sensory,pain 2-3rd year

8/3/2019 Sensory,Pain 2-3rd Year

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Sensory Function of the

Nervous System

By:Prof.Dr.Lobna Bayoumi


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Classificationof receptors:

1-nociceptors:pain

2-thermoreceptors:temperature

3-mechanoreceptors

deformed by force

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

4-chemoreceptors

chemicals in solution

Smell, taste, blood chemistry.

5-electromagnetic receptors


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Generator Potential

(Receptor Potential)


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The generator potentials [=receptorpotential]: its the change in the

membrane potential of the receptorwhen excited by a stimulus.

Its a non-propagated depolarizingpotential resembling EPSP.


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Source of generator

potential:


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Sensory Transduction


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Receptor Potentials


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Generator potential

*Is a non propagated localised state of partialdepolarization,

*It has a long duration(more than 5msec),

*Not obeying the all or none rule,then it canbe graded,

*Not having a refractory period ,then it can besummated,

*Not blocked by local anaesthesia.


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Differences between generator and action potential:

Generator potential

GradedDoesnt obey all or

none ruleCan be summatedUnpropagated5 millisec

Action potential

NotObeys all ornon ruleNot summatedPropagated2 millisec


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Somatic sensations

I-MECHANORECEPTIVE

1-tactile(touch,pressure,vibration)2-kinethetic(conscious ,unconscious)

II-THERMORECEPTIVE

III-PAIN.


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Ascendingsensory tracts


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Objective 3b: Somatotopic organization of the tracts

Sacral


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Dorsal column- Lemniscus Pathway Proprioception

andkinesthesia,

Vibration,

Discriminativetouch,

Weightdiscrimination,

Stereognosis


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Dosalcolumn

lemniscalsystem


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Spinothalamic Pathways

Lateralspinothalamictract : carriespain &

temperature Anterior

spinothalamictract: carries

tickle,itch, crudetouch &

pressure


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Dorsal column and

ventral spinothalamicpathways


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Posterolateral nucleus of


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Posterolateral nucleus ofthalamus


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Sensory areas of the cerebral cortex


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y

I. Primary areas: 1. Somatic sensory area I,

2. Somatic sensory area II,

3. Primary visual cortex area (17)

4. Primary auditory cortex area (41, 42)

II. Secondary or association areas:

1. Somatosensory association areas (5, 7)

2. Visual association areas (18,19)

3. Auditory association area (22)


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Some points to remember:

Levels for decussation of either first orsecond order neurons.

Some specific characters or differencesand /or similarities between tracts.


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Spinothalamic damage


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p g

spinothalamic pathway

Leftspinal cord injury

Loss of sense of:TouchPainWarmth/coldin right leg

Dorsaldorsal column

th

Leftspinal cord injury


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Dorsalcolumndamage

pathway

Loss of sense of:touchproprioceptionvibrationin left leg


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sensory,pain 2-3rd year

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