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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).
Introduction: Background Material
Published in Nassir H. Sabah, Neuromuscular Fundamentals, 2020
Neurons are the core of the nervous system. Cell bodies and dendrites of neurons are specialized for the reception and processing of electric signals from other neurons, whereas axons are specialized for the transmission of the AP from a given neuron to the axon terminals. Axon terminals are usually specialized for the release of a neurotransmitter.
The cell
Published in Laurie K. McCorry, Martin M. Zdanowicz, Cynthia Y. Gonnella, Essentials of Human Physiology and Pathophysiology for Pharmacy and Allied Health, 2019
Laurie K. McCorry, Martin M. Zdanowicz, Cynthia Y. Gonnella
Most neurons, particularly in the CNS, receive thousands of inputs. The function of a neuron is to communicate or relay information to another cell by way of an electrical impulse. A synapse is the site where the impulse is transmitted from one cell to the next. A neuron may terminate on a muscle cell, a glandular cell or another neuron. The discussion in this chapter will focus on neuron-to-neuron transmission. At these types of synapses, the presynaptic neuron transmits the impulse toward the synapse and the postsynaptic neuron transmits the impulse away from the synapse. Specifically, it is the axon terminal of the presynaptic neuron that synapses with the cell body or the dendrites of the postsynaptic neuron. As will become evident, the transmission of the impulse at the synapse is unidirectional and the presynaptic neuron influences the activity of the postsynaptic neuron only.
Deep brain stimulation programming strategies: segmented leads, independent current sources, and future technology
Published in Expert Review of Medical Devices, 2021
Bhavana Patel, Shannon Chiu, Joshua K. Wong, Addie Patterson, Wissam Deeb, Matthew Burns, Pamela Zeilman, Aparna Wagle-Shukla, Leonardo Almeida, Michael S. Okun, Adolfo Ramirez-Zamora
How the biological changes translate into potential mechanisms of action remains unknown. One common early hypothesis on the potential mechanism of action for DBS is the ‘inhibition hypothesis,’ in which DBS would exert a dampening effect on overactive neurons within the basal ganglia. This idea was derived from benefits noted from lesioning procedures and STN and GPi DBS animal models have provided support for this idea [23,24]. Several mechanisms have since been proposed to underpin the inhibitory effects of DBS. These include 1) depolarization-induced blocking of ion channels (inactivation of sodium channels and an increase in potassium currents contributing to a sustained depolarization), 2) presynaptic inactivation of excitatory afferent axon terminals, and 3) activation of inhibitory afferents [25–31].
A primer on sleeping, dreaming, and psychoactive agents
Published in Journal of Social Work Practice in the Addictions, 2023
In order to gain an understanding of how psychoactive drugs affect the central nervous system (CNS), one must have a basic understanding of the process that underlies the functioning of the brain. Of the billions of cells for which the brain is composed, it is only the neuron or nerve cell that processes information. Messages travel within each cell as electrical transmissions, but as one neuron has no direct physical contact with another, electrical transmission between cells cannot occur. Thus, information between nerve cells must be communicated chemically. A neuron consists of a cell body or soma, where metabolic activity occurs featuring the nucleus and dendrites. Dendrites are the extension of the soma that receives messages from the axons of adjoining cells. The axon is the part of the neuron along which signals are transmitted to adjoining cells that terminate in axon terminals. It is in the axon terminals where the various neurotransmitters including Gamma-Aminobutyric Acid (GABA), dopamine, norepinephrine, serotonin, endorphins, and endocannabinoids are found (Figure 2). The gap across which the neurotransmitters must travel is referred to as the synaptic cleft. The synaptic cleft is typically 10–20 nanometers across. This is such a tiny space that it takes only 0.1 ms for a neurotransmitter to drift, or defuse, across the gap to the next axon. Neurotransmitters are chemicals found in the brain that are used to relay, amplify, and modulate signals between neurons that produce physical actions, feelings, and behaviors and also affect sleeping and dreaming (Brick & Erickson, 2013; Dorland, 2019; Goldstein & Cacciamani, 2021).
Improved spinal cord gray matter morphology induced by Spirulina platensis following spinal cord injury in rat models
Published in Ultrastructural Pathology, 2020
Dauda Abdullahi, Azlina Ahmad Annuar, Junedah Sanusi
The ultrastructure of the gray matter in the ventral horn of the sham (laminectomy) group demonstrate typical cytoarchitectonics of the neuronal perikarya (Figure 3A), depicting normal nucleus containing chromatin which is surrounded by an intact nuclear envelop. Axon terminals were seen in relation with the somata (perikarya) forming axo-somatic synapse, the homogenous cytoplasm of the somata depicts typical mitochondria with normal cristae and matrix density, and Nissl substances with respect to the rough endoplasmic reticulum. The ultrastructure of the gray matter in the ventral horn of the control group revealed a spectrum of severed neuronal cell bodies with atypical nucleus undergoing karyorrhexis and irregular contours with deep infoldings/indentations of the nuclear membrane and focal discontinuity of the perinuclear cistern. The electron dense cytoplasm reveals lipofuscin and mitochondrial swelling with loss of matrix density and cristae as shown in Figure 3B, and swelling of the rough endoplasmic reticulum with detached ribosomes within the severed perikarya. The fine structure of the gray matter in the ventral horn of the S. platensis group showed near-normal neuronal perikarya profile depicting typical rounded nucleus containing chromatin bounded by an intact perinuclear cistern of the nuclear envelop. Seen within the cytoplasm of the somata are granular bodies, Nissl substances, with respect to rough endoplasmic reticulum studded with rosette of ribosomes and mitochondria. In contact with the plasma membrane of the somata are axon terminal and dendrites of neighboring neurone, and a dendrite of an adjacent neurone is seen forming dendro-somatic synapse with the somata as shown in Figure 3C.