SENSORY%20SYSTEM

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SENSORY SYSTEM

• D. C. Mikulecky
• Professor of Physiology

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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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TYPES OF ENERGY TRANSDUCED
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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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SENSORY TRANSDUCTION
ADEQUATE STIMULUS
MEMBRANE CONDUCTANCE CHANGE
GENERATOR POTENTIAL
ACTION POTENTIAL
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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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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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THE SPINAL CORD IN SOMATIC SENSORY FUNCTION

• WHITE AND GREY MATTER
• SEGMENTAL ORGANIZATION

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SPINAL CORD
DORSAL HORN
DORSAL
GREY MATTER
DORSAL ROOT GANGLION
LATERAL
VENTRAL HORN
WHITE MATTER
SPINAL NERVE
VENTRAL
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TOUCH AND PRESSURE
DORSAL COLUMN PATHWAY
INCOMONG SENSORY NERVE TRAVELS UPWARD IN THE
DORSAL COLUMN AND SYNAPSES IN THE DORSAL COLUMN
NUCLEUS
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PAIN AND TEMPERATURE
ANTEROLATERAL PATHWAY
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SEGMENTAL STRUCTURE OF SPINAL NERVES
DERMATOMES
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THE THALAMUS IN SOMATIC SENSATION

• MAJOR SITE FOR RECEIVING SENSORY INFORMATION
• VENTRAL POSTERIOR LATERAL NUCLEUS (VPL)
• SENDS SENSORY INFORMATION TO THE CORTEX

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THE THALAMUS IN SOMATIC SENSATION
SENSORY NEOCORTEX
MEDIAL LEMNISCUS
DORSAL COLUMN NUCLEI
MEDULLA
DORSAL COLUMN
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THE SOMATOSENSORY CORTEX
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SOMATOTOPIC ORGANIZATION OF THE SENSORY CORTEX
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CORTICAL AREAS INVOVED IN MOTOR CONTROL
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SOMATOTOPIC ORGANIZATION OF THE MOTOR CORTEX