Nervous Tissue PDF - Principles of Anatomy and Physiology

Principles of Anatomy and Physiology Gerard Tortora and Bryan Derrickson Sixteenth Edition Chapter 12 Nervous Tissue This slide deck contains animations. Please disable animati...

Principles of Anatomy and Physiology Gerard Tortora and Bryan Derrickson Sixteenth Edition Chapter 12 Nervous Tissue This slide deck contains animations. Please disable animations if they cause issues with your device. Copyright ©2021 John Wiley & Sons, Inc. Introduction The purpose of the chapter is to: 1. Understand how the nervous system helps to keep controlled conditions within limits that maintain health and homeostasis 2. Learn about different branches of the nervous system 3. Identify and describe the various types of cells that are found in nervous tissue Copyright ©2021 John Wiley & Sons, 2 Inc. Overview of the Nervous System Copyright ©2021 John Wiley & Sons, 3 Inc. Nervous System Overview Nervous System Overview Interactions Animation: Introduction to Structure and Function of th e Nervous System Copyright ©2021 John Wiley & Sons, 5 Inc. Layout of the Nervous System Copyright ©2021 John Wiley & Sons, 6 Inc. Organization of the Nervous System Copyright ©2021 John Wiley & Sons, 7 Inc. Functions of the Nervous System Sensory Detect changes through sensory receptors Integrative Analyze incoming sensory information, store some aspects, and make decisions regarding appropriate behaviors Motor Respond to stimuli via effectors Copyright ©2021 John Wiley & Sons, 8 Inc. Organization of the Nervous System Interactions Animation: Nervous System Copyright ©2021 John Wiley & Sons, 9 Inc. Histology of Nervous Tissue Copyright ©2021 John Wiley & Sons, 10 Inc. Nervous Tissue Anatomy Overview: Neurons and Nerve Neuroglia Copyright ©2021 John Wiley & Sons, 11 Inc. Neurons (1 of 2) Neurons Electrically excitable Cellular structures Nerve impulse is called an action potential Copyright ©2021 John Wiley & Sons, 12 Inc. Neurons (2 of 2) Copyright ©2021 John Wiley & Sons, 13 Inc. Structural Classification of Neurons Neurons can be classified based on the number of processes extending from the cell body Copyright ©2021 John Wiley & Sons, 14 Inc. Examples of Dendritic Branching Copyright ©2021 John Wiley & Sons, 15 Inc. Functional Classification of Neurons (1 of 2) Neurons can be classified based on the direction of nerve impulse propagation Sensory/Afferent neurons o Conveys information to the CNS Motor/Efferent neurons o Conveys action potential from the CNS Interneurons/Association neurons o Process sensory information and elicit motor response Copyright ©2021 John Wiley & Sons, 16 Inc. Functional Classification of Neurons (2 of 2) Copyright ©2021 John Wiley & Sons, 17 Inc. Neuron Structure and Function Interactions Animation: Types of Neurons Copyright ©2021 John Wiley & Sons, 18 Inc. Neuroglia Neuroglia Not electrically excitable Make up about half the volume of the nervous system Can multiply and divide 6 kinds total (4 in CNS, 2 in PNS) Copyright ©2021 John Wiley & Sons, 19 Inc.  Neuroglia There are 4 types of neuroglia in the CNS: Astrocytes - support neurons in the CNS Maintain the chemical environment (Ca2+ & K+) Oligodendrocytes - produce myelin in CNS Microglia - participate in phagocytosis Ependymal cells - form and circulate CSF There are 2 types of neuroglia in the PNS: Satellite cells - support neurons in PNS Schwann cells - produce myelin in PNS Neuroglia of the CNS Copyright ©2021 John Wiley & Sons, 21 Inc. Neuroglia of the PNS Copyright ©2021 John Wiley & Sons, 22 Inc. Myelination of Neurons (1 of 2) The myelin sheath is produced by Schwann cells (PNS) and oligodendrocytes (CNS) and it surrounds the axons of most neurons Copyright ©2021 John Wiley & Sons, 23 Inc. Myelination of Neurons (2 of 2) Copyright ©2021 John Wiley & Sons, 24 Inc. Gray Matter vs. White Matter Copyright ©2021 John Wiley & Sons, 25 Inc. Electrical Signals in Neurons: An Overview Copyright ©2021 John Wiley & Sons, 26 Inc. Electrical Signals in Neurons Excitable cells communicate with each other via Action Potentials or Graded Potentials Action Potentials (AP) allow communication over short and long distances whereas Graded Potentials (GP) allow communication over short distances only o Production of an AP or a GP depends upon the existence of a resting membrane potential and the existence of certain ionCopyright channels ©2021 John Wiley & Sons, 27 Inc. Excitable Cells and the Resting Membrane Potential 3D Physiology: Membrane Potentials: Excitable Cells and the Resting Membrane Potential Copyright ©2021 John Wiley & Sons, 28 Inc. Graded Potentials & Action Potentials Copyright ©2021 John Wiley & Sons, 29 Inc. Graded Potentials & Action Potentials 3D Physiology: Membrane Potentials: Excitable Cells and the Resting Membrane Potential Copyright ©2021 John Wiley & Sons, 30 Inc. Ion Channels in Neurons (1 of 5) Leak channels alternate between open and closed K+ channels are more numerous than N a+ channels Copyright ©2021 John Wiley & Sons, 31 Inc. Ion Channels in Neurons (2 of 5) Ligand-gated channels respond to chemical stimuli (ligand binds to receptor) Copyright ©2021 John Wiley & Sons, 32 Inc. Ion Channels in Neurons (3 of 5) Mechanically-gated channels respond to mechanical vibration or pressure stimuli Copyright ©2021 John Wiley & Sons, 33 Inc. Ion Channels in Neurons (4 of 5) Voltage-gated channels respond to direct changes in membrane potential Copyright ©2021 John Wiley & Sons, 34 Inc. Ion Channels in Neurons (5 of 5) Type of Ion Description Location Channel Leak channels Gated channels that Found in nearly all cells, and dendrites, randomly open and close. cell bodies, and axons of all types of neurons. Ligand-gated Gated channels that open Dendrites of some sensory neurons channels in response to binding of such as pain receptors and dendrites ligand (chemical) and cell bodies of interneurons and stimulus. motor neurons. Mechanically gated Gated channels that open Dendrites of some sensory neurons channels in response to mechanical such as touch receptors, pressure stimulus (such as touch, receptors, and some pain receptors. pressure, vibration, or tissue stretching). Voltage-gated Gated channels that open Axons of all types of neurons. channels in response to voltage stimulus (change in membrane potential). Copyright ©2021 John Wiley & Sons, 35 Inc. Resting Membrane Potential Copyright ©2021 John Wiley & Sons, 36 Inc. Membrane Potentials Interactions Animation: Membrane Potentials Copyright ©2021 John Wiley & Sons, 37 Inc. Resting Membrane Potential The membrane of a non-conducting neuron is positive outside and negative inside. This is determined by: 1. Unequal distribution of ions across the plasma membrane and the selective permeability of the neuron’s membrane to N a+ and K+ 2. Most anions cannot leave the cell 3. N a+/K+ pumps Copyright ©2021 John Wiley & Sons, 38 Inc. Resting Membrane Potential: Voltage Difference Copyright ©2021 John Wiley & Sons, 39 Inc. Factors Contributing to Resting Membrane Potential Copyright ©2021 John Wiley & Sons, 40 Inc. Graded Potentials (1 of 2) Small deviations in resting membrane potential Copyright ©2021 John Wiley & Sons, 41 Inc. Graded Potentials (2 of 2) A graded potential occurs in response to the opening of a mechanically-gated or ligand- gated ion channel Copyright ©2021 John Wiley & Sons, 42 Inc. Graded Potentials: Stimulus Strength The amplitude of a graded potential depends on the stimulus strength Copyright ©2021 John Wiley & Sons, 43 Inc. Graded Potentials: Summation Graded potentials can be added together to become larger in amplitude Copyright ©2021 John Wiley & Sons, 44 Inc. Action Potentials Copyright ©2021 John Wiley & Sons, 45 Inc. Action Potentials (1 of 2) An action potential is a sequence of rapidly occurring events that decrease and eventually reverse the membrane potential and eventually restore it to the resting state. Action Potentials have two phases: 1. Depolarization 2. Repolarization Copyright ©2021 John Wiley & Sons, 46 Inc. Action Potentials (2 of 2) Copyright ©2021 John Wiley & Sons, 47 Inc. Action Potentials: Stimulus Strength Action potentials can only occur if the membrane potential reaches threshold Copyright ©2021 John Wiley & Sons, 48 Inc. Action Potentials: the Status of Na+ and K+ Voltage-Gated Channels (1 of 4) Copyright ©2021 John Wiley & Sons, 49 Inc. Action Potentials: the Status of Na+ and K+ Voltage-Gated Channels (2 of 4) Copyright ©2021 John Wiley & Sons, 50 Inc. Action Potentials: the Status of Na+ and K+ Voltage-Gated Channels (3 of 4) Copyright ©2021 John Wiley & Sons, 51 Inc. Action Potentials: the Status of Na+ and K+ Voltage-Gated Channels (4 of 4) Copyright ©2021 John Wiley & Sons, 52 Inc. Comparison of Graded & Action Potentials (1 of 2) Characteristic Graded Potentials Nerve Impulses Origin Arise mainly in dendrites Arise at trigger zones and and cell body. propagate along axon. Types of Ligand-gated or Voltage-gated channels for Na+ channels mechanically gated ion and K+. channels. Conduction Decremental (not Propagate and thus permit propagated); permit communication over longer communication over distances. short distances. Amplitude Depending on strength All or none; typically about 100 (size) of stimulus, varies from mV. less than 1 mV to more than 50 mV. Copyright ©2021 John Wiley & Sons, 53 Inc. Comparison of Graded & Action Potentials (2 of 2) Characterist Graded Potentials Nerve Impulses ic Duration Typically longer, ranging Shorter, ranging from 0.5 to 2 from several milliseconds msec. to several minutes. Polarity May be hyperpolarizing Always consist of depolarizing (inhibitory to generation of phase followed by repolarizing action potential) or phase and return to resting depolarizing (excitatory to membrane potential. generation of action potential). Refractory Not present; summation Present; summation cannot occur. period can occur. Copyright ©2021 John Wiley & Sons, 54 Inc. Propagation of Action Potentials In order for communication to occur from one body part to another, action potentials must travel from where they arise at the trigger zone to the axon terminals This traveling is called propagation Action potentials do not die out; they keep their strength as they spread across the membrane of a neuron Copyright ©2021 John Wiley & Sons, 55 Inc. Continuous vs. Saltatory Conduction Copyright ©2021 John Wiley & Sons, 56 Inc. Factors That Affect Propagation Speed 1. Axon diameter Larger diameter axons propagate APs faster 2. Amount of myelination Myelin increases speed of AP propagation 3. Temperature Higher temperature increases speed of AP propagation Copyright ©2021 John Wiley & Sons, 57 Inc. Factors That Affect Propagation Speed Interactions Animation: Myelination and Conduction Rates Copyright ©2021 John Wiley & Sons, 58 Inc. Signal Transmission at Synapses Copyright ©2021 John Wiley & Sons, 59 Inc. Signal Transmission at Synapses A synapse is the junction between neurons or between a neuron and an effector Electrical Synapse o Gap junctions connect cells and allow the transfer of information to synchronize the activity of a group of cells Chemical Synapse o One-way transfer of information from a presynaptic neuron to a postsynaptic neuron Copyright ©2021 John Wiley & Sons, 60 Inc. Synapses Between Neurons Copyright ©2021 John Wiley & Sons, 61 Inc. Events at the Synapse Interactions Animation: Events at the Synapse Copyright ©2021 John Wiley & Sons, 62 Inc. Signal Transmission at a Chemical Synapse Copyright ©2021 John Wiley & Sons, 63 Inc. Synapses and Neurotransmitter Action 3D Physiology: Synapses and Neurotransmitter Action Copyright ©2021 John Wiley & Sons, 64 Inc. Postsynaptic Potentials Excitatory postsynaptic potentials A depolarizing postsynaptic potential Inhibitory postsynaptic potentials A hyperpolarizing postsynaptic potential A postsynaptic neuron can receive many signals at once Copyright ©2021 John Wiley & Sons, 65 Inc. Structure of Neurotransmitter Receptors Neurotransmitters at chemical synapses cause either an excitatory or inhibitory graded potential Neurotransmitter receptors have two structures o Ionotropic receptors Contains a neurotransmitter binding site and ion channel o Metabotropic receptors Contains a neurotransmitter binding site and is coupledCopyright ot a ©2021 separate ion John Wiley & Sons,channel by a G 66 Inc. Ionotropic Receptors (1 of 2) Copyright ©2021 John Wiley & Sons, 67 Inc. Metabotropic Receptor Copyright ©2021 John Wiley & Sons, 68 Inc. Removal of Neurotransmitter Neurotransmitter can be removed from the synaptic cleft by: 1. Diffusion 2. Enzymatic degradation 3. Uptake into cells Copyright ©2021 John Wiley & Sons, 69 Inc. Summation If several presynaptic end bulbs release their neurotransmitter at about the same time, the combined effect may generate a nerve impulse due to summation Summation may be spatial or temporal Copyright ©2021 John Wiley & Sons, 70 Inc. Spatial Summation Copyright ©2021 John Wiley & Sons, 71 Inc. Temporal Summation Copyright ©2021 John Wiley & Sons, 72 Inc. Summation of Postsynaptic Potentials Copyright ©2021 John Wiley & Sons, 73 Inc. Summary of Neuronal Structure and Function (1 of 2) Copyright ©2021 John Wiley & Sons, 74 Inc. Neurotransmitters Copyright ©2021 John Wiley & Sons, 75 Inc. Neurotransmitters (1 of 2) Small molecule neurotransmitters Acetylcholine Amino acids Biogenic amines ATP and other purines Nitric oxide Carbon monoxide Copyright ©2021 John Wiley & Sons, 76 Inc. Neurotransmitters (2 of 2) Copyright ©2021 John Wiley & Sons, 77 Inc. Neuropeptides (1 of 3) Neuropeptides Substance P Enkephalins Endorphins Dynorphins Hypothalamic releasing and inhibiting hormones Angiotensin II Cholecystokinin Copyright ©2021 John Wiley & Sons, 78 Inc. Neuropeptides (2 of 3) Substanc Description e Substanc Found in sensory neurons, spinal cord pathways, and eP parts of brain associated with pain; enhances perception of pain. Enkephali Inhibit pain impulses by suppressing release of ns substance P; may have role in memory and learning, control of body temperature, sexual activity, and mental illness. Endorphi Inhibit pain by blocking release of substance P; may ns have role in memory and learning, sexual activity, control of body temperature, and mental illness. Dynorphi May be related to controlling pain and registering ns emotions. Copyright ©2021 John Wiley & Sons, 79 Inc. Neuropeptides (3 of 3) Substance Description Hypothalamic Produced by hypothalamus; regulate release of releasing and hormones by anterior pituitary. inhibiting hormones Angiotensin II Stimulates thirst; may regulate blood pressure in brain. As a hormone, causes vasoconstriction and promotes release of aldosterone, which increases rate of salt and water reabsorption by kidneys. Cholecystokinin Found in brain and small intestine; may regulate (CCK) feeding as a “stop eating” signal. As a hormone, regulates pancreatic enzyme secretion during digestion, and contraction of smooth muscle in gastrointestinal tract. Neuropeptide Y Stimulates food intake; may play a role in the stress response. Copyright ©2021 John Wiley & Sons, 80 Inc. Neural Circuits Copyright ©2021 John Wiley & Sons, 81 Inc. Neural Circuits A neural circuit is a functional group of neurons that process specific types of information Types of circuits Simple series Diverging Converging Reverberating Parallel after-discharge Copyright ©2021 John Wiley & Sons, 82 Inc. Neural Circuits: Diverging & Converging Copyright ©2021 John Wiley & Sons, 83 Inc. Neural Circuits: Reverberating & Parallel After-Discharge Copyright ©2021 John Wiley & Sons, 84 Inc. Regeneration & Repair of Nervous Tissue Although the nervous system exhibits plasticity, neurons have a limited ability to regenerate themselves Plasticity – the capability to change based on experience Regenerate – the capability to replicate or repair Copyright ©2021 John Wiley & Sons, 85 Inc. Neurogenesis in the CNS In the CNS, there is little or no repair due to: Inhibitory influences from neuroglia, particularly oligodendrocytes Absence of growth-stimulating cues that were present during fetal development Rapid formation of scar tissue Copyright ©2021 John Wiley & Sons, 86 Inc. Damage and Repair in the CNS (1 of 2) In the PNS repair is possible if the cell body is intact, Schwann cells are functional, and scar tissue formation does not occur too rapidly Steps involved in the repair process are: Chromatolysis Wallerian degeneration Formation of a regeneration tube Copyright ©2021 John Wiley & Sons, 87 Inc. Damage and Repair in the CNS (2 of 2) Copyright ©2021 John Wiley & Sons, 88 Inc. Neural Disorders – Multiple Sclerosis Autoimmune disease that causes progressive destruction of myelin sheath Cause is unclear; may be genetic and/or environmental Symptoms include muscle weakness, abnormal sensations and double vision Copyright ©2021 John Wiley & Sons, 89 Inc. Neural Disorders – Depression Several types of depression 1) Major depression 2) Dysthymia 3) Bipolar depression (manic-depressive illness) 4) Seasonal affective disorder (SAD) Common feelings are lack of interest in activities, sadness, helpless and possibly suicidal thoughts Commonly treated through selective serotonin reuptake inhibitors (SSRIs) Copyright ©2021 John Wiley & Sons, 90 Inc. Signal Transmission at a Chemical Synapse Copyright ©2021 John Wiley & Sons, 91 Inc. Other Neural Disorders Epilepsy o Short, recurrent attacks of motor, sensory or psychological function o Initiated by abnormal synchronous electrical discharges from the millions of neurons in the brain Excitotoxicity o Destructions of neurons through prolonged activation of excitatory synaptic transmission o Caused by high levels of glutamine in CNS interstitial fluid Copyright ©2021 John Wiley & Sons, 92 Inc. Copyright © 2017 John Wiley & Sons, Inc. 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