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SENSORY SYSTEMS

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a specific stimulus that activates sensory receptor(s) e.g. Pacinian corpuscle ... e.g. Pacinian corpuscle. hair receptor. Ruffini ending. Lecture 3 Sensory/Motor ... – PowerPoint PPT presentation

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Title: SENSORY SYSTEMS


1
  • SENSORY SYSTEMS
  • 1. General Principles of Sensory Transduction
  • Adequate stimulus
  • a specific stimulus that activates sensory
    receptor(s)
  • e.g. Pacinian corpuscle
  • Change in membrane conductance
  • Generator potential
  • Action potential

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  • Stimulus intensity and frequency of action
    potentials
  • frequency code of stimulus intensity
  • stimulus intensity ? generator potential ?
    frequency of action potential
  • This allows the receptor to have a extreme range
    of response, from very weak to very intense
  • population code
  • More sensory receptors are activated as stimulus
    gets greater

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  • B. Modality of sensation
  • Each type of sensation (pain, touch, sound, etc.)
    is called modality of sensation
  • The quality of a stimulus is encoded by the
    pathway of transmission
  • Different modality of sensation is transmitted
    by a specific nerve fiber and determined by where
    the nerve fiber terminates in the brain
  • Labeled-line code principle
  • The specificity of nerve fibers for transmitting
    only one modality of sensation

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  • B. Mechanisms of adaptation
  • can occur at the brain and the receptor
  • sensory adaptation at receptor site

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  • 1. Somatic Sensory System
  • A. Types of somatic sensory receptors
  • tactile receptors (mechanoreceptors)
  • stimuli touch, pressure, vibration
  • e.g. Pacinian corpuscle
  • hair receptor
  • Ruffini ending

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  • thermal receptors
  • stimuli heat and cold
  • nociceptors (pain receptors)
  • stimuli painful touch, cut, extreme temperatures
  • proprioceptive receptors
  • detect position and movement
  • static proprioceptors
  • tonic discharge
  • dynamic proprioceptors/kinesthesia
  • phasic discharge

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  • joint capsules
  • muscle spindle receptors
  • general principles for somatic sensory receptors
    mediated transmission
  • specificity
  • cross-over of most pathways
  • topographical organization
  • B. The dorsal root ganglion
  • a cluster of cell bodies
  • different size of nerve fibers

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  • large fibers D 13-22 ?m, glutamate as
    neurotransmitters
  • myelinated, fast action potential conduction
    70-120m/sec
  • small fibers D 1-5 ?m, substance P as
    neurotransmitters
  • unmyelinated, slow conduction of action
    potential 2-15m/sec
  • two major pathways dorsal column and
    anterolateral
  • C. The spinal cord in somatic sensory function
  • anatomy of the spinal cord

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  • useful anatomic terms rostro-caudal axis
    dorsal/ventral medial/lateral
    anterior/posterior
  • transverse section gray matter and white matter
  • segments of the spinal cord
  • 31 segments 8 cervical (C1-C8)
  • 12 thoracic (T1-T12)
  • 5 Lumbar (L1-L5)
  • 5 sacral (S1-S5)
  • 1 sacro-coccygeal
  • dermatomes
  • lesions of the spinal cord

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  • D. The thalamus in somatic sensory function
  • One of the brain areas that receives most types
    of sensory information
  • VPL receives somatic sensory information
  • E. The somatic sensory cortex
  • somatotopic organization
  • F. Receptive field of neurons
  • The area monitored by a single receptor cell is
    called the receptive field for that cell
  • The receptive fields differ in different parts of
    body.
  • small in more sensitive areas like fingertips,
    tongue (1 mm in diameter)
  • large in less sensitive areas such as in the back
    (7 cm)

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  • Lateral inhibition
  • Two-points threshold discrimination test
  • Pain sensation
  • Pathway anterolateral pathway
  • Neurotransmitter substance P
  • Modification of pain sensation
  • Brain stem
  • Other sensory fibers (touch, pressure)
  • Higher brain center
  • The gating theory
  • Referred pain

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Referred pain. Nociceptors from several
locations converging on a single ascending tract
in the spinal cord may cause referred pain.
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