Essentials of Human Anatomy & Physiology

Seventh Edition

Elaine N. Marieb

Chapter 7

The Nervous System

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Slides 7.1 – 7.102

The Nervous System

Lecture Slides in PowerPoint by Jerry L. Cook

Functions of the Nervous SystemFunctions of the Nervous System

Sensory input – gathering information

To monitor changes occurring inside and outsidethe body

Changes = stimuli

Integration

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Integration

To process and interpret sensory input and decideif action is needed

Motor output

A response to integrated stimuli

The response activates muscles or glands

Structural Classification of the NervousStructural Classification of the NervousSystemSystem

Central nervous system (CNS)

Brain and Spinal cord

Acts as integrating and command center – interpretincoming sensory information and issue instructions

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incoming sensory information and issue instructionsbased on past experiences and current conditions

Peripheral nervous system (PNS)

Nerves outside the brain and spinal cord

Link all parts of the body by carrying impulses to theCNS and back

Functional Classification of theFunctional Classification of thePeripheral Nervous SystemPeripheral Nervous System

Sensory (afferent) division

Nerve fibers that carry information to thecentral nervous system

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Figure 7.1

Functional Classification of theFunctional Classification of thePeripheral Nervous SystemPeripheral Nervous System

Motor (efferent) division

Nerve fibers that carry impulses away fromthe central nervous system

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Figure 7.1

Functional Classification of theFunctional Classification of thePeripheral Nervous SystemPeripheral Nervous System

Motor (efferent) division

Two subdivisions

Somatic nervous system = voluntarynervous system

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nervous system

Skeletal muscle reflexes such as stretchreflex are initiated involuntarily by samefibers

Autonomic nervous system = involuntarynervous system

Sympathetic and parasympatheticdivisions

Organization of the Nervous SystemOrganization of the Nervous System

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Figure 7.2

Nervous Tissue: Support CellsNervous Tissue: Support Cells(Neuroglia)(Neuroglia) -- gliaglia

Astrocytes

Abundant, star-shaped cells

Brace neurons

Form barrier

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Form barrierbetween capillariesand neurons and makeexchanges betweenthe two

Control the chemicalenvironment ofthe brain by capturing ions andneurotransmitters

Figure 7.3a

Nervous Tissue: Support CellsNervous Tissue: Support Cells

Microglia

Spider-like phagocytes

Dispose of debris –dead cells and bacteria

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Ependymal cells

Line cavities of thebrain and spinal cord

Circulatecerebrospinalfluid with cilia

Figure 7.3b, c

Nervous Tissue: Support CellsNervous Tissue: Support Cells

Oligodendrocytes

Wrap their flat

extensions tightly

around the nerve

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around the nerve

fibers

Produce myelin

sheath around nerve

fibers in the central

nervous systemFigure 7.3d

Nervous Tissue: Support CellsNervous Tissue: Support Cells Satellite cells

Protect neuron cell bodies

Schwann cells

Form myelin sheath in the peripheral nervoussystem

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Figure 7.3e

system

Neuroglia are not able to transmit nerve impulses butdo not lose their ability to divide, unlike neurons

Nervous Tissue: NeuronsNervous Tissue: Neurons

Neurons = nerve cells

Cells specialized to transmit messages

Major regions of neurons

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Major regions of neurons

Cell body – nucleus and metabolic centerof the cell

Processes – fibers that extend from thecell body

Neuron AnatomyNeuron Anatomy

Cell body

Nisslsubstance –specializedrough

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roughendoplasmicreticulum

Neurofibrils –intermediatecytoskeletonthat maintainscell shape Figure 7.4a

Neuron AnatomyNeuron Anatomy

Cell body

Nucleus

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Nucleus

Largenucleolus

Figure 7.4a

Neuron AnatomyNeuron Anatomy

Extensionsoutside the cellbody

Dendrites –conduct

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conductimpulses towardthe cell body

Axons – conductimpulses awayfrom the cellbody

Figure 7.4a

Axons and Nerve ImpulsesAxons and Nerve Impulses

Axons end in axonal terminals

Axonal terminals contain vesicles withneurotransmitters

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Axonal terminals are separated from thenext neuron by a gap

Synaptic cleft – gap between adjacentneurons

Synapse – junction between nerves

Nerve Fiber CoveringsNerve Fiber Coverings

Schwann cells –produce myelinsheaths in jelly-rolllike fashion

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like fashion

Nodes of Ranvier –gaps in myelinsheath along theaxon

Figure 7.5

Neuron Cell Body LocationNeuron Cell Body Location

Most are found in the central nervous system inclusters called nuclei

Bundles of nerve fibers in CNS = tracts

Gray matter – cell bodies and

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Gray matter – cell bodies andunmyelinated fibers

White matter – myelinated fibers

Bundles of nerve fibers in PNS = nerves

Ganglia – collections of cell bodies outside thecentral nervous system

Functional Classification of NeuronsFunctional Classification of Neurons

Sensory (afferent) neurons

Cell bodies in a ganglion outside the CNS

Carry impulses from the sensory receptors to CNS

Cutaneous (skin) sense organs

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Cutaneous (skin) sense organs

Proprioceptors – detect stretch or tension inmuscles, tendons, joints

Motor (efferent) neurons

Cell bodies found in the CNS

Carry impulses from the central nervous system

Functional Classification of NeuronsFunctional Classification of Neurons

Interneurons (association neurons)

Found in neural pathways in the centralnervous system

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nervous system

Cell bodies in the CNS

Connect sensory and motor neurons

Neuron ClassificationNeuron Classification

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Figure 7.6

Structural Classification of NeuronsStructural Classification of Neurons

Multipolar neurons – many extensionsfrom the cell body

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Figure 7.8a

Structural Classification of NeuronsStructural Classification of Neurons

Bipolar neurons – one axon and onedendrite

Rare in adults – in eye and ear only

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Figure 7.8b

Structural Classification of NeuronsStructural Classification of Neurons

Unipolar neurons – have a short, singleprocess leaving the cell body

Axon conducts nerve impulses both to andfrom the cell body

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from the cell body

Figure 7.8c

Functional Properties of NeuronsFunctional Properties of Neurons

Two main functions

Irritability – ability to respond to stimuli

Conductivity – ability to transmit animpulse

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impulse

The plasma membrane at rest is polarized

Fewer positive ions (usually K+) are inside thecell than outside the cell (usually Na+)

Starting a Nerve ImpulseStarting a Nerve Impulse

Depolarization – astimulus depolarizes theneuron’s membrane

A deploarized membraneallows sodium (Na+) to

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allows sodium (Na ) toflow inside the membrane

The exchange of ionsinitiates an actionpotential (nerve impulse)in the neuron

Figure 7.9a–c

The Action PotentialThe Action Potential

If the action potential (nerve impulse) starts, it ispropagated over the entire axon – all-or-noneresponse

Potassium ions rush out of the neuron aftersodium ions rush in, which repolarizes themembrane

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membrane

The sodium-potassium pump restores theoriginal configuration

This action requires ATP

Until repolarization occurs, a neuron cannotconduct another impulse

Nerve Impulse PropagationNerve Impulse Propagation

The impulse continues tomove toward the cell body

Impulses travel fasterwhen fibers have a myelinsheath

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sheath

Nerve impulse literallyjumps from node tonode because it cannotcross myelin insulation

Figure 7.9c–e

Continuation of the Nerve ImpulseContinuation of the Nerve Impulsebetween Neuronsbetween Neurons

Impulses are unable to cross the synapse toanother nerve

Neurotransmitter is released from a nerve’s axonterminal

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The dendrite of the next neuron has receptorsthat are stimulated by the neurotransmitter

An action potential is started in the dendrites ofthe next neuron

Transmission of an impulse is an electrochemicalevent

How Neurons Communicate atHow Neurons Communicate atSynapsesSynapses

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Figure 7.10

The Reflex ArcThe Reflex Arc

Reflex – rapid, predictable, andinvoluntary responses to stimuli

Reflex arc – direct route from a sensoryneuron, to an interneuron, to an effector

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neuron, to an interneuron, to an effector

Figure 7.11a

Simple Reflex ArcSimple Reflex Arc

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Figure 7.11b, c

Types of Reflexes and RegulationTypes of Reflexes and Regulation

Autonomic reflexes

Smooth muscle regulation

Size of eye pupils

Heart and blood pressure regulation

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Heart and blood pressure regulation

Regulation of glands and sweating

Digestive system and elimination regulation

Somatic reflexes

Activation of skeletal muscles

Types of Reflexes and RegulationTypes of Reflexes and Regulation

Reflex arcs have a minimum five elements

A sensory receptor – reacts to stimuli

An effector receptor – muscle or glandstimulated

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stimulated

Afferent and efferent neurons connectingthe two

The CNS integration center

Central Nervous System (CNS)Central Nervous System (CNS)

CNS develops from the embryonic neuraltube – a simple tube

The neural tube becomes the brain and spinalcord

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The opening of the neural tube becomes theventricles

Four chambers within the brain

Filled with cerebrospinal fluid

Regions of the BrainRegions of the Brain

Cerebral hemispheres

Diencephalon

Brain stem

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Cerebellum

Figure 7.12

Cerebral Hemispheres (Cerebrum)Cerebral Hemispheres (Cerebrum)

Paired (leftand right)superior partsof the brain

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of the brain

Include morethan half ofthe brainmass

Figure 7.13a

Cerebral Hemispheres (Cerebrum)Cerebral Hemispheres (Cerebrum)

The surface ismade ofelevated ridges(gyri) and

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(gyri) andshallow grooves(sulci)

Figure 7.13a

Lobes of the CerebrumLobes of the Cerebrum

Fissures (deep grooves) divide thecerebrum into lobes

Surface lobes of the cerebrum – named forcranial bone over them

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cranial bone over them

Frontal lobe

Parietal lobe

Occipital lobe

Temporal lobe

Lobes of the CerebrumLobes of the Cerebrum

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Figure 7.15a

Specialized Areas of the CerebrumSpecialized Areas of the Cerebrum

Somatic sensory area in parietal lobe –receives impulses from the body’s sensoryreceptors (except special senses)

Occipital lobe – vision and temporal lobe

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Occipital lobe – vision and temporal lobe– auditory

Primary motor area – sends impulses toskeletal muscles – frontal lobe

Broca’s area – involved in our ability tospeak – base of the precentral gyrus

Sensory and Motor Areas of theSensory and Motor Areas of theCerebral CortexCerebral Cortex

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Figure 7.14

Specialized Area of the CerebrumSpecialized Area of the Cerebrum

Cerebral areas involved in specialsenses

Gustatory area (taste)

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Gustatory area (taste)

Visual area

Auditory area

Olfactory area

Specialized Area of the CerebrumSpecialized Area of the Cerebrum

Interpretation areas of the cerebrum

Speech/language region

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Speech/language region

Language comprehension region

General interpretation area

Specialized Area of the CerebrumSpecialized Area of the Cerebrum

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Figure 7.13c

Layers of the CerebrumLayers of the Cerebrum

Gray matter

Outermost layer

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Outermost layer

Composedmostly of neuroncell bodies

Cerebral cortex

Figure 7.13a

Layers of the CerebrumLayers of the Cerebrum

White matter

Fiber tractsinside the graymatter

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matter

Example:corpus callosumconnectshemispheres

Figure 7.13a

Layers of the CerebrumLayers of the Cerebrum

Basal nuclei –internal islandsof gray matter

Helps regulate

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Helps regulatevoluntary motoractivities bymodifyinginstructions sentto the skeletalmuscles Figure 7.13a

DiencephalonDiencephalon -- interbraininterbrain

Sits on top of the brain stem

Enclosed by the cerebral hemispheres

Made of three parts

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Made of three parts

Thalamus

Hypothalamus

Epithalamus

DiencephalonDiencephalon

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Figure 7.15

ThalamusThalamus

Surrounds the third ventricle of the brain

The relay station for sensory impulsespassing upward to the sensory cortex

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The relay station for sensory impulsespassing upward to the sensory cortex

Transfers impulses to the correct part ofthe cortex for localization andinterpretation

HypothalamusHypothalamus

Under the thalamus

Important autonomic nervous systemcenter

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center

Helps regulate body temperature

Controls water balance

Regulates metabolism

HypothalamusHypothalamus

An important part of the limbic system(emotions) – emotional-visceral brain

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(emotions) – emotional-visceral brain

The pituitary gland is attached to andregulated by the hypothalamus

EpithalamusEpithalamus

Forms the roof of the third ventricle

Houses the pineal body (an endocrinegland)

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Houses the pineal body (an endocrinegland)

Includes the choroid plexus – formscerebrospinal fluid

Brain StemBrain Stem

Attaches to the spinal cord

Parts of the brain stem

Midbrain

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Midbrain

Pons

Medulla oblongata

Brain StemBrain Stem

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Figure 7.15a

MidbrainMidbrain

Mostly composed of tracts of nerve fibers

The cerebral aqueduct – canal that connectsthe 3rd ventricle of the diencephalon to the 4th

ventricle

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Has two bulging fiber tracts – cerebralpeduncles – convey ascending and descendingimpulses

Has four rounded protrusions – corporaquadrigemina – Reflex centers for vision andhearing

PonsPons

The bulging center part of the brainstem

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Mostly composed of fiber tracts

Includes nuclei involved in the control ofbreathing

Medulla OblongataMedulla Oblongata

The lowest part of the brain stem

Merges into the spinal cord

Includes important fiber tracts

Contains important control centers

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Contains important control centers

Heart rate control

Blood pressure regulation

Breathing

Swallowing

Vomiting

Reticular FormationReticular Formation

Diffuse mass of gray matter along thebrain stem

Involved in motor control of visceralorgans

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organs

Reticular activating system plays a role inawake/sleep cycles and consciousness

Damage here results in a permanentcoma

Reticular FormationReticular Formation

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Figure 7.15b

CerebellumCerebellum

Two hemispheres with convolutedsurfaces

Provides involuntary coordination of bodymovements – of skeletal muscles, balance

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movements – of skeletal muscles, balanceand equilibrium

Automatic pilot – continually comparingbrain’s intentions with actual bodyperformance

CerebellumCerebellum

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Figure 7.15a

Protection of the Central NervousProtection of the Central NervousSystemSystem

Scalp and skin

Skull and vertebralcolumn

Meninges

Cerebrospinal fluid

Blood brain barrier

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Meninges

Figure 7.16a

MeningesMeninges

Dura mater

Double-layered external covering the brain

Periosteum – attached to surface of theskull

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skull

Meningeal layer – outer covering of thebrain and continues as the dura matter ofthe spinal cord

Folds inward in several areas thatattaches the brain to cranial cavity

MeningesMeninges

Arachnoid layer

Middle layer that is web-like

Pia mater

Internal layer that clings to the surface of the brain

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Internal layer that clings to the surface of the brainfollowing every fold

Subarachnoid space filled with cerebrospinalfluid

Arachnoid villi – projections of arachnoidmembrane protruding through the dura matter

Cerebrospinal FluidCerebrospinal Fluid

Similar to blood plasma composition

Less protein, more vitamin C, different ions

Formed by the choroid plexus

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Forms a watery cushion to protect the brain

Circulated in arachnoid space, ventricles,and central canal of the spinal cord

Ventricles and Location of theVentricles and Location of theCerebrospinal FluidCerebrospinal Fluid

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Figure 7.17a

Ventricles and Location of theVentricles and Location of theCerebrospinal FluidCerebrospinal Fluid

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Figure 7.17b

Blood Brain BarrierBlood Brain Barrier Includes the least permeable capillaries of

the body – only H2O, glucose, and essentialamino acids get through

Excludes many potentially harmfulsubstances

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Useless against some substances

Fats and fat soluble molecules

Respiratory gases

Alcohol

Nicotine

Anesthesia

Traumatic Brain InjuriesTraumatic Brain Injuries Concussion

Slight brain injury – dizzy or lose consciousnessbriefly

No permanent brain damage

Contusion

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Contusion

Nervous tissue destruction occurs - does notregenerate

If cortex is damaged, coma for hours or life

Cerebral edema

Swelling from the inflammatory response

May compress and kill brain tissue

Cerebrovascular Accident (CVA)Cerebrovascular Accident (CVA)

Commonly called a stroke

The result of a clot or a ruptured bloodvessel supplying a region of the brain

Brain tissue supplied with oxygen from

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Brain tissue supplied with oxygen fromthat blood source dies

Loss of some functions or death mayresult

Alzheimer’s DiseaseAlzheimer’s Disease

Progressive degenerative brain disease

Mostly seen in the elderly, but maybegin in middle age

Structural changes in the brain include

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Structural changes in the brain includeabnormal protein deposits and twistedfibers within neurons

Victims experience memory loss,irritability, confusion and ultimately,hallucinations and death

Spinal CordSpinal Cord

Extends from themedulla oblongata tothe region of T12

Below T12 is the caudaequina (a collection of

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equina (a collection ofspinal nerves)

Enlargements occur inthe cervical and lumbarregions

Figure 7.18

Spinal Cord AnatomySpinal Cord Anatomy

Internal gray matter - mostly cell bodiesthat surround the central canal of the cord

Dorsal (posterior) horns

Anterior (ventral) horns

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Anterior (ventral) horns

Contains motor neurons of the somaticnervous system, which send their axons outthe ventral root

Together they fuse to form the spinal nerves

Nerves leave at the level of each vertebrae

Spinal Cord AnatomySpinal Cord Anatomy

Cell bodies of sensory neurons, whose fibersenter the cord by the dorsal root, are found in anenlarged area called the dorsal root ganglion

Damage to this area causes sensation from thebody area served to be lost

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Figure 7.19

Spinal Cord AnatomySpinal Cord Anatomy Exterior white mater – conduction tracts

Posterior, lateral, and anterior columns

Each contains a number of fiber tracts makeup of axons with the same destination andfunction

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function

Figure 7.19

Spinal Cord AnatomySpinal Cord Anatomy

Central canal filled with cerebrospinalfluid

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Figure 7.19

Peripheral Nervous SystemPeripheral Nervous System

Nerves and ganglia outside the centralnervous system

Nerve = bundle of neuron fibers

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Nerve = bundle of neuron fibers

Neuron fibers are bundled by aconnective tissue sheath

Structure of a NerveStructure of a Nerve

Endoneuriumsurrounds each fiber

Groups of fibers arebound into fascicles

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bound into fasciclesby perineurium

Fascicles are boundtogether byepineurium

Figure 7.20

Classification of NervesClassification of Nerves

Classified according to the direction inwhich they transmit impulses

Mixed nerves – carry both sensory andmotor fibers – spinal nerves

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motor fibers – spinal nerves

Afferent (sensory) nerves – carryimpulses toward the CNS

Efferent (motor) nerves – carry impulsesaway from the CNS

Cranial NervesCranial Nerves

12 pairs of nerves that mostly serve thehead and neck

Numbered in order, front to back – names

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Numbered in order, front to back – namesreveal structures they control

Most are mixed nerves, but three aresensory only

Optic, olfactory, and vestibulocochlear

DistributionDistributionof Cranialof CranialNervesNerves

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Figure 7.21

Cranial NervesCranial Nerves

I Olfactory nerve – sensory for smell

II Optic nerve – sensory for vision

III Oculomotor nerve – motor fibers to

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III Oculomotor nerve – motor fibers toeye muscles

IV Trochlear – motor fiber to eyemuscles

Cranial NervesCranial Nerves

V Trigeminal nerve – sensory for theface; motor fibers to chewing muscles

VI Abducens nerve –motor fibers to eye muscles

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motor fibers to eye muscles

VII Facial nerve – sensory for taste;motor fibers to the face

VIII Vestibulocochlear nerve –sensory for balance and hearing

Cranial NervesCranial Nerves

IX Glossopharyngeal nerve – sensoryfor taste; motor fibers to the pharynx

X Vagus nerves – sensory and motorfibers for pharynx, larynx, and viscera

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fibers for pharynx, larynx, and viscera

XI Accessory nerve – motor fibers toneck and upper back

XII Hypoglossal nerve – motor fibers totongue

Spinal NervesSpinal Nerves

There is a pair of spinal nerves at thelevel of each vertebrae for a total of 31pairs

Spinal nerves are formed by the

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Spinal nerves are formed by thecombination of the ventral and dorsalroots of the spinal cord

Spinal nerves are named for the regionfrom which they arise

Spinal NervesSpinal Nerves

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Figure 7.22a

Anatomy of Spinal NervesAnatomy of Spinal Nerves

Spinal nerves dividesoon after leaving thespinal cord

Dorsal rami – serve theskin and muscles of theposterior trunk

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skin and muscles of theposterior trunk

Ventral rami – forms acomplex of networks(plexus) for the anterior,which serve the motorand sensory needs ofthe limbs

Figure 7.22b

Examples of Nerve DistributionExamples of Nerve Distribution

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Figure 7.23

Autonomic Nervous SystemAutonomic Nervous System

The involuntary branch of the nervoussystem

Consists of only motor nerves

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Consists of only motor nerves

Divided into two divisions

Sympathetic division – mobilizes the body

Parasympathetic division – allows body tounwind

Differences Between Somatic andDifferences Between Somatic andAutonomic Nervous SystemsAutonomic Nervous Systems Nerves

Somatic – one motor neuron – axons extendall the way to the skeletal muscle they serve

Autonomic – preganglionic and

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Autonomic – preganglionic andpostganglionic nerves

Effector organs

Somatic – skeletal muscle

Autonomic – smooth muscle, cardiac muscle,and glands

Differences Between Somatic andDifferences Between Somatic andAutonomic Nervous SystemsAutonomic Nervous Systems

Nerurotransmitters

Somatic – always use acetylcholine

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Somatic – always use acetylcholine

Autominic – use acetylcholine, epinephrine,or norepinephrine

Comparison of Somatic andComparison of Somatic andAutonomic Nervous SystemsAutonomic Nervous Systems

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Anatomy of the ParasympatheticAnatomy of the ParasympatheticDivisionDivision

Originates from the brain stem and S2 – S4

Neurons in the cranial region send axons outin cranial nerves to the head and neck organs

They synapse with the second motor neuron

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They synapse with the second motor neuronin a terminal ganglion

Terminal ganglia are at the effector organs

Always uses acetylcholine as aneurotransmitter

Anatomy of the SympatheticAnatomy of the SympatheticDivisionDivision –– thoracolumbar divisionthoracolumbar division

Originates from T1 through L2

Preganglionic axons leave the cord in the ventral root,enter the spinal nerve, then pass through a ramuscommunications, to enter a sympathetic chain

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communications, to enter a sympathetic chainganglion at the sympathetic chain (trunk) (near thespinal cord)

Short pre-ganglionic neuron and long postganglionicneuron transmit impulse from CNS to the effector

Norepinephrine and epinephrine are neurotransmittersto the effector organs

Sympathetic PathwaysSympathetic Pathways

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Figure 7.26

Anatomy of the Autonomic NervousAnatomy of the Autonomic NervousSystemSystem

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Figure 7.25

Autonomic FunctioningAutonomic Functioning

Sympathetic – “fight-or-flight”

Response to unusual stimulus

Takes over to increase activities

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Takes over to increase activities

Remember as the “E” division = exercise,excitement, emergency, andembarrassment

Autonomic FunctioningAutonomic Functioning

Parasympathetic – housekeepingactivites

Conserves energy

Slide 7.100Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Conserves energy

Maintains daily necessary body functions

Remember as the “D” division - digestion,defecation, and diuresis

Development Aspects of theDevelopment Aspects of theNervous SystemNervous System

The nervous system is formed during thefirst month of embryonic development

Any maternal infection can have extremely

Slide 7.101Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Any maternal infection can have extremelyharmful effects

The hypothalamus is one of the last areas ofthe brain to develop – contains centers forregulating body temperature

Development Aspects of theDevelopment Aspects of theNervous SystemNervous System

No more neurons are formed after birth,but growth and maturation continues forseveral years largely due to myelination

Slide 7.102Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

The brain reaches maximum weight asa young adult