NERVE TISSUE Part 1 Instructor Terry Wiseth ANATOMY & PHYSIOLOGY

NERVE TISSUENERVE TISSUEPart 1Part 1

Instructor Terry Instructor Terry WisethWiseth

ANATOMY & ANATOMY & PHYSIOLOGYPHYSIOLOGY

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Nervous System Nervous System FunctionFunction

1) Sensory inputstimuli

2) Integrationprocess and interpret

3) Motor outputactivates effector organs

“Stop light" “Taste food"

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Nervous System Nervous System OrganizationOrganization

Central Nervous System (CNS)Central Nervous System (CNS)brain, spinal cordintegration command center

Peripheral Nervous System Peripheral Nervous System (PNS)(PNS)cranial nerves,

spinal nervescommunication lines



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Somatic NervousSomatic NervousSystemSystem

"voluntary" Sensory neuronsSensory neurons

convey information from cutaneous and special sense organs, body wall and limbs to the CNS

Motor neuronsMotor neuronsthat conduct impulses from

CNS to skeletal muscle only

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Autonomic Nervous Autonomic Nervous SystemSystem

"involuntary" Sensory neurons

convey information from receptors in viscera to CNS

Motor neurons that conduct impulses to smooth muscle, cardiac muscle and glands

Autonomic Nervous SystemAutonomic Nervous System

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Branches of ANSBranches of ANS

Sympatheticinvolves expenditure of energy

Parasympathetic

restores or conserves energy

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Branches of ANSBranches of ANS

two divisions have opposing actionsex: sympatheticsympathetic

speed up heart rateex: parasympatheticparasympathetic

slows down heart rate

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Nerve TypesNerve Types

1) Neuroglia2) Neurons

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1) NeurogliaSupport neurons Nurture neuronsProtect neurons

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2) Neurons

Sense

Think

Remember

Regulate gland function

Control muscle movement

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NeurogliaNeuroglia

"glia cells“Support

neuronsMore

numerous than neurons

Make up half the mass of the brain

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NeurogliaNeuroglia

Able to multiply and divide

Multiply and fill in areas of neurons that are destroyed by injury

Brain tumors commonly arise from glia cells and are highly malignant

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Neuroglia TypesNeuroglia Types

CNSAstrocytesMicrogliaOligodendrocytesEpendymal cells

PNSNeurolemmocytesSatellite cells

Neuroglia Neuroglia TypesTypes

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AstrocytesAstrocytes"nursing neurons“Largest an most

numerous glial cells

Many processesMaintain proper

balance of K+ for generation of nerve impulse

Participate in neurotransmitter metabolism

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AstrocytesAstrocytesParticipate in brain

development by assisting migration or neurons

Provides link between neurons and blood vessels

Form blood-brain barrier (BBB)

Regulate entry of substances into brain

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Blood Brain BarrierBlood Brain Barrier

BBB allows diffusion only of lipid soluble substances across the astrocyte membrane surrounding the capillaryNicotine, ethanol, heroin

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Blood Brain BarrierBlood Brain Barrier

Water soluble substances may pass but only by mediated transportGlucose, amino acids

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Parkinson’s DiseaseParkinson’s Disease

caused by a lack of the neurotransmitter dopamine

normally produced by neurons of the brain

Lack of dopamine causes the characteristic shaking anddecreased muscle control

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Administration of dopamine is not helpful because it cannot cross the BBB

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Administration of L-dopa (a precursor of dopamine)

reduces the symptoms because it can pass the BBB and is converted to dopamine by the CNS neurons

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MicrogliaMicroglia

Derived from monocytesSmall, phagocyticengulf bacteriaclear away debris

from dead cellsmay migrate to

areas of injurednerve tissue

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OligodendrocytesOligodendrocytes

Support neurons by twining around them and producing a lipid protein wrap called a myelin sheath

Each oliodendrocyte wraps myelin around severalaxons

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Ependymal CellsEpendymal Cells

Derived from epithelial cellsMany may be ciliatedLine the fluid filled

ventricles of the brainForm cerebrospinal

fluid (CSF) and assist its circulation

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NeurolemmocytesNeurolemmocytes

"Schwann cells“produce myelin

sheaths around PNS neuron axons

each cell produces part of the myelin sheath around a single axon of a PNS neuron

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Satellite CellsSatellite Cells

support neurons in ganglia clusters of the PNS

Surroundganglionneuron cellbodiesprovidingnutrients Neuron

Satellite Cell

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NeuronsNeurons

various sizes and shapesthe basic functions of all neurons

are more or less similar1)receive and integrate inputs2)relay their output to some

other target cell

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NeuronsNeuronscell that has an excitable

cell membranecapable of producing

an electrical impulsecommunication between

neuronspassing of a chemical message

from one nerve cell to another across space between them called the synapse

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Neuron AnatomyNeuron Anatomy

1) Soma2) Dendrites3) Axon4) Synapse

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1) SomaNissl bodiesNucleus

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2) Dendrites

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3) AxonNeurolemmaSchwann cellNode of Ranvier

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4) Synapsesynaptic knobsynaptic cleftsynaptic vesicles

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Soma (Cell Body)Soma (Cell Body)

lack spindle fibers necessary for cell division

acts as a bridge between the dendrite and the axon

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Soma (Cell Body)Soma (Cell Body)

site of an extremely high rate of metabolism

numerous mitochondria, ribosomes and endoplasmic reticulum

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Nissl BodiesNissl Bodies

Clusters of ER and ribosomesOrganelles of function in the

production of neurotransmitters

Darkened area around the nucleus

are Nissl Bodies

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Ganglia And NucleiGanglia And Nuclei

Grouped soma having similar functionsGanglia

along spinal cordNuclei

within CNSGanglia

Nuclei

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DendritesDendrites

Short, branched arms that stick out from the soma

Receive incoming signals and carry them to the soma

Soma

Axon Dendrites

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DendritesDendrites

Cell membrane of soma and dendrites sensitive to chemical, mechanical or electrical stimulation

Stimulation leads togeneration of actionpotential (nerveimpulse) conductedalong the axon

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AxonAxon

Conduct impulse away from the somaNeurolemmaSchwann cellNode of Ranvier

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NeurolemmaNeurolemma

Axonal membrane found only in myelinated neurons

Primarily in peripheral nervous system

Neurolemma

Axon

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Schwann CellSchwann Cell

Cells that wrap around the axons

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Schwann CellSchwann CellForm myelin

A fatty protein sheathWhitish in colorActs as an electrical

insulatorIncrease the speed

and efficiency at which nerve impulses may be transmitted

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Node of RanvierNode of Ranvier

Gaps located between neighboring Schwann cells on myelinated neurons

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Action potential occurs at the node (gap) only

Na+ diffusion occursalong inside of axonneurolemma to thenext node


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SynapseSynapse

Gap that acts as a junction between axon of presynaptic neuron and dendrite of postsynaptic neuron

Presynaptic axon ends in synaptic knob

SynapseSynapse

Synaptic vesicles

Synapse

Direction of Nerve Transmission

Synaptic cleft

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Synaptic KnobSynaptic Knob

Contains numerous mitochondria and synaptic vesicles full of neurotransmitters

Neurotransmitters act toexcite or inhibitneighboring neurons

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Synaptic CleftSynaptic Cleft

Short distance between synaptic knob and postsynaptic dendrite is very small

Place for regulation of transmission

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If a signal is too weak, it will not traverse the synaptic gap

If the signal is strong enough, it will go on to excite the postsynaptic membrane, andthereby continuethe transmission

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Many drugs that act on the nervous system interfere with activity in the synaptic cleft

Events of SynapseEvents of Synapse

STEP ONE: Arrival of action potential at the synaptic knob


STEP TWO: Entry of extracellular Ca+2 and exocytosis of Acetylcholine


STEP THREE: Acetylcholine action promotes entry of Na+ into the presynaptic neuron initiating action potential


STEP FOUR: Breakdown of acetylcholine by acetylcholinesterase and reabsorption of choline by postsynaptic neuron knob

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Functional Functional ClassificationClassification

1) Sensory neurons (Afferent)Receptors

2) Motor neurons (Efferent)Effectors

3) Interneurons

Functional Functional ClassificationClassification

Motor neuronInterneuronsSensory neuron

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Sensory NeuronsSensory Neurons

Approximately 10 million sensory neurons in bodyAlso known as Afferent fibers

Carry information from receptors to central nervous system

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ReceptorsReceptors

May be a process of a sensory neuron

May be a specialized cell whichcommunicates with a sensory neuron

Receptors

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ReceptorsReceptorsExtroreceptors

Touch, temperature, pressure, sight, smell, touch, hearing

ProprioreceptorsMonitor position of skeletal

muscles and jointsInteroreceptors

Monitor the activities of the viscera, taste, pain

ReceptorsReceptors

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Motor NeuronsMotor Neurons

Approximately 1/2 million motor neurons in bodyAlso known as Efferent fibers

Carry signals from the CNS to the effector organs (muscles and glands)

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EffectorsEffectors

Peripheral targets of motor neurons

Change their activities in response to motor neuron impulseSkeletal muscle, cardiac

muscle, smooth muscle, glandsMotor End Plate

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InterneuronsInterneurons

Approximately 20 billion interneurons in body

Located entirely within the CNSInterconnect other neurons

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InterneuronsInterneurons

Analysis of sensory input

Coordination of motor output

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MyelinationMyelination

Most neuron axons are surrounded by a myelin sheath

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MyelinationMyelination

Protein lipid covering produced by neuroglia1) Electrically insulates axon2) Speeds up the transmission

of nerve impulse through the axon

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White MatterWhite Matter

The major component of a cell membrane is the phospholipid bilayer

Many layers of membrane stacked on top of one another creates a fatty appearance due to the presence of this phospholipid

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White MatterWhite Matter

Lipid has a glistening white appearance

Such as fat found on meats

Myelinated axons have a glistening white appearance

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Gray MatterGray Matter

Areas containing mainly cell bodies tend to lack myelin

Myelinated Axon

Unmyelinated Axon

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Neurolemma Neurolemma

Neurolemmocytes (Schwann cells) wrap several times around a small portion of the PNS axon

Myelin sheath is called a neurolemma

NeurolemmNeurolemma a

NeurolemNeurolemma ma





1

2


3

4

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Aids regeneration of an axon if it is injured

Forms a regeneration tube that guides and stimulates regrowth of the axon


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Nodes of RanvierNodes of Ranvier

Intervals along the axon where there are gaps between the myelin sheath

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Neurolemmocytes wrap (neurolemma) the axon segment between the two nodes

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Oligodendrocytes myelinate many cells of the CNS in much the same manner as aneurolemmocytemyelinates partsof a single PNSaxon

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CNS Lacks CNS Lacks NeurolemmaNeurolemma

Many broad flat processes spiral about CNS axons and deposit a myelin sheath

Neurolemma is not formed

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CNS Lacks CNS Lacks NeurolemmaNeurolemma

Axons in the CNS display little regrowth after injury

Due to absence of neurolemma and inhibitory influence exerted by CNS neuroglia

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Myelin and Nerve Myelin and Nerve RegenerationRegeneration

Possible only if the axon is myelinated

Myelinated Axon

Unmyelinated Axon

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Regeneration of Nerve Regeneration of Nerve TissueTissue

Neurons have very limited powers of regeneration

Neurons lose the ability todivide at 6 months of age

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Regeneration of Nerve Regeneration of Nerve TissueTissue

Any neuron destroyed is permanently lost

Only certain types of damage to neuron cells can be repaired

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PNS RegenerationPNS Regeneration

PNS dendrites and axons may be repaired:1) If the cell body remains

intact2) If Schwann cells remain

active

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CNS RegenerationCNS Regeneration

CNS shows little repair of damage to neurons

Injury to brain or spinal cord is usually permanent

Stroke Damage

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CNS RegenerationCNS Regeneration

Why does the CNS lack the ability for nerve cell regeneration?1) Lack of neurolemma 2) Axon regrowth inhibition3) Scar tissue formation

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Lack of NeurolemmaLack of Neurolemma

Axons of CNS are myelinated by oligodendrocytes and do not form neurolemmas

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Axon Regrowth Axon Regrowth InhibitionInhibition

Neuroglia of CNS inhibit axon regrowthPossibly the same mechanism

that inhibits axonal growth during development once a target region has been reached

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Scar Tissue FormationScar Tissue Formation

Astrocytes invade area forming scar tissues which act as physical barriers to regeneration

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Neuronal RegrowthNeuronal Regrowth

Neuronal tumor cellsTumor cells developing

from neurons (rare) havethe ability to divide

Current research on neuronal regrowth is centered on how these tumor cells have gained the ability to reproduce

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Neuronal RegrowthNeuronal RegrowthBrains of some songbirds

Nerve tissue appears and disappears every year

Researchers hope tofind how songbirds areable to regenerate CNStissues

This gives newmeaning to the phrase“Bird Brain”

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Neuronal RegrowthNeuronal Regrowth

Lack of mammalian CNS regeneration1) Inhibitory influences from

neuroglia2) Absence of growth cues

present during development

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Neuronal RegrowthNeuronal RegrowthDevelopmental cues are electrical

and chemical in nature Use electrical or chemical

stimulation to promote axon regrowthEGF (1992) used to trigger mitosis

Epidermal GrowthFactor is the hormonewhich skin cellsrespond to divide andreproduce

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Myelin DevelopmentMyelin Development

Amount of myelin increases from birth to maturity

Myelin presencegreatly increasesthe speed ofnerve impulseconduction

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Myelin DevelopmentMyelin Development

Infant response to stimuli are not as rapid or coordinated as those of older children or adults

Myelination is still in progress

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Diseases of the Myelin Diseases of the Myelin SheathSheath

Destruction of the myelin sheathsTay-Sachs diseaseDiabetes mellitusMultiple sclerosis

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Diseases of the Myelin Diseases of the Myelin SheathSheath

Results in slowed action potential and impaired control of skeletal and smooth muscle

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Multiple Sclerosis (MS)Multiple Sclerosis (MS)

Progressive destruction of myelin sheath in CNS neurons

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Chronic, disabling disease affecting over 2.5 million people world wide

Myelin sheaths deteriorate to scleroses (hardened scars or plaques) in multiple regions

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Characteristics of the disease1) Progressive loss of muscle

strength2) Strange

sensations

Demyelinated plaques formed in the brain from MS

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Characteristics of the disease3) Double vision occurs

periodically4) “Attacks" every year or two

with periods of remission

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Implications of a viral cause which precipitates the activation of killer T-cells to destroy myelin producing oligodendrocytes

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1993 FDA approved use of Betaseron (a form of interferon)

Note greyish plaques around the ventricles


Demyelination in Spinal Cord

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Nerve TractsNerve Tracts

What we call a nervenerve is actually many nerve axons bundled together by sheaths of tissuesEndoneuriumPerineuriumEpineurium

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EndoneuriumEndoneurium

A connective tissue wrapping enveloping individual axons

EndoneuriumEndoneurium

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PerineuriumPerineurium

A connective tissue wrapping bundles or fascicles of axons

Perineurium

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EpineuriumEpineurium

A connective tissue sheath enveloping the nerve as a whole

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EpineuriumEpineurium

These connective tissue sheaths help to give peripheral nerves a certain toughness and resistance to tearing

EndEndNerve Nerve TissueTissuePart 1Part 1

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NERVE TISSUE Part 1 Instructor Terry Wiseth ANATOMY & PHYSIOLOGY