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Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings

Fundamentals of Anatomy & Physiology

SIXTH EDITION

Frederic H. M

artini

PowerPoint® Lecture Slide Presentation prepared by Dr. Kathleen A. Ireland, Biology Instructor, Seabury Hall, Maui, Hawaii

Chapter 12, Neural tissue


Learning Objectives

• Describe the two major divisions of the nervous system and their characteristics.

• Identify the structures/functions of a typical neuron.

• Describe the location and function of neuroglia.

• Explain how resting potential is created and maintained.

• Describe the events in the generation and propagation of an action potential.


Learning Objectives

• Define the structure/function of a synapse.• List the major types of neurotransmitters

and neuromodulators.• Explain the processing of information in

neural tissue.


SECTION 12-1 An Overview of the Nervous System


nervous system overview

• Nervous system• Provides swift, brief responses to stimuli

• Endocrine system• Adjusts metabolic operations and directs

long-term changes• Nervous system includes

• All the neural tissue of the body• Basic unit = neuron


Divisions of the Nervous system

• CNS (Central Nervous system)• Brain and spinal cord

• PNS (Peripheral Nervous system)• Neural tissue outside CNS• Afferent division brings sensory

information from receptors• Efferent division carries motor

commands to effectors• Efferent division includes somatic nervous system and autonomic nervous system

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12.1

Figure 12.1 Functional Overview of the Nervous System


SECTION 12-2 Neurons


• Perikaryon• Neurofilaments, neurotubules,

neurofibrils• Axon hillock• Soma• Axon• Collaterals with telodendria

Neuron structure

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12.2b

Figure 12.2 The Anatomy of a Multipolar Neuron


• Site of intercellular communication• Neurotransmitters released from synaptic

knob of presynaptic neuron

Synapse


Figure 12.3 The Structure of a Typical Synpase

Figure 12.3


• Anatomical• Anaxonic • Unipolar• Bipolar• Multipolar

Neuron classification


Figure 12.4 A Structural Classification of Neurons


• Sensory neurons • deliver information from exteroceptors, interoceptors, or proprioceptors

• Motor neurons• Form the efferent division of the PNS

• Interneurons (association neurons)• Located entirely within the CNS• Distribute sensory input and coordinate motor output

Functional


Figure 12.5 A Functional Classification of Neurons


SECTION 12-3 Neuroglia


• Four types of neuroglia in the CNS• Ependymal cells

• Related to cerebrospinal fluid• Astrocytes

• Largest and most numerous• Oligodendrocytes

• Myelination of CNS axons• Microglia

• Phagocytic cells

Neuroglia of the Central Nervous System


Figure 12.6 An Introduction to Neuroglia

Figure 12.6


Figure 12.7 Neuroglia in the CNS

Figure 12.7a


Figure 12.7 Neuroglia in the CNS

Figure 12.7b


• Two types of neuroglia in the PNS• Satellite cells

• Surround neuron cell bodies within ganglia

• Schwann cells• Ensheath axons in the PNS

Neuroglia of the Peripheral Nervous System

Animation: Nervous system anatomy reviewPLAY


• Electrochemical gradient• Sum of all chemical and electrical forces

acting across the cell membrane• Sodium-potassium exchange pump

stabilizes resting potential at ~70 mV

The transmembrane potential


Figure 12.11 An Introduction to the Resting Potential


Figure 12.12 Electrochemical Gradients

Figure 12.12


• Membrane contains • Passive (leak) channels that are always

open• Active (gated) channels that open and

close in response to stimuli

Changes in the transmembrane potential


Figure 12.13 Gated Channels

Figure 12.13


• Chemically regulated channels• Voltage-regulated channels• Mechanically regulated channels

Three types of active channels


• A change in potential that decreases with distance • Localized depolarization or

hyperpolarization

Graded potential


Figure 12.14 Graded Potentials

Figure 12.14.1


Figure 12.14 Graded Potentials

Figure 12.14.2


Figure 12.15 Depolarization and Hyperpolarization


• Appears when region of excitable membrane depolarizes to threshold

• Steps involved• Membrane depolarization and

sodium channel activation• Sodium channel inactivation• Potassium channel activation• Return to normal permeability

Action Potential

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12.16.1

Figure 12.16 The Generation of an Action Potential


Figure 12.16 The Generation of an Action Potential


• Generation of action potential follows all-or-none principle

• Refractory period lasts from time action potential begins until normal resting potential returns

• Continuous propagation • spread of action potential across

entire membrane in series of small steps

• salutatory propagation• action potential spreads from node

to node, skipping internodal membrane

Characteristics of action potentials


Figure 12.17 Propagation of an Action Potential along an Unmyelinated Axon


Figure 12.18 Saltatory Propagation along a Myelinated Axon


• Type A fibers• Type B fibers• Type C fibers

• Based on diameter, myelination and propagation speed

Axon classification


• Muscle tissue has higher resting potential• Muscle tissue action potentials are longer

lasting• Muscle tissue has slower propagation of

action potentials

Animation: The action potentialPLAY

Muscle action potential versus neural action potential


• Action potential travels along an axon• Information passes from presynaptic

neuron to postsynaptic cell

Nerve impulse


• Electrical • Rare• Pre- and postsynaptic cells are bound by

interlocking membrane proteins

General properties of synapses


• Chemical synapses• More common• Excitatory neurotransmitters cause

depolarization and promote action potential generation

• Inhibitory neurotransmitters cause hyperpolarization and suppress action potentials

General properties of synapses


• Release acetylcholine (ACh) • Information flows across synaptic cleft• Synaptic delay occurs as calcium influx and

neurotransmitter release take appreciable amounts of time

• ACh broken down• Choline reabsorbed by presynaptic

neurons and recycled• Synaptic fatigue occurs when stores of ACh

are exhausted

Cholinergic synapses


Animation: Overview of a cholinergic synapsePLAY

Figure 12.19 The Function of a Cholinergic Synapse

Figure 12.19.1


Figure 12.19 The Function of a Cholinergic Synapse

Figure 12.19.2


• Adrenergic synapses release norepinephrine (NE)

• Other important neurotransmitters include• Dopamine• Serotonin• GABA (gamma aminobutyric acid)

Other neurotransmitters


• Influence post-synaptic cells response to neurotransmitter

• Neurotransmitters can have direct or indirect effect on membrane potential• Can exert influence via lipid-soluble

gases

Neuromodulators

Animation: Synaptic potentials, cellular integration, and synaptic transmissionPLAY


Figure 12.21 Neurotransmitter Functions

Figure 12.21a



Figure 12.21b



Figure 12.21c


SECTION 12-6 Information Processing


• Simplest level of information processing occurs at the cellular level• Excitatory and inhibitory

potentials are integrated through interactions between postsynaptic potentials

Information processing


• EPSP (excitatory postsynaptic potential) = depolarization • EPSP can combine through summation

• Temporal summation• Spatial summation

• IPSP (inhibitory postsynaptic potential) = hyperpolarization

• Most important determinants of neural activity are EPSP / IPSP interactions

Postsynaptic potentials


Figure 12.22 Temporal and Spatial Summation

Figure 12.22a


Figure 12.22 Temporal and Spatial Summation

Figure 12.22b


Figure 12.23 EPSP – IPSP Interactions

Figure 12.23


• GABA release at axoaxonal synapse inhibits opening calcium channels in synaptic knob• Reduces amount of neurotransmitter

released when action potential arrives

Presynaptic inhibition


Figure 12.24 Presynaptic Inhibition and Facilitation

Figure 12.24


• Activity at axoaxonal synapse increases amount of neurotransmitter released when action potential arrives• Enhances and prolongs the effect of the

neurotransmitter

Presynaptic facilitation


Figure 12.24 Presynaptic Inhibition and Facilitation

Figure 12.24


• Neurotransmitters are either excitatory or inhibitory• Effect on initial membrane segment

reflects an integration of all activity at that time

• Neuromodulators alter the rate of release of neurotransmitters

Rate of generation of action potentials


• Can be facilitated or inhibited by other extracellular chemicals

• Effect of presynaptic neuron may be altered by other neurons

• Degree of depolarization determines frequency of action potential generation

Rate of generation of action potentials


You should now be familiar with:

• The two major divisions of the nervous system and their characteristics.

• The structures/ functions of a typical neuron.

• The location and function of neuroglia.• How resting potential is created and

maintained.


You should now be familiar with:

• The events in the generation and propagation of an action potential.

• The structure / function of a synapse.• The major types of neurotransmitters and

neuromodulators.• The processing of information in neural

tissue.

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