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Electrically excitable nerve elements: excitation sites in peripheral and central stimulation
Published in Hans O Lüders, Deep Brain Stimulation and Epilepsy, 2020
In this chapter the focus was on the direct effects of stimulation within the central nervous system. However, several other factors should be considered when designing therapies or interpreting results of CNS stimulation. First, the threshold for activation of presynaptic terminals projecting into the region of stimulation is often less than or equal to the threshold for direct excitation of local cells.21,22,25,26 Thus, indirect effects mediated by synaptic transmission may alter the direct effects of stimulation on the postsynaptic cell.21 Further, antidromic activation of axon terminals can lead to widespread activation or inhibition of targets distant from the site of stimulation through axon collaterals. Second, synapses may have activity-dependent transmission properties (i.e. synaptic depression) that influence the downstream effects of local stimulation.28,29 Finally, stimulation may cause activity-dependent changes in the local ionic milieu that can modulate neuronal excitability.30 These ‘indirect’ effects of stimulation must be considered when electrodes are placed within the heterogeneous environment of the CNS.
Biological Basis of Behavior
Published in Mohamed Ahmed Abd El-Hay, Understanding Psychology for Medicine and Nursing, 2019
Operation of the nervous system is achieved through electrochemical processes. Within each neuron, when a signal is received by the dendrites, it is transmitted to the soma in the form of an electrical signal, and, if the signal is strong enough, it may then be passed on to the axon and then to the terminal buttons. If the signal reaches the terminal buttons, it triggers the release of chemical substances called “neurotransmitters” into the synapse. The binding of the neurotransmitter to the receptor molecules on the membrane of the postsynaptic cell gives rise, in turn, to a new class of signals called synaptic potentials. Thus, whereas the action potential is a purely electrical signal, the synaptic potential is an electrical signal initiated by a chemical one. The neurotransmitters fit into receptors on the receiving dendrites in a lock and key manner. More than 100 chemical substances produced in the body have been identified as neurotransmitters, and these substances have a wide and profound effect on emotion, cognition, behavior, appetite, memory, as well as muscle action and movement. Neurotransmitters range from small molecules such as acetylcholine, noradrenaline, and serotonin to much larger molecules such as peptides.
The Chemistry of the Brain
Published in Gail S. Anderson, Biological Influences on Criminal Behavior, 2019
Neurons (or nerve cells) are specialized cells in the nervous system that transmit signals from one part of the body to another and instruct the body on how to act. For a greatly simplified example, imagine nerve cells sending signals through the neural systems to the hand to pick up a fork, use it to pick up a piece of broccoli, and then move the hand up to the mouth to deposit the food therein. Other signals tell the mouth to close the lips, so the food will not fall out, and signals are sent to the mouth to chew, to the glands in the mouth to start secreting digestive enzymes, and so on. This is greatly simplified but gives an idea of the messages going through your body in nanoseconds. There are many other kinds of nerve cells that we do not need to go into here, but it is essential to learn a little more about how nerve cells communicate. The communications take place between junctions called synapses. Figure 9.1 shows two nerve cells communicating. The cell sending the message uses the axon’s synaptic terminals, and the dendrites of the receiving cell receive the message. The transmitting cell is called the presynaptic cell (Figure 9.1), and the cell receiving the signal is called the postsynaptic cell (inset). There are two main types of synapses: (1) electrical synapses, which conduct electrical signals, and (2) chemical synapses, which conduct chemical signals. It is the chemical ones in which we are interested.
Modulation of neuromuscular synapses and contraction in Drosophila 3rd instar larvae
Published in Journal of Neurogenetics, 2018
Kiel G. Ormerod, JaeHwan Jung, A. Joffre Mercier
The activation or inhibition of any neural pathway, ultimately depends on communication at chemical synapses, where neurotransmitters are released from presynaptic terminals, bind to receptors in the postsynaptic membrane (Figure 1) and alter electrical activity of the postsynaptic cell. ‘Classical’ neurotransmitters, such as acetylcholine, GABA and glutamate, bind to ionotropic receptors, chemically gated ion channels that directly alter the cell’s transmembrane potential. Other chemical signals, notably biogenic amines and neuropeptides, bind to metabotropic receptors that alter activity indirectly, typically through second messenger systems. Peptides and biogenic amines can be released as co-transmitters from presynaptic terminals to alter the effectiveness of ionotropic receptor activation (e.g. Adams & O’Shea, 1983; Fung et al., 1994; Nusbaum, Blitz, Swensen, Wood, & Marder, 2001), or they can be secreted by neuroendocrine cells and carried through the circulation to synapses, where they can alter transmitter release, postsynaptic responsiveness or both (e.g. Christie, Stemmler, & Dickinson, 2010; Ewer, 2005; Kravitz et al., 1980). These effects, which alter the efficacy of synaptic transmission, are referred to as ‘modulation’, and the signaling molecules that elicit them are often referred to as ‘modulators’ or ‘neuromodulators’. Thus, the ‘classical’ view of chemical synaptic transmission, in which a neurotransmitter acts directly to either depolarize or hyperpolarize a postsynaptic cell, represents only one component of synaptic communication; intercellular signaling in vivo involves many more components.
Molecular mechanisms that change synapse number
Published in Journal of Neurogenetics, 2018
Alicia Mansilla, Sheila Jordán-Álvarez, Elena Santana, Patricia Jarabo, Sergio Casas-Tintó, Alberto Ferrús
Pre- and postsynaptic specializations compose a full synapse. Since both components need to be properly localized in register for normal function, coordinated signalling to control the dynamics of their proteins assembly must be at work. Genetic driving of PI3K in fly motor neurons, even late in development, elicits the clustering of postsynaptic densities and GluRII receptors. Overexpressing PI3K selectively in the muscle target cell, however, does not elicit an equivalent reaction by the genetically normal motor neuron. This is yet another demonstration that the presynaptic cell has the capacity to induce a response of the postsynaptic cell to complete a full synapse (Jordan-Alvarez et al., 2012).
Functional role of ascorbic acid in the central nervous system: a focus on neurogenic and synaptogenic processes
Published in Nutritional Neuroscience, 2022
Morgana Moretti, Ana Lúcia S. Rodrigues
Synapses are specialized intercellular junctions for information transfer from a presynaptic neuron to a postsynaptic cell. Alterations in synapse structure and function are important for learning and memory [51], while abnormal synaptic development is implicated in several diseases, including mood disorders and neurodegenerative diseases [52]. Compounds that can rearrange aberrant concentrations of neurotransmitters in the synaptic clefts or have the ability to reshape neuronal circuits by enhancing synaptogenesis or promoting synaptic stabilization in specific regions of the brain could be of great value for the management of various diseases associated with synaptic dysfunction [53].