8 - Sensory Systems and Pain

Question 1

Sensory Systems:
RECEPTOR – TRANSDUCTION – AFFERENT SIGNAL

Answer 1

Question 2

General Visceral Afferents (GVA)

Answer 2

• Travel with the ANS. Receptors respond to mechanical, chemical and nociceptive stimuli
• Pseudo-unipolar neurons, cell bodies in the dorsal root ganglion (DRG) or along cranial nerves,
  synapse in the dorsal horn of spinal cord, info
  relayed to higher CNS centers

CN VII, IX, X examples:
Carotid body chemoreceptor (oxygen)
Carotid sinus baroreceptor (mechanical)
Bladder tension (mechanical)
Pain, inflammation (nociceptors)

CNX connected to tongue, larynx, pharynx,
trachea, esophagus, lungs, bronchi, stomach,
heart, and intestines.

• Info destined for the solitary nucleus of the
  brainstem medulla, then thalamus/hypothalamus
  and finally the cerebral cortex
• GVE (efferents) respond to stimuli of GVA and
  influence smooth and cardiac muscle and
  glandular activity

Question 3

spinal cord nerve anatomy

Answer 3

Question 4

Peripheral Receptors in Skin

Answer 4

Encapsulated
* Pacinian corpuscle = vibration/fast adapting
* Meissner corpuscle = touch/ two-point discrimination
* Ruffini ending = continuous pressure
* Some thermo & mechano receptors

Free Nerve Endings
Nerves on hair follicle = touch, movement
Merkel endings = light touch, pressure, movement
Nociceptors = temperature, pain, itch, mechanical, chemical (one receptor may respond to multiple stimuli)

Question 5

classes of motor neurons and their innervations

Answer 5

Alpha Motor Neurons innervate skeletal muscle for voluntary contraction

Gamma Motor Neurons innervate muscle spindle fibers to monitor muscle position and coordinate reflexs

Question 6

Afferent Pathways

Answer 6

Question 7

dorsal column system vs spinal thalamic tract (afferent pathways)

Answer 7

Question 8

Pain (overview)

Answer 8

• Primary reason to seek medical help!
• Complex: Physiology, neuroscience, psychology…pain is both sensation and emotion! Extreme variability between individuals
• Acute vs Chronic

Nociceptive pain:
* Normal nervous system function in detection of noxious stimuli that is damaging to tissue: temperature, mechanical, chemical, tumor, distension, inflammation, necrosis…

Neuropathic pain:
* Abnormal nervous system function due to disease or injury. Pain is described as burning, stabbing, electrical, tingling, pins and needles: i.e. “funny bone”. Can occur after damage to PNS and or CNS

• Nociceptors innervate superficial structures, deep somatic structures and deep visceral organs

Question 9

Pain Theories

Answer 9

• The Gating Theory: Wahl and Melzak 1965. “Distract” pain sensation by additional stimulation (touch, pressure and/or nociceptors in nearby region) via inhibition of pain fiber transmission through competing sensory input

Question 10

Melzack and Casey 1968: The Three Dimensions of Pain

Answer 10

Question 11

Pain Molecules: Some act as both ligands and neurotransmitters!

Answer 11

• Nocicpetor ligands: bradykinin, NGF, H+, potassium, prostaglandins, leukotrienes, ATP/adenosine, histamine, serotonin, IL, TNF, NO, VIP, temperature, chemical (wasabi, capsaicin, menthol), mechanical (pressure, distension) …
• Axon Reflex: activated free nerve ending triggers release of neurotransmitters in local area, leads to inflammation, swelling… only reflex known without a synapse
• Neurotransmitters: Glutamate (AMPA & NMDA), Substance P, CGRP (antagonists and migraine), endothelins, histamine, prostaglandins …

Question 12

Brain Regions and Pain Sensation

Answer 12

Question 13

Ascending Pathways: Collateral Synapses in Brainstem

Answer 13

Question 14

Referred Pain

Answer 14

Question 15

Sensitization

Answer 15

Question 16

Peripheral Neuropathy

Answer 16

Question 17

Chronic Pain Syndromes

Answer 17

Question 18

Analgesia (Greek, an (without) algos (pain)

Answer 18

Question 19

CNS Mediated Analgesia

Answer 19

Question 20

CNS Mediated Analgesia
Descending CNS modulation of Pain Sensation

Answer 20

Question 21

Pain Pharmacology

Answer 21

Question 22

surgeries for pain

Answer 22

• Rhizotomy: ablation techniques used for patients with drug refractory chronic pain, but where to cut? Dorsal roots, spinothalamics, thalamus, cortex??
• Regardless of surgical site, relief is generally transient
• Implantation of drug delivery pumps, electric stimulators…
• Neuropathic pain is associated with pathological wiring and neural activation
• A-beta fibers can replace damaged C fibers and convey pain and temperature information after mechanical stimulation that is not normally noxious.
• Neuropathic pain leads to activation of silent nociceptors and sensitization !

Question 23

Pain - External Electrical solutions

Answer 23

Transcutaneous Electrical Nerve Stimulation
-not proven for chronic pain
-good evidence for relief of acute pain postoperative, osteoarthritis, other
-Mechanism appear to be stimulation of endogenous opioid/GABA/glutamate and serotonin systems
Transcranial Direct Current Stimulation
– Stimulate skull with electrodes, cortex, mechanism unknown ?
– Evidence for relief of depression
– Some evidence for relief of pain in animal models and human case reports

Question 24

Pain - behavioral remedies

Answer 24

• PT/OT
  – Force rewiring through therapy – Enable alternative routes
• Movement – Feldenkrais – Mind body –Yoga
  – Tai-Chi

Question 25

Pain - Alternative/Complementary Medicine

Answer 25

Question 26

relationship between physical and emotional pain

Answer 26

Question 27

Pain - do you know these things?

Answer 27