Neurophysio Of Anxiety And Pain Conduction Flashcards
(14 cards)
Define Local Anesthesia?
LOCAL ANESTHESIA
Loss of sensation in a circumscribed area of the body caused by a depression of excitation in nerve endings or inhibition of the conduction process in peripheral nerves; no loss of consciousness occurs.
Properties Of LA?
PROPERTIES OF LOCAL ANESTHETICS
1) Not irritating to the tissue
2) No permanent alteration of nerve structure
3) Systemic toxicity should be low
4) Effective whether injected or applied topically
5) Time of onset of anesthesia should be as short as possible
6) Duration of action must be long enough to complete the procedure but not so long as to require an extended recovery
7) Should be stable in solution and easily biotransformed
8) Should not cause allergic reactions
9) Should be sterile or capable of being sterilized by use of heat
MOA of LA?
- Local anesthetics interfere with the excitation process in the nerve membrane in one or more of the following ways:
1) Altering the basic resting potential of the nerve membrane
2) Altering the threshold potential (firing level)
3) Decreasing the rate of depolarization
4) Prolonging the rate of repolarization
Where do LA works?
The nerve membrane is the site at which local anesthetics exert their pharmacological actions
What are the theories explaining where do LA works?
Acetylcholine theory
Calcium displacement theory
Surface charge theory
Membrane expansion theory
Specific receptor theory
Specific Receptor theory?
Most favored
LAs act by binding to specific receptors on sodium channels
Both biochemical and electrophysiological studies indicated specific receptor site for LAs exists in sodium channels either on its external surface or on internal axoplasm surface
Most injectable anesthesia are ________
Tertiarry Amines
Kinetics Of LA onset?
Following administration of LA into soft tissues near nerve molecules of LA traverse the distance from one site to another according to their concentration gradient.
During induction phase of anesthsia the LA moves from its extra neural site of deposition to wards the nerve as wee as all other possible directions this process is termed diffusion
Penetration of anatomic barrier to diffusion occurs when drug passes through a tissue that tends to restrict free molecular movement
THE PERINURIUM Is the greatest barrier to penetration of local anesthetics
Anesthetic duration is increased in areas of decreased vascularity eg(GOW-GATES mandibular block vs IANB
t/f
t
Gow-Gates Block = Lower vascularity → slower systemic absorption → longer duration
IANB = Higher vascularity → faster systemic absorption → shorter duration
What are the two main regions of nerve fiber bundles in a peripheral nerve?
A: Mantle bundles (outer) and Core bundles (inner).
What is the outermost layer of a peripheral nerve called?
A: Epineural sheath
Q: What structure surrounds individual nerve bundles within the peripheral nerve?
A: Perineurium.
Q: Why do local anesthetics block mantle fibers before core fibers?
A: Mantle fibers are closer to the site of injection and are exposed to a higher concentration of the anesthetic.
Q: Why is there a delay in anesthetic action on core fibers?
.
A: Core fibers receive the drug later and at a lower concentration
