Neuroscience Nocioception Steven Youngentob

Question 1

What is the difference between pain and nocioception?

Answer 1

-

Question 2

Where are the cell bodies of nocioceptors found?

Answer 2

DRG, trigrminal ganglia (like other sensory nerves)

Question 3

T or F: Nocioceptors are free nerve endings with no peripheral structures to transduce and filter peripheral stimuli.

Answer 3

True

Question 4

What kinds of nocioceptors are responsible for detecting sharp, pricking pain?

Answer 4

Thermal or mechanical nocioceptors

Question 5

What are the characteristics of thermal or mechanical nocioceptors?

Answer 5

1. Small diamter
2. Thinly myelinated A-delta fibers
3. Conduct at 5-30 m/s (fast)
4. Transmit sharp, pricking pain

Question 6

What are the characteristics of polymodal nocioceptors?

Answer 6

1. Small diameter
2. Unmyelinated C fibers
3. Conduct at 0.5-2 m/s (slow)
4. Transmit high-intensity mechanical, vhemical and temperature extreme

Question 7

A noxious stimulus activates the nocioceptors by depolarizing what? What is the trigger for this discharge?

Answer 7

Noxious stimuli strong enough to do actual damage depolarize the membrane of the sensory ending.

Question 8

What happens when pain persists?

Answer 8

A-delta fibers stop being activated, then after that through conducting C fibers, then after that, a dull pain

Question 9

T or F: The TrpV1 receptor is only found in unmyelinated C fibers.

Answer 9

False, the TrpV1 receptor is found in both A-delta and C fibers.

Question 10

Name four stimuli that activate a TrpV1 receptor.

Answer 10

1. Capsaicin
2. Anandamide
3. Heat
4. Acids
   (there are others, these are just examples)

Question 11

What kind of receptor is TrpV1?

Answer 11

Ligand-gated ion channel, ie Ca2+ and Na+

Question 12

What is hyperalgesia?

Answer 12

When peripheral tissues are damaged, the sensation of pain in response to subsequent stimuli is enhanced around the damaged tissue.

Question 13

The release of _________ and other agents from the site of injury enhances the responsiveness of nocioceptive endings.

Answer 13

bradykinin, histamine, prostaglandins

Question 14

Electrical activity in the nocioceptors stimulates the local release of chemical substances, such as substance P, that cause:

Answer 14

vasodilation, swelling, release of histamine from mast cells

Question 15

Aspirin and other NSAIDS act by inhibiting __1__, whose function is __2__.

Answer 15

1. cyclooxygenase

2. an enzyme important in the biosynthesis of prostaglandins

Question 16

Name some of the chemicals involved in injury reaction/response.

Answer 16

1. ATP
2. Prostaglandins
3. Histamine (released from mast cells)
4. 5-HT
5. Substance P
6. Bradykinin, NGF, IL-1B, TNF-a (all released from macrophages)

Question 17

T or F: Pain can arise spontaneously in the absence of activity in the nocioceptors.

Answer 17

True, if the nocioceptive pathways are damaged

Question 18

What happens in a brachial plexus avulsion?

Answer 18

Patients feel a burning sensation in the dermatomes corresponding to the dernervated area. The pain is thought to arise from hyperactivity of dorsal horn neurons in the deafferented region of the cord. This commonly occurs in motorcycle accidents.

Question 19

Like somatosensory neurons in the dorsal root ganglia, the central axons of nocioceptive nerve cells enter the spinal cord via:

Answer 19

the dorsal roots

Question 20

With what tract do nocioceptor nerve fibers travel once they enter (and split) in the spinal cord.

Answer 20

Dorsolateral

Question 21

Where do nocioceptive fibers primarily terminate in the spinal cord?

Answer 21

Superficial dorsal horn, lamina I and II (Nocioceptive afferents terminate on dorsal horn projection neurons.)

Question 22

FUN FACT!

Answer 22

Some A-deltanocioceptive fibers project more deeply into Lamina 5.

Question 23

Lamina I neurons contain a high density of what?

Answer 23

Projection neurons that process pain information. They respond exclusively to A-delta and C fibers and are termed “nocioceptive specific” (NS)

Question 24

Lamina 5 receives input from:

Answer 24

Both mechanoreceptors and nocioceptors. These are termed WDRs, wide dynamic range neurons

Question 25

Which have a larger receptive field, WDRs or NSs?

Answer 25

WDRs, they respond to both somatosensory an noxious stimuli.

Question 26

What is referred pain?

Answer 26

The displacement of pain from a visceral structure such as to a somatic area of the body because of the convergence of visceral and cutaneous nocioceptors onto the same dorsal horn projection neurons.

Question 27

Nocioceptive input from the upper body (not face) and lower body are relayed to the thalamus by what tract?

Answer 27

Anterolateral spinothalamic pathway

Question 28

Nocioceptive information follows a different pathway than the rest of the body. Axons from the __1__ ganglion cells from the ganglia associated with cranial nerves __2__ carry information from the facial nocioceptors and thermoreceptors into the brainstem, cross the midline and then ascend in the __3__ tract.

Answer 28

1. trigeminal
2. 7, 9, 10
3. trigeminothalamic

Question 29

What is the main target in the thalamus of ascending pain and temperature axons?

Answer 29

Ventral Posterior Nuclear Complex

Question 30

A unilateral spinal lesion of the somatosensory pathway would produce:

Answer 30

Sensory loss of touch, pressure and vibration, ie two-point discrimination and proprioception

Question 31

REMEMBER:

Answer 31

Somatosensory pathway ascends ipsilaterally in the dorsal columns of the spinal cord. AND
The pathways for pain and temperature projection neurons cross the midline to ascend on the opposite side of the spinal cord.

Question 32

Associate Raphe nucleus with:

Answer 32

serotonin

Question 33

Associate locus ceruleus with:

Answer 33

norepi

Question 34

Where do descending pain modulatory neurons make excitatory connections in the brain? What other important structure is also found here?

Answer 34

1. Rostroventral medulla

2. Nucleus Raphe magnus is also found in this area.

Question 35

What kind of connections do neurons in the rostroventral medulla make in laminae I, II and V of the dorsal horn?

Answer 35

1. Inhibitory connections

Question 36

Where are opiate receptors found?

Answer 36

1. Terminals of nocioceptive afferents

2. On the dendrites of postsynaptic neurons

Question 37

What are two ways opiates function?

Answer 37

1. Inhibit release of glutamate, substance P and other NTs from sensory neurons
2. Suppress the activity of nocioceptive dorsal horn neurons at the postsynaptic level

Question 38

Opiate alkaloids and endogenous opioid peptides (released by enk interneurons) modulate nocioceptive transmission at the level of the __1__ by a combination of __2__.

Answer 38

1. Primary afferent synapse

2. Presynaptic and postsynaptic actions