Thalamus and Pain Flashcards
Important pain pathways are?
Neo-spinothalamic pathway
Paleo-spinothalamic pathway
Neo-spinothalamic pathway relays what types of signals?
Lateral Sensory Discriminative.
This is an evolutionary newer pathway and it encodes for the location, intensity, and quality of pain. Mediates fast pain.
Paleo-spinothalamic pathway relays what types of signals?
Emotional and visceral responses to pain. Also influences the descending pathways from the brain stem that modulate pain. Pain responses carried by this pathway are dull throbbing, poorly localized pain
Importnant thalamic pain nuclei and the pain types they transmit?
- VPL (ventral posterior lateral- fast discrete pain- body
- VPM- fast discrete pain face
- Dorsal Medial- slowly, poorly localized pain from face and body
- Centromedian- “
- Parafascicular- “
VPL and VPM receive pain fibers from which of the pain pathways?
Neo-spinothalamic tract
VPL and VPM relay fibers from the Neo-spinothalamic tract to which of the pain systems?
Lateral Pain system
Dorsal Medial, Centromedian, and Parafascicular nueclei receive pain information from which of the two pain pathways?
Paleo-spinothalamic….relay these fibers to the Median Pain system
Pain sensors are free nerve endings
truth
Temperature is sensed via what type of channel?
Transient Receptor Potential Channels (TRP)
V1- (hot) sensitive to temps over 43 and capsaicin
M8- cold, less than 25 celsius
Pain transduction is via what types of nerve fibers?
Adelta and C fibers. These are the fibers that come from free nerve endings.
Adelta fibers description:
thinly myelinated, transmit temp and mechanical pain, FAST
C fibers
unmyelinated, transmit temp, mechanical, and chemical pain, DIFFUSE AND SLOW
Peripheral pain receptor activation occurs how
- Tissue injury triggers release of : H+, 5-HT, Bradykinin, Prostaglandins
- These substances activate free nerve endings to fire an action potential back to the dorsal horn of spinal cord.
- Activation of pain receptors causes local release of Substance P (Sp) and CGRP from teh free nerve ending. SP and CGRP cause release of histamine from mast cells and vasodilation of local vessels.
- These processes of inflammation sensitize free nerve endings so that their threshold for activation is lowered.
What are Nociceptive Specific Neurons?
SPNs- Neurons in the laminae I and II of the dorsal horns that respond only to Adelta or C fiber APs and ENCODE ONLY PAIN
SO where are the SPN’s located
Laminae I and II
Wide Dynamic Range Neurons-
Lie in Laminae V of the Dorsal horn. Respond to pain and non-pain stimuli. Fire AP’s in a graded fashion depending on intensity. The greater the C-fiber AP frequency the greater the AP response in the WDRNs
What is wind-up
Signal Amplification of pain.
What trigger’s wind-up
Repetitive action potentials from C-fibers
How do repeated action potentials from the C-Fibers trigger wind up
Glutamate activates WDRN AMPA and CGRP receptors which cause WDRN depolarization and the release of MG block of the NMDA channel. Enhanced calcium influx through the NMDA channel causes insertion of more Na channels and blockade of K channels in the WDRN
Substance P activates NK1 receptors which contributes to the process of wind-up how?
WDRN depolarization
What is the functional consequenvce of wind-up
Relative brief C-fiber stimulation can lead to long lasting pain pathway stimulation
Describe modulation of pain via “gate control mechanism”
Abeta fibers activate dorsal column interneurons that inhibit WDRN neurons, thus blunting their response to C-fibers and Adelta
Descending pathway of pain modification
Cortex, Amygdala, hypothalamus, all impinge upon periaqueductal gray and reticular formation neurons that in turn send descending fibers to modulate lamina II neurons in the dorsal horn. May inhibit or fascilitate pain
Endogenous Opioid modification of pain:
Activation of opioid receptors block the presynaptic voltage gated calcium channel and/or opening of the postsynaptic K channel thus HYPERPOLARIZING THE POSTSYNAPTIC NEURON and reducing action potentials.
Realize taht visceral organs are sparsely populated by pain receptors and that there is significant sharing of these receptors with the dermatomal system.
This is the basis of referred pain
Describe the newly discovered “visceral pain pathway”
Comprised of the same visceral nociceptive receptors but they bypass the dorsal horn neurons associated with the anterior-lateral spinothalamic tract to synapse on gray zone neurons lying near the central canal. fibers travel very close to the dorsal column
What is the clinical consequence of this visceral pathway
small midline lesions of the dorsal column at the lower thoracic cord alleviates chronic visceral pain such as cancer pain.
