Sistem Saraf Dasar-dasar

5/21/2018 Sistem Saraf Dasar-dasar

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SISTEM SARAF I

Dasar- dasar

Dr. Agus Budi Utomo


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Nervous System

Master control and communication system


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Nervous System: Functions

Three overlapping functions Sensory receptors monitor changes inside and

outside the body

Changea stimulus

Gathered informationsensory input

CNS Processes and interprets sensory input Makes decisionsintegration

Dictates a response by activating effector organs Responsemotor output


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Basic Divisions of the Nervous System: CNS

Central nervous system(CNS)

Brain and spinal cord

Integrating andcommand center


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Basic Divisions of the Nervous System: PNS

Peripheral nervoussystem (PNS) Outside the CNS Nerves extending

from brain and spinalcord

Cranial nerves Spinal nerves

Link all regions of thebody to the CNS


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Sensory Input and Motor Output

Sensory signals picked up by sensory receptors Carried by afferent nerve fibers of PNS to the CNS

Motor signals are carried away from the CNS

Carried by efferent nerve fibers of PNS to effectors Innervate muscles and glands


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Sensory Input and Motor Output

Divided according to region they serve Somatic body region

Visceral body region

Results in four main subdivisions Somatic sensory Visceral sensory

Somatic motor

Visceral motor



Somatic Sensory

Somatic sensory General somatic sensesreceptors are widely

spread

Touch, pain, vibration, pressure, and temperature

Proprioceptive sensesdetect stretch in tendons andmuscle

Body senseposition and movement of body inspace

Special somatic senses Hearing, balance, vision, and smell



Visceral Sensory

Visceral sensory General visceral sensesstretch, pain, temperature,

nausea, and hunger

Widely felt in digestive and urinary tracts,reproductive organs

Special visceral sensestaste



Somatic Motor

Somatic motor General somatic motorsignals contraction of

skeletal muscles

Under voluntary control

Often called voluntary nervous system



Visceral Motor

Visceral motor Regulates the contraction of smooth and cardiac

muscle and gland secretion

Makes up autonomic nervous system

Controls function of visceral organs

Often called involuntary nervous system


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Peripheral Nervous System Summary

Figure 12.3


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Types of Sensory and Motor Information

Figure 12.3


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Types of Sensory and Motor Information

Figure 12.3


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Nervous Tissue

Cells are densely packed and intertwined

Two main cell typesNeuronstransmit electrical signals Support cells (neuroglial cells)nonexcitable

Surround and wrap neurons


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The Neuron

The human body contains billions of neurons Basic structural unit of the nervous system

Specialized cells conduct electrical impulses alongthe plasma membrane

Graded potentials

Action potentials


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The Neuron: Special Characteristics

Longevitycan live and function for a lifetime Do not dividefetal neurons lose their ability to

undergo mitosis; neural stem cells are an exception

High metabolic raterequire abundant oxygen andglucose


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Neuron Structure


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The Cell Body or Soma (also called Perikaryon)

Size varies from 5140m Contains nucleus, organelles plus other structures

Chromatophilic bodies (Nissl bodies)

Clusters of rough ER and free ribosomes

Stain darkly and renew membranes of the cell

Neurofibrilsbundles of intermediate filaments

Form a network between chromatophilic bodies


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Nissl Body Staining


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The Cell Body

Most neuronal cell bodies Located within the CNS (clustered in nuclei)

Protected by bones of the skull and vertebralcolumn

Gangliaclusters of cell bodies in PNS


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Cell Body Structure

Figure 12.4


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Neuron Processes: Dendrites

Dendrites Extensively branching from

the cell body

Transmit electrical signals(graded potentials) toward the

cell body

Chromatophilic bodiesonlyextend into the basal part of

dendrites

Function as receptive sites


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Dendritic Spines


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Dendritic Spines


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Neuron Processes: Axons

Axons (nerve fibers)

Neuron has only one, but it canbranch

Impulse generator and conductor

Transmits action potentials awayfrom the cell body

Chromatophilic bodies absent

No protein synthesis in axon


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Neuron Processes: Axons

Axons

Neurofilaments, actinmicrofilaments, and

microtubules

Provide strength along

length of axon Aid in the transport of

substances to and

from the cell body

Axonal transport


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Neuron Processes

Neuron Structure

Axons

Branches along length areinfrequent

Axon collaterals Multiple branches at end of axon

Terminal branches (telodendria) End in knobs called axon

terminals (also called end bulbsor boutons)


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Neuron Processes: Action Potentials

Nerve impulse (action potential)

Generated at the initial segment of theaxon

Conducted along the axon

Releases neurotransmitters at axon

terminals Neurotransmittersexcite or inhibit

neurons

Neuron receives and sends signals


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Synapses

Site at which neurons communicate Signals pass across synapse in one direction

Presynaptic neuron

Conducts signal toward a synapse Postsynaptic neuron

Transmits electrical activity away from a synapse


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Two Neurons Communicating at a Synapse

Figure 12.6


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Types of Synapses

Axodendritic Between axon terminals of one neuron anddendrites of another

Most common type of synapse

Axosomatic Between axons and neuronal cell bodies

Axoaxonic, dendrodendritic, and dendrosomatic Less common types of synapses Function not as well understood


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Types of Synapses

Figure 12.7


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Synapses

Axodendritic synapsesrepresentative type Synaptic vesicles on presynaptic side

Membrane-bound sacs containing neurotransmitters

Mitochondria abundant in axon terminals Synaptic cleft separates the plasma membrane of thetwo neurons


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Structure of a Synapses

Figure 12.8a, b

PLAY Synapse
http://e/PowerPoint_Lect/12_ppt_lect/12_ppt_anim/Neuro_Synapse.movhttp://e/PowerPoint_Lect/12_ppt_lect/12_ppt_anim/Neuro_Synapse.movhttp://e/PowerPoint_Lect/12_ppt_lect/12_ppt_anim/Neuro_Synapse.mov


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Synapse


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Signals Carried by Neurons: Resting Membrane Potential

Plasma membranes of neuronsconduct electrical signals

Resting neuronmembrane ispolarized

Inner, cytoplasmic side isnegatively charged


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Changes in Membrane Potential

Signals occur as changes in membrane potential


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Directional Signals

Stimulation of the neurondepolarization Inhibition of the neuronhyperpolarization


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Action Potentials

Figure 12.9a, b


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Action Potentials on Axons

Strong depolarizing stimulus applied to the axonhillock triggers

Action potential

Membrane becomes positive internally

Action potential travels the length of the axon

Membrane repolarizes itself


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Action Potentials on Axons

Figure 12.9c

e


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Graded Potentials on Dendrites and the Cell Body

Natural stimuli applied to dendrites and the cellbody Receptive zone of the neuron

Membrane stimulation causes local depolarization

A graded potentialinner surface becomes lessnegative

Depolarization spreads from receptive zone to theaxon hillock

Acts as the trigger that initiates an action potential inthe axon


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Synaptic Potentials

Excitatory synapses

Neurotransmitters alter the permeability of thepostsynaptic membrane

Leads to an inflow of positive ions Depolarizes the postsynaptic membrane

Drives the postsynaptic neuron toward impulsegeneration


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Synaptic Potentials

Inhibitory synapses

The external surface of the postsynaptic membranebecomes more positive

Reduces the ability of the postsynaptic neuron togenerate an action potential

l i i i


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Classification of Neurons

Structural Classification Functional Classification

S l Cl ifi i f


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Structural Classification of Neurons

Classification based on number of processes Multipolar

Bipolar

Unipolar (pseudounipolar)

M l i l N


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Multipolar Neurons

Figure 12.10a

c

Possess more than twoprocesses

Numerous dendrites and

one axon

Bi l N


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Bipolar Neurons

Figure 12.10a

c

Possess two processes

Rare neuronsfound

in some special

sensory organs

U i l (P d i l ) N


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Unipolar (Pseudounipolar) Neurons

Figure 12.10a

c

Possess one single process

Start as bipolar neurons

during development

F ti l Cl ifi ti f N


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Functional Classification of Neurons

Classification based on direction of actionpotential propagation

Afferentsfrom CNS to periphery

Efferentsfrom periphery to CNS

Interneuronswithin CNS

Aff t


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Afferent neurons

Afferent (sensory) neuronstransmit impulses toward the CNS

Virtually all are pseudounipolar neurons (some truebipolar)

Cell bodies in ganglia outside the CNS Short, single process divides into

The central processruns centrally into theCNS

The peripheral processextends peripherally tothe receptors

Aff t N


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Afferent Neurons

Sensory receptorsAxon terminals

Periphery CNS

Eff t N


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Efferent Neurons

Efferent (motor) neurons

Carry impulses away from the CNS to effectororgans

Most efferent neurons are multipolar

Cell bodies are within the CNS Form junctions with effector cells

I t


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Interneurons

Interneurons (association neurons)most aremultipolar

Lie between afferent and efferent neurons

Confined to the CNS

Ne rons Classified b F nction


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Neurons Classified by Function

Figure 12.11

Variety of Interneurons


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Purkinje cell, stellate cell, granule cell, and basketcell

Located in the cerebellum

Pyramidal celllocated in the cerebral cortex



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Glial Cells (Supporting Cells)


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Glial Cells (Supporting Cells)

Six types of glial cells Four in the CNS

Two in the PNS

Provide supportive functions for neurons

Cover nonsynaptic regions of the neurons

Supporting Cells (Neuroglial Cells) in the CNS


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Supporting Cells (Neuroglial Cells) in the CNS

Neurogliausually only refers to supporting cellsin the CNS, but can be used for PNS Glial cells have branching processes and a central

cell body

Outnumber neurons 10 to 1 Make up half the mass of the brain

Can divide throughout life

Types of Glial Cells in the CNS


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Types of Glial Cells in the CNS

Astrocytes

Microglia Ependymal Cells

Oligodendrocytes

Astrocytes


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Astrocytes

Astrocytesmost abundant glial cell type Take up and release ions to control the environmentaround neurons

Recapture and recycle neurotransmitters

Involved with synapse formation in developingneural tissue

Produce molecules necessary for neural growth(BDTF)

Propagate calcium signals that may be involved inmemory

Astrocytes


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Astrocytes

Figure 12.12a

Necessary for development and maintenance of

theblood brain barrier

Microglia


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Microgliasmallest andleast abundant Phagocytes

the macrophagesof the CNS

Engulf invadingmicroorganisms and deadneurons

Derived from blood cellscalled monocytes

Microglia

Figure 12.12b

Ependymal Cells


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Ependymal Cells

Ependymal cells Line the central cavity of the spinal cord and brain Bear ciliahelp circulate the cerebrospinal fluid

Oligodendrocytes


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Oligodendrocytes

Oligodendrocyteshave few branches

Wrap their cell processes around axons in CNS

Produce myelin sheaths

Supporting Cells in the PNS


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Supporting Cells in the PNS

Satellite cellssurround neuron cell bodies within

ganglia Schwann cells (neurolemmocytes)surround

axons in the PNS

Form myelin sheath around axons of the PNS

Myelin Sheaths


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Myelin Sheaths

Segmented structures composed of the lipoproteinmyelin

Surround thicker axons

Form an insulating layer Prevent leakage of electrical current

Increase the speed of impulse conduction

Myelin Sheaths in the PNS


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Formed by Schwann cells Develop during fetal period and in the first year of

postnatal life

Schwann cells wrap in concentric layers aroundthe axon

Cover the axon in a tightly packed coil ofmembranes



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Nodes of Ranviergaps along axon Allow current exchange across axon membrane



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Thick axons are myelinated Fast conduction velocity

Thin axons are unmyelinated Slow conduction velocity



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Figure 12.14a

Myelin Sheaths in the PNS myelinated axon


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Myelin Sheaths in the PNS myelinated axon

Figure 12.15b

Myelin Sheaths in the PNS unmyelinated axons


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ye S eat s t e NS u ye ated a o s

Figure 12.15b

Myelin Sheaths in the CNS


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y

Oligodendrocytes form themyelin sheaths in the CNS Have multiple processes

Coil around severaldifferent axons

Oligodendrocytes


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g y

Nerves


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Nervescordlike organs in the PNS Consists of numerous axons wrapped in

connective tissue

Axon is surrounded by Schwann cells

Nerves


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Endoneuriumlayer of delicateconnective tissue surrounding theaxon

Nerve fasciclesgroups of axonsbound into bundles

Perineuriumconnective tissuewrapping surrounding a nervefascicle

Epineuriumwhole nerve issurrounded by tough fibroussheath

Simplified Design of the Nervous System


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p g y

Sensory neuronslocated dorsally Cell bodies outside the CNS in sensory ganglia Central processes enter dorsal aspect of the spinal

cord

Motor neuronslocated ventrally Axons exit the ventral aspect of the spinal cord

Interneuronslocated centrally

Provide communication between sensory andmotor neurons and between levels of the CNS

Example of Neuronal Organization: Reflexes


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p g

Reflex arcssimple neural pathways Responsible for reflexes Rapid, autonomic motor responses

Can be visceral or somatic

Five Essential Components to the Reflex Arc


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p

Receptordetects the stimulus Afferent (sensory neuron)transmits impulses tothe CNS

Integration centerconsists of one or moresynapses in the CNS

Efferent (motor neuron)conducts impulses fromintegration center to an effector

Effectormuscle or gland cell Responds to efferent impulses

Contraction or secretion

Example of the Five Components to the Reflex Arc


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p p

Figure 12.17

Reflex Classification


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Monosynaptic or polysynaptic Spinal or cranial

Somatic or autonomic

Innate or learned

Types of Reflexes: Number of Classes


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Monosynaptic reflexsimplest of all reflexes Just one synapse The fastest of all reflexes

Exampleknee-jerk reflex

Polysynaptic reflexmore common type of reflex Most have a single interneuron between the sensory

and motor neuron

Examplewithdrawal reflexes

Monosynaptic Reflex


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Polysynaptic Reflex


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Spinal vs Cranial Reflexes


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Spinal = spinal cord integration center Ex. Knee-jerk reflex

Cranial = brain as integration center Ex. Pupillary light reflex

Somatic vs Autonomic Reflexes


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Somatic = motor neurons to skeletal muscles Ex. Knee-jerk reflex

Autonomic = autonomic neurons to smoothmuscle and glands

Ex. Pupillary light reflex

Innate vs Learned Reflexes


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Innate = born-with Knee-jerk reflex, pupillary reflex

Learned = develops based on experiences Pavlovs dogs salivation in response to bell

Neuronal Circuits


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Diverging circuit Converging circuit

Reverberating circuit

Diverging Circuit


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Diverging circuitone presynapticneuron synapses with several otherneurons (divergence)

Converging Circuit


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Converging circuitmanyneurons synapse on a single

postsynaptic neuron

(convergence)

Reverberating Circuit


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Reverberating circuitcircuitthat receives feedback via a

collateral axon from a neuron

in the circuit

Neural Processing


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Serial processing Parallel processing

Serial Processing


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Serial processingneurons pass asignal to a specific destination along

a single pathway from one to

another

Parallel Processing


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Parallel processinginput isdelivered along many pathways; a

single sensory stimulus results in

multiple perceptions

Gray versus White Matter in the Central Nervous System


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Gray matter

Cell bodies Dendrites

Synapses

White matter

Axons (myelin)

Gray Matter in the Spinal Cord


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Gray matter in the spinal cord

H-shaped (butterfly) regionsurrounds central cavity

Dorsal half contains cell bodies of interneurons

Ventral half contains cell bodies of motor neurons

Cell bodies are clustered in the gray matter

White Matter in the Spinal Cord


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White matter in the spinal cord

Located externally to the gray matter Contains no neuronal cell bodies, but millions of axons

Myelin sheathwhite color

Consists of axons running between different parts of

the CNS Tractsbundles of axons traveling to similar

destinations

Gray Matter in Brain


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Cortex and nuclei

White Matter in Brain


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Pathways, tracts and commissures

Disorders of the Nervous System


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Multiple sclerosiscommon cause of neuraldisability Varies widely in intensity among those affected

Cause is incompletely understood

An autoimmune disease Immune system attacks the myelin around axons in

the CNS

Sistem Saraf Dasar-dasar

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