A&P Somatosensory & Pain Processing

Question 1

How can pain become a disease?

Answer 1

Pain can become a disease when it occurs or persists in the absence of tissue damage or following appropriate healing of injured tissues.

Chronic pain is disabling, has considerable negative impact on quality of life, and has profound economic impact on family and society.

Question 2

What is the International Association for the Study of Pain definition of pain?

Answer 2

Pain is “an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.”

• acknowledges that pain is not only a sensory experience, but may be associated with affective and cognitive responses.
• recognizes that the relationship between pain and tissue damage is not necessarily correlated.

Question 3

Define somatosensation

Answer 3

Somatosensation is the physiologic process by which neural substrates are activated by physical stimuli resulting in the perception of what we describe as touch, pressure, and pain.

Question 4

Define nociception

Answer 4

Nociception is the physiologic process of activation of neural pathways by stimuli that are potentially or currently damaging to tissue.

Question 5

What are the sequence of events by which a stimulus is perceived?

Answer 5

1. Transduction
2. Transmission
3. Modulation
4. Perception

Question 6

What is transduction?

Answer 6

Transduction occurs in the peripheral terminals of primary afferent neurons where different forms of energy (e.g., mechanical, heat, chemical, or cold) are converted to electrical activity (action potentials).

Question 7

What is transmission?

Answer 7

Transmission is the process by which electrical activity induced by a stimulus is conducted through the nervous system.

3 major components of the transmission system:

1. Peripheral sensory cells in the dorsal root ganglia transmit impulses from the site of transduction at their peripheral terminal to the spinal cord where the central terminals synapse with second-order neurons.
2. The spinal neurons send projections to the thalamus and various brainstem and diencephalic structures.
3. Neurons of the brainstem and diencephalon project to various cortical sites.

Question 8

What is modulation?

Answer 8

The process whereby neural activity may be altered along the pain transmission pathway.

• major site of modulation = dorsal horn of spinal cord
• pain modulation systems usually result in less activity in the pain transmission pathway following a noxious stimulus, however modulation in some circumstances can also result in enhancement of pain signaling

Question 9

What is perception?

Answer 9

Perception is the final stage of the pain-signaling process:

• neural activity in the somatosensory transmission pathway results in a subjective sensation of pain
• presumed this process results from the concerted activation of primary and secondary somatosensory and limbic cortices