Central Nervous System Students Intrnational Program (2)

8/3/2019 Central Nervous System Students Intrnational Program (2)

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BYProf Dr: LOBNA BAYOUMI


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Central NervousSystem

CNS

Brain

Spinal cord


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Four Main Regions ofthe Brain

Cerebralhemispheres

Diencephalon

Brain stem:midbrain

Pons

medulla

Cerebellum


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Directional Terms of the Central

Nervous System

Directionalterms unique

to the CNSRostral :

toward thenose(anterior)

Caudal: toward thetail (posterior)

Dorsal :superior

Ventral :-inferior


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rostral caudal

cerebellum

dorsal

ventral

Anatomical directions

PosteriorAnterior


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Cerebrum -The largest division of the

brain. It is divided into two hemispheres,each of which is divided into four lobes.

Cerebrum

Cerebrum

Cerebellum


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Superior and inferior

surfaces of the brain


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Gyri (ridge)

Fissure

(deep groove)

Sulci(groove)


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CerebralCortex

Cerebral

Cortex

Cerebral Cortex - The outermost layerof gray matter making up thesuperficial aspect of the cerebrum.


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SPINAL CORD


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White and Gra Matter


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White and Gray Matter


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Lateralventricles

Fourthventricle

Thirdventricle

Cerebralaqueduct Lateral

ventricle

Thirdventricle

Cerebralaqueduct

Lateralaperture

Fourthventricle

Median

aperture

Ventricles are filled with CS


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General Senses

Sensation of temperature, pain, touch,pressure, vibration, andproprioception

Sensation: Information provided bysensory receptors to the CNS.

Perception:The conscious awarenessof sensation(to give a meaning to

sensation).

General Senses


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General Senses

Classification by sensation1-nociceptors

pain

2-thermoreceptors

temperature3-mechanoreceptors

deformed by force

touch, pressure (BP), vibration, stretch, itch

4-chemoreceptorschemicals in solution

Smell, taste, blood chemistry.


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Pacinian corpuscle


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Golgi tendon organs


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Muscle spindles


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Generator

Potential(Receptor Potential)


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Sensory Receptors


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The generator potentials [=receptorThe generator potentials [=receptor

potential]: its the change in thepotential]: its the change in the

membrane potential of the receptormembrane potential of the receptorwhen excited by a stimulus.when excited by a stimulus.

Its a non-propagated depolarizingIts a non-propagated depolarizing

potential resembling EPSP.potential resembling EPSP.


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Receptorpotential

#gradedeffect:strongerstimulus= largerreceptor

potential.#when the

receptorpotentialexceeds

thethreshold ,an actionpotentialis fired


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RECEPTOR POTENTIAL & ACTION POTENTIAL


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Sensory Transduction


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Generator potential

*Is a non propagated localised state ofpartial depolarization,

*It has a long duration(more than5msec),

*Not obeying the all or none rule,then itcan be graded,

*Not having a refractory period ,then itcan be summated,

*Not blocked by local anaesthesia.


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Differences between generator and action potential:Differences between generator and action potential:

Generator potential

GradedDoesnt obey all or

none ruleCan be summated

Unpropagated5 millisec

Action potential

NotObeys all or

non ruleNot summated

Propagated2 millisec


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ADAPTATION OF RECEPTOR


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Somatic sensations

Mechanoreceptive


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Mechanoreceptivesensations:


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Objective 3b: Somatotopic organization ofthe tracts

Sacral

D l l l i l t


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Dosal column lemniscal system


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Fasiculus gracilis and

cuneatus


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Characteristics of dorsalcolumn system

*Its fibres are heavily myelinated,

*High velocity of conduction(35-70

meters/sec),*Modality,locality and intensity of

sensations are transmitted with extremeaccuracy,

*DCN fibres reflec Cutaneous nervesdematomal arrangement of,

*Somatotopic(topographic)organization of

the body.

Somatotopic


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SomatotopicRepresentation ofthe SpinothalamicTract

Spinothalamic Tract


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Dorsal column and

ventralspinothalamic

pathways


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Dorsalcolumn and

spino-thalamictracts


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Spinothalamic systems


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Objective 3b: Somatotopic organization ofthe tracts

Sacral


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The Spinocerebellar


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pPathway

proprioceptiveinput frommuscles,tendons and

joints

first-order

neurons synapse onsecond-orderneurons in dorsalgray horn


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The Spinocerebellar

Pathway second-order neurons soma in spinal cord

axons ascend in: posterior spinocerebellar

tract

dont decussate

anterior spinocerebellartract

usually decussate

Posterior Spinocerebellar TractsPosterior Spinocerebellar Tracts


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Posterior Spinocerebellar TractsPosterior Spinocerebellar Tracts

The cell bodies of 2ndorder neuron lie in

Clarks column

Axons of 2nd order

neuron terminate

ipsilaterally (uncrossed)

in the cerebellar cortex

by entering through theinferior cerebellar

peduncle


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Neurotransmitters and

Pain Sensory Neurons glutamate and Substance P

excitatory

facilitate neurons along pain pathway

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Neurotransmitters and

Pain Natural painkillers endorphins and enkephalins (in small

red neuron)

inhibit the perception of pain by the CNSby inhibiting the release of Substance Pfrom sensory neurons

Keep in mind:

The perception of pain may be

gone, but the stimulus remains.


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Central Nervous System Students Intrnational Program (2)

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