The neuron thrives in a fluid environment, extracellular fluid around it and intracellular fluid, cytoplasm, within it. Neuronal membranes play a crucial function in separating the two fluids as the signal that travels through the neuron requires them to be electrically distinct. The differential powers and movement in energy across the membrane, are known as the membrane potential. Neurons are the primary cell populations in the brain that process information, learn, remember, and make decisions. The synapse is when two neurons communicate with one another. The neurons communicate as follows; the presynaptic neuron discharges neurotransmitters into the synaptic cleft in a chemical synapse. Zareh et al. (2019) add that chemical synapses, as opposed to electrical synapses, are the most prevalent synapses in the brain, offering gain control and directionality. Subsequently, Zareh et al. (2019) emphasize that the neurotransmitters attach themselves to receptors on the postsynaptic neuron. As a result, they prompt the ion channels to open and stimulate the postsynaptic neuron.
Within a neuron specifically in the axon to the dendrite end, a wave is transmitted via a transient recurrence of the relatively static membrane potential known as action potential (Zareh et al., 2019). As such, nerve impulses or spikes must move through the axon to arrive at the synaptic terminal. Once at the synaptic terminal, the neurotransmitter starts to relay information to other neurons. The thickness of a synaptic terminal and its resilience to divulge determines the rate with which an action potential is transmitted.
The processes of the development of an action potential can be summarized as follows: First, the target cell depolarizes toward the threshold potential in response to a spur from a nerve cell together with other neurons. Second, when the stimulation threshold is exceeded, all sodium ion channels are free, depolarizing the membrane. Furthermore, the potassium ion channels continue to open during the maximum nerve spikes, and the potassium ions commence to escape the cell. Thus, the sodium ion channels shut at the exact moment. The membrane gets hyperpolarized as the potassium ions continue to leave the cell. As K+ ions continue to exit the cell, the membrane becomes hyperpolarized. The membrane is hyperpolarized and is therefore unable to fire a signal. Finally, the transporter of sodium and potassium ions restores the resting voltage potential by closing the potassium channels.
The activation of neurotransmitters is required for connection at chemical synapses. Wang et al. (2016) further elaborate that chemical synaptic transmissions carry nerve impulses in a manner that is dependent on chemical messengers generated by activating presynaptic neurons that spread across the synaptic cleft. Neurotransmitters are discharged into the synaptic gap, the extracellular area engulfed by the postsynaptic and presynaptic membranes when the presynaptic membranes fuse with a vesicle. When neurotransmitters reach the membrane of the postsynaptic cells and engage with certain receptors, the firing activity of a postsynaptic neuron is altered (Wang et al., 2016). As a result of their molecular architectures and the physical placements of the tree branches, also known as dendrites, upon which they dwell, chemical synaptic transmissions can modify and convey neural information more efficiently.
The calcium ions channel, which allows or prevents the passage of the electrical stimulus in and out of a cell membrane, opens whenever the presynaptic membrane is depolarized. The calcium ions are allowed entry into the cell for the postsynaptic neuron to receive the chemical synapse obtained from the action potential. Calcium entry causes synaptic vesicles to bind to the membrane and discharges chemical transmitter particles into the synapse gap. The chemical messenger spreads across the synapse gap and attaches the ionotropic receptors to the postsynaptic membrane. As a result, the postsynaptic neuron depolarizes or hyperpolarizes locally.
References
Wang, R., Li, J., Du, M., Lei, J., & Wu, Y. (2016). Transition of spatiotemporal patterns in neuronal networks with chemical synapses. Communications in Nonlinear Science and Numerical Simulation, 40, 80-88. Web.
Zareh, M., Manshaei, M. H., Adibi, M., & Montazeri, M. A. (2019). Neurons and astrocytes interaction in neuronal network: A game-theoretic approach. Journal of Theoretical Biology, 470, 76-89. Web.