Local Anaesthesia Flashcards
What is the definition of local anaesthesia?
A loss of sensation in a circumscribed area of the body by a depression of excitation in nerve endings or an inhibition of the conduction process in peripheral nerves
What are the requirements of an ideal local anaesthetic?
Specific (effects exerted on specific nerves) and reversible action
Non-irritant
Temporary/produces no permanent damage
No systemic toxicity
High therapeutic ratio
Active topically and by injection
Rapid onset
Suitable duration of action
Chemically stable and sterilisable
Combinable with other agents
Non-allergic
Non-addictive
What are the uses of LA in dentistry?
Operative pain management
Post-operative pain management
Diagnosis (determine source of chronic pain in multiple deeply carious teeth)
Haemostasis (LA has vasoconstrictors)
What are the two theories of LA action?
Membrane expansion
Specific receptor
What happens to a nerve when stimulated/what’s involved in an action potential of a nerve transmitting messages?
Depolarisation
Repolarisation
Refractory period
What are the charges outside and inside the cell when the nerve is at rest?
Positive outside
Negative inside
What causes depolarisation of the nerve?
Any stimulation of the cell e.g. drill hitting the dentine of a tooth
What happens during depolarisation?
The main (M) gate opens, allowing sodium to move from the outside to the inside of the cell, causing an electrochemical gradient shift and the cell becomes negative on the outside and positive inside of the cell
What happens during repolarisation?
The hold (H) gate closes to stop any further sodium from entering
Potassium moves outside of the cell, causing the electromagnetic gradient to shift back to positive outside, negative inside
What happens in the membrane expansion theory?
LA diffuses into the nerve cell membrane causing it to expand and physically blocking off the sodium channel so sodium can’t move to the inside of the cell hence nerve cannot fire off any action potential
What happens in the specific receptor theory?
LA binds to a binding site on the inside of the H gate, holding it closed, hence holding the nerve cell in its refractory period and action potential cannot be fired off
What are the three subunits in a sodium channel?
α
β1
β2
Which subunit in the sodium channel is where sodium passes through?
α
How many protein domains are each sodium channel surrounded by?
4 (I - IV)
How many segments are there in each protein domain surrounding the sodium channels?
6 (S1 - S6)
