22: Thalamus Integration of Senstation and Pain

Question 1

areas of the thalamus important for sensation

Answer 1

VPM
VPL
DPM
CM
PF

Question 2

name the two pain pathways of the ascencing spinothalamic tract

Answer 2

1. neo-spinothalamic

2. paleo-spinothalamic

Question 3

neo-spinothalamic ecnodes

Answer 3

intensity, location and quality of pain

-mediates fast pain that is shard, well localized and relayed rapidly to somatosensory cortex

Question 4

pelo-spinothalamic pathways encodes

Answer 4

emotional and visceral response to pain and also influences descending pathways from the braim stem that modulate pain.

dull, throbbing, poorly localized pain

Question 5

AKA lateral sensory-discriminative pathway

Answer 5

neo0spinothalamic

Question 6

aka medial affective-motivative

Answer 6

paleo-spinothalamic

Question 7

VPL recieves which type of sensory info

Answer 7

BOTH protopathic and epiciritic from limbs and body

Question 8

VPM recieves what info?

Answer 8

sensory from the face

Question 9

VPM and VPL receive what spinothalamic info

Answer 9

pain fibers from NEO-SPINOTHALAMIC tract-relayed onto lateral pain system

Question 10

paleo-spinothalamic information is thus received by

Answer 10

DM, CM, PF nuclei and relay it onto medial pain system

Question 11

trpv1

transient receptor potential*

Answer 11

sensitive to pain > 43 degrees Celsius

Question 12

trpm8

transient receptor potential*

Answer 12

sensitive to <25 degrees Celsius

Question 13

fast, myelinated pain fibers

Answer 13

Adelta

Question 14

slow, unmyelinated pain fibers

Answer 14

C fibers

Question 15

Adelta and C fiber cell bodies lie in

Answer 15

DRG

Question 16

adelta and C fibers use

Answer 16

glutamate, substance P, calcitonin-gene related peptide,

Question 17

injury in periphery causes _______ which____ to _____

Answer 17

triggers release of H, serotonin, ATP, bradykinin, prostagalndins

activates free nerve endings

to send AP back to spinal cord dorsal column

Question 18

activation of nocioreceptors also causes ______ which results in ____

Answer 18

local release of substance p and CGRP in the periphery

release of histamine from mast cells and vasodilation of local blood vessels

Question 19

the combo os local tissue injury and FNE release of histamine and cgrp causes

Answer 19

sensitization of FNE receptors such that their threshold for activation is lowered

(positive feedback)

Question 20

final step in pain sensation form periphery….

Answer 20

inflammatory millieu activate previously silent nocioreceptive receptors opn free nerve endings to become active thereby increasing the temporal and spaital summation of APs traveling to dorsal horn

Question 21

Noscioreceptive specific neurons

encode only pain

Answer 21

neurons in the Laminae I and II of dorsal horn that resonde only to adelta or c fibers

Question 22

wide dynamic range neurons

encode pain and non pain stimuli,

Answer 22

neurons in lamina 5 or dorsal horn, that respond to ariety of synaptic input

Question 23

pain fiber where stimulus intensity is proportional to magnitude of graded potential/AP and frequency of firing

Answer 23

WDRN’s

Question 24

WDRN’s fire what kind of potential

Answer 24

graded

Question 25

neurons responsible for wind up (signal amp)

Answer 25

WDRN’s

Question 26

WDRN’s are found in

Answer 26

lamina 5

Question 27

describe wind up in lamina 5

Answer 27

repetitive c fiber AP’s genereated onto WDN’s in lamina 5 by glutamin/AMPA and CGRP/CGRPrs's=WDRN depolarization

releases MG2+ inhibition

calcium now flows thru the AMPA receptor

causes insertion of more Na channels and blockade of K channels (greater degree of depoalrization

-> substance P prolongs WDRN depol

end result=lower threshold for AP generation

Question 28

functional consequence of wind up (central desensitization)

Answer 28

releatively brief c fiber stimulation can lead to a long lasting fcilitation of the pain pathway stimulated

Question 29

explain gate control mechs

Answer 29

Abeta fibers activate INTERNEURONS in dorsal column that inhibit WDR (central desensitization) thus bluncting activation of the WDRNs to a delta and c fiber afferents

Question 30

how do descending pathways modulate pain

Answer 30

cortex amygdala hypothalamus impenge upon periaqueductal gray and reticular formation neurons

these neurons send descending fibers to modulate lamina II neurons

either inhibit or facilitate pain

Question 31

how do endogenous opioids modulate pain

Answer 31

HYPERPOLARIZE THE POSTSYNAPTICE NEURON AND REDUCE AP GENERATION

activation of opioid receptors BLOCK PRESYNAPTIC voltage gates Ca2+ channels and/ or opening of postsynaptic K cahhels=hyperpol

Question 32

DOES VISCERAL DERMATOMAL SYSTEM OVERLAP

Answer 32

YES -SIGNIFICANT SHARING OF NOCIOCEPTIVE ACTIVITY

Question 33

LIVER PAIN REFERREDTO

Answer 33

RIGHT SHOULDER

Question 34

VISCERAL PATHWAY DIFFERENCE

Answer 34

SAME RECEPTORS

BUT SOME FIBERS BYPASS SECONDARY DORSAL HORN NUCLEUS WITHOUT SYNAPSING (ANTERIOR-LATERAL SPINOTHALAMIC TRACT)

SYNAPSE IN INTERMEDIATE GRAY ZONE NEURONS NEAR CENTRAL CANAL

TRAVEL IN DORSAL COLUMN VERY CLOSE TO MIDLINE

Question 35

VISCERAL TRACT SYNAPSE IN

Answer 35

VPL OF NUCLEUS

TERTIARY FIBERS DISTRIBUTED TO SENSORY CORTEX

Question 36

CLINICAL CONSEQUENCE OF VISCERAL PATHWAY

Answer 36

SMALL MIDLINE LESIONS OF DORSAL COLUMN AT LOWER THORACIS CORD ALLEVIATED CHRONIC VISCERAL PAIN SUCH AS CANCER