Physiology-Pain and Temperature Flashcards
What are the different types of pain?
Fast: 0.1s after stimulus, superficial, localized, no tissue destruction. Slow: > 1s after stimulus, superficial & deep, tissue destruction.
What are the three types of pain receptors? What do they sense?
Thermal (Type III or A-delta fibers): hot/cold on skin, Mechanical (Type III or A-delta fibers): high pressure, Polymodal (Type IV or c-fibers): hot/cold, pressure and chemicals.
Action potential propagation in which sensory fibers causes the first pain and second pain seen below?
First pain: III (A-delta fibers). Second burning pain: IV (C fibers)
Why do group III (A-delta) fibers typically arrive before group IV (c-fibers)?
Group III fibers are thinly myelinated where group IV fibers are not myelinated.
Where do group III (A-delta) fibers terminate in the spinal cord? What neurotransmitter do they release when the arrive at this location?
Upper part of the dorsal horn in superficial laminae (this is the location of many interneurons). They secrete glutamate which causes an EPSP in secondary neurons.
What molecules are released by group IV fibers (c-fibers) at the upper part of the dorsal horn where they synapse in the spinal cord?
Glutamate and Subastance P (prolongs glutamate-induced EPSP)
On what fibers do group III and group IV fibers synapse?
Anterolateral Spinothalamic tract fibers that will take the signal to the thalamus.
You slam your shin into the coffee table. Why does massaging the area of pain help the pain go away? ;alkjdfl;kaj;ldfj;aljdf;lajdal;
Gait theory. The original pain stimulus travels through the type IV (c) fibers to through the zone of Lissau. Here it releases substance P and glutamate that cause an EPSP in the secondary neuron and inhibit the inhibitory interneuron, causing pain signals to be sent through the ALSTT. Massaging the area stimulates I,II (A-alpha/A-beta) fibers to release massive amounts of glutamate on the inhibitory interneuron that activates it. This inhibits pain sensation transmission throughout the ALSTT
How can glutamate released by c-fibers cause inhibition of the interneuron and excitation of the secondary neuron?
Secondary neuron: Glu opens Na+ channels. Interneuron: glutamate activated metabotropic receptor that opens K+ channels.
What is the descending pathway of pain inhibition?
A collateral pain sensory branch is thrown toward the periaqueductal gray on the way to the thalamus. The periaqueductal gray neurons send axons to the raphe nucleus in the upper medulla and lower pons. The raphe nucleus sends serotonergic axons into the spinal cord which stimulates the inhibitor interneurons and attenuates the pain.
How does the interneuron inhibit transmission of pain signals to the CNS?
GABA is released on the actual secondary neuron and GABA can be released presynaptically on the type IV (C) fiber which will inhibit presynaptic release of glutamate, preventing stimulation of the secondary neuron by type IV (c) fibers.
What regions of the CNS are modulated by the cortex when decreasing pain sensations?
Reticulate pathway, cingulate gyrus and insula.
How does morphine modulate pain sensation?
It stimulates the descending pathway of pain inhibition through the periaqueductal gray and raphe nucleus that ultimately stimulates the inhibitor interneuron.
Why don’t opiates work for people with carpal tunnel?
Compression of the nerve results in repetitive frequent firing of the nerves.
What are the two types of hyperalgesia?
Peripheral hyperalgesia: pain threshold decreases in areas that have been sensitized by a previous pain stimulus due to action potential-induced release of substance P and other release of PG, 5-HT, bradykinin & histamine in collateral fibers. Central hyperalgesia: pain fibers in the CNS develop memory just as other neurons do
What is the reason for patients feeling arm pain during a heart attack and abdominal wall pain during appendicitis?
The GVA fibers run in conduction with the GSA fibers and the brain cannot discern which one the pain stimulus is coming from (MI: C8-T1 and appendicitis T10)
What types of thermal receptors do we have?
Hot nociceptors (mostly c-fibers) and cold nociceptors (A-delta and c-fibers). Hot receptors fire when the skin is warm and cold fire when it gets cold.
