somatosensory system and pain prof. marshall devor, ph.d. dept. of cell & animal biology and...
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Somatosensory Systemand Pain
Prof. Marshall Devor, Ph.D.Dept. of Cell & Animal Biology and Center for Research on Pain Institute of Life SciencesHebrew University of Jerusalem
lecture 3: The primary somatosensory neuron
פיסיולוגיה מורחב פיסיולוגיה מורחב 08-908-9
primary sensory neuron
from stimulus to impulse trainfrom stimulus to impulse train……varietyvariety
1. force transmission to sensory ending2. transduction3. spike encoding
primary sensory neuron
neural crest
neural crest
Primary sensory neurons are pseudounipolarPrimary sensory neurons are pseudounipolar
bipolar
pseudounipolar
growth cone
sensoryending
A
C
A
100 uM
CGRPCGRP peptide neurotransmitterpeptide neurotransmitter
RTRT9797 neurofilamentneurofilament
Theory of "target derivedTheory of "target derivedneurotrophism"neurotrophism"
Matsuda et al
no synaptic contacts in DRG
microvilli on DRG somata
• enlarged surface area• numerous neurotransmitter and other receptor types
primary sensory neurons
nociceptors
skin nerve muscle nerve m/sec A, A Ia, Ib, II 15-100+A III 2-15C (Remak bundle) IV 0.2-2
axonepineurialblood vessel
perineurium endoneurium
node ofRanvier
internode
paranode
1-2 mm
nodal gap2 um
Schwann cellsoma
Schwann cell (glia)
internode 1-2 mmnode of Ranvier 1-2 um
30 um
myelin formation
axon, myelin, Schwann cell, oligodendroglia
myelin formationmyelin formation
axon, myelin, Schwann cell
myelin formation in the CNSmyelin formation in the CNS
Schwann cell vs. oligodendroglial cell
node of Ranvier
contactin associated protein
adult: DRG neuron adult: DRG neuron phenotypephenotype depends dependson regulation of both on regulation of both expression expression andand traffic trafficof molecules ofof molecules ofexcitability (NTs)excitability (NTs)
A: LTMs: SA, RA, PC, hair A: warming, cooling, down hair, mechano-nociceptorsC: mechanical nociceptors mechano-heat nociceptors CMH polymodal nociceptors silent nociceptors
variety of primary afferent neurons variety of primary afferent neurons (stimulus encoding)(stimulus encoding)
“neuronal phenotype” (correlates of sensory receptor types)
response CV
m/sec
axon
diam.
myelin neurochem. periph.morph.
A LTM 15-100 3-15m heavy glutamate central morph.
A nociceptionthermal+LTM
2-15
1st pain
1-3 m light glutamate+
peptides
transductionchannels
C most
nocicept.
0.2-2
2nd pain
<1 m none glutamate+peptides (NGF)IB4 (GDNF)
electrogenicchannels
spike shape
TTX-STTX-R
neuro-filam.
channeldistrib.
somadiameter
surface receptors
DRG peptidesDRG peptides: SP, CGRP, NPY, NT, VIP, SOM, GAL, CCK… substance P, calcitonin gene related peptide….
“neuronal phenotype” (correlates of sensory receptor types)
response CV
m/sec
axon
diam.
myelin neurochem. periph.morph.
A LTM 15-100 3-15m heavy glutamate central morph.
A nociceptionthermal+LTM
2-15
1st pain
1-3 m light glut+
peptides
transductionchannels
C most
nocicept.
0.2-2
2nd pain
<1 m none glut+peptides (NGF)IB4 (GDNF)
electrogenicchannels
spike shape
TTX-STTX-R
neuro-filam.
channeldistrib.
somadiameter
surface receptors
DRG peptides: SP, CGRP, NPY, NT, VIP, SOM, GAL, CCK…
Somatosensory System and Pain
Prof. Marshall Devor, Ph.D.Dept. of Cell & Animal Biology and Center for Research on Pain Institute of Life SciencesHebrew University of Jerusalem
lecture 3: The primary sensory neuron
פיסיולוגיה מורחבפיסיולוגיה מורחב
spike invasion and the safety of through-conduction in DRG neurons …. why are DRG neurons excitable ?
NEURONsimulation
spike invasion
Conclusion: spike invasion is a design feature ofDRG neurons… but to what end ??
somatic
through-conduction