UB BIO 203 - 4-Somatic Sensation 10-02-2018 (21 pages)

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4-Somatic Sensation 10-02-2018



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4-Somatic Sensation 10-02-2018

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Pages:
21
School:
University at Buffalo-SUNY
Course:
Bio 203 - General Physiology Lec

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SOMATIC SENSATION 1 Modalities of somatic sensation qualitatively different sensations CUTANEOUS SKIN DEEP touch pressure pain pain warm position cool Separate and independent neural systems for each modality from periphery up to cortex How are the cutaneous modalities distributed across the skin 2 Punctate nature of cutaneous sensation Any point on skin gives rise to one and only one sensation T C W P 1 mm T W C P Why is this true There is a physiological anatomical explanation look at how the skin is innervated 3 Innervation transduction DEFINITION axons that innervate the body are the primary afferent fibers first order fibers Cell bodies are in the DRG Dorsal Root Ganglion axons branch one end to periphery other into the spinal cord Transduction is accomplished by channels at the fiber ending no separate class of receptor cells 4 Shingles disease of DRG Shingles causes a painful rash with blisters It is caused by the varicella virus the same virus that causes chickenpox it is a herpes virus also called herpes zoster The virus lies dormant in the DRG but may reactivate as shingles It travels down the sensory nerve fibers and affects the skin 5 What activates the virus Rash is seen in skin innervated by that nerve sometimes with severe pain Skin can remain painful and sensitive to touch for months or even years after the rash clears up postherpetic neuralgia Conditions that weaken the body s immune system such as aging cancer or certain drugs increase the chance that the virus will become active again Not known why any particular DRG is affected nor what happens in the skin to cause the rash Half of the nearly 1 million shingles cases in the United States each year occur in people aged 60 years and older It is treated with antiviral drugs there is a vaccine 6 Functional classification of primary afferent fibers innervating the skin 4 functional types 1 Pain nociceptors noxious damaging stimuli 2 Touch mechanoreceptors 3 Warm and 4 Cool thermoreceptors 7



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