GENERAL PRINCIPLES OF SENSORY TRANSDUCTION

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GENERAL PRINCIPLES OF SENSORY TRANSDUCTION

• Donald C. Mikulecky
• Department of Physiology
• and
• Faculty Mentoring Program

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ORGANIZATION OF THE NERVOUS SYSTEM
BRAIN SPINAL CORD
CENTRAL NERVOUS SYSTEM (CNS)
AFFERENT NERVES
EFFERENT NERVES
PERIPHERAL NERVOUS SYSTEM
EXTERO- RECEPTORS
INTERO- RECEPTORS
SOMATIC
AUTONOMIC
EFFECTOR ORGANS
SKELETAL MUSCLES
SMOOTH AND CARDIAC MUSCLES AND GLANDS
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GENERAL PRINCIPLES OF SENSORY SYSTEMS

• SENSORY TRANSDUCTION SPECIFIC MODALITIES WITH
  ADEQUATE STIMULUS
• A SENSORY UNIT SENSORY NEURON AND ALL THAT IT
  INNERVATES
• EXTERORECEPTIVE AND PROPRIORECEPTIVE
• PATHWAYS
• INTEGRATION

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SENSORY INFORMATION TRAVELS TO THE BRAIN VIA
SPECIALIZED PATHWAYS
NEOCORTEX
LIMBIC CORTEX
NOSE
SMELL
THALAMUS
EYE
VISION
TASTE
TONGUE
BRAIN STEM
EAR
AUDITION
SKIN
SOMATIC
SPINAL CORD
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SENSORY MODALITIES AND RECEPTOR CELLS
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SENSORY MODALITIES AND RECEPTOR CELLS
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TYPES OF ENERGY TRANSDUCED
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ADEQUATE STIMULUS

• A SPECIFIC STIMULUS UNIQUE TO A SENSORY RECEPTOR
• FOR EXAMPLE, PHOTORECEPTORS IN THE EYE RESPOND
  ONLY TO ELECTROMAGNETIC RADIATION

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GRADED VS ALL OR NONE

• A RECEPTORS RESPONSE TO A STIMULUS IS GRADED
• IF THRESHOLD IS EXCEEDED, THE ACTION POTENTIAL
  RESULTING IS ALL OR NONE

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EXAMPLE THE PACINIAN CORPUSCLE

• PRESSURE RECEPTOR
• PRESSURE DISTORTS THE CAPSULE, STRETCHING THE
  CELL MEMBRANE
• SODIUM CHANNELS OPEN, DEPOLARIZING THE MEMBRANE
• IF BEYOND THRESHOLD, ACTION POTENTIAL RESULTS

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SENSORY TRANSDUCTION
ADEQUATE STIMULUS
MEMBRANE CONDUCTANCE CHANGE
GENERATOR POTENTIAL
ACTION POTENTIAL
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HOW IS THE INTENSITY OF THE STIMULUS ENCODED?

• FREQUENCY CODING
• POPULATION CODING

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FREQUENCY CODING
LIGHT PRESSURE
LOW FREQUENCY
MORE PRESSURE
HIGHER FREQUENCY
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POPULATION CODING
LIGHT PRESSURE
MORE PRESSURE
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THE LABELED LINE CODE OF STIMULUS QUALITY
NEOCORTEX
LIMBIC CORTEX
NOSE
SMELL
THALAMUS
EYE
VISION
TASTE
TONGUE
BRAIN STEM
EAR
AUDITION
SKIN
SOMATIC
SPINAL CORD
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LOCALIZATION, DISTRIBUTION, AND ACUITY

• CODING OF LOCATION DEPENDS ON RECEPTOR LOCATION
• AREA COVERED BY RECEPTORS IN A SENSORY UNIT IS A
  RECEPTIVE FIELD
• ACUITY DEPENDS ON THE DENSITY OF RECEPTORS

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