pain and temperature Flashcards
Thermoreceptors
respond to temp and temp changes
Nociceptors
pain receptors, free nerve endings, respond to variety of stimuli such as: mechanical (crushing pressure, cutting) thermal (noxious heat or cold) chemical (bradykinin prostglandin histamine)
Primary afferent axons for pain and temp?
A-delta fibers and C fibers. A delta are lightly myelinated/for sharp pain. C fibers are unmyelinated and for dull aching pain (2nd pain). Both also carry crude tactile sensations like stretching or squeezing and itch.
Anterolateral system
carries pain and temperature and some crude sensation.
Anterolateral 2nd order neurons
travel within anterior lateral aspect of spinal cord and anterior lateral aspect of brainstem tegmentum
Tracts of Anterolateral system
spinothalamic, spinoreticular, spinohypothalamic, spinomesencephalic
spinothalamic tract
Includes Neospinothalamic tract and peleospinothalamic tract. Carries noxious and innocuous temp info and crude/ non discriminative sensory info as well as pain
neospinalthalamic tract
carries SHARP localized pain info to primary somato cortex,
Paleospinothalamic Tract
carries dull aching and poorly localized pain info to secondary somatosensory cortex and other cotical areas, most fibers take multisynaptic course through reticular formation before reaching the cerebral cortex
1st order neurons of spinothalamic tract
Generally A-delta fibers transmit sharp pain and C fibers carry dull pain, BOTH carry temp info.
major synaptic site for pain and temperature in spinothalamic tract
Substantia Gelatinosa (lamina 2)
Lissauer’s Tract
ascends or descends 1 to 3 segments
Flow of pain info starting at a delta fibers
primarry afferent a delta fibers carry sharp pain to lamina 2, within lamina 2 a delta fibers synapse onto lamina 2 interneurons or lamina one or five projection neurons. Neurons in lamina 1 and 5 can also recieve pain signal from lamina 2 interneurons. Lamina one and 5 projection neurons form neospinothalamic tract (second order neurons)
flow of info starting at C fibers
Primary afferent C fibers carry dull aching pain to lamina 2. Lamina 6-8 recieve it from interneurons from lamina 2. , Lamina 6-8 projection neurons form paleospinothalamic tract
Describe how the neospinothalamic tract enters the brain
a delta fibers enter anterior white commissure and decussate, ascent to VPL nucleus of the thalaus, then third order neurons go to primary somatosensory cortex (location and nature of pain)
Describe how paleospinothalamic tract enters brain
primary C fibers enter and synapse with 2ndary neurons and they go through anterior white commissure decussate and go to Intralaminar Thalamic Nuclei (10-40%), third order neurons go to S-2 anterior cingulate insula,
Where do both neo and paleospinothalamic tracts project 3rd order neurons
3rd order neurons from either VPL or ILN go through posterior limb of internal capsule in order to reach cerebral cortex
Where does the anterolateral pathway travel?
through the anterolateral aspect of the spinal cord and the anterolateral aspect of the brainstem tegmentum
referred pain
Visceral afferent fibers respond to excessive pressure tension and inflammation in visceral organs, visceral afferents from heart enter upper thoracic spoinal cord segments then converge on same spinothalamic tract cells reached by pain fibers, so you will have pain in left side of the chest and left arm
Spinoreticular tract
c fibers come in synapse on lamina 2 then go to lamina 6-8, this makes spinoreticular fiibers
spinoreticular fibers
can be described as part of collateral branches of paleospinothalamic tract. They pass to reticular formation
where does reticular formation project to
Thalamus ILN then to anterior cingulate cortex and insula (suffering/emotional response to pain) and frontal lobe. The amygdala and hypothalamus
Spinohypothalamic tract fibers
axons from ALS originate in spinal cord and terminate in hypothalamus. Involved in autonomic outflow in response to pain. They can go straight up or decussate at the very end
Spinomesencephalic tract fibers
axons of ALS that originate in spinal cord and terminate in mesencephalon (midbrain). It is important in descending system of pain modulation. It synapses on the periaqueductal Gray
Which laminae give rise to spinomesencephalic tract?
1 and 5, they are collaterals of the neospinothalamic tract
Periaqueductal gray
opiate receptors in abundance, can inhibit pain response
