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41 Cards in this Set

  • Front
  • Back
What is local anesthesia?
Anesthetic applied to a specific local area that eliminates sensation and pain without loss of consciousness
What type of molecule is cocaine?
An ester
Who developed the inferior dental nerve block techniques for dentistry?
William Stewart Halsted and Richard John Hall in 1884
What drug is commonly known as Novocaine?
Procaine an ester type drug
What was the first amide used in local anesthesia?
Lidocaine which was marketed as Xylocaine. This is a mainstay of local anesthesia in dentistry today
What type of drug is Lidocaine/Xylocaine?
Amide
What are the properties of ester type anesthetics?
Short acting (ok for dentistry in the early 1900’s) Increased incidence of allergy, very slow onset 10-15 min
What are the characteristics of Amide type anesthetics?
Longer duration, short onset 3-5 min, less allergy
Why was epinephrine added to procaine and who did this?
Braun (called the father of local anesthesia) was the person who added it to increase the duration of its effects.
What does the inflammatory soup released by damaged cells do?
Depolarizes nociceptors and stimulates the generation of AP’s
What short peptide is cleaved by proteolytic enzyme from plasma protein that is released into damaged tissue?
Bradykinin which makes free nerve endings more sensitive to noxious stimuli
What does release of substance P cause?
More bradykinin formantion and activation of mast cells and platelets
What substances can diffuse between nerve cells and sensitize them?
Histamine and 5HT
What substances are involved in sensitizing pain response?
PGE2 from COX activity on arachidonic acid, Bradykinin, Histamine and serotonin from mast cells, and substance P from nociceptors, also TRP channels
How is pain sensed in dentin?
Nociceptor nerve endings project along odontoblast processes into dentinal tubules. Tooth damage causes hydrostatic pressure changes that stimulate nociceptor endings
What does local anesthetics block?
Neurotransmission along nociceptor axons
What are the two types of pain fibers?
Type A-delta fibers – fast pain, myelinated
What is a stimulus that is not strong enough to reach threshold called?
A graded receptor potential
What happens in an action potential?
Rapid activation of voltage-gated Na+ channels followed by slower activation of voltage-gated K+ channels
Under resting conditions are the K+ channels or the Na+ channels open?
The K+channels are open the Na+ channels remain closed
What is equilibrium voltage?
The point at which a significant charge accumulation along the membrane opposes further diffusion across the membrane
How many ions actually move across the membrane during an AP?
Very few the membrane is very effective in separating charges so few ions are required
What does a voltage gated channel consist of?
4 clusters of 6 transmembrane domains
How do K+ channels and Na+ channels differ?
K+ channels are made 4 individual polybeptides and Na+ the 4 parts of the cluster are part of a large single polypeptide.
What channels do local anesthetic block?
Voltage-gated channels
How does local anesthetic act on the nerve membrane?
Must be lipophilic to cross nerve membrane. Blocks Na+ channels from the axoplasmic (inside) side. Once in axoplasm anesthetic becomes protonated to enter Na+ channels
What are the two factors involved in the action of LA?
Diffusion of the drug and binding at receptor site
What must the charge be on the LA to diffuse across the membrane?
Uncharged (neutral)
Why is most LA positive once it gets into the cytoplasm?
The lower pH protonates the anesthetic which acts to keep it inside the cell for a longer period of time
What type of molecule is procaine?
Procain was the first synthesized ester
What class of molecules is standard practice for LA today?
Amides such as lidocaine
What are 2 disadvantages of esters?
High allergy rate, slow onset
What is special about amides?
Only type available in US as injectable, less allergy, faster onset of action
Which LA lacks an amino terminus?
Benzocaine
A larger ka translates into what for LA?
More anesthetic remains in the charged form, LA is less permeable across the axon membrane so it takes longer to take effect (the lower the pKa the faster the drug onset)
Are anesthetics vasoconstrictors or vasodilators?
Vasodilators. Vasodilation leads to increased blood flow to region which = rapid removal of anesthetic molecules from injection site
In the specific receptor theory Benzocaine is under which classification?
Class C - agents act by a receptor-independent physico-chemical mechanism
What is class C in the specific receptor theory?
Most useful LA agents – agents act by combination of receptor and receptor-independent mechanisms
At physiological pH what is the ration of charged to neutral LA?
3:1
In inflamed tissue how much more charged LA is there than neutral LA?
10X more charged = LA takes longer to begin working
What does epinephrine in LA do?
Constricts blood flow in capillaries via a1 receptors