Process of Synaptic Transmission

12 Key excerpts on "Process of Synaptic Transmission"

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  Physiological Psychology

  • Thomas Brown(Author)
  • 2012(Publication Date)
  • Academic Press

    (Publisher)

  The study of synaptic transmission has been one of the most fasci-nating stories in physiological psychology. At first, people thought that the end of one neuron and the beginning of the next actually touched each other, and the message was carried electrically through-out the nervous system. (Some neurons actually do touch each other, but these gap junctions are less well understood, and are also less usual in vertebrates.) When anatomists observed that neurons did not touch and that there was a small space between them, people sus-pected that the action potential might be carried across the space like a spark. But eventually it became clear that the synapse uses a com-pletely different coding process for passing along information—one that involves the release of one of several different neurotransmitters. In this chapter we will first discuss the structure of the synapse. Then we will explore the Process of Synaptic Transmission which in-volves three basic steps: (1) release of neurotransmitter, (2) the effect of the neurotransmitter on the next cell, and (3) inactivation of the Figure 3.1 The synapse. Presynaptic cell Postsynaptic cell Synaptic terminal Neurotubules 30 physiological psychology introduction neurotransmitter. The next section of this chapter examines some of the alternative ways that neurons can communicate with one another. Last, we will look at some of the neurotransmitters, particularly those which appear again and again throughout this book. The synapse, shown in Figure 3.1, is composed of three basic parts: (1) stvUCtUVB the axon endings, or synaptic terminals of the presynaptic cell (the £ -neuron sending the message), (2) the space between the neurons, also OJ trie Synapse called the synaptic cleft, and (3) the portion of the postsynaptic cell which is across from the terminal and which receives the message by means of the postsynaptic membrane.

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  Behavioral Neuroscience

  • George Spilich(Author)
  • 2023(Publication Date)
  • Wiley

    (Publisher)

  51 CHAPTER OUTLINE 3.1 The Synapse • The Presynaptic Mechanism • The Postsynaptic Mechanism • A Closer Look at Interneuron Communication • Chemical versus Electrical Synapses Check It Out: Electrical Synapses and Atrial Fibrillation 3.2 Receptors and Postsynaptic Effects • Ionotropic and Metabotropic Receptors • Downregulation and Upregulation Think About It: How Upregulation Explains Nicotine Cravings • Autoreceptors and Heteroreceptors 3.3 An Overview of Major Neurotransmitters • Four Key Neurotransmitter Systems Check It Out: The Sleepy Sickness Epidemic • Other Neurotransmitters of Note 3.4 Disorders and Treatments Related to Neurotransmission • Synaptopathies Advances in Behavioral Neuroscience: Dimitri Kullmann and the Silent Synapse • Alcohol, Drugs, and Addiction • Drug Treatments Targeting Neurotransmission LEARNING OBJECTIVES LO 3.1 Describe how information is transmitted between neurons through neurotransmitters, synapses, and receptor sites. LO 3.2 Outline the different regulatory processes involved in neurotransmission. LO 3.3 Identify the most common neurotransmitters, explaining the functions of each. LO 3.4 Integrate your understanding of synaptic processes to understand related disorders and their treatments. CHAPTER 3 Information transfer from one neuron to the next occurs across the synapse, like the gap between these two hands. PeopleImages/iStock/Getty Images Synapses and Neuro- transmitters 52 C H A P T E R 3 Synapses and Neurotransmitters Stories of the Brain Kurt was a professor of mathematics at a small college. He loved to teach his students about the many ways mathematics can solve real-world problems. After a long career, he retired to enjoy his hobbies of gardening and playing the violin in the town’s adult orchestra. One morning while he was eating breakfast, his coffee cup slipped out of his hand and fell to the floor, shattering into pieces. “How careless of me,” he thought and gave it no mind.

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  Neuropsychotherapy

  How the Neurosciences Inform Effective Psychotherapy

  • Klaus Grawe(Author)
  • 2017(Publication Date)
  • Routledge

    (Publisher)

  The collaboration of specialized neurons in neural circuits is made possible by the transmission of action potentials among the individual neurons. This potential is transmitted via the synapses, which connect two neurons with one another. Before we turn to the transactions among neurons on the level of the entire brain, it is critical to elaborate on the processes transpiring within the neurons themselves and at the synapses during the transmission of action potentials. These microlevel processes are the basis of all other processes within the brain. They determine what is and is not possible within the brain. If therapeutic changes achieve their effects via changes of the brain, then they are ultimately effective—on a microlevel—because they modulate synaptic efficacy. Let us take a closer look at the fundamental process underlying the transmission of action potentials to see whether relevant implications for psychotherapy can be derived.

  2.2 WHAT EXACTLY HAPPENS DURING THE TRANSMISSION OF ACTION POTENTIALS BETWEEN NEURONS?

  The functions of individual neurons depend on three factors: their localization within the brain, their connections with other neurons, and their individual characteristics. Even the internal organization and appearance of neurons can differ considerably. Figure 2–1 illustrates some of the more common types of neurons.

  However, it is not only in their visible appearance (in the electron microscope) that neurons differ from one another. Neurons are designed to communicate with other neurons. They do this via electrical transmissions and chemical synapses. For the chemical transmission of signals, neurons use transmitters that they themselves produce. These are, narrowly defined, the neurotransmitters, neuromodulators, neuropeptides, and neurohormones—often all of these are collectively referred to as neurotransmitters. There are nine different kinds of just the classical neurotransmitters (glutamate, glycin, gamma amino butric acid [GABA], dopamine, norepinephrine, epinephrine, serotonin, histamine, and acetylcholine) and more than 50 types of neuroactive peptides. Until recently, it was assumed that each neuron produces only one specific neurotransmitter, but this assumption has by now been shown to be inaccurate. Most neurons produce multiple neurotransmitters, which is only reasonable, as this multiplies the neuron’s options to influence other neurons. Of importance, the neurotansmitters work on very different time schedules. The effects of glutamate and GABA transpire within milliseconds, those of dopamine and serotonin within seconds or minutes, and those of the neuropeptides and neurohormones often within hours, days, or even weeks.

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  From Molecules to Networks

  An Introduction to Cellular and Molecular Neuroscience

  • John H. Byrne, Ruth Heidelberger, M. Neal Waxham, James L. Roberts(Authors)
  • 2003(Publication Date)
  • Academic Press

    (Publisher)

  CHAPTER 9 Pharmacology and Biochemistry of Synaptic Transmission: Classic Transmitters

  Ariel Y. Deutch, Robert H. Roth

  The study of the nervous system 100 years ago was a period of claim and counterclaim, confusion, and recrimination—not unlike politics today or, for that matter, science. The reason for the tempestuous entry into the 20th century was the radical overthrow of the idea that the brain is one large continuous melded network (a syncytium), with each cell in physical contact. In contrast to this view, the pioneering studies of Santiago Ramón y Cajal revealed a very different picture, in which neurons, the units of the brain, are independent structures (see Shepherd, 1991 , and Chapter 1 ). Although final confirmation of this view would await the development and application of electron microscopy, there soon became a generalized acceptance of neurons as the independent units of the nervous system. In turn, this acceptance brought about a new debate: What is the mode of communication between neurons? The answer is not static, but is evolving continuously. In this chapter we discuss briefly several means through which cells communicate with each other and then discuss in considerable detail one such mechanism—chemical synaptic transmission. Another means of communication, electrical transmission through gap junctions, is discussed in Chapter 15 .

  As discussed in Chapter 1 , neurons, although varying widely in both morphology and function, share certain structural characteristics. A cell body (soma) from which processes emanate is present, with the processes (axons and dendrites) representing polarized compartments of the cell. Axons can be short or long, and remain local or alternatively project to distant areas. In contrast, dendrites are local. The general concept arose that axons transmit information, which is conveyed to the dendrites or soma of follower cells. The critical gap between the transmitting element of the neurons (axon) and the recipient zone of the follower cell (e.g., the dendrite) is the area across which transmission of information occurs; this area was termed the synapse by Charles Sherrington (Shepherd, 1991 ). Thus, there were presynaptic and postsynaptic neurons. This general conceptual framework remains in place today, although there are many exceptions, including dendrites that release neuroactive substances and axons that receive inputs from other neurons. One other characteristic proposed by Sherrington that is central to the concept of chemical communication between neurons is that synaptic transmission does not follow all-or-none rules, but is graded in strength and flexible (Sherrington, 1906

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  Advances in Neural Signal Processing

  • Ramana Vinjamuri(Author)
  • 2020(Publication Date)
  • IntechOpen

    (Publisher)

  Undoubtedly, independently from the level of inves-tigation (from the molecular to the neurological and psychological level), almost all the neurosciences deal, directly or indirectly, with the brain information processing and/or its malfunctioning. In this chapter, we will illustrate some basic aspects of information transfer and elaboration showing how much complex is the control of its flow among the neurons. Neurons share information mainly by the synaptic contacts which they use both to transmit and to receive. The input and output contact among many neurons are the system which operate the neural networks and the whole brain. Synapses are, then, the key points for the information transfer among neurons, but, as we will see in details later, they are also the primarily system of information coding and elabo-ration. Their activity, in fact, produces the codification of the information by a neuron in form of spike sequences into a sequence of postsynaptic potentials (PSP) which we can define as the first step of the postsynaptic representation of the 91 presynaptic code. If we consider the spike sequence of a presynaptic neuron as the representation of a stimulus, the PSPs produced at the synaptic level will be the synaptic representation of that stimulus. The meaning of stimulus, however, does not only refer to the codification of an environmental stimulation. The spike sequences, in several neurons, are not only the codification of stimuli but partici-pate also to the high-level performances connected to memory recall, thought, reasoning, and so on. Whatever is the role of the spike sequence, it represents an information which, transmitted to other neurons, is translated at the synaptic level in a sequence of PSP. How this will be further recoded into a postsynaptic spike sequence depends on a complex integration of all the inputs arriving to the neuron in a compatible time window.

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  Language Learning and the Brain

  Lexical Processing in Second Language Acquisition

  • Ulf Schütze(Author)
  • 2016(Publication Date)
  • Cambridge University Press

    (Publisher)

  The neurotransmitters serotonin, dopamine, acetylcholine, and glutamate are particularly important. Serotonin, dopamine, and acetylcholine function as chemical messengers that drift from the axon terminals of neurons across the synaptic gap in order to reach the receptor sites of other neurons. The role of glutamate is somewhat different, as it works as a mediator. Among neurons, we have to further distinguish between interneurons (the initial phase: the electrical signal leads to the first chemical reaction by releas- ing a neurotransmitter), sensory neurons (the relay: the main biochemical pro- cesses), and motor neurons (the receptor: receiving the neurotransmitter and converting it back to an electrical signal). The strength of the signal, as well as repetition of the same signal, can cause changes in the neurotransmitter system that will eventually lead to the forma- tion of a synapse that attaches to another neuron to form a permanent bridge. Groundbreaking research in this area has been carried out by Kandel, who started his research in the 1950s and was one of the first neuroscientists to fully explain the biochemical processes of long-term memory (summarized in his 2006 book In Search of Memory, written after winning the Nobel prize in 2000). The brilliance of his approach was in its simplicity: instead of study- ing complex organisms, he chose to study a sea slug of the species Aplysia. About 90 percent of the genes we find in human nerve cells are also found in slugs. The principle of information transmission is the same as it is for humans. An electric signal leads to a chemical reaction that is converted back to an electrical signal. The chemical reaction happens in the synapse that connects two neurons and it is necessary to bridge the gap between the neurons so the signal can travel from one neuron to the other. So, by studying a sea slug, we can draw conclusions that are relevant for humans.

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  Drugs and Behavior

  • Fred Leavitt(Author)
  • 1994(Publication Date)
  • SAGE Publications, Inc

    (Publisher)

  Thompson's small gem (The Brain, 1985) includes considerable information on neurotransmission. The Cooper et al. book (The Biochemical Basis of Neuropharmacology, 1991), deserv-edly in its sixth edition, is a classic in the field of neuropharmacology. Both books are lucid and stimulating. 28 DRUGS AND BEHAVIOR Neurons communicate with each other chemically, by a process called neurotransmission. The presynaptic neuron releases a chemical, called a neurotransmitter, at the synapse. The NT diffuses across the synaptic cleft and triggers a reaction in the postsynaptic neuron. Presynaptic receptors modulate the release of NT; postsynaptic re-ceptors increase (decrease) in number if stimulated infrequently (excessively). Metabolism of ACh terminates its actions. The actions of other NTs are terminated primarily by reuptake. Each NT binds to one or more receptors, and effects depend on inter-actions between the NTs and the specific receptors with which they bind. Most psychoactive drugs act by one or more mechanisms on receptors. Many substances have been identified as probable NTs, but con-clusive evidence exists for only a few. ACh and NE are transmitters in both the CNS and autonomic nervous system. Other NTs include dopamine, serotonin, histamine, GABA, and various amino acids and neuropeptides. 29 Neurotransmission Mini-Quiz: Neurotransmission Name the three principal parts of neurons. cell body, dendrites, axon When an action potential reaches the terminal of the axon, ions rush into the terminal and trigger the release of . calcium; one or more NTs When a neuron fires, NTs diffuse across the to attach to on a second neuron. synaptic cleft; receptors When an excitatory NT interacts with a receptor, ion channels open.

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  Selected Topics from Neurochemistry

  • Neville N. Osborne(Author)
  • 2013(Publication Date)
  • Pergamon

    (Publisher)

  In his review of the evolution and status of the concept of chemical synaptic transmission, Neville Osborne especially attends to the possibility that one neurone can synthesize more than one transmitter substance. He restricts his approach to the still prevailing notion that the important questions are (1) does information transmission involve chemically mediated alteration of postsynaptic excitability; (2) if so, what is the transmitter involved (and by what criteria can a substance be identified as a transmitter substance); (3) which chemical pathway(s) lead(s) to its synthesis; (4) where and by what mechanism is the transmitter released; (5) what is the fate of the released transmitter (enzymatic inactivation, reuptake, removal by diffusion) and, finally, (6) what are the biochemical and biophysical processes effected by the transmitter?

  Neuropharmacologists, by and large, have taken a similar view of the problem of chemical synaptic transmission and have investigated the mechanism of action of substances which, in one way or another, affect biochemical and biophysical processes involved in transmitter synthesis, release action and removal.

  My critique is not directed against this perfectly valid approach to chemical (synaptic) transmission; instead, I take issue with the notion that this set of questions is adequate and sufficient for reaching a satisfactory understanding of the functional role of chemical synaptic transmission.

  There is no doubt that synapses are relay stations which convey information from one neuron to another cell. There is also no question that synapses in which each presynaptic impulse sets up a propagated action potential in the postsynaptic cell are the exception rather than the rule and that there is a great variety of synapses (including all those commonly referred to as inhibitory synapses) which simply generate more or less graded postsynaptic potentials.

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  Nolte's The Human Brain E-Book

  Nolte's The Human Brain E-Book

  • Todd W. Vanderah, Douglas J. Gould(Authors)
  • 2020(Publication Date)
  • Elsevier

    (Publisher)

  8

  Synaptic Transmission Between Neurons

  Chapter Outline

  • There Are Five Steps in Conventional Chemical Synaptic Transmission,
    174
    • Neurotransmitters Are Synthesized in Presynaptic Endings and in Neuronal Cell Bodies, 175
    • Neurotransmitters Are Packaged Into Synaptic Vesicles Before Release, 175
    • Presynaptic Endings Release Neurotransmitters Into the Synaptic Cleft, 176
    • Neurotransmitters Diffuse Across the Synaptic Cleft and Bind to Postsynaptic Receptors, 177
    • Neurotransmitter Action Is Terminated by Uptake, Degradation, or Diffusion, 177
  • Synaptic Transmission Can Be Rapid and Point-to-Point, or Slow and Often Diffuse,
    178
    • Rapid Synaptic Transmission Involves Transmitter-Gated Ion Channels, 179
    • Slow Synaptic Transmission Usually Involves Postsynaptic Receptors Linked to Intracellular Proteins, 179
    • The Postsynaptic Receptor Determines the Effect of a Neurotransmitter, 181
    • The Size and Location of a Synaptic Ending Influence the Magnitude of Its Effects, 182
      • Synapses With Many Active Zones Have a Greater Effect,
        182
      • Synapses Closer to the Action Potential Trigger Zone Have a Greater Effect,
        182
      • Presynaptic Endings Can Themselves Be Postsynaptic,
        182
  • Synaptic Strength Can Be Facilitated or Depressed,

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  Brain Sciences in Psychiatry

  • David M. Shaw, A.M.P. Kellam, R.F. Mottram(Authors)
  • 2013(Publication Date)
  • Butterworth-Heinemann

    (Publisher)

  The chemical nature of neurotransmission 67 Drug A NaCI Figure 4.10 The techniques of micro-iontophoresis 1—40 jum Figure 4.11 The techniques of micro-iontophoresis continued These experiments, and many others giving quantitative measures of transmitter release and activity, are quite convincing. Acetylcholine is believed to be one of the transmitters between the thalamus and the neocortex. The experiments are difficult to conduct, however, and need to be repeated for each of the many pathways converging onto cortical cells, for all the cellular areas of the brain and for each of the chemicals that have been suggested as possible transmitters in the brain. This is a daunting prospect indeed, and explains why, at so many synapses, the neurotrans-mitters are still unidentified. Figure 4.12 is a diagram of the synaptic terminal under the electron microscope, which shows that terminals do not make contact with cells. There is a gap or 68 Transmission between neurons Microfilaments -Mitochondria Synaptic vesicles Synaptic cleft Thickening of the postsynaptic membrane Figure 4.12 The synaptic terminal (diagrammatic) synapse of 20 nm between the presynaptic and the postsynaptic membranes. The terminals contain many mitochondria which synthesize ATP among other things and it is concluded that many of the processes in axon terminals consume energy. Terminals usually contain synaptic vesicles, which are small round or oval sacs which cluster near to the synapse. Two experiments identify their function. Sucrose gradient ultracentrifugation was described on page 47. If homogenized brain is centrifuged in this way, a layer can be found which contains synaptosomes. These are the axon terminals and a small piece of the postsynaptic membrane. If these are subjected to osmotic shocks (i.e. are placed in ^ solution of low osmotic pressure), the synaptosomes rupture, spilling their contents.

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  Environmental Physiology of Animals

  • Pat Willmer, Graham Stone, Ian Johnston(Authors)
  • 2009(Publication Date)
  • Wiley-Blackwell

    (Publisher)

  The synapse is normally the only point of com-munication between two neurons, and somehow the signal from one cell has to pass to the other across the discontinuity of an inter-cellular gap. There are two ways in which this can happen: either by direct electrical signaling, or by a chemical message crossing the gap. Both systems occur, though the latter is more common and we will therefore consider it first. 9.3.1 Chemical synapses For chemical transmission to be useful in a nervous system it must have three characteristics: it must be fast, it must be point-to-point (rather than diffuse), and it must be simple (excitatory or inhibit-ory, but not complex or ambiguous). Chemical synapses are the main system for communicating between cells in a nervous system. They may occur between any two neurons, or occasionally between different parts of one neuron. A chemical synapse (Fig. 9.12) is a zone where two neuronal surfaces lie close together (commonly the axon terminals of one neuron abutting onto the dendrites or cell body of another) and a chemical transmitter diffuses across the gap between them. It is constructed by the close apposition of specialized regions of the plasma membranes of the two participating neurons, forming a clearly defined synaptic interface with a narrow interven-ing cleft. The presynaptic cell contains a cluster of transmitter-filled vesicles and may have a somewhat thickened membrane, while the postsynaptic membrane is usually clearly thickened due to an accumulation of receptor sites and the associated submembrane “scaffolding”. In essence, the functioning of a synapse requires that: 1 The spreading depolarization at the presynaptic terminal of neu-ron A brings about a specific release of chemical. 2 The chemical diffuses from the membrane into the synaptic cleft. 3 The diffusing chemical arriving at receptors on the postsynaptic terminal in neuron B initiates a new depolarization.

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  Pharmacotherapeutics in General, Mental and Sexual Health

  • Donald E. Greydanus, Dilip R. Patel, Hatim A. Omar, Cynthia Feucht, Joav Merrick, Donald E. Greydanus, Dilip R. Patel, Hatim A. Omar, Cynthia Feucht, Joav Merrick(Authors)
  • 2012(Publication Date)
  • De Gruyter

    (Publisher)

  The axon terminal may also end on the cell body of the postsynaptic neuron. Neurotransmitter is stored in the synaptic vesicles in the axon terminal. Axons carry the neuronal impulse to var-ious other neurons in the brain. The information or input is carried to the cell body of the receiving neuron. On the receiving end, the information or impulse is received at the dendrites. 5.2.2 The synapse At the synapse, the electrical impulse from the presynaptic neuron is converted to a chemical signal that is carried to the postsynaptic receptors where it is again converted to an electrical impulse in the postsynaptic neuron (1,2). There are two types of neuronal synapses: electrical and chemical. The electrical synapses are located at gap junctions and allow free bidirectional movement of ions across cell membranes. Their function in the brain varies at different sites; they provide for fast transmission of impulses. Most of the synaptic transmission in the brain occurs at the chemical synapses. Autoreceptors are membrane-bound receptors on the pre-synaptic membrane and regulate the release and in some cases synthesis of the intrin-sic neurotransmitter. Certain other receptors on the presynaptic membrane can be modulated by neurotransmitters from nearby neurons and are called heteroreceptors. The membrane-bound postsynaptic neuroreceptors can generally be classified into two types: (a) transmitter-gated (or ligand-gated) ion channels and (b) G-protein-coupled receptors (1,2,3,4,5,6,7,8,9,10). The transmitter-or ligand-gated ion channel receptor consists of five subunits that are arranged as columns in a circle, thus forming a pore or a channel in the middle (11). The neurotransmitter binds to the specific site on the extracelluar portion of the receptor, leading to opening of the channel. The effect on the postsynaptic neuron depends on which ion is preferentially passed through the channel into the postsynaptic neuron.

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