nociception I-III Flashcards
Know the pathways for processing of pain and temperature information.
Anterolateral system
For anterolateral system: what are the primary sensory neurons, where is the first synapse, where does it corss
Ad and C type fibers in periphery (free nerve endings), 1st synapse in spinal cord at dorsal horn, second order neuron crosses in spinal cord the ascends in the anterolateral system (to thalamus as spinothalamic, to reticular system as spinoreticular or midbrain)
What is the thermo-neutral point, what temps do cool receptors and warm receptors detect, and which has more receptors
At a skin temperature of 33°C, we sense neither coolness nor warmth, and this is the thermo-neutral point. cool receptors, fire in the range of 10-37°C, while warm receptors are activated at temperatures ranging between 30-48 °C. There are 10 times as many cool receptors as there are warm receptors
compare receptor firing at thermo neutral point
same rate of firing in cool and warm receptors
Do temp receptors detect gradual or fast change better
fast changes are detected better than gradual. Ie. When fast temp change is occuring, firing rate changes more drastic than at gradual temp change
Where is temperature information first detected?
Temperature information from the periphery is transduced into a receptor potential, which can then trigger action potentials. The frequency of action potentials provides information about the intensity of
the stimulusTemperature information from the periphery is transduced into a receptor potential, which can then trigger action potentials. The frequency of action potentials provides information about the intensity of
the stimulusTemperature information from the periphery is transduced into a receptor potential, which can then trigger action potentials. The frequency of action potentials provides information about the intensity of
the stimulusTemperature information from the periphery is transduced into a receptor potential, which can then trigger action potentials. The frequency of action potentials provides information about the intensity of
the stimulus
Compare action potential firing in cold vs warm receptors as temp changes from 33 to 28 deg C
At 33 deg C, both warm and cold receptors fire at similar rates. As temp decreases to 28, cold receptors increase their firing rate, and warm receptors decrease firing rate. As temp is increased back to 33, cold receptors stop firing until 33 deg is reached, then begin firing at the same steady state as the beginning. As temp is increased back to 33, warm receptors increase firing rate until 33 is reached, then begin firing at same steady state as the beginning.
Know the pathways for processing of temperature and pain information.
Warm/cool receptors in skin on free nerve endings or pain receptors > cell bodies in dorsal root (trunk and limbs) or trigeminal (head and neck) ganglia > axons form synapse on second order neurons in dorsal horn (DRG) or spinal trigeminal nucleus (trigeminal) > anterolateral system: second order axons either go to thalamus then somatosensory cortex via spinothalamic tract (concious appreciation of tmp) OR second order axons go to the hypothalamus via the reticular formation in the spinoreticular tract (autonomic control of body temp)
What kind of fibers are cool and warm receptors
Typically, cool receptors are associated with Aδ fibers, whereas warm receptors tend to be on C fibers.
Does temperature and pain ascend ipsilaterally or contralaterallyin the spinal cord with respect to the site of origin of sensory information?
contralaterally- fibers cross in the spinal cord at the level of the dorsal horn where the first synapse occurs
list three anterolateral system tracts
spinothalamic, spinoreticular and spinomesencephalic
Pathway of spinothalamic tract
This tract projects to the nuclei of the ventrobasal thalamus, which includes VPL. Neurons in these nuclei process information related to localization of pain and project to somatosensory cortex.
pathway of spinoreticular tract
This tract projects to the reticular formation in the medulla and pons which then sends fibers to hypothalamus and various thalamic nuclei. Conveys pain inputs that lead to forebrain arousal and elicits emotional/behavioral responses via connections to emotional circuits of brain (limbic system)
pathway of spinomesencephalic tract
Projects to the midbrain periaqueductal gray region (PAG) and is important for descending control of pain
Two cortical regions activated when pain/temp is being processed
cingulate gyrus (limbic system- emotional component) and insular cortex (autonomic component)
Trigeminal pathway
trigeminal axons enter CNS at pons >descend to caudal position then form first synapse in spinal trigeminal nucleus (btw brainstem and spinal cord)
Types of pain receptors and their associated fibers
- Thermal nociceptors: activated by extreme temperatures, 43°C. Nociceptors activated by extreme hot temperatures (>43°C) are associated with Aδ fibers; Nociceptors that signal extremely cold temperatures (<5°C) are associated with C fibers. 2. Mechanical nociceptors: activated by intense pressure, associated with afferent Aδ fibers. 3. Polymodal nociceptors: activated by high intensity mechanical, chemical or thermal stimuli, C fiber afferents
Why is capsaicin used for chronic pain
Used in conditions that involve spontaneous or aberrant activity of C fibers. Activation of capsaicin receptors causes massive secretion and eventual depletion of
Substance P from sensory fibers. Substance P is a neuropeptide transmitter found in pain afferentsUsed in conditions that involve spontaneous or aberrant activity of C fibers. Activation of capsaicin receptors causes massive secretion and eventual depletion of
Substance P from sensory fibers. Substance P is a neuropeptide transmitter found in pain afferentsUsed in conditions that involve spontaneous or aberrant activity of C fibers. Activation of capsaicin receptors causes massive secretion and eventual depletion of
Substance P from sensory fibers. Substance P is a neuropeptide transmitter found in pain afferents
What is VR-1
Vanilloid receptor-1 is the capsaicin receptor, strongly activated by capsaicin and weakly activated by acids. Also activated by moderate heat (43 deg C). VR-1 is expressed on polymodal nociceptors (c fibers) and is part of an ion channel complex. When activted, the non-selective cation channel opens leading to depolarization
Which nociceptor ion channels are gated by ATP and acids
ATP opens ionotropic P2X receptors. Acid-sensing channels are known as ASICs. Four different ASIC genes are expressed in C fiber nociceptors