Pain Modulaton

Stopping the Hurt

Pain Modulaton

Stopping the Hurt

The Problem with Pain

• > 2 Million workers incapacitated by pain all the time. >$2.5 billion Sensation with Authority– Sensation versus

Perception– Pain Sensation versus

Pain Perception

• The Mighty Placebo

Why does aspirin help alleviate pain?

All Mighty Aspirin

• Chemoreceptors and Prostaglandin– Sensitization of Receptors

• Prostaglandin Synthesis – Blocked by Aspirin

• Anti-Inflamatory Drugs– Pain and the Immune System

If you hurt yourself, you often rub the affected area to make it

feel better. Why does this work?

Counter Irritant Theory

• Gate Control Theory– Gate Cells– Tract Cells

• Touch Input– AFibers

• Local Inhibition– GABA and Enkephalin

• TENS, and other Rx

Opium, an extract of a poppy plant, has very powerful analgesic properties. It does this because the neurons in the pain system have receptors that bind opiods. Why would the nervous system develop neurotransmitter receptors to a poppy plant?

Searching for Endogenous Opium

• Opiods (Opium, Heroin, etc) are analgesics

• Opiods act on neuron chemoreceptors

• Does the CNS makes Opiods?– Yes!

• Proteins -- -Endorphin

• Peptides -- Enkephalin, Dynorphin

• One site of action– Dorsal Horn Gate Cells

Descending Pain Control• Periaqueductal Gray

– Opiod Receptors

– Projects to Raphe Nuclei

• Raphe Nuclei– Project down to dorsal horn and Spinal 5 Nucleus

– Serotonin (5-HT)

– Inhibits Ascending Systems• Blocks Substance P release by Primary Afferents

• Locus Coeruleus– Descending Norepinephrine

– Activates Enkephalin Interneurons

• Hormonal Analgesia– Beta Endorphin

What is referred pain? What is the current explanation of this phenomena?

Localization of Visceral Pain

• Visceral Pain– Nociceptors in the

Viscera– Not Localizable

• Convergence on ALF Tract Cell– Mislocalization in cord

What are several different types of chronic pain and how do they

differ in terms of etiology?

Good Pain and Bad Pain

• Good Pain -- It Hurts, but Helps– Acute Pain, Hurts until the problem is solved

• Bad Pain -- It Hurts for no good reason– Chronic Pain, Pain Persists after healing

Types of Chronic Pain

• Nociceptive Chronic Pain– SemiGood Pain– Cancer, Arthritis, Nerve Compression

• Neuropathic Chronic Pain– Peripheral Mechanisms– CNS Mechanisms– Sympathetic Maintained Pain

Peripheral Chronic Pain

• Neuroma• Ectopic Foci

• Receptor Changes• Immune Responses

• Maybe not all peripheral

CNS and Neuropathic Pain• Spinal Plasticity

– Synapses and Receptors

• Cortical Plasticity – Changes in the Homunculus

Sympathetically Maintained Pain• Syndrome

– Minor Trauma, Limb Immobility– Poor Healing and Red, Sweating Skin– Extreme Pain Early on and gets worse

• Rx– Block (cut) the Sympathetic Ganglia

• Etiology– Unknown– Theories