pain Flashcards
what spinal cord tract carries pain and temperature sensation?
The lateral spinothalamic tract.
where does the spinothalamic tract cross?
INSIDE the spinal cord, at the anterior white comissure.
The spinothalamic tract is somatotopically arranged. How?
cervical section medial, sacral segments lateral.
how many neurons are involved in the spinothalamic utilisation of sensory info from skin to sensorimotor cortex?
3
Where are the psudounipolar neurons located ?
cellbodies in the dorsal root ganglion.
Where do the pseudounipolar neurons enter the dorsal horn?
At the same segmental level as their cellbodies are in the dorsal root ganglion.
what two types of fibers transmit pain?
A-delta fibers
C fibers
what type of pain does the A-delta fibers transmit?
Fast and immediate pain.
How does A-delta fibers look?
They have a large diameter and transmit as fast as 6 milliseconds.
What type of fibers transmit slow aching pain (dermatome wise) that comes from inflammation?
C fibers.
C fibers make several connections in the dorsal horn before ascending. WHy?
WHat happen in the Lissauer tract and where is it localized?
Its a collection of descending or ascending collaterals of the primary pain-neuron.
What happens with the primary pain neuron after travelling up or down in the lissauer tract?
They synapse to a secondary neuron, wither in substantia gelatinosa or in nucleus proprius.
both localised in the apex of the posterior grey matter horn. - they are usually 1-2 levels higher than the point of entry of the 1st nerve.
What does the 2nd level pain neurons do after synapsing with the primary neuron in the nucleus gelatinousa or nucleus proprius in the posterior horn apex?
The AXONS of the 2nd order neuron travel anteriorly and cross in the anterior white comissure.
Where are the 2nd level neurons of pain travelling after crossing in the anterior white commissure?
Through the lateral spinothalamic tract, up in between the inferior olivary nucleus and the trigeminal nerve spinal tract nucleus in medulla oblongata where it aligns with the anterior spinothalamic tract and form the “spinal lemniscus”
What is “the spinal lemniscus”?
Its the anterior and lateral spinothalamic tract forming a common lemniscus at the level of the inferior olivary nucleus/trigeminal spinal nucleus in medulla oblongata.
Where in pons does the spinal lemniscus travel?
In the dorsal pons.
What happen with the spinal lemniscus in the midbrain?
They synapse with 3rd order neurons in Thalamus.
What nuclei of Thalamus are synpasing with 2nd order neurons from the spinal lemniscus?
- ventral posterior lateral
- ventral medial posterior
- medial dorsal.
*
In what thalmic nucleus does most of the lateral spinothalamic tract 2nd order neurons synapse?
In the ventral posterolateral nucleus of thalamus..
What will be “arranged” through synapses of crude pain and temperature 2nd order fibers in the ventral posterolateral nucleus of Thalamus?
Initiation of emotional reactions.
HOw do the 3rd order neurons from the spinothalamic tract get from Thalamus to the primary sensory cortex in the postcentral gyrus?
Through the posterior limb of the internal capsule then through corona radiata and then reach the target.
What more targets except for the primary sensory cortex is 3rd order neurons from the spinal lemniscus synapsing to?
- insular cortex
- primary somatosensory cortex (postcentral gyrus)
- cingulate cortex.
what is “affective sensation”
its a cause of the spinothalamic tract initiating eg withdrwal from hot or sharp objects and itching from a scratch etc.
what is the role of the spino-mesencephalic-limbic pathway?
its one of two indirect systems in the spinothalamic tract. Its main role is to cause the pain to have an impact and cause a reaction to it.
there is a specific condition in which fine touch and proprioception is lost ipsilateral and pain and temperature perception is lost contralaterally to the hemisection. What is it called?
Brown-Sequard syndrome.
what may cause chronic pain?
- injury to nerve endings
- scar formation in nerves
- abberrant reinnervation following nerve damage, causing the person to interpret touch as pain - Allodynia.
- inflammation
- cancer
What is a “winding up” effect?
repeated stimulation of C-fibers by eg inflammation; will cause repeated release of glutamate. This causes a winding up phenomenon where the individual is more prone to that pain.
another name for glutamate
NMDA
What drugs can reduce and even abolish wind-up?
NSAIDs and Opioids. They do it by reducing excitability of spinal cord neurones.
What is central sensitisation?
A combination of:
* enhancement in function of neurons and circuits in the nociceptive pathways caused by increases in membrane excitability and synaptic efficiacy.
* Reduced inhibition
- A manifestation of plasticity of the somatosensory NS in response to activity, inflammation and neural injury.
What is hyperalgesia?
WHat is central sensitisation?
What is “wind up” of pain?
A frequency dependent upregulation of excitability of spinal cord neurones evoked by stimulation of C-fibers. Glutamate/NMDA seems to have a part in this. (eg. repeat provocation of inflammed joint)
What drugs may reduce or even abolish wind up and how?
NSAID and Opioids. By reducing exitability of spinal cord neurones.
Central sensitisation is not the same as wind up. What is it?
Its a patophysiologic process in which the CNS undergo changes that alter its processing of pain.
What is the difference between the two “central sensitisation” types - allodynia and hyperalgesia?
Allodynia - normally not painful stimuli create a painful reaction
Hyperalgesia - painful stimuli become out of proportion painful.
What might cause chronic pain?
Chronic pain can be caused by a variety of factors, such as:
injury to the nerve endings
scar formation in the nerves
aberrant reinnervation following nerve damage, causing the person to interpret touch as pain (allodynia)
Inflammation
cancer
Manifestation of central sensitization
Central sensitization manifests as pain hypersensitivity, particularly dynamic tactile allodynia, secondary punctate or pressure hyperalgesia, aftersensations, and enhanced temporal summation.
It can be readily and rapidly elicited in human volunteers by diverse experimental noxious conditioning stimuli to skin, muscles or viscera, and in addition to producing pain hypersensitivity, results in secondary changes in brain activity that can be detected by electrophysiological or imaging techniques.
What are deschending pain control pathways?
There are facilitatory and inhibitory nociceptive pain control pathways that alters the respons to pain stimuli in the spinal cord.
What is the descending antinociceptive pathway?
The descending antinociceptive pathways begin at the supraspinal level and project to neurons in the dorsal horn of the spinal cord. The periaqueductal gray matter (midbrain), locus ceruleus (pons), and nucleus raphemagnus (medulla) are important structures in the modulation of nociceptive input.
Which are the main neurotransmittors imlicated in descending pain control?
5-HT, NA and endogenous opioids.
