0 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved....

1Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.Copyright © 2005, Elsevier, Inc. All rights reserved. Slide 11

Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.

Chapter 8Chapter 8

The Nervous System

2Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.

• List the organs and divisions of the nervous system and describe the generalized functions of the system as a whole

• Identify the major types of cells in the nervous system and discuss the function of each

• Identify the anatomical and functional components of a three-neuron reflex arc. Compare and contrast the propagation of a nerve impulse along a nerve fiber and across a synaptic cleft

Learning ObjectivesLearning Objectives


• Identify the major anatomical components of the brain and spinal cord and briefly comment on the function of each

• Compare and contrast spinal and cranial nerves.

• Discuss the anatomical and functional characteristics of the two divisions of the autonomic nervous system

Learning Objectives (cont’d.)Learning Objectives (cont’d.)


Organs and Divisions of the Nervous SystemOrgans and Divisions of the Nervous System

• Central nervous system (CNS): Brain and spinal cord

• Peripheral nervous system (PNS): All nerves Autonomic nervous system (ANS)


Divisions of the Nervous SystemDivisions of the Nervous System


Cells of the Nervous SystemCells of the Nervous System

• Neurons Consist of three main parts

Dendrites Cell body Axon

Classified according to function Sensory Motor Interneurons


NeuronNeuron

Cells of the Nervous System (cont’d.)Cells of the Nervous System (cont’d.)


Cells of the Nervous System (cont’d.)Cells of the Nervous System (cont’d.)

Schwann cells form myelin sheaths of axons in the peripheral nervous system (PNS).


• Glia (neuroglia) Support cells, bringing the cells of nervous

tissue together structurally and functionally Three main types of glial cells of the CNS

Astrocytes Microglia Oligodendrocytes

Cells of the Nervous System (cont'd.)Cells of the Nervous System (cont'd.)


GliaGlia

Cells of the Nervous System (cont'd.)Cells of the Nervous System (cont'd.)


NervesNerves

• Nerve: Bundle of peripheral axons Tract of central axons White matter: Tissue composed primarily

of myelinated axons (nerves or tracts) Gray matter: Tissue composed primarily

of cell bodies and unmyelinated fibers


Nerves (cont'd.)Nerves (cont'd.)

• Nerve coverings: Fibrous connective tissue Endoneurium: Surrounds individual fibers

within a nerve Perineurium: Surrounds a group (fascicle)

of nerve fibers Epineurium: Surrounds the entire nerve


The NerveThe Nerve

Blood vesselepineurium

perineurium

endoneurium


Reflex ArcsReflex Arcs

• Nerve impulses are conducted from receptors to effectors over neuron pathways or reflex arcs

• Conduction by a reflex arc results in a reflex, either contraction by a muscle or secretion by a gland


Reflex Arcs (cont'd.)Reflex Arcs (cont'd.)

• Simplest reflex arcs are two-neuron arcs; they consist of sensory neurons synapsing in the spinal cord with motor neurons

• Three-neuron arcs consist of sensory neurons synapsing in the spinal cord with interneurons that synapse with motor neurons


Nerve ImpulsesNerve Impulses

• Self-propagating waves of electrical disturbances that travel along the surface of a neuron membrane


Nerve Impulses (cont'd.)Nerve Impulses (cont'd.)

• Mechanism Stimulus triggers the opening of Na+

channels in the plasma membrane of the neuron

Inward movement of positive sodium ions leaves a slight excess of negative ions outside at a stimulated point Marks beginning of a nerve impulse


Conduction of Nerve ImpulsesConduction of Nerve Impulses


The SynapseThe Synapse

• Chemical compounds are released from axon terminals (of a presynaptic neuron) into a synaptic cleft

• Neurotransmitters bind to specific receptor molecules in the membrane of a postsynaptic neuron Open ion channels, stimulate impulse

conduction by the membrane


The Synapse (cont'd.)The Synapse (cont'd.)

• Types of neurotransmitters Acetylcholine Catecholamines (norepinephrine,

dopamine, and serotonin) Other compounds


Components of a SynapseComponents of a Synapse


Central Nervous SystemCentral Nervous System

• Divisions of the brain Brainstem

Medulla oblongata Pons Midbrain


Central Nervous System (cont'd.)Central Nervous System (cont'd.)

Diencephalon Hypothalamus Thalamus



Cerebellum Second largest part of the human brain Helps control muscle contractions to

produce coordinated movements so that we can maintain balance, move smoothly, and sustain posture



Cerebrum Largest part of the human brain Outer layer of gray matter is the cerebral

cortex, composed mainly of dendrites and cell bodies of neurons

Interior of the cerebrum composed mainly of white matter (nerve fibers arranged in bundles called tracts)


Major Regions of the Central Nervous System

Major Regions of the Central Nervous System



The CerebrumThe Cerebrum




• Spinal cord Outer part composed of white matter made

up of many bundles of axons called tracts Interior is composed of gray matter made up

mainly of neuron dendrites and cell bodies Functions as the center for all spinal cord

reflexes Sensory tracts conduct impulses to the

brain Motor tracts conduct impulses from the

brain


Spinal Cord and Spinal NervesSpinal Cord and Spinal Nerves



• Coverings and fluid spaces of the brain and spinal cord Coverings

Cranial bones and vertebrae Cerebral and spinal meninges—dura

mater, arachnoid mater, and pia mater

Fluid spaces—subarachnoid spaces of meninges, central canal inside cord, and ventricles in the brain



Fluid Spaces of the BrainFluid Spaces of the Brain


Cerebral hemisphere

Cerebellum

Lateral ventrical Pons


Flow of Cerebrospinal FluidFlow of Cerebrospinal Fluid


Choroid plexus

Subarachnoid space


Peripheral Nervous SystemPeripheral Nervous System

• Cranial nerves Structure—12 pairs are attached to the

undersurface of the brain Function—conducts impulses between the

brain and structures in the head and neck and in the thoracic and abdominal cavities


Peripheral Nervous System (cont’d.)Peripheral Nervous System (cont’d.)

• Spinal nerves Structure—contains dendrites of sensory

neurons and axons of motor neurons Functions—conducts impulses necessary

for sensations and voluntary movements


Cranial NervesCranial Nerves


Cranial Nerves (cont'd.)Cranial Nerves (cont'd.)


Autonomic Nervous SystemAutonomic Nervous System

• Motor neurons that conduct impulses from the central nervous system to cardiac muscle, smooth muscle, and glandular epithelial tissue

• Regulates the body’s autonomic or involuntary functions


Innervation of the Major Target Organs by the Autonomic Nervous SystemInnervation of the Major Target Organs by the Autonomic Nervous System

Autonomic Nervous System (cont'd.)Autonomic Nervous System (cont'd.)


• Autonomic neurons Preganglionic autonomic neurons conduct

from spinal cord or brainstem to autonomic ganglia

Postganglionic neurons conduct from autonomic ganglia to cardiac muscle, smooth muscle, and glandular epithelial tissue



• Autonomic or visceral effectors Tissues to which autonomic neurons conduct

impulses• Autonomic conduction paths

Consist of two-neuron relays



• Sympathetic nervous system Structure

Sympathetic preganglionic neurons have dendrites and cell bodies in gray matter of thoracic and upper lumbar segments of the spinal cord

Sympathetic postganglionic neurons have dendrites and cell bodies in sympathetic ganglia



• Sympathetic nervous system: Functions

Serves as the emergency or stress system Group of changes induced by sympathetic

control is called the fight-or-flight response



• Parasympathetic nervous system: Structure

Parasympathetic preganglionic neurons have dendrites and cell bodies in the gray matter of brainstem and sacral segments of the spinal cord

Parasympathetic preganglionic neurons terminate in parasympathetic ganglia located in the head and the thoracic and abdominal cavities close to visceral effectors



• Parasympathetic nervous system Function

Dominates control of many visceral effectors under normal, everyday conditions



Autonomic Conduction PathsAutonomic Conduction Paths



• Autonomic neurotransmitters: Cholinergic fibers

Preganglionic axons of parasympathetic and sympathetic systems and parasympathetic postganglionic axons

Release acetylcholine




• Autonomic neurotransmitters Adrenergic fibers

Axons of sympathetic postganglionic neurons

Release norepinephrine (noradrenaline)


Autonomic NeurotransmittersAutonomic Neurotransmitters




• Autonomic nervous system as a whole Regulates the body’s autonomic functions

in ways that maintain or quickly restore homeostasis


DiseasesParkinson’sShingles or Herpes Zoster

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