Neuroscience Nocioception Steven Youngentob Flashcards
What is the difference between pain and nocioception?
-
Where are the cell bodies of nocioceptors found?
DRG, trigrminal ganglia (like other sensory nerves)
T or F: Nocioceptors are free nerve endings with no peripheral structures to transduce and filter peripheral stimuli.
True
What kinds of nocioceptors are responsible for detecting sharp, pricking pain?
Thermal or mechanical nocioceptors
What are the characteristics of thermal or mechanical nocioceptors?
- Small diamter
- Thinly myelinated A-delta fibers
- Conduct at 5-30 m/s (fast)
- Transmit sharp, pricking pain
What are the characteristics of polymodal nocioceptors?
- Small diameter
- Unmyelinated C fibers
- Conduct at 0.5-2 m/s (slow)
- Transmit high-intensity mechanical, vhemical and temperature extreme
A noxious stimulus activates the nocioceptors by depolarizing what? What is the trigger for this discharge?
Noxious stimuli strong enough to do actual damage depolarize the membrane of the sensory ending.
What happens when pain persists?
A-delta fibers stop being activated, then after that through conducting C fibers, then after that, a dull pain
T or F: The TrpV1 receptor is only found in unmyelinated C fibers.
False, the TrpV1 receptor is found in both A-delta and C fibers.
Name four stimuli that activate a TrpV1 receptor.
- Capsaicin
- Anandamide
- Heat
- Acids
(there are others, these are just examples)
What kind of receptor is TrpV1?
Ligand-gated ion channel, ie Ca2+ and Na+
What is hyperalgesia?
When peripheral tissues are damaged, the sensation of pain in response to subsequent stimuli is enhanced around the damaged tissue.
The release of _________ and other agents from the site of injury enhances the responsiveness of nocioceptive endings.
bradykinin, histamine, prostaglandins
Electrical activity in the nocioceptors stimulates the local release of chemical substances, such as substance P, that cause:
vasodilation, swelling, release of histamine from mast cells
Aspirin and other NSAIDS act by inhibiting __1__, whose function is __2__.
- cyclooxygenase
2. an enzyme important in the biosynthesis of prostaglandins
Name some of the chemicals involved in injury reaction/response.
- ATP
- Prostaglandins
- Histamine (released from mast cells)
- 5-HT
- Substance P
- Bradykinin, NGF, IL-1B, TNF-a (all released from macrophages)
T or F: Pain can arise spontaneously in the absence of activity in the nocioceptors.
True, if the nocioceptive pathways are damaged
What happens in a brachial plexus avulsion?
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.
Like somatosensory neurons in the dorsal root ganglia, the central axons of nocioceptive nerve cells enter the spinal cord via:
the dorsal roots
With what tract do nocioceptor nerve fibers travel once they enter (and split) in the spinal cord.
Dorsolateral
Where do nocioceptive fibers primarily terminate in the spinal cord?
Superficial dorsal horn, lamina I and II (Nocioceptive afferents terminate on dorsal horn projection neurons.)
FUN FACT!
Some A-deltanocioceptive fibers project more deeply into Lamina 5.
Lamina I neurons contain a high density of what?
Projection neurons that process pain information. They respond exclusively to A-delta and C fibers and are termed “nocioceptive specific” (NS)
Lamina 5 receives input from:
Both mechanoreceptors and nocioceptors. These are termed WDRs, wide dynamic range neurons
Which have a larger receptive field, WDRs or NSs?
WDRs, they respond to both somatosensory an noxious stimuli.
What is referred pain?
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.
Nocioceptive input from the upper body (not face) and lower body are relayed to the thalamus by what tract?
Anterolateral spinothalamic pathway
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.
- trigeminal
- 7, 9, 10
- trigeminothalamic
What is the main target in the thalamus of ascending pain and temperature axons?
Ventral Posterior Nuclear Complex
A unilateral spinal lesion of the somatosensory pathway would produce:
Sensory loss of touch, pressure and vibration, ie two-point discrimination and proprioception
REMEMBER:
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.
Associate Raphe nucleus with:
serotonin
Associate locus ceruleus with:
norepi
Where do descending pain modulatory neurons make excitatory connections in the brain? What other important structure is also found here?
- Rostroventral medulla
2. Nucleus Raphe magnus is also found in this area.
What kind of connections do neurons in the rostroventral medulla make in laminae I, II and V of the dorsal horn?
- Inhibitory connections
Where are opiate receptors found?
- Terminals of nocioceptive afferents
2. On the dendrites of postsynaptic neurons
What are two ways opiates function?
- Inhibit release of glutamate, substance P and other NTs from sensory neurons
- Suppress the activity of nocioceptive dorsal horn neurons at the postsynaptic level
Opiate alkaloids and endogenous opioid peptides (released by enk interneurons) modulate nocioceptive transmission at the level of the __1__ by a combination of __2__.
- Primary afferent synapse
2. Presynaptic and postsynaptic actions
