Exam 3: L2 Pain Flashcards
Explain the various fiber group and name for the following receptor types:
Hot temperature
Cold temperature
Sharp Pricking pain
Burning Pain
Freezing Pain
Slow burning pain
Hot temp: A-delta III
Cold: C IV
Sharp pricking pain: A-delta III
Burning pain: A-delta III
Freezing pain: C IV
Slow, burning pain: C IV (polymodal receptor)
Receptor Locations on the Skin:
Superficial receptors include _______ (slowly adapting) and ________ (radpidly adapting, low freq)…. both have ______ receptive fields and are quite sensitive
Deep Receptors are found in subcutaneous tissues, and include ______ (rapidly adapting, high freq stimulation) and _______ (slowly adapting, deep pressure)….. both have ______ receptive fields
Receptor Locations on the Skin:
Superficial receptors:
- Merkel’s Receptor (slowly adapting)
- Meissner’s corpuscle (rapidly adapting low frequency)
- SMALL receptive fields and are quite sensitive
Deep Receptors: found in subcutaneous tissue:
- Pacinian’s corpuscle (rapidly adapting, high freq stimulation)
- Ruffini’s corpuscle (slowly adapting, deep pressure)
- LARGE receptive fields
Which kind of receptors let you feel the difference between an apple, vs a tennis ball in your hand (sensing the difference surfaces)?
Explain the difference in what Ruffini and Pacinian receptors sense
Superficial receptors: Messiner’s and Merkel’s
Deep Receptors:
Ruffini: pressure
Pacinian: vibration
Encoding of Action Potentials:
Explain the difference between slowly adapting and rapidly adapting receptors
Encoding of Action Potentials:
- slowly adapting: give continous information (APs) during stimulation. Note that there is some adaptation (slowly) of the output over time, but the output does not cease until the stimulatus is removed (Merkel’s and Ruffini’s are slowly adapting)
- rapidly adapting: output only on “on” and ‘of” of the stimulus (gives good temporal info). The rapidly adapting receptors DO continue to function as long as the stimulus is changing, but once the stimulus becomes constant, the output ceases (Meissiner’s and Pacinian are rapidly adapting)
Myelination and Fiber Diameter:
The diameter of the axon and its myelination play a key role in the rate of transmission of sensory info:
- large, myelinated fibers are the _______ and carry proprioceptive information (____ is the spindle GTOs)
- small, thinly myelinated fibers carry ______ info (skin mechanoreceptors)
- the smallest myelinated and unmyelinated fibers carry ____ and ___ info
Myelination and Fiber Diameter:
- The diameter of the axon and its myelination play a key role in the rate of transmission of sensory info:
- large, myelinated fibers are the fastest, and carry proprioceptive info (fastest are spindle GTOs)
- small, thinly myelinated fibers carry general sensory info (skin mechanoreceptors)
- slowest fibers are the smallest myelinated and unmyelinated fibers, and they carry pain and temperature info
PAIN is the slowest, with A delta being a little faster than C
The sensory system uses a basic outline or common plan for ALL of its modalities:
Receptors ->> ______ —> ____ -> cortex (where perception occurs)
Each receptor is sensitive to a particular form of energy, and this energy is converted into electrochemical signal by the receptor (this concept is called “_________”)
The signal is then relayed to the next neuron in the pathway via a series of APs until it reaches the cortex. This process is called “______”
The sensory system uses a basic outline or common plan for all of its modalities:
Receptor –> 2nd order neurons –> 3rd order neurons —> cortex : where perception occurs
Each receptor is sensative to a particular form of energy, and this energy is converted into electrochemical signal by the receptor (this concept is called “Signal Transduction”)
The signal is then relayed to the next neuron in the pathway via a series of APs until it reaches the cortex. This process is called “Neural Encoding.”
Medial Pain System vs Lateral Pain System
Where does each project through?
What does each focus on?
Explain the importance of S1 activation
Medial Pain System vs Lateral Pain System:
- Medial pain system:
- projects through medial thalamic nuclei to AAC, insular cortex and other brain regions
- processing affective-motivational aspects of pain (how terrible is the pain. EMOTIONAL aspect of pain)
- Lateral pain system:
- projects through lateral thalamic nuclei to primary and secondary somatosensory cortices (SI and SII)
- sensory-discriminative aspects of pain (where is the pain)
S1 activation: discriminating and learning different aspects of pain, localization and discrimination of pain intensity
The Spinothalamic Tract:
- The peripheral process of _______ end as receptors sensing pain, temp, and complex chemical sensation
- The central processes of the dorsal root ganglion cells synpase with neurons of the _______
- The axons of these second order neurons cross via the _____ white commisure, enter the _____ white matter, ascend in the _____ funiculus, and synpase on third order neurons located in ___
- The axons of the third order neurons project to the _____
The spinothalamic tract:
- The peripheral processes of dorsal root ganglion cells end as receptors sensing pain, temp, etc
- The central processes of these dorsal root ganglion cells synpase with neurons of the nucleus proprius
- The axons of these second order neurons cross via the anterior white commisure, enter the contralalteral white matter, and ascend in the lateral funiculus, and synpase on third order neurons located in the thalamus
- The axons of third order neurons project to primary somatosensory cortex
The first order neurons/dorsal root ganglion cells synpase within the dorsal root into the _______
The first order neurons/dorsal root ganglion cells synpase within the dorsal root into the nucleus proprius
then the second order neurons cross over and ascend in the lateral faniculus
Statification of Afferent Subtypes in the Dorsal Horn:
____ and ____ terminate superficially, synpase on large neurons in lamina I and II of dorsal horn
_______ terminate in inner part of lamina II
Projecting neurons in lamina V receive direct input from __ and __ and indirect input from ___ via interneurons
Stratification of Afferent Subtypes in the Dorsal Horn:
Peptidergic C fibers and A delta fibers terminate superficially (lamina I and II)
Nonpetidergic C fibers terminate in inner part of lamina II
A-beta fibers terminate in interneurons in lamina II
Projection neurons in lamina V receive direct input from A beta and A delta, and indirect from C fibers via interneurons
Remember:
A lot of pain fibers, especially C fibers can be modified and are often modified by _______ within the dorsal horn itself
A lot of pain fibers, especially C fibers can be modified and are often modified by interneurons within the dorsal horn itself
Area ______ (number) within the primary cortex is where all of the pain tracts end up
Distribution occurs within the columns of info:
4:
5:
6:
Area 312 within the cortex
Distribution occurs within the columns of info:
4 is an input (from thalamus)
5 is an output (to basal ganglia, brain stem, etc)
6 is the feedback loop (back to the thalamus)
Spinothalamic Tract;
Primary Afferent Neurons:
where do they synpase?
Secondary Afferent Neurons:
where do they synpase/terminate
Tertiary Afferent Neurons
Spinothalamic Tract:
Primary Afferent Neurons: Dorsal Root Ganglion, synpase in nucleus proprius in the dorsal horn
Secondary Afferent Neurons: axons within the lamina of the dorsal horn cross the anterior white commisure and form contralateral ALSTT that ascends to the thalamus
Tertiary Afferent Neurons: thalamus, synpase on the primary somatosensory cortex
Pain: is a _____ of aversive sensations originating from a specific area
Nociception: the _______ and ____ of signals from specialized sensory receptors concerning tissue damage
Nociceptors are the GREATEST/LEAST specialized of sensory receptors. They are free nerve endings with little or no specialized structures
Thermal or mechanical: moderately ___, convey __ pain
Polymodal: respond to variety of stimuli, C fibers are the ____, convey ____ pain
Silent: found in viscera, unresponsive to normal stimuli, only respind to ______
Pain: the perception of aversive sensations from a specific area
Nociception: the transduction and conveyance of signals from an area concerning tissue damage
Nociceptors are the LEAST specialized of sensory receptors, they are free nerve endings wiht little/no specialized structures
Thermal or Mechanical: moderately slow (A-delta), convey sharp pain
Polymodal: respond to variety of stimuli, C fibers, slowest, respond to dull or diffuse pain
Silent: viscera, unresponsive to normal stimuli, respond only to inflammatory stimuli
First and Second Pain:
First pain causes a ________ sensation (which fiber?)
Second pain causes a _____ sensation (which fiber)
Nociceptors are the common entry point for pain pathways. However, pain pathways diverge upon entering the CNS
First and Second Pain:
First pain causes a fast, sharp, well localized sensation (A delta)
Second pain causes a less well-defined aching or burning (C)
Nociceptors are the common entry point for pain pathways. However, pain pathways diverge upon entering the CNS
Explain superficial vs deep pain
Explain the body’s reaction to both
Superficial pain: is a “call to action.” The motor response to superficial pain includes withdrawl from the stimulus, escape the pain
Deep pain is inescapable. We respond by complete withdrawl from everything: socially, eating, cardiac output decreases
Hyperalgesia: “an increased response to a stimulus which is normally painful”
How does hyperalgesia happen?
What is primary hyperalgesia?
Hyperalgesia: an increased response to a stimulus which is normally painful
Due to the lowering of the nociceptor’s threshold by either peripheral (primary) or central (secondary) mechanisms resulting in an increase in APs sent to the CNS
Primary Hyperalgesia: occurs at the site of the lesion, when the fiber is sensitive or directely activated by chemical agens released by damage tissue nearby
Primary Hyperalgesia:
When tissue damage occurs, the damaged cells release chemical agents which depolarize the pain, sending APs to the CNS AND get conducted through each branch point
When the AP reaches the nerve ending, peptides are released
Explain what the following do:
CGRP
SubP and NKA
Primary Hyperalgesia:
When tissue damage occurs, damaged cells release chemical agents which depolarize the pain fibers, sending APs to the CNS and they also get conducted through each branch point
When APs reach nerve endings, peptides are released
CGRP: causes flare/vasodilation
SubP and NKA cause edema
Primary Hyperalgesia:
Which things cause activation and which things cause sensitization:
Activation: K, Serotonin, Bradykinin, Histamine
Sensitization: Prostaglandin, Leukotrienes, Substance P
TopHat:
Rank the following sensory nerve fiber groups according to speed:
A delta, A beta, C fibers, Ia and Ib
Fastest: Ia and Ib
Medium: A beta is slightly faster than A delta
Slowest: C fibers
Individuals lacking the ______ receptor (due to a gene mutation which inactivates the channel) are completely insensitive to pain. All other sensations, however are normal.
Individuals lacking the Nav 1.7 receptor are completely insensitive to pain.
For the TRPV1 receptor subtype:
What is the threshold temp
Chemical stimuli?
TRPv1:
Threshold: > 43 degrees celcius
Chemical Stimuli: capsaicin, extracellular H+
Explain Secondary Hyperalgesia
What does “central sensitization mean”
Secondary Hyperalgesia:
- this doesn’t occur at the site of the lesion, but rather at the dorsal horn
- secondary hyperalgesia occurs during severe or persistent injury where the nociceptors fire repeatedly, increasing fire of neurons in dorsal horn (“wind up”) resulting in long term changes in to the overall excitability of of these cells
- The resulting long term changes in sensitization in excitability of the neurons in the doral horn is called central sensitization
Short Term effects of Painful Stimuli:
normally (minor cut to finger eg) most of the interneurons within the dorsal horn have only _______ responses and do/do not contribute to central sensitization
Short Term Effects of Painful stimuli:
normally (example, small cut to the finger) most of the interneurons within the dorsal horn have only subthreshold responses and do not contribute to central sensitization
Long Term effects of painful stimuli:
during prolonged or persistent activation, the second order neurons and interneuron become sensitized, thus leading to _____ firing, ______ thresholds, _____ release of NTs to normally subthreshold stimuli.
If very persistent, these changes can result in long term changes to the properties of neurons and a memory for this type of pain
Long term effects of painful stimuli:
during prolonged or persistent activation, the second order neurons and interneurons become sensitized, thus leading to spontaneous firing, lowered thresholds, and increased release of NTs to normally subthreshold stimuli
Effects of primary and secondary hyperalgesia following an injury:
Before the injury (mild burn) the thresholds of all neurons were quite high. After the injury, you would expect the threshold to be ____ at the site of injury where tissue damage occured and in the adjacent tissues where chemical agents could have easily diffused to (______ hyperalgesia)
Due to central sensitization (________ hypergelsia), sites distant from the original injury show a decreased threshold to pain. This is due to the sensory afferents ascending and descending in the tracts of _____ before synpasing.
Effects of primary and secondary hyperalgesia following an injury:
Before the injury (mild burn) the thresholds of all of the neurons were quite high. After the injury, you would expect the threshold to be lower at the site of the injury where the tissue damage occured and in the adjacent tissues where chemical agents could have easily diffused to (primary hyperalgesia)
Due to central sensitization (secondary hyperalgesia), sites distant also show a decreased threshold to pain. This is due to sensory afferents ascending and descending in the tract of Lissauer before synpasing, and modifying additional interneurons.
Difference between A-delta fiber stimulation and C fiber stimulation
A-delta fiber stimulation: release of ____ (fast transient membrane depolarization)
C fiber stimulation: majority is due to __________
Also an increase in ____ or _____ will increase the perception of pain
Difference between A-delta fiber stimulation and C fiber stimulation:
A-delta fiber stimulation: release of glutamate (fast, transient membrane depolarization)
C fiber simtulation: majority is due to second order transmission, secondary messenger systems (long lasting depolarization)
An increase in receptors or an increase in channels can increase the perception of pain
Spinal Afferents:
A-delta and C fibers enter the dorsal horn, ascend 1 or 2 levels in thr tract of Lissauer and terminate on:
- ______ projection neurons to the CNS (ALS)
- local excitatory or inhibitory ______
- sympathetic motorneurons located in the ____
- long and short propriospinal interneurons (which control what?)
Spinal Afferents:
A-delta and C fibers enter the dorsal horn, ascend one or 2 levels in the tract of Lissauer, and terminate on
- 2º projection neurons to the CNS (ALS)
- local excitatory or inhibitory interneurons
- sympathetic motorneurons in the IML
- long and short propriospinal interneurons (which control posture and voluntary movements)
Priopriospinal Interneurons:
A-delta and C fibers can terminate onto long and short propriospinal interneurons that control posture and voluntary movements:
- _________ propriospinal interneurons mediate reflexes
- _______ propriospinal interneurons mediate postural adjustment
Propriospinal Interneurons:
A-delta and C fibers can terminate onto long and short propriospinal interneurons that control posture and voluntary movements:
- short propriospinal interneurons mediate reflexes
- long propriospinal interneurons mediate postural adjustments
Explain the concept of referred pain
Give a classic example of referred pain
Referred pain is due to convergence of synapses from pain and stretch receptors on common interneurons and 2 neurons by sensory info and visceral afferents.
Classic example: shoulder pain during a heart attack
Dorsal Column and Spinothalamic Tracts
Dorsal Column: discriminitive touch, proprioception, vibration, type 1 and type 2 fibers
ALS/STTr: pain, temp, crude touch, type III and IV fibers
Primary difference between DC and ALS:
- ALS cells are ________
- ALS axons cross ____ ascending
- ____ projects to thalamus only, while ____ projects to brainstem, thalamus, RAAS, PAG, and hypothalamus
- Both project to contralateral cortex, but ALS has ipsilateral connections as well
Dorsal Column and Spinothalamic Tracts:
Dorsal Column: discriminative touch, proprioception, vibration, type 1 and 2 fibers
ALS/STTr: pain, temp, crude touch, type III and IV fibers
Primary difference between DC and ALS pathways:
- ALS cells are post-synaptic (synpased in nucleus proprius)
- ALS axons cross spinal cord BEFORE ascending
- DC projects to thamaus only, whereas ALS projects to Brainstem, Thalamus, RAAS, PAG, and hypothalamus
- Both project to contralateral cortex, but ALS has ipsilateral connections as well
What does analgesia mean?
The Gate Control Theory:
by stimulating the _______ fibers of the somatosensory system, you will also excite the _________, resulting in a decreased output and supression of pain. This is why ice, heat, shaing it out and rubbing a mildly painful stimulus is effective in reducing the amount of perceived pain
The Gate control theory only works on what kind of pain?
Analgesia: the modulation or reduction of pain
Gate Control Theory:
By stimulating the non-nociceptive fibers of the somatosensory system, you will excite the inhibitory interneurons, suppressing the pain you feel. That is why ice, heat, and shaking it out wor ks
Gate control theory: only works on MILDly painful stimulus, NOT overcome pain from severe injuries
Cortical Modification of Severe Pain:
Direct stimulation of the ____ and ____ results in excitation of rostroventral medulla, which stimulates cells in dorsal horn of spinal cord. These connections in the spinal cord are inhibitory and thus supress nociceptive neurons for severe pain
Cortical Modification of Severe Pain:
Direct stimulation of PVG and PAG (periventricular and periaqueductal gray)
PAG and PVG pathways:
The PAG and PVG pathway are extremely sensitive to _______, and therefore the primary action site of ______ and ____ like drugs (opiates)
________ opiodes are present at the sites associated with nociceptive processing, and therefore stimulate PAG and PVG.
The PAG and PVG pathways:
PAG and PVG are extremely sensitive to morphine, and therefore the primary action site of morphine and morphine like drugs (opiates)
Endogenous opioids are present at sites associated with processing of nociceptive input, and therefore stimulate PAG and PVG.
CNS Modulation of Pain: Presynpatic Inhibition
Explain CNS presynaptic inhibition:
Presynpatic inhibition (indirect) results in ___ K conductance and ______ of the presynpatic terminal. This causes a _____ in AP duration, ____ Ca influx, and _____ in amount of NT released into post synpatic cell
Presynpatic Inhibition (indirect) results in increased K+ conductance and hyperpolarization of the presynpatic terminal. This hyperpolarization of the presynaptic terminal results in a decrease in the duration of the AP, decreased Ca2+ influx and a decrease in the amount of NT released onto the post-synpatic cell
CNS Modulation of Pain: Postsynpatic Inhibition
Postsynaptic (direct) modification of the EPSP via _______ of the postsynaptic membrane via opiate receptors on the postsynaptic cell - _______ the resting membrane potential of the postsyaptic neuron, taking it ___ from threshold
The net result is a significant but temporary reduction in output from the second order neuron into the CNS and a reduction in perceived pain
Postsynaptic (direct) modification of the EPSP via hyperpolarization of the postsynaptic membrane via opiate receptors on the postsynaptic cell : hyperpolarizes the resting membrane potential of the postsynaptic cell, taking it further from threshold
The net result is reduction in output from the secondary order neuron and therefore a reduction in perceived pain
What does the term allodynia mean?
Allodynia:
Pain due to a stimulus which does not normally provoke pain
sensitization is typically associated with allodynia
