Neuron Structure and Function

11 Key excerpts on "Neuron Structure and Function"

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  eBook - ePub

  Biological Psychology

  • Suzanne Higgs, Alison Cooper, Jonathan Lee(Authors)
  • 2023(Publication Date)
  • SAGE Publications Ltd

    (Publisher)

  Chapter 2 Structure and Communication in the Nervous SystemHiggs

  Chapter Breakdown

  • An introduction to some key terminology in the field.
  • A basic introduction to the components of the human nervous system.
  • Overview of the organisation of the human nervous system.
  • Overview of the key processes that underlie neuronal function.

  Roadmap

  The relationship between biology and psychology is predominantly focused on the function of the nervous system (particularly the brain) in underpinning normal and abnormal behaviour. Therefore, a full understanding of biological psychology necessitates starting with the structure and function of the nervous system, from the cellular level right up to the whole system. This is important as it will enable us to understand how the ability of the nervous system to change and adapt enables it to perform the functions that will be described in subsequent chapters, and how these processes may be interrupted, resulting in dysfunction of the nervous system.

  Putting the nervous system into the context of the body (central versus peripheral), we will outline the overall structure of the brain and spinal cord. The nervous system, moreover, comprises specialised cells (neurons), which allow for the communication of information, ultimately supporting behaviour. This necessitates, first, a form of intracellular communication that allows for the faithful transfer of information over relatively long distances from one end of the cell to another, via electrical signals. The neurons then need to be able to communicate with each other at structures called synapses. This intercellular communication allows networks of neurons to act cooperatively to underpin brain function, and takes the form of chemical signalling processes. The complexity of chemical signalling will be introduced by discussing the different neurotransmitters that are present and function within the brain. An understanding of these processes is necessary as the importance of them in determining normal neuronal function and as targets for modification, both by physiological processes and exogenous substances such as drugs, will be discussed in subsequent chapters. Clearly, these processes and their modification are critical for determining behaviour.

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  Available until 5 Dec |Learn more

  The Student's Guide to Cognitive Neuroscience

  • Jamie Ward(Author)
  • 2019(Publication Date)
  • Routledge

    (Publisher)

  Chapter 2 Introducing the brain

  DOI: 10.4324/9781351035187-2

   CONTENTS

  • Structure and function of the neuron
  • The gross organization of the brain
  • The cerebral cortex
  • The subcortex
  • The midbrain and hindbrain
  • Summary and key points of the chapter
  • Example essay questions
  • Recommended further reading

  It is hard to begin a chapter about the brain without waxing lyrical. The brain is the physical organ that makes all our mental life possible. It enables us to read these words, and to consider thoughts that we have never considered before—or even to create thoughts that no human has considered before. This book will scratch the surface of how this is all possible, but the purpose of this chapter is more mundane. It offers a basic guide to the structure of the brain, starting from a description of neurons and working up to a description of how these are organized into different neuroanatomical systems. The emphasis is on the human brain rather than the brain of other species.

  Structure and Function of the Neuron

  All neurons have basically the same structure. They consist of three components: a cell body (or soma), dendrites and an axon, as shown in Figure 2.1 . Although neurons have the same basic structure and function, it is important to note that there are some significant differences between different types of neurons in terms of the spatial arrangements of the dendrites and axon.

  Figure 2.1 Neurons consist of three basic features: a cell body, dendrites that receive information and axons that send information. In this diagram the axon is myelinated to speed the conduction time.

  The cell body contains the nucleus and other organelles. The nucleus contains the genetic code, and this is involved in protein synthesis. Proteins serve a wide variety of functions from providing scaffolding to chemical signaling (they can act as neurotransmitters and receptors in neurons). Neurons receive information from other neurons and they make a “decision” about this information (by changing their own activity) that can then be passed on to other neurons. From the cell body, a number of branching structures called dendrites enable communication with other neurons. Dendrites receive information from other neurons in close proximity. The number and structure of the dendritic branches can vary significantly depending on the type of neuron (i.e., where it is to be found in the brain). The axon, by contrast, sends information to other neurons. Each neuron consists of many dendrites but only a single axon (although the axon may be divided into several branches called collaterals).

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  Biology of Perceptual Systems

  • Edward Carterette(Author)
  • 2012(Publication Date)
  • Academic Press

    (Publisher)

  Chapter 2 NEURONAL PROPERTIES CHARLES F. STEVENS I. Structural Basis for Nervous System Functioning 21 II. The Nerve Impulse 24 III. Synaptic Function 26 IV. Neural Integration 29 V. Encoding Information 31 VI. Special Properties 33 VII. Summary 36 VIII. Guide to the Neurophysiological Literature 37 References 37 The human central nervous system contains a vast complex of informa-tion processing circuits formed by interconnecting networks of nerve cells. This chapter describes the properties of the individual components from which these neural circuits are constructed. Because information about neuronal properties has grown so rapidly in recent years, it would be im-possible in a brief article to give anything approaching a comprehensive description; thus the following discussion will focus on certain features believed to be most important in neuronal information processing. I. STRUCTURAL BASIS FOR NERVOUS SYSTEM FUNCTIONING Before beginning a discussion of mechanisms responsible for neuronal information processing, it will be necessary to describe the structure of the nervous system's basic anatomic unit, the nerve cell (or, equivalently, neu-ron). All cells are surrounded by a thin (100 A) plasma membrane and filled with cytoplasm containing various organelles, such as mitochondria and the nucleus. Nerve cells share many properties with cells from other types of tissue, but are distinguished by a particularly complicated geo-metric form which is related to neuronal function. Although many various 22 CHARLES F. STEVENS shapes and sizes of nerve cells are found in the central nervous system, three different types of structural components can be recognized in almost all neurons: the cell body (or, equivalently, soma), the dendrites, and the axon. The soma, dendrites, and axon of a typical neuron are indicated in Fig. 1, and a variety of dendritic trees from a particular cortical region are illustrated in Fig.

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  Psychology Around Us

  • Nancy Ogden, Michael Boyes, Evelyn Field, Ronald Comer, Elizabeth Gould(Authors)
  • 2021(Publication Date)
  • Wiley

    (Publisher)

  But neurons are not the only cells in the nervous system. Neuroscientists have increased their research into understand- ing the role of glial cells, the other type of cell found in our ner- vous systems. Neurons and Glia The basic structure of a neuron is shown in Figure 3.8. Like most of the other cells that make up who we are, the neurons have a cell body filled with cytoplasm that contains a nucleus (the residence of chromosomes that contain the genetic material). In addition, neurons contain organelles that enable the neuron to make proteins and other molecules, produce energy, and permit the break- down and elimination of toxic substances. Just as our own organs make it possible for our bodies to live and function, organelles make it possible for our neurons to live and function (Britt et al., 2016). David Scharf/Science Source Neurons Human cortical neurons (brain cells), showing an extensive network of interconnecting dendrites between the large triangular- shaped cell bodies. 86 CHAPTER 3 Neuroscience However, as Figure 3.8 shows, neurons have a different shape than the round shape many people think of when picturing a cell in their mind. They have specialized structures called den- drites and axons that are important for communication with other neurons. Dendrites extend like branches from the cell body to receive inputs from other neurons. Neurons can have many dendrites and, indeed, some have very extensive dendritic “trees.” These trees receive signals from the ends of axons on other neurons and a single cortical neuron may received upward of 200,000 inputs, or signals from other neurons in the brain. An axon also extends from the cell body. Unlike dendrites, however, axons function to carry signals away from the cell body. Axons have a specialized region at the end, called the axon terminal, where the signal from the cell body, which flows down the axon, is passed on to the dendrites of the neurons the axon communicates with.

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  Child Psychology

  A Canadian Perspective

  • Alastair Younger, Scott A. Adler, Ross Vasta(Authors)
  • 2014(Publication Date)
  • Wiley

    (Publisher)

  What are the techniques for imaging the anatomical structure of the brain? 5. How useful are the techniques that image the brain’s anatomical structure for determining the development of the brain’s anatomical structure? 6. What techniques have been devised for determining the function of different brain structures? 7. To what extent can the techniques for determining brain function be used to assess the development of those brain functions? LEARNING OBJECTIVE 6.1 THE NEURON:THE BUILDING BLOCK OF THE BRAIN It is hardly necessary to say that the brain is central to every aspect of development and every sort of human function. We have already reviewed the methodologies that have been used to assess and map the structure and function of the brain. In this section, we look at the building block of brain structure—the neuron. STRUCTURE OF THE NEURON The brain consists of two general types of cells: the neurons and the glial cells. Though glial cells are generally thought not to play a direct role in the brain’s computations, they do play a role in the development of the brain, as we will see later. The brain contains approximately 100 billion nerve cells, or neurons; each of these cells has around 3,000 connections with other cells, which add up to several quadrillion message paths. No one completely understands how all these communication paths work, but we do know quite a bit. Like every other cell, each neuron has a nucleus and a cell body. But neurons are unique among cells in that they develop extensions on opposite sides, as shown in Figure 6.7. On the incoming side, the extensions, called dendrites, often form a tangle of strands that look like the roots of plants. By the incoming side, what is meant is that the dendrites receive electrical impulses or signals that code various types of information from other neurons. The dentrites then pass the signal along to the soma or cell body. The outgoing extension, called an axon, is more like a single strand.

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  Anatomy and Human Movement

  Structure and Function

  • Nigel Palastanga, Derek Field, Roger W. Soames(Authors)
  • 2013(Publication Date)
  • Butterworth-Heinemann

    (Publisher)

  Neurons differ in size and shape according to their function and location within the nervous system, but all neurons have three characteristi c compon-ents: a cell-body, an axon, and dendrites (Fig. 7.2). The cell body of a neuron is an expanded portion of the cell which contains the nuc-leus and the apparatu s necessary to sustain the metabolic activities of the cell. The axon is a longitudinal , tubular extension or pro-cess of the cell membrane and cytoplasm; its function is to transmi t information away from the cell body. The cell membrane sur-rounding the axon is referred to as the axo~ lemma. Dendrites are processes of the cell membrane that radiate from the cell body in various directions, and are responsible for receiving information and transmitting it to the cell body. Structurally , dendrites differ from axons as they typically undergo extensive branch-ing very close to the cell body. Axons, in contrast , remain singular for most of their course. They do not branch until their termi-nal ends are well away from the parent cell body. A neuron has only one axon, but may have several dendrites; the lengths and calibre of axons and dendrites vary, depend-ing on the particular function of the neuron. INTERNEURAL CONNECTIONS Individua l neurons convey information by conducting electrical action potentials along their cell membrane . Electrical information , however, does not pass from one neuron to another . Communication between separ-ate neurons occurs chemically and involves a specialized structure called a synapse. Synapses are formed by the close approxi-mation of a small discrete area of the cell membrane of one neuron to a reciproca l area of the membrane of a second neuron (Fig. 7.3). The apposed membranes are specially modified in structure and are separated by a narrow gap, measuring about 0.02 μιη in width, called the synaptic cleft. Across the synapse, one cell communicates with the next, and communication is uni-directional .

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  Discovering Psychology

  The Science of Mind

  • John Cacioppo, Laura Freberg(Authors)
  • 2015(Publication Date)
  • Cengage Learning EMEA

    (Publisher)

  F i g u r e 4.20 The Neuron. Neurons share many features with other living cells but are specialized for the processing of information. (a) Parts of the neuron. Like other types of animal cells, the neuron features a nucleus in its cell body and a fatty membrane that separates the intracellular and extracellular fluids. Unlike most other cells, the neuron has specialized branches, the axon and the dendrites, that pass information to and receive information from other cells. (b) A close-up view of the axon membrane. A thin oily membrane separates the intracellular fluid inside the neuron from the extracellular fluid outside the neuron. Pores spanning the membrane act as channels that allow ions to move into and out of the neuron. (c) A close-up view of the axon terminal. Within the axon terminal are synaptic vesicles, which contain chemical messengers called neurotransmitters that transmit signals between neurons. Later in the chapter, we’ll see how these neurotransmitters communicate with receptors on the dendrites of other neurons. myelin The insulating material cov-ering some axons. Copyright 2016 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. Chapter 4 | THE BIOLOGICAL MIND: THE PHYSICAL BASIS OF BEHAVIOR 136 cord form scar tissue, inhibiting repair to the damaged nerves. Because of this feature, we consider damage in the central nervous system to be permanent. Considerable research is under way to figure out how to repair such damage, including work using stem cells to grow bridges across the damaged areas.

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  Discovering Behavioral Neuroscience

  An Introduction to Biological Psychology

  • Laura Freberg(Author)
  • 2018(Publication Date)
  • Cengage Learning EMEA

    (Publisher)

  Loss of VENs in frontotemporal dementia (see Chapter 15) might result in the relative lack of empathy, social awareness, and self-control associated with this condition. The most common structural type of neuron in the vertebrate nervous system is the multipolar neuron. Multipolar neurons have many branches extending from the cell body. Usually, this means that the cell has one axon and numerous dendrites. Multipolar neurons may be further classified according to shape. For example, pyrami-dal cells in the cerebral cortex and the hippocampus have cell bodies that are shaped like pyramids. The Purkinje cells of the cerebellum have dramatic dendritic trees that allow a single cell to form as many as 150,000 synapses. Functional Variations in Neurons Neurons can be classified according to the roles they play within the nervous system. Sensory neurons are specialized to receive information from the outside world and from within our bodies. Our senses of vision, hearing, touch, taste, smell, and pain all depend on specialized receptor neurons. These neurons can translate many types of information, such as light or sound waves, into neural signals that the nervous system can process. Motor neurons transmit commands from the CNS directly to muscles and glands. The vast majority of neurons are known as interneurons. Interneurons are not specialized for either sensory or motor functions but act as bridges between the sensory and motor systems. INTERIM SUMMARY 3.1 Summary Points 1. The nervous system is made up of two types of cells, glia and neurons. Glia perform a variety of support functions, and neurons are responsible for processing and commu-nicating information. (LO1) 2. Macroglia provide a variety of support functions to neurons, including the formation of myelin. Microglia remove weak synapses and debris resulting from damage to neurons. (LO2) 3. The neural membrane is composed of a two-molecule-thick layer of phospholipids.

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  Visualizing Human Biology

  • Kathleen A. Ireland(Author)
  • 2018(Publication Date)
  • Wiley

    (Publisher)

  The Nervous System Is Categorized by Structure and Function 131 TABLE 7.2 Neuroglia size and shape, location, and function Name Function Name Function PNS Satellite cells Regulate oxygen, carbon dioxide, nutrient, and neurotransmitter levels around ganglia Schwann cells Surround axons in PNS, causing myelination of axons and faster impulse transmission, aid in repair after injury CNS Oligodendrocytes Surround axons in CNS, causing myelination and providing structural support Microglia Clean up cellular debris and pathogens via phagocytosis Astrocytes Maintain blood–brain barrier; regulate nutrient, ion, and dissolved gas concentra- tions; absorb and recycle neurotransmitters; form scar tissue after injury Ependymal cells Line ventricles and central canal of spinal cord, assist in cerebrospinal fluid production FIGURE 7.3 Motor neurons, interneurons, and sensory neurons Neurons can be classified function- ally or structurally. This illustration depicts functional classification. Structurally, a. is a multipolar neuron, b. is a bipolar neuron, and c. is a unipolar neuron. The short portion of the axon that attaches the sensory neuron cell body to both the axon and the dendrite functions to carry impulses to and from the cell body. a. Motor neuron: Cell body located in CNS, axon in PNS (except in postganglionic neurons of the ANS) b. Interneuron: Found entirely within CNS and special senses c. Sensory neuron: Cell body and dendrites located in PNS, axon in CNS Cell body Dendrites Axon Axon terminal Cell body Dendrites Axon Axon terminal Cell body Axon Axon terminal Dendrites 132 CHAPTER 7 The Nervous System carry impulses both to and from the cell body. Each neuronal axon can have many terminal branches, so when the nerve fires, it can stimulate more than one cell. Concept Check 1. What are the main functions of the nervous system? 2. What are the three types of receptors in the afferent nervous system? 3.

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  King's Applied Anatomy of the Central Nervous System of Domestic Mammals

  • Geoff Skerritt(Author)
  • 2017(Publication Date)
  • Wiley-Blackwell

    (Publisher)

  5

  The Neuron

  The Anatomy of Neurons

  5.1 General Structure

  A typical neuron has dendrites, a cell body (perikaryon), an axon, collateral branches, axon terminals, and synaptic end bulbs.

  5.1.1 Relationships of the Dendrites and the Axon to the Cell Body

  The usual arrangement of neurons lying within the neuraxis is for the dendrites to lead directly to the cell body, and for the axon to lead from the cell body (Figure 5.1 (a)). However, the position of the cell body can vary. A primary afferent neuron (the first neuron in a sensory pathway from the periphery) has its cell body in a dorsal root ganglion of a spinal nerve or the equivalent ganglion of a cranial nerve. In this type of neuron, the cell body has relocated along the axon and, in functional terms, is now near the end of the axon instead of its beginning (Figure 5.1 (b)). The peripheral end of a primary afferent neuron typically consists of fine branching receptor terminals, which correspond to the dendrites of an ordinary neuron; the extreme tip of a receptor terminal is specialised, structurally and electrophysiologically, as a receptor ending. The re‐siting of the neuronal cell body of a primary afferent neuron reflects the evolutionary advantage of removing the cell body as far as possible from the surface of the animal’s body, where it could be too easily damaged. No matter what the position of the cell body, the nerve impulse normally travels from either the dendritic or the receptor endings towards the axon terminals, and ends at the synaptic end bulbs.

  Figure 5.1

  Two types of neuron with the cell body in different positions on the axon. (a) Typical unipolar neuron within the neuraxis. The numerous dendrites lead directly into the cell body, and the whole of the axon follows the cell body. (b)

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  Psychology

  • Ronald Comer, Elizabeth Gould, Adrian Furnham(Authors)
  • 2014(Publication Date)
  • Wiley

    (Publisher)

  Neural Networks In the brain, the number of neurons involved in a neural circuit is typically much greater than two. Collections of neurons that communicate with one another are referred to plasticity change in the nervous system. Synapse Presynaptic terminal Membrane of postsynaptic neuron Neurotransmitter receptor Neurotransmitter receptor Neurotransmitter Action potential Ion channels open Synaptic vesicle 1 2 3 4 FIGURE 5.6 Communication across the synapse. (1) A positive charge reaches the end of the axon; (2) the positive charge stimulates release of neurotransmitters contained in membrane-bound vesicles into the synapse; (3) neurotransmitters bind to receptors on the post- synaptic neuron; (4) ion channels open and an electrical charge in the postsynaptic neuron is generated. CHAPTER 5 BEHAVIOURAL NEUROSCIENCE 110 for basic bodily functions, including respiration and heart rate regulation. Although most of the actions of the brainstem occur without our conscious/ explicit awareness or involvement, this part of the brain is critical for survival and normal func- tioning. Damage to the brainstem, as a result of stroke or trauma, is often fatal. The brainstem is also important for integrating infor- mation about pain and touch from the head and neck with motor output. Neurons from the face, mouth and tongue related to touch, pain, pressure and vibration send inputs into the central nervous system that connect first in the brainstem. Parts of the brainstem are important for controlling eye movement, tongue movement and facial expressions. Several neuron groups, or nuclei, in the brainstem work together to form an area known as the reticular forma- tion , which is important for sleep and The Brain’s Structural and Functional Organization LEARNING OBJECTIVE 3 List key structures of the brain, and describe their relationships to our behaviour. The brain is divided into regions that serve varying functions.

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