5. Synaptic neuropharmacology

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• 5. Synaptic neuropharmacology
• agonists mimic NT action
• nicotine and muscarine for ACh
• antagonists block NT action
• atropine and curare for ACh
• caffeine for adenosine
• Can also block NT release (botulinum toxin),
• activate NT release (amphetamines),
• or block NT destruction (nerve gas blocks
  ACHase)

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• III. Sensory Physiology
• A. Function of sensory cells
• Receive environmental energy and produce
  electrical potentials
• Requires specialized receptor cells

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• 1. Detect specific kind of environmental energy
• Very selective light, heat, amino acids, etc.
• 2. Transduce environmental energy into passive
  potentials
• 3. Amplify signal for transmission over
  distance
• Generate action potentials

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• B. Sensory Transduction
• 1. Stimulus energy

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• B. Sensory Transduction
• 1. Stimulus energy
• 2. Strikes specialized structure on receptor
  cell
• (membrane, pigment, hair, etc.)

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• B. Sensory Transduction
• 1. Stimulus energy
• 2. Strikes specialized structure on receptor
  cell
• (membrane, pigment, hair, etc.)
• 3. Changes ion conductance of membrane
• (requires stimulus-gated channels)

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• 4. Results in change in EM of receptor cell
• Receptor Potential
• passive potential
• local at reception site
• graded with stimulus intensity

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• 5. Production of action potentials
• a. Receptor cell has axon
• e.g. crayfish stretch receptor
• (1) SIZ adjacent to receptive structure
• (2) Receptor potentials summated to action
  potentials

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• b. Receptor cell synapses with action
  potential-generating neuron
• E.g., hair cell
• Receptor potentials result in release of NT
  to postsynaptic neuron
• Postsynaptic potentials summate to action
  potentials

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• C. Coding of sensory information
• Receptor potential magnitude reflects stimulus
  intensity,
• but action potential magnitude is fixed

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• 1. Frequency Modulation
• a. Alter frequency of action potentials so that
  it is proportional to stimulus strength
• Setup record action potentials from axon
  leading from receptor as you stimulate

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• action potential frequency changes in
  proportion to stimulus strength
• e.g., crayfish stretch receptor

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• action potential frequency changes in
  proportion to stimulus strength
• e.g., crayfish stretch receptor

a.p.s sec
intensity
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• action potential frequency changes in
  proportion to stimulus strength
• e.g., crayfish stretch receptor

a.p.s sec
intensity
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• action potential frequency changes in
  proportion to stimulus strength
• e.g., crayfish stretch receptor

a.p.s sec
intensity
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• b. Sensory Adaptation
• decreased activity of receptor system in
  response to constant stimulus
• (1) change in electrical or chemical
  properties of receptor cell over time
• (2) inhibition of receptor by CNS

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• 2. Recruitment of new receptors
• a. Activate more receptors with increased
  stimulus intensity
• b. Activate different receptors with
  increased stimulus intensity
• range fractionation (receptors cover
  different stimulus intensity ranges)

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• D. Classification of receptor cells
• 1. Chemoreceptors detect molecules/ ions
• a. received molecule interacts with membrane
  protein to change membrane permeability
• b. e.g. smell, taste

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• 2. Mechanoreceptors detect physical distortion
  of cell
• a. physical distortion of membrane alters
  channel activity
• b. e.g., touch, stretch, fluid motion,
  pressure (baroreceptors)

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• 2. Mechanoreceptors detect physical distortion
  of cell
• a. physical distortion of membrane alters
  channel activity
• b. e.g., touch, stretch, fluid motion,
  pressure (baroreceptors)

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• 3. Thermoreceptors detect thermal energy
• a. function?
• internal and external
• b. snake facial pit organ

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• 3. Thermoreceptors detect thermal energy
• a. function?
• internal and external
• b. snake facial pit organ

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• 4. Electroreceptors detect currents
• a. Function environmental electrical current
  directly depolarizes cell membrane
• b. Fish only

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• 5. Photoreceptors detect light energy
• a. Light absorption by pigment results in
  change in membrane potential
• b. e.g., eye