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SOMATIC SENSORY SYSTEMS
AND PAIN
D. C. MIKULECKY
PROFESSOR OF PHYSIOLOGY
AND
FACULTY MENTORING PROGRAM
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
RECEPTIVE FIELDS BY CELL BODY
LOCATION: DORSAL ROOT GANGLION
+
+
RECEPTIVE FIELDS BY CELL BODY
LOCATION: DORSAL ROOT GANGLION
+
+
RECEPTIVE FIELDS BY CELL BODY
LOCATION: DORSAL COLUMN NUCLEI
HIGH
OUTPUT
INHIBITORY
INTERNEURON
RECEPTIVE FIELDS BY CELL BODY
LOCATION: DORSAL COLUMN NUCLEI
SMALL
OUTPUT
INHIBITORY
INTERNEURON
ANNULAR RECEPTIVE FIELDS
-
+
-
DORSAL
COLUMN
NERVE CELLS
ANNULAR RECEPTIVE FIELDS
-
+
-
-
DIFFERENT TYPES OF
RECEPTIVE FIELDS
RECTANGULAR
AREA 1- CORTEX
ANNULAR
AREA 3- CORTEX
ANNULAR
THALAMUS
ANNULAR
DORSAL COLUMN
SIMPLE
DORSAL ROOT
OVERLAPPING ANNULAR RECEPTIVE
FIELDS ARE RECTANGULAR
+
-- +
-+- -
SOMATOSENSORY
CORTEX
SOMATOTOPIC ORGANIZATION
MORE AREA TAKEN BY SENSITIVE
REGIONS (GREATER RECEPTOR DENSITYSMALLER RECEPTIVE FIELDS)
CELLS RESPONDING TO ONE TYPE OF
SENSATION IN VERTICLE COLUMNS(FOR
EXAMPLE..PACINIAN CORPUSCLES IN A
FINGERTIP)
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
THE ANTEROLATERAL
PATHWAY
SUBSTANTIA
GELITANOSA
THE SENSATION OF PAIN
FAST PAIN
SLOW PAIN
MECHANICAL PAIN
CHEMICAL PAIN
THERMAL PAIN
PAIN NERVES:
TYPE DIAMETER CONDUCTI SENSORY
ON
INFORMATION
(m)
VELOCITY
(m/s)
III(A)
5
15
IV(C)
1
2
LIGHTLY
MYELINATED:
TOUCH,
PRESSURE, AND
PAIN
UNMYELINATED:
PAIN AND
TEMPERATURE
FAST PAIN
 OCCURS IN ABOUT 0.1 SECONDS
 SUBJECTIVE DESCRIPTION:SHARP, 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
FAST PAIN PATHWAY
VENTROBASAL
NUCLEUS
LAMINA
MARGINALIS I
II
IV
III VI
V
VII
SUBSTANTIA
GELITANOSA
IX
VIII
ANTEROLATERAL
PATHWAY
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
SLOW PAIN PATHWAY
VENTROBASAL
NUCLEUS
LAMINA
MARGINALIS I
II
IV
III VI
V
VII
SUBSTANTIA
GELITANOSA
IX
VIII
ANTEROLATERAL
PATHWAY
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
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
PAIN CONTROL (ANALGESIA)
THE ANALGESIA SYSTEM
THE BRAIN’S OPIATE SYSTEM
INHIBITION OF PAIN BY TACTILE
STIMULATION
TREATMENT OF PAIN BY ELECTRICAL
STIMULATION
REFERED PAIN
THE ANALGESIA SYSTEM
PREAQUEDUCTAL GRAY
RAPHE MAGNUS NUCLEUS
PAIN INHIBITORY COMPLEX IN DORSAL
HORNS
PAIN INHIBITORY COMPLEX:
PRESYNAPTIC INHIBITION
BRAIN STEM.NEURON
ANTEROLATERAL
PATHWAY
INHIBITORY NEURON
PAIN
RECEPTOR
+
DORSAL HORN OF
SPINAL CORD
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)
THE BRAIN’S 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
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?
ELECTRICAL
STIMULATION
STIMULATION OF LARGE SENSORY
NERVES
ELECTRODES IN SKIN OR SPINAL
IMPLANTS
INTRALAMINAR NUCLEUS OF THALAMUS
REFERED PAIN
VISCERAL PAIN FIBERS SYNAPSE ON
SAME SECONDARY NEURONS AS RECEIVE
PAIN FIBERS FROM SKIN