Sensory Nervous System

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Sensory Nervous System

• Objectives
• ?Describe the process of sensory transduction in
  general
• ?List the stimuli to which we have receptors and,
  for each, identify the general type of receptor
• ?Distinguish receptor potential from action
  potential
• ?Distinguish tonic and phasic receptor function

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• Somatic senses
• fine touch, deep touch, pressure, temp, pain,
  joint and muscle position, muscle stretch

Visceral senses pH, O2, CO2, OsM, glucose, blood
pressure, lung inflation, stomach stretch
Special senses olfaction, gustation, hearing,
equilibrium, vision
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Receptors are transducers, neural or
non-neural Types chemo-, mechano-, photo-,
thermo-, noci-
ear (sense organ) with mechanoreceptors (transduce
rs)
Vestibulocochlear nerve
graded potentials
CNS (decoder) -medulla to thalamus to auditory
cortex
action potentials
non-neural receptors -receptor potentials (like
graded potentials)
coding which receptors are activated and AP
frequency
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General principles of sensory function

1. Each sensory organ and receptor is specialized to
   convert one form of stimulus into sensory neuron
   action potentials.
2. Each modality has a discrete pathway to the
   brain.
3. The specific sensation and location of stimulus
   perceived is determined by area of brain
   activated.
4. Intensity is coded by frequency of action
   potentials and number of receptors activated.

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Group the following senses according to whether
they use chemical or mechanical receptors.
taste (gustation) pain (nociception) smell
(olfaction) touch vibration vision ox
ygen levels pressure (baroreception) Which one
can be both and which one is neither?
-chem -chem and mech -chem -mech -mech -neither -c
hem -mech
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• A somatic sense touch
• Free nerve endings
• Meissners corpuscle (light)
• Pacinian corpuscles (deep)

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• Example sensory pathway touch
• (receptor cell)
• sensory neuron
• to spinal cord or brainstem
• to thalamus
• to somatosensory cortex

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General principles of sensory function

1. Each sensory organ and receptor is specialized to
   convert one form of stimulus into sensory neuron
   action potentials.
2. Each modality has a discrete pathway to the
   brain.
3. The specific sensation and location of stimulus
   perceived is determined by area of brain
   activated.
4. Intensity is coded by frequency of action
   potentials and number of receptors activated.

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The specific sensation and location of stimulus
perceived is determined by area of brain
activated.
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FREQUENCY CODING
Intensity is coded by frequency of action
potentials and number of receptors activated.
LIGHT PRESSURE
LOW FREQUENCY
MORE PRESSURE
HIGHER FREQUENCY
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POPULATION CODING
Intensity is coded by frequency of action
potentials and number of receptors activated.
LIGHT PRESSURE
MORE PRESSURE
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Receptor Types

• Chemoreceptors pH, O2, CO2, glucose, taste,
  odor, some pain
• Mechanoreceptors muscle, cell, joint, lung,
  blood vessel and stomach stretch, sound,
  equilibrium
• Photoreceptors light
• Thermoreceptors hot or cold
• All receptors are transducers sensitive to a
  specific stimulus. Some are neurons, some are not.

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General principles of sensory function Somatic
senses -touch, pressure, temp, pain

• Objectives For each sense identify
• Any specialized structures or sense organs
• Receptor type
• Receptor signal transduction mechanism
• Coding of intensity and duration
• Pathway of conduction to the CNS
• Coding for perceived sensation

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