Week 4: Pain

Question 1

Define pain and discuss pain theories

Answer 1

Pain is a protective and complex phenomenon made up of dynamic interactions among physical, cognitive, spiritual, emotional, and environmental factors

Question 2

Transduction

Answer 2

Begins when tissue is damaged by exposure to chemical, mechanical, or thermal noxious stimuli and is converted to electrophysical activity.

Question 3

Transmission

Answer 3

Conduction of pain impulses along the A and C fibers into the dorsal horn of the spinal cord and eventually to the reticular formation, hypothalamus, thalamus, and limbic system.

Question 4

Perception

Answer 4

The conscious awareness of pain (reticular and limbic systems and the cerebral cortex). A sensory discriminating system, affective motivational system, cognitive evaluative system.

Question 5

Modulation

Answer 5

Process of increasing or decreasing transmission of pain signals throughout the nervous system

Question 6

Compare myelinated vs. unmyelinated pain fibers

Answer 6

Myelinated A-delta fibers: transmission is fast and causes reflex withdrawal of affected body part from stimulus before pain sensation is perceived. Pain sensations are sharp, well-localized, “fast”.

Unmyelinated C polymodal fibers (most numerous): stimulated by mechanical, thermal, and chemical nociceptors. Transmission is slower and conveys dull, aching, or burning sensations.

Alpha-beta fibers: large myelinated fibers that transmit touch and vibration sensations.

Question 7

Neurogenic

Answer 7

Neuralgia - pain in the distribution of a nerve (constant)

Question 8

Temporal

Answer 8

Time related category of pain can be acute or chronic

Question 9

Regional

Answer 9

Refers to the location of pain

Question 10

Etiologic

Answer 10

Refers to the etiology (cause) of pain

Question 11

Differentiate pain threshold and pain tolerance

Answer 11

Pain threshold: the lowest intensity of pain that a person can recognize; intense pain at one location may increase the threshold in another location

Pain tolerance: the greatest intensity of pain that an individual can endure - is very individualized but decreases with repeated exposure to pain, fatigue, anger, boredom, apprehension, and sleep deprivation

Question 12

Nociception

Answer 12

The processing of potentially harmful (noxious) substances through a normally functioning nervous system. Nociceptors are free nerve endings in the afferent peripheral nervous system that sense pain.

Nociceptive pain is considered pain with normal tissue injury from a known cause (i.e., somatic and visceral). This type of pain is considered acute as it typically lasts less than 3 months.

Question 13

Describe Neuroanatomy of Pain

Answer 13

Afferent pathways begin in the peripheral nervous system (PNS), travel to the spinal gate in the dorsal horn, and then ascend to higher centers in the CNS.

Interpretive centers are located in the brain stem, midbrain, diencephalon (thalamus, epithalamus, and hypothalamus), and cerebral cortex.

Efferent pathways descend from the CNS to the dorsal horn of the spinal cord.

Nociception (processing of pain) involves four phases:
1. Transduction
2. Transmission
3. Perception.
4. Modulation

There are primary order neurons (nociceptors), secondary order neurons (interneurons), and third order neurons (afferent neurons)

Question 14

Secondary-order neurons

Answer 14

Interneurons in the dorsal horn of the spinal column that can be excitatory or inhibitory.

Question 15

Third-order neurons

Answer 15

Afferent neurons in the spinothalamic tract that carry information to reticular formation, hypothalamus, thalamus, and limbic system to interpret pain location and intensity.

Question 16

Gate control theory

Answer 16

Purposes that pain is modulated by a “gate” in the cells of the substantia gelatinosa in the spinal cord. Gate either allows or blocks transmission of pain. Stimuli from non-nociceptive transmissions (such as touch) and larger A-beta fibers “close” or partially close the gate - for example, if you smash your leg against the desk but then rub the muscle - it feels better.

Question 17

Segmental inhibition

Answer 17

A-beta fibers stimulated and impulses arrive at same spinal level as A-delta or C fiber impulses. Inhibitory interneuron is stimulated and transmission of pain is decreased (e.g., rubbing a painful area)

Question 18

Conditioned pain modulation

Answer 18

Diffuse noxious inhibitory control (DNIC) simultaneous pain stimulation and inhibition (e.g., you have a stomach ache and a headache but might not feel one because the other is overtaking it)

Question 19

Expectancy-related cortical activation

Answer 19

Cognitive expectations can have an affect on pain (e.g., placebo)

Question 20

Neuropathic pain

Answer 20

Pain that comes from the pathology of the nervous system - is considered non-nociceptive and non-protective.

Central neuropathic pain is caused by a lesion or neuroplastic changes in the brain or spinal cord.

Peripheral neuropathic pain is caused by injured nerves that become hyperexcitable.

Question 21

Referred pain

Answer 21

Pain in an area that is distant from its point of origin but the area of referred pain is supplied by the same spinal segment as the actual site. Can be acute or chronic.

Question 22

Analgesics

Answer 22

medications used to relieve pain and are available in two basic categories:
1. Opioid analgesics
2. Non-opioid analgesics

Question 23

Opioid

Answer 23

A natural or synthetic morphine-like substance capable of reducing severe pain. Is a narcotic substance which is a general term to describe morphine-like drugs that produce analgesia and CNS depression.

Opioids neither lower the threshold for pain at the nociceptor level nor slow or block transmission of the pain impulse - it is the perception and the emotional response to pain that is altered by these medications.

Question 24

Mechanism of anti-depressants

Answer 24

Anti-depressants block the enzymatic breakdown of norepinephrine and slow the reuptake of epinephrine - there are four primary classes:
1. Tricyclic anti-depressants (TCAs)
2. Selective serotonin re-uptake inhibitors (SSRIs)
3. Monoamine oxidase (MAO) inhibitors
4. Atypical antidepressants

Question 25

Neurophysiologic

Answer 25

Can be nociceptive (somatic, visceral, referred) or neuropathic pain (central or peripheral)