Flashcards in Pharm- 11 Deck (78)
Which sensations do A(delta) fibers transmit for pain?
myelinated transmit impulses much faster, used for first pain, noxious cold below 5 degrees C and injurious force on the skin
Which sensations do C-fibers transmit for pain?
nonmyelinated transmit impulses slower, used for second pain, temperatures above 45 degrees C and chemical and mechanical stimuli
Describe the pathway of pain peception from the periphery to the thalamus?
Impulses from the skin generated by the nociceptors activation are conducted to the dorsal horn of the spinal cord
In the dorsal horn the nociceptors form synapses with interneurons and second order neurons
Second order neurons travel in the lateral areas of the spinal cord (ALS from pain, temp crude touch), and project mainly to the thalamus
Where does the thalamus then project pain fibers in the CNS?
somatosensory Cx of the parietal lobe
Which fibers transmit the first pain signals?
transmitted by the Aδ fibers and is quick sharp (pinprick-like) in quality, and is perceived as highly localized on the body
Which fibers transmit the second pain signals?
transmitted by C-fibers and is slower to develop but longer lasting, feels dull, throbbing, or burning (the clap), and only diffusely localized, and endures after the stimulus ends
Are Aδ or C fibers more susceptible to local anesthetics?
are specific inhibitors of pain pathways
How does codeine work?
signals the cell to increase K+ conductance in postsynaptic neurons and decrease Ca entry into presynatpic neurons --> double whammy decrease in NT action/release
What is local anesthesia?
- are nonspecific inhibitors of peripheral sensory (including pain), motor, and autonomic pathways
How does lidocaine work?
inhibits conductance of AP's in all afferent and efferent nerve fibers in the PNS
How do all local anesthetics block pain perception?
Inhibiting Na-channels --> prevents AP's on pain fibers
Procaine, tetracaine, and cocaine are example of what type of local anesthetics?
Lidocaine, prilocaine, bupivacaine, articaine, and EMLA are example of what types of local anesthetics?
What happens to ester-linked local anesthetics in the presence of water and esterases?
easily hydrolyzed to carboxylic acid and alcohol
Do amide or ester linked local anesthetics have a longer duration of action?
What is the role of the aromatic group in the local anesthetic (LA)?
Hydrophobicity --> passage through cell membranes
What happens if there is too much hydrophobicity in the LA?
It's bad cuz the drug wont leave the hydrophobic interior of the cell --> continually acting
What are the 2 forms the amine group of the LA exist in?
protonated (+) or deprotonated (0)
What is the range of pKa for LAs?
8-10 (theyre weak bases)
So at physiological pH (7.4), are LA's protonated or unprotonated?
almost equal amts of both
Which form (+ or 0) crosses the cell membrane?
Which form (+ or 0) binds stronger to the voltage-gated Na channel?
Procaine (novocain)- use
epidural for delivery, dentists
Procaine- plasma T1/2
low b/c of hydrophobicity and rapid removal
Low b/c of rapid dissociated from Na channel
topical and spinal anesthesia
tetracaine- plasma T1/2
logn b/c of high hydrophobicity, can stay in tissues for a while
high because of high hydrophobicity and longer binding to Na channel