Pain

Question 0

Can you have nociception without the perception of pain?

Answer 0

Yes. Nociception is the sensory information

Question 1

What are the three definitions of nociception?

Answer 1

1. Perception of injurious stimuli
2. Measurable physiological event (AP) with noxious stimuli
3. system that caries info about inflammation or damage in tissue

Question 2

What is pain?

How is it different from nociception?

Answer 2

Pain is the perception of the noxious stimulus so the unpleasant sensory or emotional experience associated with actual, potential or perceived tissue damage.

Nociception is the sense, pain is the perception of the sense.

Question 3

What are the two major types of pain?
What cause them?
What descriptions do people usually give for each type of pain?

Answer 3

1. Nociceptive pain- due to activation of peripheral nocioceptors (sharp, stabbing, achy)
2. Neuropathic pain- perception in the absence of noxious stimuli usually due to peripheral nerve damage or CNS injury that disrupts transmission and processing of the painful stimuli (itchy, burning, freezing, prickly, pins and needles)

Question 4

For pain, what is the center of a Venn diagram for normal pain (nociception) and pathophysiological pain (neuropathic)?

Answer 4

Inflammation

Question 5

What is paresthesia?

What is dyesthesia?

Answer 5

Spontaneous sensation that occurs without stimulus
Ex. Pins and needles sensation

When the paresthesia is associated with unpleasant stimuli

Question 6

What is sensitization to pain?

Answer 6

There is a greater intensity of pain perceived for the same amount of Nociceptive input.

Question 7

What is hyperalgesia?

Answer 7

When a mild Nociceptive stimuli is perceived as strongly painful

Question 8

What is neuropathic pain?

Answer 8

The perception of pain in the absence of Nociceptive stimuli (as opposed to hyperalgesia where the perception of a painful stimuli is amplified)

Question 9

What is allodynia.?

Answer 9

When a non-painful sensation (light touch, vibration, temperature) is perceived as painful
Ex. Bed sheets are painful against that persons legs

Question 10

What is causalgia?

Answer 10

Neuropathic pain that persists after an injury to a peripheral nerve

Question 11

What is analgesia?

What is hypesthesia(hypoalgesia)?

Answer 11

1. Absence of sensation of pain

2. Diminished sensation of pain

Question 12

What types of fibers sense pain and temperature?

Answer 12

A-delta and C fibers

Many more C fibers than other afferents

Question 13

What fiber type is the most common sensory afferent?

What type of receptor is the most common sensory receptor?

Answer 13

1. c fibers

2. Nociceptive receptors

Question 14

What type of pain sensation has the highest spatial resolution and why?

Answer 14

Superficial pain because nocioceptors are more densely packed innervating the skin and have distinct receptive fields

Question 15

How is spatial resolution of receptors graded or measured?

Answer 15

By number of fibers activated

Question 16

What are the three main classes of nociceptors in the skin?

Answer 16

1. A-delta mechanosensitive
2. A-delta mechanothermal
3. C fiber polymodal nociceptor

Question 17

How do A-delta and C fibers differ in terms of threshold for activation and Axonal conduction speeds?

Answer 17

A-delta mediate the sharp first pain (activate sooner and at lower threshold, but short duration)

C fibers mediate the second pain (longer diffuse delayed pain)

Question 18

The process of nociception requires what type of receptor at the nerve endings?
What signals do these receptors respond to?

Answer 18

TRP- transient receptor potential proteins that depolarize in response to mechanical, chemical or thermal stimuli

Question 19

What type of TRP family receptors are found in a-delta and c fibers that respond to moderate head and capsaicin ?

Answer 19

Vanilloid receptor VR-1

Question 20

What do VR-1 receptors respond to?

What type of fiber are they in?

Answer 20

Capsaicin and high temp

A-delta and c fibers

Question 21

What do VR-2 receptors respond to?

What type of fiber are they found in?

Answer 21

Respond to high heat and are found in A-delta fibers

Question 22

What is the effect of damaged tissue signals on the response of free nerve ending pain perception?

Answer 22

1. Damaged tissue releases bradykinin, histamine, and prostaglandins as chemical signals to sensitize the TRP receptors
2. Damaged tissue releases substances to augment inflammation

Question 23

From the dorsal root ganglion, what is the path of pain and temperature fibers in the spinal cord?

Answer 23

1. Nociceptive fibers enter the cord and travel up and down the cord a level or two in Lissaurs tract.
2. They synapse with their second order neuron in substantia gelatinosa or nucleus propria (rexed 2,3,4) in the dorsal horn
3. These neurons cross the midline and ascend in the Spinothalamic tract (anterolateral pathway)

Question 24

Why is there such a wide overlap in dermatome sensation?

Answer 24

Because of Lissaurs tract

Question 25

What are the two types of projection neurons in the dorsal horn for Nociceptive response?

Answer 25

1. Nociceptive-specific neurons | 2. Wide Dynamic Range neurons

Question 26

What sensory signals do Wide Dynamic Range neurons integrate?

Answer 26

Nociceptive and non-Nociceptive inputs

Question 27

What is the effect of C fibers on the inhibitory interneurons that synapse on WDR neurons? What is the effect of A-beta fibers on the inhibitory interneurons that synapse on WDR neurons? What is the implication of this? What is this implication called?

Answer 27

C-fibers inhibit the inhibitory neuron on the WDR so the WDR will transmit the pain signal up the spinal cord. A-beta fibers excite the inhibitory interneurons on the WDR so they will stop the WDR from transmitting signal. The implication is that if non-Nociceptive and Nociceptive stimuli fire together, the A-beta fiber can "gate" or block the pain fibers from being transmitted. This is called "gating theory of pain" and is why you rub a pained area to smooth it (pressure overtakes pain)

Question 28

What are the three tracts of the anterolateral system? Where do the second order neurons synapse? What do they regulate?

Answer 28

1. Spinothalamic- VPL, VPM of dorsal thalamus 2. Spinomesencephalic - hypothalamus, Amygdala (emotion) 3. Spinoreticular - reticular formation of medulla, pons, and dorsal thalamus (medullary RF modulates arousal)

Question 29

What tract do fibers travel in to reach the reticular formation of the medulla? What does this signal generate?

Answer 29

The spinoreticular tract. | The fibers regulate arousal in response to pain ("wake up! You are in pain!)

Question 30

What Nociceptive tract brings pain fibers to the primary somatosensory cortex? What information does this cortical area tell us?

Answer 30

Spinothalamic to VPL(body) and VPM (face) to the primary somatosensory cortex. Where the pain is located.

Question 31

What two anterolateral tracts synapse on the dorsal thalamus? Where do projections from the dorsal thalamus go? What information does this provide to us about the pain?

Answer 31

Spinothalamic and spinoreticular. From the dorsal thalamus it projects to the supplementary motor areas, prefrontal cortex, association cortex, limbic areas to determine what the pain is.

Question 32

What type of pain does not travel in the anterolateral system? Where does it travel in the spinal cord? What does it synapse with in the brainstem? What part of the thalamus does it go to? What is the ultimate cortical area? What does this explain about this particular type of pain?

Answer 32

Visceral pain is carried in the dorsal columns to the nucleus gracilis and then to the ventral thalamus and then to the insular cortex. This is why visceral pain is often difficult to localize and if referred to another place (left arm pain for a heart attack)

Question 33

What are the four ways we control pain?

Answer 33

1. Gating 2. Spinal Interneurons 3. Descending CNS 4. Central perception

Question 34

What is the major site of descending pain control in the brainstem? What does it receive input from? What does it communicate with?

Answer 34

The periaquaductal gray in the midbrain It receives input from the cortex, Amygdala, hypothalamus, and brainstem nuclei It communicates with the dorsal horn neurons in the spinal cord through: -reticular formation -parabranchial nucleus - locus ceruleus (NE) - raphe nucleus (serotonin)

Question 35

What is the function of endogenous opioids? What are examples of three opioids? How do they perform their function? Where are they made and how are they released?

Answer 35

To modulate central pain. Three examples are enkephalins, endorphins, and dynorphins They are used by interneurons in the dorsal horn to relay descending pain modulation via presynaptic inhibition of c fiber terminals. They are made in various places in the CNS and are released by various mechanisms ranging from exercise high to acupuncture

Question 36

How did scientists discover that opioids were a released substance and not an electical signal?

Answer 36

They did acupuncture on a rabbit and that rabbit experienced analgesia. CSF from that rabbit was transferred to another rabbit experiencing pain and the analgesic effect was present in the second rabbit as well.

Question 37

With opioids, is nociception still present?

Answer 37

Yes, but the c fibers are being inhibited so there will be no pain perception. The painful stimulus is still present though