nerve tissue part 1 instructor terry wiseth anatomy & physiology
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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
Nervous System Nervous System OrganizationOrganization
Nervous System Nervous System OrganizationOrganization
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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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Nerve TypesNerve Types
1) NeurogliaSupport neurons Nurture neuronsProtect neurons
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Nerve TypesNerve Types
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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Parkinson’s DiseaseParkinson’s Disease
Administration of dopamine is not helpful because it cannot cross the BBB
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Parkinson’s DiseaseParkinson’s Disease
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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Neuron AnatomyNeuron Anatomy
1) SomaNissl bodiesNucleus
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Neuron AnatomyNeuron Anatomy
2) Dendrites
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Neuron AnatomyNeuron Anatomy
3) AxonNeurolemmaSchwann cellNode of Ranvier
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Neuron AnatomyNeuron Anatomy
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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Node of RanvierNode of Ranvier
Action potential occurs at the node (gap) only
Na+ diffusion occursalong inside of axonneurolemma to thenext node
Node of RanvierNode of Ranvier
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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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Synaptic CleftSynaptic Cleft
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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Synaptic CleftSynaptic Cleft
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
Events of SynapseEvents of Synapse
STEP TWO: Entry of extracellular Ca+2 and exocytosis of Acetylcholine
Events of SynapseEvents of Synapse
STEP THREE: Acetylcholine action promotes entry of Na+ into the presynaptic neuron initiating action potential
Events of SynapseEvents of Synapse
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
Neurolemma Neurolemma
Neurolemma Neurolemma
Neurolemma Neurolemma
Neurolemma Neurolemma
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Neurolemma Neurolemma
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Neurolemma Neurolemma
Aids regeneration of an axon if it is injured
Forms a regeneration tube that guides and stimulates regrowth of the axon
Neurolemma Neurolemma
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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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Nodes of RanvierNodes of Ranvier
Neurolemmocytes wrap (neurolemma) the axon segment between the two nodes
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Nodes of RanvierNodes of Ranvier
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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Multiple Sclerosis (MS)Multiple Sclerosis (MS)
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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Multiple Sclerosis (MS)Multiple Sclerosis (MS)
Characteristics of the disease1) Progressive loss of muscle
strength2) Strange
sensations
Demyelinated plaques formed in the brain from MS
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Multiple Sclerosis (MS)Multiple Sclerosis (MS)
Characteristics of the disease3) Double vision occurs
periodically4) “Attacks" every year or two
with periods of remission
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Multiple Sclerosis (MS)Multiple Sclerosis (MS)
Implications of a viral cause which precipitates the activation of killer T-cells to destroy myelin producing oligodendrocytes
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Multiple Sclerosis (MS)Multiple Sclerosis (MS)
1993 FDA approved use of Betaseron (a form of interferon)
Note greyish plaques around the ventricles
Multiple Sclerosis (MS)Multiple Sclerosis (MS)
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