SOMATIC SENSORY SYSTEMS AND PAIN

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SOMATIC SENSORY SYSTEMS AND PAIN

• D. C. MIKULECKY
• PROFESSOR OF PHYSIOLOGY
• AND
• FACULTY MENTORING PROGRAM

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RECEPTIVE FIELDS

• SIZE DETERMINES ACUITY
• LOCATION OF CELL BODY CORRESPONDS TO LOCATION AND
  SHAPE OF RECEPTIVE FIELD
• THIS ORGANIZATION IS PRESERVED IN THE SOMATOTOPIC
  MAPS IN THE SOMATIC SENSORY CORTEX

RECEPTIVE FIELDS TUTORIAL
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RECEPTIVE FIELDS BY CELL BODY LOCATION DORSAL
ROOT GANGLION


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RECEPTIVE FIELDS BY CELL BODY LOCATION DORSAL
ROOT GANGLION


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RECEPTIVE FIELDS BY CELL BODY LOCATION DORSAL
COLUMN NUCLEI
HIGH OUTPUT
INHIBITORY INTERNEURON
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RECEPTIVE FIELDS BY CELL BODY LOCATION DORSAL
COLUMN NUCLEI
SMALL OUTPUT
INHIBITORY INTERNEURON
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ANNULAR RECEPTIVE FIELDS
-
-
DORSAL COLUMN NERVE CELLS

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ANNULAR RECEPTIVE FIELDS
-
-
-

-
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DIFFERENT TYPES OF RECEPTIVE FIELDS
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OVERLAPPING ANNULAR RECEPTIVE FIELDS ARE
RECTANGULAR
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SOMATOSENSORY CORTEX

• SOMATOTOPIC ORGANIZATION
• MORE AREA TAKEN BY SENSITIVE REGIONS (GREATER
  RECEPTOR DENSITY-SMALLER RECEPTIVE FIELDS)
• CELLS RESPONDING TO ONE TYPE OF SENSATION IN
  VERTICLE COLUMNS(FOR EXAMPLE..PACINIAN CORPUSCLES
  IN A FINGERTIP)

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THE ANTEROLATERAL PAIN AND TEMPERATURE PATHWAY

• SENSORY NEURONS SYNAPSE IN SUBSTANTIA GELATINOSA
• SECONDARY NEURONS CROSS MIDLINE AND ASCEND IN
  ATEROLATERAL COLUMN
• BRANCHES GO TO THE RETICULAR FORMATION
• TERMINATE IN VENTROBASAL NUCLEUS OF THALMUS
• TERTIARY NEURONS GO TO SENSORY CORTEX

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THE ANTEROLATERAL PATHWAY
SUBSTANTIA GELITANOSA
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THE SENSATION OF PAIN

• FAST PAIN
• SLOW PAIN
• MECHANICAL PAIN
• CHEMICAL PAIN
• THERMAL PAIN

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PAIN NERVES
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FAST PAIN

• OCCURS IN ABOUT 0.1 SECONDS
• SUBJECTIVE DESCRIPTIONSHARP, ACUTE, ELECTRIC OR
  PRICKING
• A? FIBERS SYNAPSE ON CELLS IN LAMINA I (LAMINA
  MARGINALIS) IN THE DORSAL HORNS
• SECONDARY NEURONS CROSS AND TRAVEL THROUGH THE
  ANTEROLATERAL PATHWAY TO THE VENTROBASAL COMPLEX
  OF THE THALAMUS
• TERTIARY NEURONS GO TO THE PRIMARY SENSORY CORTEX

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FAST PAIN PATHWAY
VENTROBASAL NUCLEUS
LAMINA MARGINALIS
I
II
IV
III
VI
V
VII
SUBSTANTIA GELITANOSA
ANTEROLATERAL PATHWAY
IX
VIII
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SLOW PAIN

• OCCURS AFTER A SECOND OR MORE
• OFTEN ASSOCIATED WITH TISSUE DESTRUCTION
• SUBJECTIVELY DESCRIBED AS BURNING,
  ACHING,THROBBING, NAUSEOUS, OR CHRONIC
• C FIBERS WHICH SYNAPSE IN THE SUBSTANTIA
  GELITANOSA
• FINAL PROJECTION IS THE FRONTAL CORTEX

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SLOW PAIN PATHWAY
VENTROBASAL NUCLEUS
LAMINA MARGINALIS
I
II
IV
III
VI
V
VII
SUBSTANTIA GELITANOSA
ANTEROLATERAL PATHWAY
IX
VIII
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MECHANICAL, CHEMICAL AND THERMAL PAIN

• FAST PAIN IS GENERALLY MECHANICAL OR THERMAL
• SLOW PAIN CAN BE ALL THREE
• CHEMICAL PAIN RECEPTORS BRADYKININ, SEROTONIN,
  HISTAMINE, POTASSIUM IONS, ACIDS, ACETYL CHOLINE
  AND PROTEOLYTIC ENZYMES
• PROSTAGLANDINS ENHANCE PAIN SENSATION

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BRAIN STRUCTURES AND PAIN

• COMPLETE REMOVAL OF THE SENSORY CORTEX DOES NOT
  DESTROY THE ABILITY TO PERCIEVE PAIN
• STIMULATION OF THE SENSORY CORTEX EVOKES A
  SENSATION OF PAIN

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PAIN CONTROL (ANALGESIA)

• THE ANALGESIA SYSTEM
• THE BRAINS OPIATE SYSTEM
• INHIBITION OF PAIN BY TACTILE STIMULATION
• TREATMENT OF PAIN BY ELECTRICAL STIMULATION
• REFERED PAIN

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THE ANALGESIA SYSTEM

• PREAQUEDUCTAL GRAY
• RAPHE MAGNUS NUCLEUS
• PAIN INHIBITORY COMPLEX IN DORSAL HORNS

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PAIN INHIBITORY COMPLEX PRESYNAPTIC INHIBITION
BRAIN STEM.NEURON
ANTEROLATERAL PATHWAY
INHIBITORY NEURON
-
PAIN RECEPTOR

DORSAL HORN OF SPINAL CORD
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PAIN TRANSMISSION AND INHIBITION

• SUBSTANCE P IS THE NEUROTRANSMITTER BUILDS UP
  SLOWLY IN THE JUNCTION AND IS SLOWLY DESTROYED
• PRESYNAPTIC INHIBITION BY INHIBITORY NEURON
  BLOCKS THE RELEASE OF SUBSTANCE P (ENKEPHALIN)

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THE BRAINS OPIATE SYSTEM

• OPIATE RECEPTORS EXIST IN MANY CENTERS OF THE
  BRAIN, ESPECIALLY IN THE ANALGESIA SYSTEM
• AMONG THE NATURAL SUBSTANCES WHICH ACTIVATE THESE
  RECEPTORS ARE ENDORPHINS, ENKEPHALINS, AND
  MORPHINE

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INHIBITION OF PAIN BY TACTILE STIMULATION

• STIMULATION OF LARGE SENSORY FIBERS FOR TACTILE
  SENSATION INHIBITS PAIN TRANSMISSION FOR SAME
  REGION
• RUBBING OFTEN EASES PAIN
• LINAMENTS, OIL OF CLOVE, ETC.
• POSSIBLE EXPLANATION FOR ACUPUNCTURE?

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TREATMENT OF PAIN BY ELECTRICAL STIMULATION

• STIMULATION OF LARGE SENSORY NERVES
• ELECTRODES IN SKIN OR SPINAL IMPLANTS
• INTRALAMINAR NUCLEUS OF THALAMUS

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REFERED PAIN

• VISCERAL PAIN FIBERS SYNAPSE ON SAME SECONDARY
  NEURONS AS RECEIVE PAIN FIBERS FROM SKIN