W2: LA- Neurophysiology and MOA Flashcards
(41 cards)
Looking at
- basic nerve structure
- sodium channels
- nerve pulse/ AP
Neuron
like a cell
- has special parts: dendrites and axons that talk with other cells by chemical transmitters
What is the epineurium layer responsible for in a nerve cell?
contains bunch of axons called fasicles
What is neuron cell membrane?
proteins embeded in PLB
3 main ions and conc to know
K, Na, Cl
difference in conc out/in cell= result in voltage
rest: inside is negative -70mv
how is resting Mem Pot maintained?
pumps
voltage gated channel on mem called? importance?
sodium channel important bc LA molecule sticks here. has 3 parts
- green out vestibule
- selectivity
- inner pore (LA binds here)
What happens when sharp tip of probe pokes your gums?
pain signal to brain
- Na open progressively (at first just bit open, then more)
- influx Na come in cell
- positive membrane potential (from -70 to +40)
depolarisation
going from -70 to +40 (threshold level -55mv which by influx of Na which goes rapid)
membrane becomes more permeable
Repolarisation
when reach full depol at +40mv, the membrane will get back to resting MP
through ATP Na/K pumps
Refractory period
- when another AP cannot be done during refractory period
- AP only gen at hyperpol
summary
- rest -70mv
- stimulus- sharp poke. Na come in. slow depol
3.threshold by 15 mv, BOOM rapid depol +40 - active pumping of ions
- repole
- rest
AP direction
wave of AP travel down axon.
only move forward bc as gen, there is a refractory period where you cannot gen another AP
Myelination effects
myeline= big jumps, no need to propogate all down nerve section by section= faster
‘sultatory conduction’ = bouncing signal (phenomenon)
When you inject LA to myelinated nerve, what happens?
LA only works at nodes where there is no Myeline. where gaps exposed.
If inject to unmyelinated nerve= blocks whole nerve
what fibre types are there, what should you know?
main subtypes to know: a-delta which are small myelinated fibres
- c even smaller unmyelinated fibres (slower)
Pain fibres of teeth
a-delta= dental pain like sharp shooting pain is from dentine sensitivity. pain when drilling cavity with no LA, go bit in dentine= sharp pain = a fibres.
c fibres= pulpal, dull aching, always in background.
basic chemical structure of LA
like Na channel , there is 3 parts
- fat (lipophilic)
- middle chain
- water loving part
2 main groups
1. Amides:
2. Esters:
- aromatic= lipic= pass thru cell, fat part can pass thru cell membrane
- middle chain: ester or amide= affects metabolism
- love water= can be present in extra/intracellular fluid = prevents it from precipitating in solution
design: pass through fat PLB, present in water
Middle chain of LA can be
ester or amide.
diff in metabolism and clearance
Why is acid added to anaesthetic?
they are acidified to form salts so they are more stable. when dissolve in solution present
1. RN- uncharged
2. RNH+= charged
inject dissolved salts in LA cartridge, will inject partial uncharged and charged particles into pt.
- inject
- RNH +- positive bit= outside cell mem, allows
- RN passes through fat PLB, then combines with
-H ions other side, reform a molecule to binds to - inner pore of Na channel (green oval)
- effectively block Na channel
when stimulus comes, will not open Na channels bc blocked, no AP. this block IS REVERSIBLE
basically: positive bit distracts pore, so RN uncharged comes in, joins with H and blocks the pore, NO AP.
what form of LA can pass through cell membrane?
RN uncharged.
reforms to cation by H, which binds to inner pore of Na channel.
stops Depol and AP
summarise in one line LA MOA
LA bind to inner pore of Na channel, no AP bc can’t depol. this is reversible (does it’s job for only limited time, body clears it)
