Flashcards in Thalamus - Integration of Sensation and Pain (20) Deck (38)
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What is the pathway responsible for transmitting all ascending nociceptive pathways and collaterals?
Anterolateral spinothalamic tract
1
What are the two main divisions of the anterolateral spinothalamic pathway?
1. Neo-spinothalamic tract
2. Paleospinothalamic tract
2
What is the other name for the neo-spinothalamic tract and what general information about pain does it transmit?
Lateral sensory-discriminative component --> location, intensity, and quality of pain; responsible for "fast" pain
*theres a sharp pain in my left arm!
3
What is the other name for the paleo-spinothalamic tract and what function does it have?
Medial affective-motivational pathway --> influences emotional and visceral responses to pain as well the descending modulation of pain; dull, throbbing, poorly localized pain
* it hurts and I don't like it!
4
What types of afferent fibers are the main input to the neo-spinothalamic tract (lateral sensory-discriminatory component)?
A delta fibers --> synapse in laminae I, IV, V in dorsal horn
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What thalamic nuclei receive info from the neo-spinothalamic tract?
VPL (body) and VPM (limb)
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Where in the brain do fibers in neo-spinothalamic tract ultimately send its fibers?
To the primary somatosensory cortex
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To which 3 thalamic nuclei does the paleo-thalamic tract(medial affective-motivational pathway) send fibers?
1. Intralaminar centromedian (CM) nucleus
2. Parafascicular (PF) nucleus
3. Dorsal medial (DM) nucleus
* these are part of the white matter that divides the medial and lateral portions of the thalamus
8
To what four more medial cortical areas do fibers of the paleo-spinothalamic ultimately go to?
1. Anterior cingulate cortex
2. Insula
3. Amygdala
4. Hypothalamus
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Initiates direct behavioral responses to pain and also is active during actual pain, perceived pain, and also when watching someone else in pain
Anterior cingulate cortex
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This structure in the medial system relays pain info to the limbic system, where pain-related learning and memory are processed
Insula
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Projections to this structure initiate the visceral response to pain
Hypothalamus
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Projections to the superior colliculus via the spinomesencephalic tract have what function?
Influence eye movements to direct gaze to the site of injury
13
Which free nerve ending receptor senses hot temperature and capsaicin?
TRPV1
* ~109 degrees (43 C)
14
What free nerve ending receptor senses cold temperature?
TRPM8
*77F (25 C)
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Which type of afferent nerve fibers transmit temperature and mechanical stimulus that is hard enough to potentially cause injury?
A delta fibers
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Which fibers transmit noxious chemical information?
C fibers
* these, like the A delta, also transmit info from mechanoreceptors that have a high threshold and therefore only fire when the stimulus is intense enough to potentially cause damage
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Where do cell bodies form both A delta and C fibers reside?
In dorsal root ganglia
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What three NTs do A delta and C fibers release?
1. Glutamate
2. Substance P
3. Calcitonin-gene related peptide (CGRP)
* are released both to the 2nd order neuron in the spinal cord and also to the periphery
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What two receptors does glutamate activate on secondary neurons in the ventral horn?
1. AMPA receptor
2. NMDA receptor
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What receptor does Substance P activate?
NK1 receptor
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What receptor does CGRP activate?
CGRP receptor
WHOAH
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What 5 products are released by nociceptive receptors by tissue injury? * collectively, what do these do to initiate a pain response?
1. Serotonin (5-HT)
2. Bradykinin
3. Prostaglandins
4. ATP
5. H+
* these activate free nerve endings to fire an AP
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Subsequent release of substance P and CGRP from free nerve endings in the periphery causes release of what 2 things at the site of injury?
Histamine --> vasodilation
Bradykinin
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What does the combination of inflammation and release of substance P and CGRP do?
Sensitizes the peripheral nerves so the threshold for activation is lowered
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What other thing happens that serves to amplify the pain response?
The inflammatory chemical milieu activates previously silent nociceptive receptors on free nerve endings
*activated by inflammatory molecules, not by noxious stimuli
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What are the neurons in laminae I and II that respond only to A delta or C fibers and encode only pain?
nociceptive specific neurons (SPN); (NS in the book)
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Which neurons in the dorsal horn respond to all fibers but respond specifically to the input from C fibers to encode the intensity of the pain stimulus?
Wide dynamic range neurons (WDRNs)
* also responsively or Wind Up
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Glutamate activation of WDRN _____ receptors and CGRP activation of WDRN CGRP receptors leads to WDRN depolarization... How does this activate the NMDA channel?
AMPA; relieves the Mg2+ block of the NMDA channel
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