Thalamus and Pain

Question 1

Important pain pathways are?

Answer 1

Neo-spinothalamic pathway

Paleo-spinothalamic pathway

Question 2

Neo-spinothalamic pathway relays what types of signals?

Answer 2

Lateral Sensory Discriminative.
This is an evolutionary newer pathway and it encodes for the location, intensity, and quality of pain. Mediates fast pain.

Question 3

Paleo-spinothalamic pathway relays what types of signals?

Answer 3

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

Question 4

Importnant thalamic pain nuclei and the pain types they transmit?

Answer 4

• 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- “

Question 5

VPL and VPM receive pain fibers from which of the pain pathways?

Answer 5

Neo-spinothalamic tract

Question 6

VPL and VPM relay fibers from the Neo-spinothalamic tract to which of the pain systems?

Answer 6

Lateral Pain system

Question 7

Dorsal Medial, Centromedian, and Parafascicular nueclei receive pain information from which of the two pain pathways?

Answer 7

Paleo-spinothalamic….relay these fibers to the Median Pain system

Question 8

Pain sensors are free nerve endings

Answer 8

truth

Question 9

Temperature is sensed via what type of channel?

Answer 9

Transient Receptor Potential Channels (TRP)
V1- (hot) sensitive to temps over 43 and capsaicin
M8- cold, less than 25 celsius

Question 10

Pain transduction is via what types of nerve fibers?

Answer 10

Adelta and C fibers. These are the fibers that come from free nerve endings.

Question 11

Adelta fibers description:

Answer 11

thinly myelinated, transmit temp and mechanical pain, FAST

Question 12

C fibers

Answer 12

unmyelinated, transmit temp, mechanical, and chemical pain, DIFFUSE AND SLOW

Question 13

Peripheral pain receptor activation occurs how

Answer 13

• 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.

Question 14

What are Nociceptive Specific Neurons?

Answer 14

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

Question 15

SO where are the SPN’s located

Answer 15

Laminae I and II

Question 16

Wide Dynamic Range Neurons-

Answer 16

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

Question 17

What is wind-up

Answer 17

Signal Amplification of pain.

Question 18

What trigger’s wind-up

Answer 18

Repetitive action potentials from C-fibers

Question 19

How do repeated action potentials from the C-Fibers trigger wind up

Answer 19

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

Question 20

Substance P activates NK1 receptors which contributes to the process of wind-up how?

Answer 20

WDRN depolarization

Question 21

What is the functional consequenvce of wind-up

Answer 21

Relative brief C-fiber stimulation can lead to long lasting pain pathway stimulation

Question 22

Describe modulation of pain via “gate control mechanism”

Answer 22

Abeta fibers activate dorsal column interneurons that inhibit WDRN neurons, thus blunting their response to C-fibers and Adelta

Question 23

Descending pathway of pain modification

Answer 23

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

Question 24

Endogenous Opioid modification of pain:

Answer 24

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.

Question 25

Realize taht visceral organs are sparsely populated by pain receptors and that there is significant sharing of these receptors with the dermatomal system.

Answer 25

This is the basis of referred pain

Question 26

Describe the newly discovered “visceral pain pathway”

Answer 26

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

Question 27

What is the clinical consequence of this visceral pathway

Answer 27

small midline lesions of the dorsal column at the lower thoracic cord alleviates chronic visceral pain such as cancer pain.