nervous system ( 26/10)

8/3/2019 Nervous System ( 26/10)

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17-1

Nervous Tissue

Controls and integrates all body activitieswithin limits that maintain life

Three basic functions sensing changes with sensory receptors

fullness of stomach or sun on your face

interpreting and remembering those changes

reacting to those changes with effectors

muscular contractions

glandular secretions


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11-2

Nervous Tissue

Found in brain, spinal cord and nerves

Property

Ability to produce action potentials (electric

signals)

Cells

Nerve cells or neurons

Neuroglia or support cells Oligodendrocytes and Schwann cells


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17-3

ajor Structures of the Nervous System

Brain, cranial nerves, spinal cord, spinal

nerves, ganglia, enteric plexuses and sensoryrece tors


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17-4

Organization of the Nervous System

CNS is brain and spinal cord

PNS is everything else


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11-5

The Nervous System

Subdivisions Central nervous system (CNS)

Peripheral nervous system (PNS)

Sensory receptor

Receptor of sensory information

Nerve

Made up of a bundle of axons

Ganglion

Collection of cell bodies of neurons

Plexus

Network of spinal nerves


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11-6

Central Nervous System

Consists of Brain

Located in cranialvault of skull

Spinal cord

Located in vertebralcanal

Brain and spinalcord Continuous with each

other at foramenmagnum

TractFig. 14.1


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11-7

Peripheral Nervous System

Two subcategories Sensory or afferent

Motor or efferent

Divisions

Somatic nervoussystem

Autonomic nervoussystem (ANS)

Sympathetic

(fight or flight)

Parasympathetic

(rest and digest)Fig. 14.2


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Components

Principle Cells: Neurons.

Support Cells: Neuroglia:

Metabolic/Structural. Astrocytes

Microglia

Oligodendrocytes Schwan Cells


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11-9

Meninges

Connective tissuemembranes surroundingspinal cord and brain

Dura mater

Arachnoid mater

Pia mater

Spaces

Epidural: Anesthesiainjected

Subdural: Serous fluid Subarachnoid:

cerebrospinal fluid (CSF)

Fig. 16.2


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Histology

Outer Cortex (Gray Matter) & Inner WhiteMatter-Folia

Cortex Made of Three Layers: Outer Molecular (Few Neurons &

Unmyeliated Nerve Fibers

Inner Granular (Small Neurons with Long

Axons That Synapse With Dendrites ofPurkinje Neurons.


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Neurons Functional unit of nervous

system

Have capacity to produce actionpotentials

electrical excitability

Cell body

single nucleus withprominent nucleolus

Nissl bodies (chromatophilicsubstance)

rough ER & freeribosomes for proteinsynthesis

neurofilaments give cellshape and support

microtubules move materialinside cell

lipofuscin pigment clumps(harmless aging)

Cell processes = dendrites &


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Neurons

Neurons: Large Cell BodyNucleus/Nucleolus(Perikaryon), Abundant RoughER (Nissl Granules)

Polar Cell Axon-Hillock/Dendrites.

Based on Arrangements ofAxons & Dendrites-Synapse:

Mutlti-Polar Neuron: Majortype Example Motor.

Bipolar Neuron: Smell, Sight,Balance

Uni/Pseudo-Polar: Sensory


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Electron MicroscopyLight-Stained Purkinje Neurons


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17-14

NucleuswithNucleolus

arts o a euron

Axons or

Dendrites

Cell body

Neuroglial cells


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17-15

Dendrites

Conducts impulsestowards the cell body

Typically short, highlybranched & unmyelinated

Surfaces specialized for

contact with otherneurons

Contains neurofibrils &Nissl bodies

A


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Axons

Conduct impulses away

from cell body Long, thin cylindrical

process of cell

Arises at axon hillock

Impulses arise from initialsegment (trigger zone)

Side branches

(collaterals) end in fineprocesses called axonterminals

Swollen tips called

synaptic end bulbs

S l Cl ifi i f N


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17-17

Structural Classification of Neurons

Based on number of processes found on cell body

multipolar = several dendrites & one axon

most common cell type

bipolar neurons = one main dendrite & one axon

found in retina, inner ear & olfactory

unipolar neurons = one process only(develops from a

bipolar)


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Synapses


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Neuroglia

1. Astrocytes.

2. Oligodendrocytes.

3. Microglia.

4. Ependymal


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17-20

Half of the volume of the CNS Smaller cells than neurons

50X more numerous

Cells can divide rapid mitosis in tumor formation (gliomas)

4 cell types in CNS

astrocytes, oligodendrocytes, microglia & ependymal 2 cell types in PNS

schwann and satellite cells

Neuroglial Cells


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17-21

Neuroglia of the central nervous system (CNS).


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Astrocytes

Revealed by Heavy Metal Staining.

Most Numerous in Gray Matter Less # inWhite Matter.

Star shaped: Long branched processes. Some Processes terminate on BM of

capillaries: Perivascular Feet.

Perivascular Feet= Barrier= Glia Limitans. Metabolic Function Mediate exchange


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17-23

Astrocytes

Star-shaped cells

Form blood-brainbarrier by covering

blood capillaries Metabolize

neurotransmitters

Regulate K+balance

Provide structuralsupport


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17-25

Oligodendrocytes

Most common glialcell type

Each forms myelinsheath around morethan one axons inCNS

Analogous toSchwann cells ofPNS


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Microglia

Small cells found near blood vessels

Phagocytic role -- clear away dead cells

Derived from cells that also gave rise tomacrophages & monocytes


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Ependymal cells

Form epithelial membrane lining cerebral cavities

& central canal Produce cerebrospinal fluid (CSF)


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Microglia

Have Small irregularnucleus. ManyProcesses.

Monocyte origin.


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Ependymal

Epithelial cell

Line surfaces of ventricles.

Have Cilia & Microvilli.

Do Not Rest on BM but branches base whichpenetrate underlying tissue..


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Myelinated Nerves

Myelinated Nerves.

Oligodendrocytes: CNS.One Oligo Can MyelinateUpto 50 Nerves

Schwan Cell: PNS

Many Schwan CellsMyelinate One PeripheralNerve

End of one SchwanSegment Node of Ranvier


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Myelination Process


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#68 Nerve bundle in transverse section

Epineurium

Perineurium


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A Schwann cell myelinateone axonA Schwann cell wraps aroundseveral unmyelinated axons


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#71-2A Motor end plate

Terminal bouton


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Spinal Ganglia

Cell bodies Lie on posterior

Nerve Root of Spinal Cord. Have Sensory Neurons

(Unipolar).

Widely Apart

SympatheticGanglia

Multipolar Type: HenceMany Dendrites HenceWidely Apart.

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