Thalamus - Integration of Sensation and Pain (20)

Question 0

What are the two main divisions of the anterolateral spinothalamic pathway?

Answer 0

1. Neo-spinothalamic tract

2. Paleospinothalamic tract

Question 1

What is the pathway responsible for transmitting all ascending nociceptive pathways and collaterals?

Answer 1

Anterolateral spinothalamic tract

Question 2

What is the other name for the neo-spinothalamic tract and what general information about pain does it transmit?

Answer 2

Lateral sensory-discriminative component –> location, intensity, and quality of pain; responsible for “fast” pain

*theres a sharp pain in my left arm!

Question 3

What is the other name for the paleo-spinothalamic tract and what function does it have?

Answer 3

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!

Question 4

What types of afferent fibers are the main input to the neo-spinothalamic tract (lateral sensory-discriminatory component)?

Answer 4

A delta fibers –> synapse in laminae I, IV, V in dorsal horn

Question 5

What thalamic nuclei receive info from the neo-spinothalamic tract?

Answer 5

VPL (body) and VPM (limb)

Question 6

Where in the brain do fibers in neo-spinothalamic tract ultimately send its fibers?

Answer 6

To the primary somatosensory cortex

Question 7

To which 3 thalamic nuclei does the paleo-thalamic tract(medial affective-motivational pathway) send fibers?

Answer 7

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

Question 8

To what four more medial cortical areas do fibers of the paleo-spinothalamic ultimately go to?

Answer 8

1. Anterior cingulate cortex
2. Insula
3. Amygdala
4. Hypothalamus

Question 9

Initiates direct behavioral responses to pain and also is active during actual pain, perceived pain, and also when watching someone else in pain

Answer 9

Anterior cingulate cortex

Question 10

This structure in the medial system relays pain info to the limbic system, where pain-related learning and memory are processed

Answer 10

Insula

Question 11

Projections to this structure initiate the visceral response to pain

Answer 11

Hypothalamus

Question 12

Projections to the superior colliculus via the spinomesencephalic tract have what function?

Answer 12

Influence eye movements to direct gaze to the site of injury

Question 13

Which free nerve ending receptor senses hot temperature and capsaicin?

Answer 13

TRPV1

* ~109 degrees (43 C)

Question 14

What free nerve ending receptor senses cold temperature?

Answer 14

TRPM8

*77F (25 C)

Question 15

Which type of afferent nerve fibers transmit temperature and mechanical stimulus that is hard enough to potentially cause injury?

Answer 15

A delta fibers

Question 16

Which fibers transmit noxious chemical information?

Answer 16

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

Question 17

Where do cell bodies form both A delta and C fibers reside?

Answer 17

In dorsal root ganglia

Question 18

What three NTs do A delta and C fibers release?

Answer 18

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

Question 19

What two receptors does glutamate activate on secondary neurons in the ventral horn?

Answer 19

1. AMPA receptor

2. NMDA receptor

Question 20

What receptor does Substance P activate?

Answer 20

NK1 receptor

Question 21

What receptor does CGRP activate?

Answer 21

CGRP receptor

WHOAH

Question 22

What 5 products are released by nociceptive receptors by tissue injury? * collectively, what do these do to initiate a pain response?

Answer 22

1. Serotonin (5-HT)
2. Bradykinin
3. Prostaglandins
4. ATP
5. H+
   * these activate free nerve endings to fire an AP

Question 23

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?

Answer 23

Histamine –> vasodilation

Bradykinin

Question 24

What does the combination of inflammation and release of substance P and CGRP do?

Answer 24

Sensitizes the peripheral nerves so the threshold for activation is lowered

Question 25

What other thing happens that serves to amplify the pain response?

Answer 25

The inflammatory chemical milieu activates previously silent nociceptive receptors on free nerve endings
*activated by inflammatory molecules, not by noxious stimuli

Question 26

What are the neurons in laminae I and II that respond only to A delta or C fibers and encode only pain?

Answer 26

nociceptive specific neurons (SPN); (NS in the book)

Question 27

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?

Answer 27

Wide dynamic range neurons (WDRNs)

* also responsively or Wind Up

Question 28

Glutamate activation of WDRN _____ receptors and CGRP activation of WDRN CGRP receptors leads to WDRN depolarization… How does this activate the NMDA channel?

Answer 28

AMPA; relieves the Mg2+ block of the NMDA channel

Question 29

How does activation of the WDRN NMDA channel via relief of the Mg++ block help begin the process of Wind Up (signal amplification)?

Answer 29

There is enhanced Ca2+ influx through the NMDA channel causes insertion of more Na+ channels and blockade of K+ channels—> increased responsiveness

Question 30

How does substance p work to contribute to Wind Up?

Answer 30

Activates NK1 receptors, which prolongs the WDRN depolarization

• all the changes lead to reduced threshold and prolonged depolarization –> sensitization

Question 31

What are the functional consequences of the Wind Up process in terms of chronic pain?

Answer 31

Relatively brief C-fiber stimulation can lead to long-lasting changes in the pain pathways that keep them overly sensitive–> leads to hyperalgesia

Question 32

Why does rubbing a painful spot help relieve some of the pain? (gate-control theory of pain)

Answer 32

Shift the balance towards touch (via A beta activation) which detracts some of the input being sent through the pain pathway via C fibers

Question 33

Cortex, amygdala, and hypothalamus all send fibers through what two structures to modulate lamina II neurons in the dorsal horn? Function of these descending pathways?

Answer 33

Through the Periaqueductal gray area and reticular formation–> serve to modulate NS and WDRN neurons and coma either facilitate or inhibit pain signals. Is useful to tell you to ignore the pain if there are more pressing issues or to take care of the pain if not (salience filter)

Question 34

How do opioid receptors work to blunt the effects of pain?

Answer 34

Block presynaptic Ca2+ channels and/ or opening of postsynaptic K+ channels –> hyperpolarize the postsynaptic neuron and reduce APs

Question 35

What is likely responsible for the phenomenon of referred pain?

Answer 35

Sharing of visceral nociceptive activity within the dermatomal systematic and the viscera are sparsely populated by nociceptive receptors

Question 36

What is different about where the 1st order neurons involved in the visceral pain pathway compared to those involved in other nociceptive signaling (anterolateral/ spinothalamic)?

Answer 36

They bypass the dorsal horn nuclei and synapse instead on intermediate gray zone neurons lying near the central canal—> so travel with the dorsal column pathway instead

Question 37

Where do visceral pain pathway 2nd order neurons synapse in the CNS?

Answer 37

In the VPL nucleus then to primary somatosensory cortex, like all the rest of these fuckers