central mechanisms of pain

Question 1

the spinal trigeminal nucleus is located where

Answer 1

the medulla

Question 2

the spinal trigeminal nucleus has 3 subdivisions, what are they

Answer 2

1. oralis (light touch)
2. interpolaris (temp perception)
3. caudalis (pain perception)

Question 3

what is another name for nucleus caudalis

Answer 3

medullary dorsal horn…pain perception located

Question 4

describe the organization of the medullary dorsal horn

Answer 4

-nociceptors are restricted to the more superficial layers (I and II)
non-nociceptive terminate in the deeper layers ( III, IV, V)
-there is some overlap b/w these fibers, in layers II and V

Question 5

what are the cell types of the medullary dorsal horn

Answer 5

1. nociceptive specific neuron (specific for pain)

2. wide dynamic range neuron

Question 6

what is a wide dynamic range neuron

Answer 6

responds to non-noxious and noxious stimuli (gets input from both of these afferents)

Question 7

what layers have noxious/non-noxious overlap

Answer 7

II and V

Question 8

what aspects of the medullary dorsal horn CONVERGE

Answer 8

1. nociceptive and non-nociceptive afferents
2. peripheral afferents that have different receptive fields (detect sensory for different areas…like joints vs. muscle sensory)

Question 9

is this convergence responsible for referred pain

Answer 9

yes? lol sorry, sucked at notes this day
referred pain is partially explained by this convergence under PATHOLOGICAL CONDITIONS when pain and non-pain afferents converge on a pain-signalling neuron

Question 10

what occurs during central sensitization

Answer 10

1. c-fiber stimulated causing acute pain and inflammation
2. substance-p is released from the c-fiber and acts on the medullary dorsal horn neuron causing its depolarization
3. the depolarization of the MDH neuron causes the NMDA receptor to be modified by the removal of its Mg2+ block
4. this “activates” the NMDA receptor
5. glutamate released (during innocuous…non-noxious…stimuli) from the a-Beta-fiber (neuron) can bind to the NMDA receptor and cause pain (where it normally wouldn’t)

Question 11

is pain confined to the medullary dorsal horn/nucleus caudalis

Answer 11

no….during a trigeminal tractotomy (input to nucleus caudalis as well as C1-C3 afferents cut) you get anesthesia (bc of cut C1-C3), analgesia (pain removed in face), and hypolgesia (less pain detection in intraoral areas)…but still have pulpal pain!….this pain must be coming from somewhere else

Question 12

if there is a lesion in the pons, what sensory is diminished

Answer 12

intraoral touch, thermal, pain is gone….this indicates that maybe there is some pain detection occuring in the SUBNUCLEUS ORALIS (in the pons)

Question 13

what is the pathway for emotional pain input

Answer 13

afferent fibers–> medullary dorsal horn–>nucleus submedius–> cingulate cortex

Question 14

what is the pathway for sensory pain input

Answer 14

afferent fibers–>MDH–>VPL (thalamus)–>cortex

Question 15

what are the reflexes associated with pain pathways (in the mouth/face)

Answer 15

jaw opening, sweating, increased HR and BP

Question 16

describe the receptive field in the VPL (sensory pain)

Answer 16

small receptive field…good localization of pain

Question 17

describe the receptive field in the nucleus submedius (emotional pain)

Answer 17

large receptive field…poor localization of pain

Question 18

describe the response the VPL gives to the cortex during the stimulus

Answer 18

tracks and detects the onset and offset of the stimulus. (once the stimulus starts it responds, and when the stimulus stops, the responses to the cortex stop)

Question 19

describe the response of the nucleus submedius to the cingulate cortex during the stimulus

Answer 19

the n.submedius sends signals to the cingulate cortex even after the stimulus stops (response outlasts the stimulus)

Question 20

describe the relationship b/w the stimulus and response for the VPL

Answer 20

the stimulus and response is LINEAR

Question 21

describe the relationship b/w the stimulus and response for the n.submedius

Answer 21

the neural response yielding a “negative emotion” (unpleasant) OUTLASTS the stimuli

Question 22

forebrain pathways can modulate pain perception….how

Answer 22

1. anxiety can increase pain perception

2. the placebo effect can decrease pain perception

Question 23

induction of anxiety and the placebo effect increase brain activity in the ….

Answer 23

anterior cingulate cortex

Question 24

name 3 CNS sites that have the ability to modulate descending pain (back to the periphery)

Answer 24

1. forebrain/anterior cingulate cortex
2. midbrain (PAG)
3. rostral ventromedial medulla

Question 25

what molecules are released from the CNS to SUPPRESS PAIN

Answer 25

endogenous opioids

Question 26

what is the mechanism for descending control of pain (suppression)

Answer 26

• descending projections from the CNS to the periphery send opioids (to enkephalinergic/opioid interneurons..with opioid receptors)
• these interneurons work pre and post synaptically to suppress pain

Question 27

how do enkephalinergic interneurons work to suppress pain

Answer 27

1. PRESYNAPTICALLY: they suppress the Ca2+ channels so that no Ca can influx and cause n.t release
2. POSTSYNAPTICALLY: they open K+ channels (which I think would hyperpolarize the cell so no a.p can occur)

Question 28

what is the local control of pain/GATE CONTROL THEORY

Answer 28

potential circuit that explains how non-noxious stimuli can suppress pain (a-beta fibers). basically a-beta fibers (detecting non-noxious stimuli) ACTIVATE inhibitory interneurons, these activated inhibitory interneurons can then INHIBIT c-fibers so that no pain signal can be released from the c-fiber to the periphery