2. Somatosensory 2 Flashcards
fast pain:
receptor, fiber type, tracts
- mechanical and thermal nocioceptors
- small myleinated fibers
- neospinothalamic tract
slow pain:
receptor, fiber type, tracts
- polymodal nocioceptors
- unmyelinated fiber
- paleospinothalamic, and spinoreticulothalamic tracts
FAST PAIN:
thalamus, cortex, and fxn
- lateral VPL (in thalamus)
- primary somatosensory cortex
- sharp, localized pain
SLOW PAIN:
thalamus, cortex, and fxn
- medial thalamus
- frontal and limbic lobes of cortex
- cortical arousal, affect
nociception:
define, and biomechanical features
- tissue damage from mechanical trauma
- proteases
- breakdown kininogen to bradykinin (causing slow contraction, involved in inflammation)
- bradykinin bind to receptors that activate ion channels
- ATP: binds to ATP-gated ion channels
- K+: depolarized neuron membranes
stimuli of nociception?
- tissue damage from mechanical trauma
- temperature extremes (heat over 43 degrees –> heat-senstivie ion channels open)
- oxygen deprivation
biochem of oxygen deprivation and nociception
- w/ oxygen deprivation (anoxia) –> anaerobic metabolism releases lactic acid
- lactic acid –> high levels of H+ ions
- activation of H+ gated ion channels on nociceptors
types of nociceptors
- polymodal (mechanical, thermal, & chemical stimuli)
- mechanical nociceptors - strong pressure
- thermal nociceptors
- chemical nociceptors
capsaicin:
function
- activates TRPV1 receptor –> which channels open at lower temperatures
- results in inflammation-induced thermal hyperalgesia
hyperalgesia:
define
a condition where a person develops an increased sensitivity to pain
key characteristics of pain & temperature fibers
- A-delta (type III) fibers
- larger diameter, lightly/thinly myelinatied
- fast conduction
- sharp, prickly pain
key characteristics of slow pain and temperaure
- C (type IV) fibers
- smaller diameter, UNMYELINATED; polymodal
- slower conduction
- dull, burning, poorly localized pain
which fibers are associated with the first pain after noxious stimulus?
which fibers are with second pain?
- First pain: A-delta (fast; sharp/prickly pain fibers) - more intense pain
- Second pain: C fibers (slow, dull burning pain) - less intense pain
ascending pathways of pain include:
- information from receptors –>
- spinal cord –>
- ascend thru spinal cord –>
- ascend thru brainstem –>
- head somatosensory information –>
- to thalamus –>
- to cortex
ascending pathway from receptors are important for which 2 key functions
- position of body in space (w/in the environment)
- arousal
ALS (anterolateral system) aka Spinothalamic pathway:
functions
- pain
- temperature
- itch
- touch (less so)
anterolateral system (spinothalamic pathway):
structure (input, relay nuclei, decussation)
- sensory input: thermo, noci, and itch receptors
- relay nuclei: spinal cord
- decussation: occurs in spinal cord –> then ascends to ALS pathway
Synapses of the Anterolateral System
(Spinothalamic pathway)
Synapses
- VPL thalamus to primary somatic sensory cortex
- Ventromedial posterior to primary somatic sensory cortex & insular cortex
- Medial dorsal thalamus to cingulate gyrus (assoc. w/ emotions)
- Intralaminar nuclei
what enters the dorsal root entry zone?
pain fibers enter the dorsal root entry zone laterally
which neurons enter the DC/ML of dorsal root entry zone?
what about the ALS system?
- DC/ML: has heavily myelinated neurons (think: fast pain)
- ALS: has lightly myelinated neurons (think: slow conduction, slow pain)
what is another name for the dorsal root entry zone?
and where is it found?
Zone of Lissauer: a small strand situated in relation to the tip of the posterior column close to the entrance of the posterior nerve roots;
spinal cord gray matter
overview of anterolateral spinothalamic tract
- these axons are located in the anterolateral tract, which extends from the lateral into the anterior funiculus of the spinal cord
- axons ascend the brainstem
- axons then cross the midline and ascend the spinal cord
where does pain/temp information from LEFT SIDE OF THE BODY ascend?
to the RIGHT side of the spinal cord;
due to decussation between brainstem/spinal cord
(info travels on the opposite side)
dorsal root ganglion neurons:
define
primary afferent neurons that transmit info. from peripheral receptors into the spinal cord
comparison of PWC-ML and ALS systems
-
PWC-ML system: neuron #1’s axons at Dorsal Root entry zone and in fasiculus gracilis and fasiculus cuneatus
- dorsal white column on same side
-
ALS system: neuron #1 at dorsal root entry zone; cell bodies in the dorsal horn; axons in anterior white commissure
- then contralateral anterolateral tract (ALS)
what are some inputs to the 2nd order neuron?
mechanoreceptors and interneurons
gate theory
by stim larger diameter fibers, to synapse on interneuron in dorsal horn –> to inhibit the second order neuron from firing
ascending in the spinal cord:
where do second order neurons ascend contralaterally?
where do these synapse?
- Second order neurons ascend contralaterally in the:
- medulla
- pons
- midbrain
- synapse in the thalamus, but spinothalamics synapse in the VP nucleus
spinoreticular tract (spinoreticulothalamic)
define and function
- indirect pathway
- info to the reticular nuclei which project to the intralaminar nuclei of the thalamus
- fxn: important in arousal
spinomesencephalic tract (paleospinothalamic):
define and function
- indirect pathway
- info to midbrain tectum –> fxn: coordinate eye & head mvmts
- info to periaqueductal gray matter (PAG) –> fxn: pain regulation
w/in the spinal cord, how do the ALS and DC-ML pathways differ?
they are on opposite sides, but meet in caudal medulla;
DC-ML pathway stays on same side as stimulus until crossing over at medulla
ALS pathway crosses over at dorsal root axon
CC: brown-sequard syndrome
mechanisms and symptoms
caused by: hemisection of spinal cord
sxs:
- loses pain from the opposite side of the body, about 2 levels below the lesion
- loses touch etc. on the same side of the body as the lesion
where does spinomesencephalic tract project to?
- superior colliculus –> orienting to pain stimulus
- periaqueductal gray –> pain modulation
3 key nuclei of thalamus, and overall functions
- 3 nuclei
- posterior thalamic nuclei
- medial dorsal nucleus
- intralaminar nuclei
- Fxn: plays a role in affective and motivational aspects of pain and in the memory of painful stimuli
where in the cortex is the painful stimuli recorded?
insular cortex, and the anterior cingulate
(insular cortex is found between the temporal and frontal lobes)
cortical projections from layers 5 & 6:
project to, function
- project to:
- thalamus
- brainstem
- spinal cord
- modulate sensory information that is ascending
decribe the pain modulation of the nucleus raphe magnus
- from periaqueductal gray
- to nucleus raphe magnus
- neurons of Raphe magnus –> project to spinal cord; are serotonergic; and excite interneurons (enkephalinergic, and inhibit 1st & 2nd order pain neurons)
decribe the pain modulation of the locus ceruleus
- neurons in LC are noradrenergic
- excite interneurons; enkephalinergic (which inhibits 1st and 2nd order pain neurons)
