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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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i d
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Neurotransmitters and
Pain Sensory Neurons glutamate and Substance P
excitatory
facilitate neurons along pain pathway
i d
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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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