Principles of Anatomy and Physiology: Nervous Tissue PDF

Principles of Anatomy and Physiology Gerard Tortora and Bryan Derrickson Sixteenth Edition Chapter 12 Nervous Tissue Introduction The purpose of the chapter is to: 1. Understand how the nervous system helps to keep controlled conditions within li...

Principles of Anatomy and Physiology Gerard Tortora and Bryan Derrickson Sixteenth Edition Chapter 12 Nervous Tissue 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 the different branches of the nervous system 3. Identify and describe the various types of cells that are found in nervous tissue Copyright ©2017 John Wiley & Sons, I 2 nc. Functions of the Nervous System To collect information from the environment, outside and inside the body To integrate and process the information To act upon the information by coordinating the actions of muscles and glands (the effectors of the nervous system) to bring about the appropriate response or to maintain homeostasis Copyright ©2017 John Wiley & Sons, I 3 nc. Nervous System Overview Interactions Animation: Introduction to Structure and Function of the N ervous System Copyright ©2017 John Wiley & Sons, I 4 nc. Layout of the Nervous System Copyright ©2017 John Wiley & Sons, I 5 nc. Organization of the Nervous System Copyright ©2017 John Wiley & Sons, I 6 nc. Functions of the Nervous System Sensory  Sense changes through sensory receptors Motor  Respond to stimuli Integrative  Analyze incoming sensory information, store some aspects, and make decisions regarding appropriate behaviors Copyright ©2017 John Wiley & Sons, I 7 nc. Organization of the Nervous System Interactions Animation: Nervous System Copyright ©2017 John Wiley & Sons, I 8 nc. Histology of Nervous Tissue Copyright ©2017 John Wiley & Sons, I 9 nc. Nervous Tissue Anatomy Overview: Neurons and Nerves Neuroglia Copyright ©2017 John Wiley & Sons, I 10 nc. Neurons Neurons  Electrically excitable  Cellular structures Copyright ©2017 John Wiley & Sons, I 11 nc. Structural Classification of Neurons Neurons can be classified based on the number of processes extending from the cell body Copyright ©2017 John Wiley & Sons, I 12 nc. Examples of Dendritic Branching Copyright ©2017 John Wiley & Sons, I 13 nc. Functional Classification of Neurons (1 of 2) Neurons can be classified based on the direction of nerve impulse propagation  Sensory/afferent neurons  Motor/efferent neurons  Inter/association neurons Copyright ©2017 John Wiley & Sons, I 14 nc. Functional Classification of Neurons (2 of 2) Copyright ©2017 John Wiley & Sons, I 15 nc. Neuron Structure and Function Interactions Animation: Types of Neurons Copyright ©2017 John Wiley & Sons, I 16 nc. 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 ©2017 John Wiley & Sons, I 17 nc. Neuroglia of the CNS Copyright ©2017 John Wiley & Sons, I 18 nc. Neuroglia of the PNS Copyright ©2017 John Wiley & Sons, I 19 nc. 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 ©2017 John Wiley & Sons, I 20 nc. Myelination of Neurons (2 of 2) Copyright ©2017 John Wiley & Sons, I 21 nc. Gray Matter vs. White Matter Copyright ©2017 John Wiley & Sons, I 22 nc.  Electrical Signals in Neurons: An Overview Copyright ©2017 John Wiley & Sons, I 23 nc. 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  Production of an AP or a GP depends upon the existence of a resting membrane potential and the existence of certain ion channels Copyright ©2017 John Wiley & Sons, I 24 nc. Excitable Cells and the Resting Membrane Potential 3D Physiology: Membrane Potentials: Excitable Cells and the Resting Membrane Potential Copyright ©2017 John Wiley & Sons, I 25 nc. Graded Potentials & Action Potentials Copyright ©2017 John Wiley & Sons, I 26 nc. 3D Physiology Membrane Potentials: Graded and Action Pot entials Copyright ©2019 John Wiley & Sons, I 27 nc. Ion Channels in Neurons (1 of 5) Leak channels alternate between open and closed K+ channels are more numerous than Na+ channels Copyright ©2017 John Wiley & Sons, I 28 nc. Ion Channels in Neurons (2 of 5) Ligand-gated channels respond to chemical stimuli (ligand binds to receptor) Copyright ©2017 John Wiley & Sons, I 29 nc. Ion Channels in Neurons (3 of 5) Mechanically-gated channels respond to mechanical vibration or pressure stimuli Copyright ©2017 John Wiley & Sons, I 30 nc. Ion Channels in Neurons (4 of 5) Voltage-gated channels respond to direct changes in membrane potential Copyright ©2017 John Wiley & Sons, I 31 nc. Ion Channels in Neurons (5 of 5) Type of Ion Description Location Channel Leak channels Gated channels that Found in nearly all cells, randomly open and close. including dendrites, cell bodies, and axons of all types of neurons. Ligand-gated Gated channels that open Dendrites of some sensory channels in response to binding of neurons such as pain receptors ligand (chemical) stimulus. and dendrites and cell bodies of interneurons and motor neurons. Mechanically- Gated channels that open Dendrites of some sensory gated channels in response to mechanical neurons such as touch stimulus (such as touch, receptors, pressure receptors, pressure, vibration, or and some pain receptors. tissue stretching). Voltage-gated Gated channels that open Axons of all types of neurons. channels in response to voltage stimulus (change Copyright in John Wiley & Sons, I ©2017 32 nc. membrane potential). Resting Membrane Potential Copyright ©2017 John Wiley & Sons, I 33 nc. Membrane Potentials Interactions Animation: Membrane Potentials Copyright ©2017 John Wiley & Sons, I 34 nc. 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 Na+ and K+ 2. Most anions cannot leave the cell 3. Na+/K+ pumps Copyright ©2017 John Wiley & Sons, I 35 nc. Resting Membrane Potential: Voltage Difference Copyright ©2017 John Wiley & Sons, I 36 nc. Factors Contributing to Resting Membrane Potential Copyright ©2017 John Wiley & Sons, I 37 nc. Graded Potentials (1 of 2) Small deviations in resting membrane potential Copyright ©2017 John Wiley & Sons, I 38 nc. Graded Potentials (2 of 2) A graded potential occurs in response to the opening of a mechanically-gated or ligand- gated ion channel Copyright ©2017 John Wiley & Sons, I 39 nc. Graded Potentials: Stimulus Strength The amplitude of a graded potential depends on the stimulus strength Copyright ©2017 John Wiley & Sons, I 40 nc. Graded Potentials: Summation Graded potentials can be added together to become larger in amplitude Copyright ©2017 John Wiley & Sons, I 41 nc. Action Potentials Copyright ©2017 John Wiley & Sons, I 42 nc. Action Potentials (1 of 2) An action potential is a sequence of rapidly occurring events that decrease and eventually reverse the membrane potential (depolarization) and eventually restore it to the resting state (repolarization) Copyright ©2017 John Wiley & Sons, I 43 nc. Action Potentials (2 of 2) Copyright ©2017 John Wiley & Sons, I 44 nc. Action Potentials: Stimulus Strength Action potentials can only occur if the membrane potential reaches threshold Copyright ©2017 John Wiley & Sons, I 45 nc. Action Potentials: the Status of Na+ and K+ Voltage-Gated Channels Copyright ©2017 John Wiley & Sons, I 46 nc. Comparison of Graded & Action Potentials (1 of 2) Characteristi Graded Potentials Action Potentials c 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 channels mechanically-gated ion Na+ and K+. channels. Conduction Decremental (not Propagate and thus permit propagated); permit communication over longer communication over short distances. distances. Amplitude Depending on strength of All or none; typically about (size) stimulus, varies from less 100 mV. than 1 mV to more than 50 mV.Copyright ©2017 John Wiley & Sons, I 47 nc. Comparison of Graded & Action Potentials (2 of 2) Characteristi Graded Potentials Action Potentials c Duration Typically longer, ranging Shorter, ranging from 0.5 from several milliseconds to 2 msec. to several minutes. Polarity May be hyperpolarizing Always consist of (inhibitory to generation depolarizing phase of action potential) or followed by repolarizing depolarizing (excitatory phase and return to resting to generation of action membrane potential. potential). Refractory Not present; summation Present; summation cannot period can occur. occur. Copyright ©2017 John Wiley & Sons, I 48 nc. 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 Action potentials do not die out; they keep their strength as they spread across the membrane of a neuron Copyright ©2017 John Wiley & Sons, I 49 nc. Continuous vs. Saltatory Conduction Copyright ©2017 John Wiley & Sons, I 50 nc. Factors That Affect Propagation Speed Axon diameter Amount of myelination Temperature Copyright ©2017 John Wiley & Sons, I 51 nc. Factors That Affect Propagation Speed Interactions Animation: Myelination and Conduction Rates Copyright ©2017 John Wiley & Sons, I 52 nc. Signal Transmission at Synapses Copyright ©2017 John Wiley & Sons, I 53 nc. Signal Transmission at Synapses A synapse is the junction between neurons or between a neuron and an effector  Electrical Synapse Gap junctions connect cells and allow the transfer of information to synchronize the activity of a group of cells  Chemical Synapse One-way transfer of information from a presynaptic neuron to a postsynaptic neuron Copyright ©2017 John Wiley & Sons, I 54 nc. Synapses Between Neurons Copyright ©2017 John Wiley & Sons, I 55 nc. Events at the Synapse Interactions Animation: Events at the Synapse Copyright ©2017 John Wiley & Sons, I 56 nc. Signal Transmission at a Chemical Synapse Copyright ©2017 John Wiley & Sons, I 57 nc. Synapses and Neurotransmitter Action 3D Physiology: Synapses and Neurotransmitter Action Copyright ©2017 John Wiley & Sons, I 58 nc. 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 ©2017 John Wiley & Sons, I 59 nc. Structure of Neurotransmitter Receptors Neurotransmitters at chemical synapses cause either an excitatory or inhibitory graded potential Neurotransmitter receptors have two structures  Ionotropic receptors  Metabotropic receptors Copyright ©2017 John Wiley & Sons, I 60 nc. Ionotropic & Metabotropic Receptors Copyright ©2017 John Wiley & Sons, I 61 nc. Removal of Neurotransmitter Neurotransmitter can be removed from the synaptic cleft by: 1. Diffusion 2. Enzymatic degradation 3. Uptake into cells Copyright ©2017 John Wiley & Sons, I 62 nc. 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 ©2017 John Wiley & Sons, I 63 nc. Spatial Summation Copyright ©2017 John Wiley & Sons, I 64 nc. Temporal Summation Copyright ©2017 John Wiley & Sons, I 65 nc. Summation of Postsynaptic Potentials Copyright ©2017 John Wiley & Sons, I 66 nc. Summary of Neuronal Structure and Function (1 of 2) Copyright ©2017 John Wiley & Sons, I 67 nc. Summary of Neuronal Structure and Function (2 of 2) Copyright ©2017 John Wiley & Sons, I 68 nc. Neurotransmitters Copyright ©2017 John Wiley & Sons, I 69 nc. Neurotransmitters (1 of 2) Small molecule neurotransmitters  Acetylcholine  Amino acids  Biogenic amines  ATP and other purines  Nitric oxide  Carbon monoxide Copyright ©2017 John Wiley & Sons, I 70 nc. Neurotransmitters (2 of 2) Copyright ©2017 John Wiley & Sons, I 71 nc. Neuropeptides (1 of 3) Neuropeptides  Substance P  Enkephalins  Endorphins  Dynorphins  Hypothalamic releasing and inhibiting hormones  Angiotensin II  Cholecystokinin Copyright ©2017 John Wiley & Sons, I 72 nc. Neuropeptides (2 of 3) Substance Description Substance P Found in sensory neurons, spinal cord pathways, and parts of brain associated with pain; enhances perception of pain. Enkephalins Inhibit pain impulses by suppressing release of substance P; may have role in memory and learning, control of body temperature, sexual activity, and mental illness. Endorphins Inhibit pain by blocking release of substance P; may have role in memory and learning, sexual activity, control of body temperature, and mental illness. Dynorphins May be related to controlling pain and registering emotions. Hypothalamic Produced by hypothalamus; regulate release of releasing and hormones by anterior pituitary. inhibiting hormones Copyright ©2017 John Wiley & Sons, I 73 nc. Neuropeptides (3 of 3) Substance Description 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 feeding (CCK) 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 ©2017 John Wiley & Sons, I 74 nc. Neural Circuits Copyright ©2017 John Wiley & Sons, I 75 nc. 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 ©2017 John Wiley & Sons, I 76 nc. Neural Circuits: Diverging & Converging Copyright ©2017 John Wiley & Sons, I 77 nc. Neural Circuits: Reverberating & Parallel After-Discharge Copyright ©2017 John Wiley & Sons, I 78 nc. 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 ©2017 John Wiley & Sons, I 79 nc. 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 ©2017 John Wiley & Sons, I 80 nc. 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 ©2017 John Wiley & Sons, I 81 nc. Damage and Repair in the CNS (2 of 2) Copyright ©2017 John Wiley & Sons, I 82 nc. Disorders Multiple Sclerosis Epilepsy Excitotoxicity Depression Copyright ©2017 John Wiley & Sons, I 83 nc. Copyright Copyright © 2017 John Wiley & Sons, Inc. 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