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Neurophysiology of local anesthesiaNeurophysiology of L A
TYPES OF NEURONSensory neuron
Motor neuron
Action of neuron
electrophysiology
Resting state ( phase 1)The unstimulated nerve or nerve at rest
Resting potential across the nerve
Negative electrical potential _ 70
More negative than outside
electrophysiology
DepolarizationWhen a stimulus applied to the nerve the nerve become less negative (slow)
Increase the positive state (rapid)
The inside of the nerve become positive + 40 and the outside of the nerve more negative lead to increase permeability of membrane to Na ion ,this will take 0.3 millisecond
Re polarization
Occurs at the end of depolarization
Electrical gradually more negative inside the nerve
This will lead to increase permeability to K ion
This process will take 0.7 millisecond
electrophysiology
The movement of Na ion to the inside of the nerve during depolarization and the movement of K ions out of the nerve during repolarization are passive process(not requre energy)Action of L A
Mechanism of action2 theories
1- membrane expansion theory
2- specific receptor theory
Factors affecting the action
Factors affecting local anesthetic action- PH value
- lipid solubility
-protein binding
- vasodilator activity
Duration of L A
Factors affecting the duration of L A
- protein binding
- vascularity of the injection site
- presence or absence of vasoactive substance
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