pain neurology Flashcards
What is a facilitate segment?
- adverse neurologic response where a segment in lesion channels normal neural activity through efferent motor and sympathetic pathways
- Likened to a glass of water that is overflowing with neural activity and spilling out as excessive facilitation or inhibition to the corresponding segment
Who is created to the initial research into the facilitated segment?
In the 40s Korr, Denslow, Krems found region EMG activity with pressure to the spinous process
How are the facilitated segment and central sensitization related?
- Both are adverse neurologic activity
2. The facilitated segment however is not central sensitization and is still a peripherally driven process
What is allodynia?
Change in the central nervous system resulting in a heightened state of the nervous system where normal levels of afferent stimulus such as brushing or stroking cause the perception of pain.
What is the neurogenic inflammatory response?
- mechanical inflammation leads to a neurologic inflammatory response?
- involves vasodilatation and activation of inflammatory cells
- reduction in type IV thresholds or peripheral sensitization
What is peripheral sensitization?
- Decrease in free nerve ending threshold resulting in afferent signally from lower levels of mechanical, chemical or thermal stimulus
- The chemical mediators of inflammation reduce the threshold
- you can also have direct injury to the nerve that reduces its threshold
How can a peripheral nerve injury create peripheral sensitization?
- abnormal DH activity- increase type IV afferent flow causes wide range DH interneurons to lower their threshold
- Lower thresholds for the newly sprouted nerve endings
- Loss of c-fibers from injury leaves interneuron opening for developing new connection which may be type IVs
- ischemic demyelination leading to ectopic depolarization of nerves
What are the different classes of DH interneurons?
- Class I-low threshold activated by mechanorecptors
- Class 2 or wide range dynamic- activated by mechanoreceptor and nocioceptors
- Class 3- activated by nocioceptors
What class of DH interneuron is most likely responsible for transmitting conscience levels of pain?
Class II or wide range dynamic
What are projection neurons?
1.neurons in the spinal cord responsible for relaying an inhibitory or facilitory signal from one region to another region in the central nervous system
What projection neurons play a role in pain?
- spinothalamic tract- takes the signal from the DH to the thalamus
- descending control system effects the sensitivity of the DH
- local interneurons effect responsiveness of the DH to peripheral afferents
What are some examples of nerves that synapse on the class II or wide range dynamic DH interneurons?
- cutaneous type IV
- cutaneous type I and IIs
- deep connective tissues afferents
- organ afferents
- muscle spindle afferents
What is convergence within the DH?
the wide range dynamic interneurons are activated by both nociceptive and non-nociceptive afferent
What are the roles of the DH horn in the pain response?
- nocioceptive afferents terminate in laminas I and II
- DH is responsible for relaying the nociceptive signal via projection interneurons
- convergence of painful and normal neural activity occurs at the class II or wide range dynamic interneurons of the DH
- DH horn can become sensitized by a decrease in activation thresholds
- DH windup
- DH field expansion
How does the DH become sensitized to painful stimulus?
There are two process once the type IV send the nociceptive signal to laminas I and II
- spinothalamic activation causes the thalamus send descend stimulus to lower DH threshold
- there is an increase in local interneuron activity at the DH creating a reduction in thresholds
Is central sensitization of the DH horn a dysfunctional process?
- it is a normal response to pain
2. it can dysfunction if it becomes centrally mediated from chronic peripheral stimulation
What effect does the neurotransmitter have on the post synaptic membrane?
- it binds to the membrane creating a voltage change in the membrane
- voltage change will open ion channels by releasing the Mg++ block
- charged ions are then able to freely flow back and forth to create an inhibitory or an excitatory response
What ions create postsynaptic inhibition and excitation?
- inhibition is Cl-
2. excite is Ca+ or Na+
What neurotransmitters create a postsynaptic inhibitory effect with pain?
- Gamma Aminobutric Acid (GABA)
2. Glycine
What neurotransmitters create a postsynaptic excitatory effect?
- glutamate
2. aspartate
What are the postsynaptic excitatory receptors?
- N-methyl-D-Aspartate (NMDA)
- Non-MNDA- Kainate and AMPA
- Neurokin second messenger
What role does the excitatory second messenger system play in pain modulation?
produces a longer lasting effect in neural activity and it primes the NMDA receptors so there threshold is decreased
What effect does substance P have on the pain receptors of the DH
activates neuron receptors
What is DH windup?
changes in NMDA behavior in the DH lowering activation threshold following repeated stimulus of C-fibers less than 3 seconds apart
What is DH field expansion?
Neurons within the DH can expand their receptive field to include synapses with pathologic neurons so that facilitation of that neuron will now cause a pathologic response
What is proto-oncogenes role in the nervous system?
- substance believed to influence the process for central neural plasticity in development of chronic pain
- pathway:noxious stimulus -> influx intracellular Ca+ unlocking NMDA receptors -> increases expression of neuropeptides for plasticity -> central mediated pain
What is long term potentiation and how is it created?
- changes in the efficiency of the nervous system that could contribution to long term memory
- requires brief high frequency inputs to develop
- inputs can be mechanical or cognitive
How can you block the neurologic contributions to inflammation?
- blocking the non-MNDA (excitatory) and GABA-A (inhibitory) receptors at the DH of the spinal cord
- blocking the sympathetics does not help
What is the dorsal root reflex?
The neurologic chain of events responsible for central nervous system influence on peripheral inflammation