Local anaesthetic Flashcards
Describe the diffusion gradient of a cell.
The extracellular fluid is positive.
The intracellular fluid is negative.
Na+ is found in the extracellular fluid & is trying to diffuse into the cell (na not tonight)
K+ is found inside the cell & the pottasium channels allow it to move out. (leaving intracellular fluid negative)
Discuss cell action potential?
This is the difference in membrane pottential.
The opening of Na+ gated channels causes a rise in action pottential. (When it hits threshold- there is depolarisation)
When these close and K+ channels open there is a fall in action pottential.(repolarisation)
Compare pottasium and sodium gated channels.
Sodium gated channels have 2 gates: A ‘h’ gate and an ‘m’ gate.
channel= closed - m gate closed(h open)
channel opens- m gate opens (h open)
channel closed - h gate closed. (m gate open)
Pottasium channels have 1 gate.
Channel open= gate open
Channel closed= gate closed.
What is the refractory period and why do we have it?
This is the period of inexcitability in a cell after an action pottential is initiated. Caused by the closing of Na channels.
To prevent nerve impulses travelling backwards & limits the maximum firing frequency of AP in axons.
Name the parts of this peripheral nerve?
A-Epineurium
B- endoneurium
C- Perineurium
D- Blood vessels
E- lipid
Compare the axon types:
A alpha- myelinated- Sensory & motor (proreception)
A beta - myelinated- mechanoreceptors
A delta- myelinated- mechano/ chemo/ nociceptors/ thermoreceptors
C fibres- unmyelinated- mechano/ nociceptors/ thermoreceptors.
What happens to nerve fibres as they enter the pulp.
They lose their myelination.
How does local anaesthetic work?
It blocks the Na+ channels stopping nerve conduction (as action pottential cannot reach the threshold)
Why are local Anaesthetics lipophillic?
So that they have an affinity to the lipid membranes of the nerves. This means that the Local Anaesthetic will move through the membranes quicker- making it work faster.
List the axon types in order of how susceptible they are to LA blockage.
A beta> C fibres> a delta > a alpha
Why does the local anaesthetic need to work on several nodes of ranvier?
The nerve action pottential is able to skip over a node of ranvier if it is blocked. The AP cannot skip over many nodes of ranvier.
Why do we want to avoid the local anaesthetic reaching general circulation?
If it reaches general circulation, it could block the Na channels of other tissues such as cardiac tissue.
This would cause bradycardia &hypotension (patient fainting)
What is local anaesthetic composed of?
A base:
- aromatic ring (hydrophobic)
- ester or amide
- Amine side chain (hydrophillic)
Why is the local anaesthetic partially dissociated?
The base & hydrochloride has to be unionised to diffuse through the membrane.
Once in the cell it can dissoicate (become ionised) and the LA is activated.
Give examples of Ester and amide local anaesthetics?
Ester e.g benzocaine
Amide e.g. lignocaine/Prilocaine.
