Pain

Question 1

Somatosensation

Answer 1

Process by which sensory neurons are activated by external stimuli

Question 2

Nociception

Answer 2

Process by which neural pathways are activated by tissue damaging substances

Question 3

Pain Pathway

Answer 3

1. Transduction–stimuli into action potentials
2. Transmission–conduction through the nervous system
3. Modulation–alteration of conduction pathways (augments or inhibits pain pathways)
4. Perception–action potential into conscious sensation

Question 4

Peripheral Nerve Pathway

Answer 4

• stimulus activates the nociceptors
• action potential sent to the dorsal root ganglion via afferent sensory (pain) fibers
• action potential travels to the dorsal root & dorsal spinal cord

Question 5

Afferent Sensory (Pain) Fibers

Answer 5

A-Beta:

• heavily myelinated, large diameter (= fastest)
• light touch & pressure

A-Delta:

• lightly myelinated, smaller diameter
• intense, stabbing pain (“first” pain)

C:

• unmyelinated, small diameter (= slowest)
• Burning pain (“second”, delayed pain)

Question 6

Central Nerve Pathway

Answer 6

• Located in the dorsal gray of the spinal cord
• Incoming sensory afferent fibers terminate directly or indirectly on cell bodies that send axons into the white of the spinal cord along tracts
• Indirect connections = projection interneurons

Question 7

Wide Dynamic Range Interneurons

Answer 7

• receives A-beta & A-delta afferent fiber information (greater response w/ noxious, A-delta stimuli)
• faster, spontaneous rate
• high-threshold or nociception-specific cells
• convergence input from the skin, muscle, & viscera (= referred pain)

Question 8

Nociceptive Specific Interneurons

Answer 8

• receive information from C afferent fibers

- slower, spontaneous rate

Question 9

Central Sensitization

Answer 9

Prolonged, intense painful stimulus –> increased pain response (larger receptive field or higher discharge rate) due to neuronal plasticity

• MC w/ WDR interneurons
• The basis of chronic pain

Question 10

Excitatory Neurotransmitters

Answer 10

Glutamate
Aspartate
ATP

Receptors = NMDA

Question 11

Inhibitory Neurotransmitters

Answer 11

GABA
Norepinephrine
Serotonine
Adenosine
Acetylcholine

Question 12

Excitatory Neuropeptides

Answer 12

Substance P
Neurokinin A

Function: nerve to nerve transmission & affect macrophages & mast cells

Primary role in sensitization & hyperalgesia

Question 13

Inhibitory Neuropeptides

Answer 13

Somatostatin

“Morphine-like effects”
Enkephalins
Endorphins