrical one (AP). Thus the signal can move across the synaptic cleft via or as a neurotransmitter before it is turned back into an electrical signal (AP) at the receptor cell. This conversion process not only assures the inter-neural conduction of signals, but also their modulation (change). Depending on what kind of neurotransmitter is released and then docks at its postsynaptic receptors, either an excitation or an inhibition will be produced. An inhibition results in a hyperpolarization. The receptor cell’s inner turns even more negative. This, in turn, minimizes the chance of another AP.

So then, what happens

A synapse consists of 2 parts: the axon terminals or axonal boutons of the presynaptic neuron or “sending” cell and the axon endings of the “receiving” cell, the postsynaptic neuron. Both parts are divided by the synaptic cleft. Unlike the axon itself, the presynaptic neuron does not possess Na/K channels. Instead, it is equipped with voltage-gated calcium channels and small vesicles that contain a neurotransmitter. The membrane of the postsynaptic neuron contains receptors that enable the neurotransmitter to dock (lock & key principle). These receptors are directly connected to an ion channel. In the case of an excitatory chemical synapse, this postsynaptic ion channel will be a Na/K ion channel. In the absence of the neurotransmitter, these channels are closed. When an AP reaches the presynaptic neuron, the voltage-gated calcium channels open and C++ flows into the cell. C++ binds to the vesicles containing the neurotransmitter and causes these to move toward the presynaptic membrane where the vesicles release the neurotransmitter into the synaptic cleft (exocytosis). The neurotransmitter