Heart Flashcards
Rest Cell Na
- High outside 140mM - membrane no so permeable - Both electrical and concentration gradients inward
- Low inside
Resting Cell K
- High INSIDE - membrane more permeable to K the electrical gradient balances the chemical gradient - slow leakage bc chemical gradient a little bigger
- low outside
- concentration gradient OUT
- electrical gradient IN
Resting Cell Ca
- Cardiac cells dont have as much SR but still need SOME flux of Ca across the membrane.
- Higher OUTSIDE
- Lower inside
- membrane relatively impermeable to Ca
Resting Cell Cl
- High OUTSIDE- balance of chemical and electrical gradient keeps it balanced
- low inside
- membrane relatively permeable to Cl
Phase 0
- Opening of fast Na channel = depolarization
- Na rushes in
Phase 1
- opening of K or Cl channel
- potential startss going back toward 0
Phase 2
- Plateau phase
- Opening of slow Ca channel
- K channels partially open - more closed than open
- letting Ca in so how is it flat? Same # positive charges coming in with Ca as with K positive charges leaving
- when fast channels opens the K channels start to close
Phase 2 into Phase 3
Throughout phase 2 K permeability is increasing and at some point Ca channels close (right before Phase 3)
Phase 3
Repolarization - K rushing out – high conducatnace and permeability
Phase 4
- resting membrane potential
- balanqce between Na and K
Resting Na gate
fast gate closed - M gate (activity gate)
slow gate open - H gate (inactivity gate)
Active Na gate
both M and H gate open
Na electrical vs chemical gradient
electrical»_space; chemical
Which gate starts to close first after active Na state?
H gate closes first ( electrical gradient is reversed but chemical gradient is same = not a lot of Na entered cell but enough to change the charge)
Inactive Na gate
H gate (inactivity gate) closed M gate (activity gate) Open CELL CANNOT BE STIMULATED RIGHT NOW = REFRACTORY PERIOD
Refractory period defined as:
H GATE CLOSED (INACTIVITY GATE)
effective refractory period
- begins at depolarization (Phase 0-Opening of fast sodium channel (m-gate opens)) and ends during repolarization (phase 3) when enough H and M gate closed have been reset to Resting state
- cant stimulate the cell here - no propagation of action potential
Relative refractory period
- A propagated action potential can be produced, but requires a stronger than normal stimulus. Action potential has abnormal characteristics.
- begins when ERP ends. Ends with normal action potential
- action potential that you get in relative refractory period is not normal –> DANGEROUS - screw up the rhythm
what prevents tetany?
the effective refractory period is LONGER than in skeletal muscle- impossible to stimulate contraction again
conductance is
actual movement of ion
permeability is
potential to move
stimulus comes during repolarization
- Low slope of phase O because many fast channels are in inactivated state.
- No plateau because PK+ and Conductance of K+ is very high resulting in repolarization.
- can ge tventricular fibrilation (ventricles out of sync) bc some cardiac muscles may still be in ERP so CANT fire while some in the RRP CAN fire.
tetrodotoxin -
Blocks fast channels - makes a hump action potential
prepotential phase
- not flat resting membrane protential that moves to threshold (Phase 4 with POSITIVE slope = slow depolarization)
- permeability to K DECREASING and Permeability to Ca and Na INCREASING
