Sensory Processing: Touch and Pain

1
Sensory Processing Touch and Pain

• Sensory receptor organs
• Receptor cells processing
• Skin and touch
• Pain

2
Sensory Receptor Systems

• Species-specific sensors
• Snakes detectors of infrared
• Compound eye of insects movement
• Adequate stimulus the sensory organ adapted to
  type of stimulus
• Classification of sensory systems
• Mechanical
• Photic
• Thermal
• Chemical
• Electrical
• Labeled Lines each receptor has distinct neural
  pathway

3
Receptor Cells

• Sensory transduction
• Pacinian Corpuscle (vibration)
• Mechanical stimulation
• Deformation leads to mechanical stretch
• Na influx
• Generator potential once at threshold, axon
  produces nerve impulses

4
Sensory System Processing

• Coding
• Stimulus intensity, location
• Adaptation
• Tonic / phasic receptors
• Sensory pathway thalamic relay to cortex
• Suppression
• Accessory structures central modulation
• Receptive fields (periphery and central)
• On-center / off-surround vs. Off-center /
  on-surround
• Attention
• Generalized activation attunes us to everything
• Selection of some input among competing ones
• Focus on stimuli / ignore other

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Touch Sensory Receptors

• Pacinian corpuscle (vibration)
• Large, vague borders
• Fast-adapting
• Meissners corpuscle (touch)
• Small, sharp borders
• Fast-adapting

• Merkels discs (touch)
• Small, sharp borders
• Slow-adapting
• Ruffinis ending (stretch)
• Large, vague borders
• Slow-adapting
• A? myelinated fibers
• Rapid-firing

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Dorsal Column System

• Skin receptor
• Axon enters spinal cord dorsal horn
• Synapses in medulla / crosses midline
• Enters thalamus

7
Plasticity of Sensory Representation

• Detailed cortical maps dynamic
• Prolonged sensory manipulations
• Neural, cellular, molecular changes
• Reorganizations occur
• Cortical subcortical levels

8
Pain

• Congenital insensitivity
• Genetic defect in gene receptor for NGF
• Neural systems
• Nociceptors / free nerve endings
• Vanilloid receptor 1 (VR1) (moderate heat)
• Capsaicin, C unmyelinated fibers
• Slow responding, slow-adapting
• VRL1 (high temperature)
• Ad myelinated fibers
• Fast responding, fast-adapting
• Cool-menthol receptor 1 (CMR1)
• Cool temperatures, C unmyelinated fibers
• Slow responding, slow-adapting

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Spinothalamic Pain System

• Ad, C fibers
• Axons synapse in dorsal horn
• Substance P and glutamate
• Spinal cord neurons cross over
• Pain information passes to brainstem sites (pons,
  midbrain - PAG)
• Thalamus
• Cortical (e.g., cingulate)

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Treatment of Pain

• Psychogenic
• Placebo
• Hypnosis
• Cognitive
• Pharmacological
• Opiates side effects
• Spinal block
• Anti-inflammatory drugs major side effects
• Aspirin does not block leukotriene synthesis
• Stimulation
• TENS / mechanical local application
• Acupuncture opiate mechanism others?
• Central gray opiate mechanism
• Surgical
• Peripheral nerve cord, rhizotomy (cut dorsal
  root), cord hemisection, frontal lobotomy

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Take Home Message

• Sensory processing
• Sensory receptors
• Receptor fields
• Suppression
• Adaptation
• Sensory pathway
• Touch
• Pain