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34 Cards in this Set

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Pain is a product of the brain's abstract interpretation of sensory experience. It depends on many factors that can be categorized into two groups:
1. Brain structure (nociceptor threshold, projections, pathways)
2. Past experiences (culture, enviro, mental status)
Define:
1. Lack of sensation
2. Lack of pain
3. lack of thermal sensation
4. increased pain from normally painful stimulus
5. pain from a normally non-painful stimulus, light touch
6. decreased pain from normally painful stimulus
7. unpleasant, abnormal sensation; tingling, pricking, tickling
8. itching
1. Anesthesia
2. Analgesia
3. Athermia
4. Hyperalgesia
5. Allodynia
6. Hypoalgesia
7. Parasthesia
8. Pruritus
What is the difference between Nociceptive pain and neuropathic pain?
Nociceptive pain is due to tissue injury.
Neuropathic pain is due to damage to neurons in the peripheral and central nervous system
Bare nerve fibers are more specifically known as:
Unmyelinated Nociceptors (C-fiber)
What is the quality of Nociceptive pain and how is it activated?
1. Well-localized, throbbing quality
2. Nociceptor receptors are activated in skin, muscle, joint, bone or viscera in response to injury or inflammation. Inflammatory chemicals are released from immune cells. Chemicals act on receptors on bare nerve terminals of unmyelinated nocieptors (C-fibers)
Nociceptive pain typically respond to which type of medications:
NSAIDs and Opioid drugs
Describe Neuropathic pain and what causes it
Burning, lancinating, electrical quality that's felt along distribution of nerves. Caused by direct damage to nerves.
What meds is neuropathic pain resistant to? What med works best?
Often resistant to NSAIDs or Opioids. Tricyclic antidepressants, anticovulsants, are more effective.
What are the three Anterolateral tracts?
1. Spinothalamic
2. Spinomesencephalic
3. Spinoreticular
Where does the Spinothalamic tract 2nd order neurons synapse?
In the VPL of the thalamus
Where do the spinomesencephalic 2nd order neurons terminate?
Some 2nd order axons terminate in the midbrain in the superior colliculus and in a region of gray matter surrounding the cerebral aqueduct (PAG)
Where does the Spinoreticular 2nd order neurons terminate?
They terminate in the reticular formation of the pons and medulla
The anterolateral system pathways are similar until this region of the brain stem - then the pathways diverge and terminate in different places:
Medulla
When considering pain, temperature, and fine discrimination sensations, what sense is eliminated when the anterolateral pathway is damaged?
Pain and Temp sensation - fine touch is left in tact
Input to anterolateral system is input by noxious mechanical, thermal, or chemical stimulus to these types of nerves:
1. Free nerve endings of myelinated A-gamma nociceptors
2. Unmyelinated C-fiber nociceptors
**Overall - unmyelinated endings is key.
Compare how A-gamma and C-fibers transmit pain with respect to
1. Speed of transmission
2. Describe pain
1. A-gamma is faster and the first pain. It is immediate, short-lasting, and pricking quality
2. C fibers mediate 2nd pain, it is delayed, long lasting, burning quality.
Central process of nociceptors enter the spinal cord dorsal horn and synapse onto 2nd order spinal neurons in the following Lamina:
1. Lamina I/II (marginal zone of substantia gelatinosa)
2. Lamina V (lateral edge)
3. Lamina X (near central canal)
What chemicals does the nociceptors involve between 1st and 2nd order neurons?
Glutamate and substance P
2nd order spinal neurons cross to contralateral side - do they do it at only one level? Once they do, what tract do they ascend?
No - they do it within 2-3 segments rostral. Anterolateral Quadrant Tracts (Ventral Lateral Funiculus)
With respect to crossing, how is Dorsal and Anterolateral systems different?
Dorsal tract ipsi until the lower medulla
Anterolateral cross immediately if not with 1, 2 or 3 segments rostral to DRG entry.
Lesion of spinal cord cause ipsi or contralateral loss of pain and temp? When is it complete?
Contralateral. Complete 2-3 segments below lesion.
The spinothalamic tract is responsible for mediating what aspects of pain?
It mediates discriminative aspects of pain and temp sensation, such as location and intensity of the noxious stimulus. Helps localize where noxious stimulus is on the body.
For pain from the body, where do the 2nd order neurons terminated (2 places)? Are these regions somatotopically organized?
In the VPL and the Central Lateral Nucleus. The VPL is somato organized however the CLN is not. Neurons project from the CLN to many parts of the cortex particularly the limbic cortex. It is involved in emotional suffering of pain.
Where does nociceptive information being to be appreciated and emotional rxn to pain initiated?
The thalamus
Where does the 3rd order neurons from nociceptors project to?
The SI cortex
Where do the 2nd order spinoreticular tract neurons terminate? Where do the 3rd order neurons project?
Medulla and pons in a region called the reticular formation. They project to the thalamus and diffusely to many areas of the cortex.
The spinoreticular tract is responsible for mediating nociceptor pain in this way:
It mediates changes in level of attention to painful stimuli; also involved in forebrain arousal and affective response to noxious stimulus.
The spinomesencephalic tract is responsible for:
Stimulating the central modulation of pain. Involved in stimulating descending control pathways that project back down to the spinal cord.
Where do spinomesencephalic tract axons terminate? (two locals)
In the midbrain in the superior colliculus and in a region of gray matter surrounding the cerebral aqueduct called the PAG.
In the cortex, thalamic pain neurons project to these three regions:
Also, what are they responsible for?
1. Somatosensory cortex - to localize pain
2. Cingulate gyrus - to process emotional component of pain
3. Insular cortex - processes information on the internal, autonomic state of body (racing hear, rapid breathing, dry mouth, can't sleep)
Pts with damage/lesions of the insular cortex might show this symptom:
Asymbolia for pain where they can perceive noxious stimulus as painful and localize it but they don't display the appropriate emotional responses to pain.
Descending pathways tend to be involved in inhibiting pain. Specifically, how is pain inhibited in this system?

what is the name of these neurons, where the cell bodies of these pathways originate, and down to what nucleus they descend.
The Periaqueductal Gray neurons in the midbrain send axons down to the Locus Ceruleus in the pons and to the Raphe Nuclei in the medulla. From there, they both send neurons down to the spinal cord where they synapse on inhibitory interneurons or directly on to spinothalamic tract projections to suppress transmission of noxious information. toward the thalamus and cortex.
Describe the referred pain theory.
Visceral pain fibers at a given level converge on the same 2nd order spinothalamic tract neurons that receive input from somatic pain fibers from that same level. Since somatic stimuli are more frequent than visceral stimuli, the brain interprets any spinothalamic tract impulses from the same somatic region of the dermatome.
With a few exceptions, pain from organs match up close to a nearby dermatome. However, the diaphram, and kidney/ureter refer pain to unexpected places...what are they?
Diaphragm: C3-C4
Kidney-Ureter: L1-L2