Exam 3 Week 13 ppt7 Pain modulation Flashcards
Two Principal theories of pain modulation and the two extra theories thrown in by Lake
- Gate-control theory
- Descending systems
Extras:
-Hormonal system
-Endogenous cannabinoids
Very basic initial mechanisms of the Gate-control theory
- involves the segmental Modulation at level of 1° afferent and relay cell.
- It begins by realizing that small caliber afferents C-fibers activate 2° neuron to signal pain
two afferent fibers involved in Gate-control theory
A-beta and C fibers
What is the role of the inhibitory interneuron?
- inhibitory interneuron block signal of pain by inhibiting the 2° neuron
- if it is inhibited then the pain signal can get through to the 2° neuron
- The inhibitory interneuron functions as the part of the gate control theory
What do A-beta fibers do? (in general)
large myelinated afferent fibers that respond to touch, pressure, vibration
How are A-beta fibers involved in gate theory?
by stimulating touch or pressure receptors in an area (of pain), Ab fiber activates an inhibitory interneuron to block signal of pain by inhibiting the 2° neuron
How do small unmyelinated C fibers block override A-beta fibers
Very active C-fibers can use another inhibitory interneuron (black in this illustration) to block the inhibitory effect of the large caliber afferents
*So with moderate pain stimulation of tactile receptors can block the pain. Very severe pain can override this effect
Where do the Descending systems start?
Cerebral cortex and hypothalamic projections to midbrain and brainstem (Periaqueductal gray, Locus coeruleus, and Raphe nuclei)
What type of neurons descend from Periaqueductal gray?
Enkephalinergic neurons
Where do Enkephalinergic neurons descend to?
Descend to both spinal cord and to control Raphe neurons
What type of neurons descend from Locus coeruleus?
adrenergic neurons (Norepinephrine)
Where do Noradrenergic neurons descend to?
Adrenergic neurons which descend to the spinal cored to release NE.
Both Noradrenergic and serotonergic pathways inhibit tract cells
What type of neurons descend from Raphe nuclei?
serotonergic neurons
Where do serotonergic neurons descend to?
descend to the spinal cord to release serotonin (5-HT)
Both Noradrenergic and serotonergic pathways inhibit tract cells
3 bullet points from slides of what is occurring in dorsal horn in the descending system
- Both Noradrenergic and serotonergic pathways inhibit tract cells (using primarily post-synaptic inhibition)
- There are also GABA pre and post-synaptic inhibitory neurons
- Enkephalinergic descending and spinal interneurons (both do pre-synaptic inhibition, but probably post-synaptic too)
What is released in the hormone pain modulation system?
release of b-endorphin which is released as part of the pro-hormone proopiomelanocortin (POMC) which is release from the pituitary during stress and injury.
What do the endorphins do?
act on spinal and other opioid receptors to block pain
How does Endogenous cannabinoids work?
separates emotional component from discriminative component of pain
Benefits of massage (2)
- Increase local blood circulation to decrease local inflammatory agents
- Activate low-threshold Ab fibers that inhibit nociceptive input to spinal cord
Benefits of using heat (2)
- increase local circulation to decrease local inflammatory agents
- Counter-irritation and also activating low-threshold Ab fibers (Gate control mechanism)
Benefits of using cold (2)
- Decrease metabolism so decrease release of local inflammatory chemicals
- Counter-irritation to blockage of nerves
Two types of TENS highlighted by Lake
- High-frequency, low intensity, electrodes over area of pain
- Low-frequency, high-intensity, electrodes over acupuncture points
How does High-frequency, low intensity TENS work?
has a counter irritation effect, activating low-threshold Ab fibers that inhibit nociceptive input to spinal cord – the Gate control mechanism
How does Low-frequency, high-intensity TENS work?
electrodes over acupuncture points may elicit release of segmental and descending enkephalins and hormonal endorphins
4 pharmacological approaches to treating pain and examples
1. Non-opioid analgesics – anti-inflammatory Aspirin, acetaminephine, ibuprofen 2. Tricyclic antidepressants – norepinephrine and serotonin reuptake blocking Imipramine, amitriptyline, doxepin 3. Anticonvulsants – Na+ blockers Phenytoin, carbamazepine 4. Narcotic (opioid) analgesics Morphine
Acupuncture
- Long, fine needles are inserted into specific points along 12 cardinal meridians on the skin – named for the meridian and point along the meridian
- Produces anesthesia significant enough that in China, surgery is frequently performed with patient under acupuncture alone
What pain modulating system does acupuncture use?
descending pain control systems
Surgical approaches to treating pain (3)
- Surgical cutting of the dorsal roots
- Surgical lesioning of thalamus
- Surgical implantation of stimulators to block pain
what are three examples of tricyclic antidepressants used for pain?
tricyclic antidepressants – norepinephrine and serotonin reuptake blocking
- Imipramine,
- amitriptyline,
- doxepin
what are two examples of anticonvulsants used for pain?
Anticonvulsants – Na+ blockers
- Phenytoin,
- carbamazepine
what is b-endorphin part of?
when is it released and from where?
proopiomelanocortin which is released from the the pituitary gland during stress and injury
