ch 13_lecture_presentation

© 2012 Pearson Education, Inc.

13The Nervous System:Neural Tissue

PowerPoint® Lecture Presentations prepared bySteven BassettSoutheast Community College Lincoln, Nebraska


Introduction

• Nervous System Characteristics• Controls and adjust the activity of the body• Provides swift but brief responses


Introduction

• The nervous system includes:• Central Nervous System (CNS)

• Associated with the brain and the spinal cord Integrating, processing, and coordinating Intelligence, memory, learning, and emotion

• Peripheral Nervous System (PNS)• Associated with the tissue outside the CNS Neural tissue outside the CNS Provides sensory information to the CNS Carries motor commands to peripheral tissues


An Overview of the Nervous System

• The Peripheral Nervous System (PNS) can be subdivided into:• Afferent: Brings sensory information toward the CNS• Receptors, which transform different stimuli into Action

Potential, belong to this division. • Which can be further subdivided into somatic and visceral

• Efferent: Carries motor commands away from the CNS

• Effectors, that respond to the CNS commands, belong to this division.• Which can be further subdivided into somatic nerves and

autonomic nerves


Figure 13.1 The Nervous SystemCENTRAL NERVOUS

SYSTEMBrain

Spinal cord

Peripheral nerves

PERIPHERAL NERVOUSSYSTEM


An Overview of the Nervous System

• The Peripheral Nervous System (PNS)• Afferent

• Sensory portion: monitors skeletal muscles and joints

• Visceral portion: monitors smooth muscles, cardiac muscle, and other internal organs

• Efferent• Somatic nerves: controls skeletal muscle

contraction• Autonomic nerves: controls internal organ

activities


Afferent division

The afferent division carries information from Somatic sensory receptors

Skeletal muscles, joints, and the skin

Visceral sensory receptors Smooth muscle, cardiac muscle, and glands

Special sense organs Eye, nose, tongue, and ear


Efferent division

The efferent division begins inside the CNS and ends at an effector. The efferent division

Somatic nervous system (SNS) Skeletal muscle contractions May be voluntary or involuntary

Autonomic nervous system (ANS) Visceral motor system Smooth muscle, cardiac muscle, and glands Involuntary Includes sympathetic and parasympathetic divisions.


Figure 13.2 A Functional Overview of the Nervous System

CENTRAL NERVOUS SYSTEM(brain and spinal cord)

PERIPHERALNERVOUSSYSTEM

RECEPTORS EFFECTORS

Informationprocessing

Sensoryinformation

withinafferentdivision

Motorcommands

withinefferentdivision

Includes

Somatic nervoussystem

Autonomic nervous system

Parasympatheticdivision

Sympatheticdivision

Skeletalmuscle • Smooth

muscle• Cardiac muscle• Glands

Special sensoryreceptors (providesensations of smell,taste, vision,balance, andhearing)

Somatic sensoryreceptors (monitorskeletal muscles, joints,skin surface; provideposition sense andtouch, pressure, pain,and temperaturesensations)

Visceral sensory receptors (monitorinternal organs, including thoseof cardiovascular, respiratory, digestive,urinary, and reproductive systems)


Cellular Organization in Neural Tissue

• Neural tissue consists of two cell types:• Neurons

• Nerve cells that are responsible for the transfer and processing of information in the nervous system

• Consist of a soma, axon, and dendrites

• Neuroglia• Supporting cells • Protect the neuron


Figure 3.23a Histology of Neural Tissue

Brain

Spinal cord

Cell body

Axon

Nucleus ofneuronNucleolus

Dendrites

Diagrammatic view of a representative neuron



• Functions of Neuroglia• Provide the framework for the neural tissue• Maintain the intercellular environment• Act as phagocytes• Over 100 billion• Roughly five times the number of neurons• Also called glial cells• Have the ability to reproduce



• Neuroglia Cells• Neuroglia cells of the CNS

• Astrocytes• Oligodendrocytes• Microglia• Ependymal cells

• Neuroglia cells of the PNS• Satellite cells• Schwann cells


Figure 13.4 The Classification of Neuroglia

Neuroglia

Peripheral Nervous System Central Nervous System

are found in

containscontains

Satellite cells Schwann cells Oligodendrocytes Astrocytes Microglia Ependymal cells

Surround neuron cellbodies in ganglia;regulate O2, CO2,nutrient, andneurotransmitter levelsaround neurons inganglia

Surround all axons inPNS; responsible formyelination ofperipheral axons;participate in repairprocess after injury

Myelinate CNSaxons; providestructuralframework

Maintain blood–brainbarrier; provide structuralsupport; regulate ion,nutrient, and dissolved-gasconcentrations; absorb andrecycle neurotransmitters;form scar tissue after injury

Remove celldebris, wastes,and pathogensby phagocytosis

Line ventricles(brain) and centralcanal (spinal cord);assist in producing,circulating, andmonitoringcerebrospinal fluid



• Neuroglia of the CNS• Astrocytes

• Largest and most numerous glial cells• Have a large number of cytoplasmic processes• Control the chemical content of the interstitial

environment• Maintain the blood–brain barrier• Isolate the neurons from general circulation Creating a three-dimensional framework for the CNS Performing repairs in damaged neural tissue Guiding neuron development



• Neuroglia of the CNS• Oligodendrocytes

• Cytoplasmic extensions contact the somas or axons

• Cytoplasmic extensions tie axons together in a sheath of myelin

• Microglia• Phagocytic cells• Protect the neuron by removing waste and debris



• Neuroglia of the CNS• Ependymal cells

• Line the ventricles of the brain• Line the central canal of the spinal cord• Monitor the CSF (cerebrospinal fluid)

composition• Some ependymal cells secrete CSF


Figure 13.5 Histology of Neural Tissue in the CNS

Graymatter

Whitematter

Internode

Neurons

Myelinatedaxons

Myelin(cut)

Axon Axolemma

Oligodendrocyte

Myelin sheathgap

Unmyelinatedaxon

Basal lamina

Capillary

Astrocyte

Microglialcell

Ependymalcells

CENTRAL CANAL


Figure 13.6a The Ependyma

Light micrograph showing theependymal lining of the central canal

POSTERIOR

ANTERIOR

LM 450

Gray matter

White matter

Central canal

Ependymalcells

Central canal

Central canal



• Neuroglia of the PNS• Satellite cells

• Regulate the exchange of material between the cell body and the environment

• Schwann cells• Also called neurolemmocytes• Form a myelin sheath


Figure 13.7 Satellite Cells and Peripheral Neurons

Nerve cell body

Nucleus

Satellite cellsConnective

tissue

Peripheral ganglion LM 25


Figure 13.8a Schwann Cells and Peripheral Axons

Axon hillock

AxonNucleus

Dendrite

Myelinatedinternode Initial

segment(unmyelinated)

Myelin sheath gaps

Schwanncell nucleus

Axon

neurolemma

neurolemma

Myelincoveringinternode

Axon

Axolemma

Axons

Myelin

TEM 20,600Myelin sheath

A single Schwann cell forms the myelin sheatharound a portion of a single axon. This situationdiffers from the way myelin forms inside the CNS.Compare with Figure 13.5.


Figure 13.8b Schwann Cells and Peripheral Axons

neurolemma

neurolemma

Schwanncell nucleus

Schwanncell

Axons

Myelinsheath

gap

Schwanncell nucleus

Axons

Axons

TEM 27,625Unmyelinated axons

A single Schwann cell can encircle severalunmyelinated axons. Unlike the situation insidethe CNS, every axon in the PNS has a completeneurolemmal sheath.



• Neuron Structure• Cell body

• Nucleus• ER• Ribosomes (Nissl bodies)• Neurofilament

• Cell extensions• Dendrite• Axone

• Initial segment: the very beginning of the axon• Axon terminal: the very end of the axon• Axon collateral: the side branches of axon.• Axolemma: the outermost covering of an unmyelinated axon.• Nodes: areas of myelinated axon that are not covered by myelin.


Figure 13.3 A Review of Neuron Structure

Dendrites Cell body Axon Terminal boutons

Stimulated byenvironmental changes orthe activities of other cells

Contains the nucleus,mitochondria, ribosomes, andother organelles and inclusions

Conducts nerve impulse(action potential) towardsynaptic terminals

Affect another neuronor effector organ(muscle or gland)

Axon hillock

Mitochondrion

Nucleus

Nucleolus

Nissl bodies(clusters of RER

and free ribosomes)

Dendriticspines


Figure 13.9 Anatomy of a Representative Neuron

A neuron may innervate (1) other neurons, (2) skeletal musclefibers, or (3) gland cells. Synapses are shown in boxes for eachexample. A single neuron would not innervate all three.

Multipolar neuron

1. Synapses with another neuron

2. Neuromuscular synapses

3. Neuroglandular synapses

Neuroglandularsynapses

Glandcells

Skeletalmuscle

Neuromuscularsynapses

Terminal boutons

Terminal arborization

Collateralbranch

Synapses withanother neuron

Neuron

Dendrites Axolemma

Neuron

Nerve cell body LM 1600

Dendrite

Nucleus

Nucleolus

Dendriticspines

Chromatophilicsubstance

Neurofilament

Nerve cell body

Mitochondrion

Golgi apparatus

Axon hillock

Initial segment of axon

Nerve cell body

Nucleolus

Nucleus

Axon hillock

Initial segmentof axon

Chromatophilicsubstance

Neurofilament

Terminalboutons

Postsynapticcell

Axon (may bemyelinated)


Figure 13.10 A Structural Classification of Neurons

Anaxonic neuron Bipolar neuron Pseudounipolar neuron Multipolar neuron

Dendrites

Dendrite

Axon

Axon

Axon

Axon

Dendrites Dendrites

Initialsegment

Terminalboutons

Terminalboutons

Terminalboutons

Anaxonic neuronshave more than twoprocesses, butaxons cannot bedistinguished fromdendrites.

Bipolar neuronshave two processesseparated by thecell body.

Pseudounipolarneurons have a singleelongate process withthe cell body situatedto one side.

Multipolar neuronshave more than twoprocesses; there is asingle axon and multiple dendrites.



• Functional Classification of Neurons• Sensory

• Sends information from the PNS to the CNS• Somatic sensory and visceral sensory

• Motor• Sends information from the CNS to the periphery

• Interneurons • Situated between the motor and sensory neurons• Analyze sensory input and coordinate motor

outputs• Can be excitatory or inhibitory


Figure 13.2 A Functional Overview of the Nervous System

CENTRAL NERVOUS SYSTEM(brain and spinal cord)

PERIPHERALNERVOUSSYSTEM

RECEPTORS EFFECTORS

Informationprocessing

Sensoryinformation

withinafferentdivision

Motorcommands

withinefferentdivision

Includes

Somatic nervoussystem

Autonomic nervous system

Parasympatheticdivision

Sympatheticdivision

Skeletalmuscle • Smooth

muscle• Cardiac muscle• Glands

Special sensoryreceptors (providesensations of smell,taste, vision,balance, andhearing)

Somatic sensoryreceptors (monitorskeletal muscles, joints,skin surface; provideposition sense andtouch, pressure, pain,and temperaturesensations)

Visceral sensory receptors (monitorinternal organs, including thoseof cardiovascular, respiratory, digestive,urinary, and reproductive systems)



Receptors are monitored by the sensory neurons Exteroceptors = external environment

Touch, temperature, and pressure sensations Special senses of sight, smell, and hearing

Proprioceptors = internal environment Position and movement of skeletal muscles and joints Information carried in somatic sensory neurons

Interoceptors = internal environment

Digestive, respiratory, cardiovascular, urinary, and reproductive systems

Sensations of deep pressure and pain as well as taste


Figure 13.11 A Functional Classification of Neurons

RECEPTORS PERIPHERAL NERVOUS SYSTEM CENTRAL NERVOUS SYSTEM

EFFECTORS

Interoceptors

Exteroceptors

Proprioceptors

Skeletal muscles

Skeletalmusclefibers

Visceral effectors

Smoothmuscles

Glands

Cardiacmuscle

Adiposetissue

Afferent fibers

Efferent fibers

Postganglionicfibers

Preganglionicfibers

Sensory neuronsin peripheral

ganglia

Visceralmotor neuronsin peripheral

motor ganglia

Somaticmotor

neurons

Visceralmotor

neuronsin CNS

Interneurons

Somatic (sensory & motor)

Visceral (sensory & motor)


The Nerve Impulse

Excitability is the ability of a plasmalemma to conduct electrical impulses.An electrical impulse, or action potential, develops after the plasmalemma is stimulated to its threshold.Nerve impulse is an action potential traveling along an axon. The rate of impulse conduction depends on the properties of the axon, specifically:

Presence or absence of myelin sheath The diameter


Figure 13.9b Anatomy of a Representative Neuron

A neuron may innervate (1) other neurons, (2) skeletal musclefibers, or (3) gland cells. Synapses are shown in boxes for eachexample. A single neuron would not innervate all three.

1. Synapses with another neuron

2. Neuromuscular synapses

3. Neuroglandular synapses

Neuroglandularsynapses

Glandcells

Skeletalmuscle

Neuromuscularsynapses

Terminal boutons


Collateralbranch

Synapses withanother neuron

Neuron

Dendrites Axolemma

Neuron


Figure 13.13a The Structure of a Synapse

Diagrammatic view of a vesicular synapse between two neurons

Terminal boutons


Postsynaptic neurons

Myelin

Axon

Dendrites

Synapse

Terminalarborization

Impulseconduction

Endoplasmicreticulum

Terminal bouton

Mitochondrion

Synaptic vesicles

Presynaptic membrane

Synaptic cleft

Postsynaptic membrane


Figure 13.14 Organization of Neuronal Circuits

Divergence Convergence Serial processing Parallel processing Reverberation

Divergence, a mechanismfor spreading stimulationto multiple neurons orneuronal pools in the CNS

Convergence, amechanism providinginput to a singleneuron from multiplesources

Serial processing,in which neuronsor pools work in a sequential manner

Parallel processing, inwhich individual neuronsor neuronal poolsprocess informationsimultaneously

Reverberation, afeedbackmechanism thatmay be excitatory orinhibitory


Figure 13.15 Anatomical Organization of the Nervous System

PERIPHERAL NERVOUS SYSTEM

RECEPTORS

CENTRAL NERVOUS SYSTEM

EFFECTORS

PATHWAYS

GRAY MATTER

WHITE MATTER WHITE MATTER ORGANIZATION

GRAY MATTER ORGANIZATION

Neural Cortex

Nuclei

Tracts

Centers

Higher Centers

Columns

Ganglia

Nerves

Collections ofneuron cell bodiesin the PNS

Bundles of axonsin the PNS

Centers and tracts that connectthe brain with other organs andsystems in the body

Ascending (sensory) pathwayDescending (motor) pathway

Bundles of CNSaxons that share acommon origin anddestination

Several tracts thatform an anatomicallydistinct mass

Collections of neuron cell bodiesin the interior ofthe CNS

The most complexcenters in the brain

Gray matter on thesurface of the brain

Collections ofneuron cell bodiesin the CNS; eachcenter has specificprocessing functions

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