The Nervous System. Functions of the Nervous System Sensory input—gathering information To monitor changes occurring inside and outside the body Changes.

The Nervous System

Functions of the Nervous SystemSensory input—gathering information

To monitor changes occurring inside and outside the body

Changes = stimuliIntegration

To process and interpret sensory input and decide if action is needed

Functions of the Nervous SystemMotor output

A response to integrated stimuliThe response activates muscles or glands

Functions of the Nervous System

Figure 7.1

Structural Classification of the Nervous SystemCentral nervous system (CNS)

BrainSpinal cord

Peripheral nervous system (PNS)Nerves outside the brain and spinal cord

Spinal nervesCranial nerves

Functional Classification of the Peripheral Nervous SystemSensory (afferent) division

Nerve fibers that carry information to the central nervous system

Motor (efferent) divisionNerve fibers that carry impulses away from

the central nervous system

Organization of the Nervous System

Figure 7.2

Functional Classification ofthe Peripheral Nervous SystemMotor (efferent) division (continued)

Two subdivisionsSomatic nervous system = voluntaryAutonomic nervous system = involuntary

Nervous Tissue: Support CellsSupport cells in the CNS are grouped

together as “neuroglia”Function: to support, insulate, and protect

neurons

Nervous Tissue: Support CellsAstrocytes

Abundant, star-shaped cellsBrace neuronsForm barrier between capillaries and neuronsControl the chemical environment of

the brain

Nervous Tissue: Support Cells

Figure 7.3a

Nervous Tissue: Support CellsMicroglia

Spiderlike phagocytesDispose of debris

Nervous Tissue: Support Cells

Figure 7.3b

Nervous Tissue: Support CellsEpendymal cells

Line cavities of the brain and spinal cordCirculate cerebrospinal fluid

Nervous Tissue: Support Cells

Figure 7.3c

Nervous Tissue: Support CellsOligodendrocytes

Wrap around nerve fibers in the central nervous system

Produce myelin sheaths

Nervous Tissue: Support Cells

Figure 7.3d

Nervous Tissue: Support CellsSatellite cells

Protect neuron cell bodiesSchwann cells

Form myelin sheath in the peripheral nervous system

Nervous Tissue: Support Cells

Figure 7.3e

Nervous Tissue: NeuronsNeurons = nerve cells

Cells specialized to transmit messagesMajor regions of neurons

Cell body—nucleus and metabolic center of the cellProcesses—fibers that extend from the cell body

Nervous Tissue: NeuronsCell body

Nissl BodySpecialized rough endoplasmic reticulum

Neurofibrils Intermediate cytoskeleton Maintains cell shape

Nervous Tissue: Neurons

Figure 7.4

Nervous Tissue: NeuronsCell body

NucleusLarge nucleolus

Processes outside the cell bodyDendrites—conduct impulses toward the cell

bodyAxons—conduct impulses away from the cell

body

Nervous Tissue: NeuronsAxons end in axonal terminalsAxonal terminals contain vesicles with

neurotransmittersAxonal terminals are separated from the

next neuron by a gapSynaptic cleft—gap between adjacent

neuronsSynapse—junction between nerves

Nervous Tissue: NeuronsMyelin sheath—whitish, fatty material

covering axonsSchwann cells—produce myelin sheaths in

jelly roll–like fashionNodes of Ranvier—gaps in myelin sheath

along the axon

Nervous Tissue: Neurons

Figure 7.5

Neuron Cell Body LocationMost neuron cell bodies are found in the

central nervous systemGray matter—cell bodies and unmyelinated

fibersNuclei—clusters of cell bodies within the

white matter of the central nervous systemGanglia—collections of cell bodies outside

the central nervous system

Functional Classification of NeuronsSensory (afferent) neurons

Carry impulses from the sensory receptors to the CNSCutaneous sense organsProprioceptors—detect stretch or tension

Motor (efferent) neuronsCarry impulses from the central nervous

system to viscera, muscles, or glands

Functional Classification of NeuronsInterneurons (association neurons)

Found in neural pathways in the central nervous system

Connect sensory and motor neurons

Neuron Classification

Figure 7.6

Figure 7.8a

Structural Classification of NeuronsMultipolar neurons—many extensions from

the cell body

Structural Classification of NeuronsBipolar neurons—one axon and one

dendrite

Figure 7.8b

Structural Classification of NeuronsUnipolar neurons—have a short single

process leaving the cell body

Figure 7.8c

Functional Properties of NeuronsIrritability

Ability to respond to stimuliConductivity

Ability to transmit an impulse

Nerve ImpulsesResting neuron

The plasma membrane at rest is polarizedFewer positive ions are inside the cell than

outside the cellDepolarization

A stimulus depolarizes the neuron’s membrane

A depolarized membrane allows sodium (Na+) to flow inside the membrane

The exchange of ions initiates an action potential in the neuron

Nerve Impulses

Figure 7.9a–b

Nerve ImpulsesAction potential

If the action potential (nerve impulse) starts, it is propagated over the entire axon

Impulses travel faster when fibers have a myelin sheath

Nerve Impulses

Figure 7.9c–d

Nerve ImpulsesRepolarization

Potassium ions rush out of the neuron after sodium ions rush in, which repolarizes the membrane

The sodium-potassium pump, using ATP, restores the original configuration

Nerve Impulses

Figure 7.9e–f

Transmission of a Signal at SynapsesImpulses are able to cross the synapse to

another nerveNeurotransmitter is released from a nerve’s

axon terminalThe dendrite of the next neuron has

receptors that are stimulated by the neurotransmitter

An action potential continues via the dendrite

Transmission of a Signal at Synapses

Figure 7.10

Axonterminal

Vesicles

Synapticcleft

Actionpotentialarrives

Synapse

Axon oftransmittingneuron

Receivingneuron

Neurotrans-mitter is re-leased intosynaptic cleft

Neurotrans-mitter bindsto receptoron receivingneuron’smembrane

Vesiclefuses withplasmamembrane

Synaptic cleftNeurotransmittermolecules

Ion channels Receiving neuron

Transmitting neuron

Receptor

Neurotransmitter

Na+

Na+

Neurotransmitterbroken downand released

Ion channel opens Ion channel closes