Chapter 10 - Pain

Question 1

What are nociceptors?

Answer 1

Nociceptors are the nerve cell endings that initiate the sensation of pain.

Question 2

Nociceptors have cell bodies where?

Answer 2

In the dorsal root ganglia

Question 3

Conduction of all nociceptive information is fast/slow?

Answer 3

It is relatively slow, when compared to other types of pathways.

Question 4

Researchers have stimulated the nocireceptors in human volunteers. In general, two categories of pain perception have been described. Which?

Answer 4

A shart first pain and a more delayed, diffuse, and longer-lasting sensation that is generally called second pain.

Question 5

What causes the “first pain” sensation?

Answer 5

The sharp first pain is caused by Aδ fibers, which are myelinated axons which conduct at 5-30m/s.

Question 6

What causes the “second pain” sensation?

Answer 6

The second pain is caused by C fibers, which are unmyelinated axons which conduct at velocities generally less than 2m/s.

Question 7

Given the variety of stimuli that can give rise to painful sensations, the transduction of nociceptive signals is a complex task. While many puzzles remain, significant isnsights have come from the identification of a specific receptor associated with the sensation of …

Answer 7

noxious heat.

Question 8

Which types of stimuli give rise to painful sensations?

Answer 8

Mechanical, thermal and chemical.

Question 9

What is the threshold for perceiving a thermal stimulus as noxious?

Answer 9

Around 43°C.

Question 10

What is TRPV1?

Answer 10

TRPV1 is the name of the vanilloid receptor, a member of the larger family of transient receptor potential (TRP) channels. It is responsible for detecting heat and capsaicin.

Question 11

What is TRP?

Answer 11

TRP is the name of a large family of receptors. Transient receptor potential (TRP).

Question 12

Why have humans evolved receptors what seem to be specifically sensitive to a chemical in chili peppers: capsaicin?

Answer 12

It seems likely that TRPV1 receptors detect endogenous substances whose chemical structure resembles that of capsaicin. In fact, some recent evidence suggests that “endovanilloids” are produced by peripheral tissues in response to injury and that these substances along with other factors, contribute to the nociceptive response to injury.

Question 13

Pathways responsible for pain enter the spinal cord where?

Answer 13

Pathways responsible for pain enter the spinal cord via the dorsal roots.

Question 14

When the pain axons reach the dorsal horn of the spinal cord, they branch into …

Answer 14

When the pain axons reach the dorsal horn of the spinal cord, they branch into ascending and descending collaterals, forming the dorsolateral tract of Lissauer.

Question 15

What is the dorsolateral tract of Lissauer?

Answer 15

When the pain axons reach the dorsal horn of the spinal cord, they branch into ascending and descending collaterals, forming the dorsolateral tract of Lissauer. Axons in Lissauer’s tract typically run up and down for one or two spinal cord segments before they penetrate the gray matter of the dorsal horn.

Question 16

Axons in Lissauer’s tract typically run up and down for one or two spinal cord segments before they penetrate the gray matter of the dorsal horn. Once within the dorsal horn, the axons …

Answer 16

Once within the dorsal horn, the axons give off branches that contact second-order neurons located in Rexed’s laminae.

Question 17

What is referred pain?

Answer 17

Patients may present to the physician with the complaint of pain at a site other than its actual source, a potentially confusing phenomenon called referred pain.

Question 18

Patients may present to the physician with the complaint of pain at a site other than its actual source, a potentially confusing phenomenon called referred pain. What could be the causal factor behind this phenomenon?

Answer 18

Surprisingly, few if any neurons in the dorsal horn of the spinal cord are specialized solely for the transmission of visceral pain. Obviously, we recognize such pain, but it is conveyed centrally via dorsal horn neurons that are also concerned with cutaneous pain. As a result of this economical arrangement, the disorder of an internal organ is sometimes perceived as cutaneous pain.

Question 19

We often distinguish between two systems of ascending pain information in the spinal cord. Which?

Answer 19

1. Anterolateral system

2. Column-medial lemniscal system

Question 20

What is the anterolateral system?

Answer 20

The anterolateral system is one of the two systems of ascending pain information in the spinal cord. It stems from axons crossing the midline. It mostly conveys pain and temperature information.

Question 21

What is the column-medial lemniscal system?

Answer 21

The column-medial lemniscal system is one of the two systems of ascending pain information in the spinal cord. It stems from axons that do not cross the midline. They mostly convey mechanosensory information.

Question 22

Knowledge of the different systems of ascending pain information can help the diagnosis of spinal cord lesions. A patient is experiencing problems with sensation, and you discover that the patient has reduced sensation of temperature and pain on the right side of her lower body, and reduced sansation of two-point discrimination, vibration, and proprioception on her lower left side of her body. Where should you look for lesions?

Answer 22

As mechanireceptive afferents travel ipsilaterally, the reduced sensation on two-point discrimination, vibration, and proprioception on the lower left side of her body would indicate a lesion restricted to the left half of the spinal cord.
Such an injury would also produce the reduced sensation of temperature and pain from her lower right body, as the nociceptive afferents travel contralaterally.

Question 23

What is hyperalgesia?

Answer 23

Following a painful stimulus associated with tissue damage, stimuli in the area of the injury and the surrounding region that would ordinarily be perceived as slightly painful are perceived as significantly more so, a phenomenon referred to as hyperalgesia.

Question 24

What is a good example of hyperalgesia?

Answer 24

A good example of hyperalgesia is the increased sensitivity to temperature that occurs after a sunburn.

Question 25

Broadly speaking, what causes hyperalgesia?

Answer 25

This effect is due to changes in neuronal sensitivity that occur at the level of peripheral receptors as well as their central targets.

Question 26

What is the gate theory of pain?

Answer 26

The gate theory of pain is one of the oldest theories on pain modulation in neuroscience. It came about from the observation that humans instinctively rub themselves on sites of injury. This lead researchers to believe that nociceptive information through the spinal cord is modulated by concomitant activation of the large myelinated fibers associated with low-threshold mechanoreceptors.

Question 27

What do we know about the role of endogenous opoiods in pain modulation?

Answer 27

We know of a class of enkephalin-containing local circuit neurons within the dorsal horn that synapse with dorsal horn projection neurons. The release of enkephalin onto the nociceptive terminals inhibit their release of neurotransmitter onto the projection neuron.