Physiology of Pain



Physiology of Pain- ANSWERS

1. Why is the sense of pain considered to be complex?

The sense of pain is complex because it involves not only a sensation but

feelings and emotions as well.

2. How is the sense of pain detected?

The sense of pain is served by free nerve endings located in the skin and

certain visceral tissues. Pain can be caused by stimuli of different nature.

3. Give three examples of stimuli that can cause pain.

Mechanical stimuli (intense pressure)

Thermal stimuli (hot or cold)

Chemical stimuli (acid or base)

4. Why is pain sensation also known as nociception?

Pain receptors generally have a high threshold of stimulation, so they are usually activated when stimulus strength is very high. Because strong stimuli are usually noxious, pain sensation is also known as nociception.

5. Give three chemicals that are released following tissue damage. What do these chemicals do?

Serotonin, substance-P, histamine and kinin peptides are examples of

chemicals that may be released following tissue damage. These substances

act on free nerve endings, activating pain signals.

6. Describe the two types of pain systems identifying their sensation and duration.

Sharp sensations – short lasting and its source can be accurately localized

Dull sensations – long lasting and diffuse; the hurt and ache cannot be

pinpointed and generally is ascribed to a larger body part.

7. What types of nerves are believed to convey the different types of pain sensations?

Sharp pain is conveyed by thin but myelinated, relatively fast nerve fibers

(type-A-delta) and the dull, aching and hurting pain by unmyelinated slow

conducting type C fibers. Sharp pain is conducted about 10 times faster.

8. Where do the two types of pain systems relay their information?

Both types of pain systems relay their information to the dorsal horn of the

spinal cord to synapse for reflexes and relay. Information then travels to

the thalamus of the brain via the spinothalamic tract. Sharp pain is signals

the sensory cortex of the thalamus while dull pain the brain stem reticular

formation.

9. What is different about how people with damage to the sensory cortex perceive pain?

Patients with damage to the sensory cortex can still feel pain and are hurt

by it, but they are unable to accurately localize the source.

10. How is it possible to make animals or humans completely oblivious to pain?

Electrical stimulation of certain neuronal groups in the brain stem reticular

formation make the conscious animal completely oblivious to pain stimuli.

11. What does enkephalin do?

Enkephalin suppresses the transmission of pain signals by binding with

particular receptor molecules present in the synapses of cells in the dorsal

horn. The binding decreases the amount of neurotransmitter (substance-P)

released.

12. Why does rubbing an area relieve dull/hurtful pain?

Rubbing activates the large, fast-conducting tactile fibers (type-A-alpha)

while the dull pain is conveyed by the slow C-fibers. Touch fibers activate

inhibitory interneurons, which inhibit the synaptic transmission of pain

signals.

13. What is referred pain?

Referred pain is when pain is felt in areas of the body different from where

the pain receptors had been stimulated. This is caused because afferent

fibers show extensive convergence onto the dorsal horn.

An example of referred pain is how pain originating in the heart is often felt

as coming from inner aspects of the left arm.

14. What is phantom limb pain?

Phantom limb pain is when sensations are felt in an amputated limb. This occurs when severed endings of pain fibers send signals to the sensory cortex region of the brain. The signals are “projected” to the original source.

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