Pain Anatomy

Question 1

Nociceptive Pain

Answer 1

activation of peripheral nociceptors - from tissue damage
typically more sensitive to opioids
can be visceral (organs) or somatic (skin muscle tissue)
Visceral: migraine, ischemia, pancreatitis, peritoneal inflammation etc.
Somatic: tendons, bursa, ligaments

Question 2

Neuropathic Pain

Answer 2

dysfunction or injury to the CNS or PNS.
better response to antidepressants or anticonvulsants
is chronic, burning, piercing
CNS: post-stroke, MS, spinal cord injury
PNS: diabetic neuropathy, postherpatic neuralgia, chemo pts etc.

Question 3

A Delta Fibers

Answer 3

large 1-4mm diameter
myelinated
fast 5-10m/s
sharp & localized 
immediate & transient

Question 4

C Fibers

Answer 4

smaller
unmyelinated 
slower 0.6-2m/s
dull, ache, burn 
poor localization 
may be constant

Question 5

Afferent Pathway

Answer 5

sensory: neurons send signals from periphery to CNS

PNS –> dorsal horn –> CNS

Question 6

Efferent Pathway

Answer 6

motor: CNS–>dorsal root–>periphery

Question 7

4 Phases of Nociception

Answer 7

1. transduction - activation
2. transmission - conduction along axons via 1,2,3 order neurons
3. perception - limbic/reticular systems & cortex
4. modulation - CNS response

Question 8

dorsal horn anatomy

Answer 8

cell bodies of peripheral nerves located here
rexed laminae I-VI - receives afferent sensory input
I: marginal layer
II: substantia gelatinosa
II-IV: nucleus proprius

Question 9

ventral horn

Answer 9

lamina VII-IX

Question 10

lamina X

Answer 10

cluster of cells around the central canal

Question 11

where do C afferent fibers terminate?

Answer 11

laminae I, II, & V

- sensory primarily in II

Question 12

where do A delta fibers terminate?

Answer 12

laminae I, II, V, X

Question 13

tract for ascending systems

Answer 13

anterolateral spinothalamic primarily
- anterior: pressure
- lateral: temp & pain
spinoreticular and spinomesencephalic also

Question 14

Lissauers Tract

Answer 14

dividing point for A & C fibers into ascending & descending branches via the anterolateral spinothalamic tract

Question 15

Drugs altering transduction

Answer 15

NSAIDs, antihistamines, local anesthetic ream, opioids, membrane stabilizers, serotonin antags

Question 16

Drugs altering transmission

Answer 16

local anesthetics - peripheral nerve block - epidural

Question 17

drugs altering perception

Answer 17

parenteral opioids
alpha 2 antagonists
GA

Question 18

drugs altering modulation

Answer 18

spinal opioids
alpha 2 antagonists
NMDA antagonists

Question 19

Spinothalamic Tract Neurons

Answer 19

1: arrives in dorsal horn via sensory nerves
2: decussates to anterolateral WHITE matter of cord - ascends to thalamus
3: projects to corresponding somatosensory area of cerebral cortex

Question 20

Spinoreticular Tract

Answer 20

heightens level of arousal to pain - memory & emotion components

• terminates in the reticular formation
• has 4 order neurons

Question 21

Gate Control Theory

Answer 21

pain is carried by small slow fibers
cells in the substantial gelatinous transmit impulses to the brain which can be modulated by C & A beta fibers.

with increased large fiber activity pain transmission can be inhibited - closes the gate to the small fibers.

Question 22

Descending Inhibitory Pathways

Answer 22

areas: midbrain, medulla, spinal cord
NTs: serotonin, NE
Endogenous opioids: B-endorphins (mu) Dynorphins (kappa) Enkephalins (delta)

Question 23

allodynia

Answer 23

sensation of pain from a stimulus that was not previously painful