action potentials Flashcards
is ICF or ECF more negative
ICF
what causes ICF to be more negative
‘leaky’ diffusion of K+ ions out of the cell , also impact of Na/K pump which generates a +1 charge outside of the cell
3 different forms of Na channels
- m gate closed , h gate open , seen at RMP , no flow
- m gate and h gate open, threshold has been reached, Na influx allowed
- m gate open , h gate closed , refractory period, no more APs can pass
how many gates to Na and K channels have
K = 1 Na = 2
describe the process of an action potential
1 - stimulus reaches threshold
2 - Na channels start to open and influx begins (positive feedback)
3 - MP reaches peak and Na channels ‘h’ gate closes and K channels open
4 - K efflux restores RMP and Na channels h gate opens and m gate closes ready for next AP
what can increase conduction speed
axon diameter and myelin sheath
saltatory conduction
propagation of APs along myelinated axons e.g between the nodes of ranvier
endoneurium
surrounds single axons
perineurium
surrounds groups of axons
epineurium
surrounds peripheral nerves - contains bundes of axons, bvs , fat etc
A- alpha axons
myelinated, proprioceptors
A-beta axons
myelinated , mechanoreceptors
A - delta axons
myelinated , mechano, thermo (cold) , nociception and chemoceptors (taste)
C axons
non-myelinated, mechano, thermo (hot) and nociception
what is the order of axon susceptibility to LA
most susceptible = a - delta then c then a - beta then a - alpha
some senses are blocked before others
what are the 3 components of LAs
they are organic molecules
aromatic region (hydrophobic)
amide or ester bond
amide side chain (hydrophillic)
why are LA bases presented as hydrochlorides
to increase their solubility in aqueous solutions
when is LA active
when it is partly dissosciated
B.H+ + Cl-
in what form can LA pass through the membrane
unionised form
B.
must be ionised again to block the channel
why are smaller diameter axons more susceptible to LA
they have less Na channels
where are Na channels blocked in myelinated axons
concentrated at nodes of ranvier
what is contained in LA solutions
base - present as a hydrochloride
reducing agent
preservative
vasoconstrictor*
alpha adrenoreceptor
vasoconstriction
beta 1 adrenoreceptor
increase HR
