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Introduction to botulinum toxin
Published in Michael Parker, Charlie James, Fundamentals for Cosmetic Practice, 2022
The axon is a long tubular structure which extends out of the cell body. The point of attachment to the cell body is known as the axon hillock, and it is at this point where an action potential is usually generated, a change in the polarisation of a neuron to allow propagation of a signal. The axon is surrounded by a myelin sheath which serves to insulate the axon and decrease the loss of electrical signal, similar to electrical cabling in your home. Neuronal impulses do not travel through the axon but skip along the outside of the myelin sheath between areas known as nodes of Ranvier. At the end of the axon is the axon terminal, a specialised region of finger-like projections which are in close proximity with but not touching another nerve or effector cells (such as muscle). See Figure 8.1. The point at which a neuron interacts with another cell is known as a synapse. A synapse is a gap between axon terminals and the next cell, for example a dendrite of another neuron. A synapse is broken down into the presynaptic terminal of the cell conducting an electrical signal and a postsynaptic terminal, which is the region which receives said signal. There are two main types of synapse: electrical and chemical (Figure 8.2).
Synapses
Published in Nassir H. Sabah, Neuromuscular Fundamentals, 2020
Plasticity of neuronal circuits is the alteration of the behavior of these circuits in response to experience or injury. Plasticity could result from: modification of the response of neurons to synaptic inputs (Chapter 7), such as a change in the intrinsic excitability of neurons; the addition or removal of synaptic pathways; or modification of the strength or efficacy of synapses, the latter being referred to as synaptic plasticity. In view of the complexity of the subject, however, only some basics of synaptic plasticity will be presented in this section.
Neuronal Function
Published in Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal, Principles of Physiology for the Anaesthetist, 2020
Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal
A synapse is the anatomical site (junction) where nerve cells communicate with other nerves, muscles and glands. Two types have been identified: electrical and chemical. Electrical synapses are formed by gap junctions that form low-resistance channels between the presynaptic and postsynaptic elements so that various ions can freely move between the two related neurons and mediate rapid transfer of signals that can spread through large pools of neurons. They may be found at dendrodendritic sites of contact between nerves that synchronize neuronal activity, but they are uncommon in the mammalian nervous system.
Homocysteine can aggravate depressive like behaviors in a middle cerebral artery occlusion/reperfusion rat model: a possible role for NMDARs-mediated synaptic alterations
Published in Nutritional Neuroscience, 2023
Mengying Wang, Xiaoshan Liang, Qiang Zhang, Suhui Luo, Huan Liu, Xuan Wang, Na Sai, Xumei Zhang
Synaptic plasticity specifically refers to the activity-dependent modification of the strength or efficacy of synaptic transmission at pre-existing synapses [9]. It is increasingly recognized that synaptic plasticity plays a critical role in functional recovery, such as learning and memory after stroke [10]. The absence of synaptic changes potentially involved in recovery has a negative influence on the final outcome of post-stroke individuals. Additionally, previous studies using an HCY injection model found that HCY changed hippocampus plasticity and synaptic transmission resulting in learning and memory deficits [11–13]. Since depression has been linked to failure in synaptic plasticity originating from environmental and/or genetic risk factors, it is likely that synaptic plasticity may be responsible for HCY-associated depressive symptoms after cerebral ischemic damage.
The neurosciences at the Max Planck Institute for Biophysical Chemistry in Göttingen
Published in Journal of the History of the Neurosciences, 2023
Synapses are the points of contact between individual neurons and mediate the signal transfer in the nervous system. The term synapse was introduced in 1897 by the British neurophysiologist and later Nobel laureate Charles Sherrington (1857–1952), long before its structure and function were clarified (Valenstein 2005, 4) and, above all, against the bitter resistance of the so-called “reticularists,” who believed that nerve cells formed a syncytium (Nissl 1903). In the first half of the last century, first the functional roles of synapses were studied—that is, the chemical signal transmission by a neurotransmitter, its quantal release, and its effect on the postsynaptic nerve cells. When electron microscopy, which had been developed from the 1930s onward, came into use in 1954 (Hentschel 2014, 311; Ruska 1955), it became possible to examine the structure of the synapses, showing that they contained large quantities of small blisters known as vesicles and that the membranes are thickened at the contact points (Figure 3; see De Robertis 1964, 27–48; Cowan and Kandel 2001, 1–87).
C. elegans MAGU-2/Mpp5 homolog regulates epidermal phagocytosis and synapse density
Published in Journal of Neurogenetics, 2020
Salvatore J. Cherra, Alexandr Goncharov, Daniela Boassa, Mark Ellisman, Yishi Jin
Synapses enable the transmission and integration of information within the nervous system. Proper synaptic connectivity is essential to govern nervous system functions such as sensory perception, learning, and coordinated movement. Aberrant synaptic connections have been associated with a variety of neurological disorders. Synapse formation, elimination, and maintenance work together to ensure precision and plasticity of neuronal circuits throughout the lifetime of an animal. Many neuronal-intrinsic mechanisms involve various classes of cell surface proteins and intracellular signaling pathways that establish synaptic connections (Cherra & Jin, 2015; de Wit & Ghosh, 2016; Sudhof, 2018). Additional work has shown how extrinsic mechanisms involving non-neuronal cells, such as astrocytes and microglia, cooperate with neurons to modulate neuronal circuits (Allen & Eroglu, 2017; Chung, Allen, & Eroglu, 2015). It is now well established that astrocytes and microglia play an active role in the pruning of synaptic connections during development of the visual system in mice (Chung et al., 2013; Stevens et al., 2007). In Drosophila, glial cells also remove synapses and axonal components as a means to eliminate neuronal connections (Awasaki et al., 2006; Fuentes-Medel et al., 2009).