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
ventricular cell haswhat permeability to the ions
LOW to Na and Ca
High to K
POSITIVEChronotropic agents do what?
-Increase the rate of INFLUX of SODIUM and
CALCIUM (MOSTLY JUST CA)
-increases HR - reaches threshold faster
-ex) norepinephrine
NEGATIVE Chronotropic agents do what?
- Increase PK.
- This results in repolarization to more negative values and in decreased rate of decay of the K+ efflux channel
- Decreases HR - reaches threshold slower
- ex) Ach
Ectopic Foci
Areas outside the SA node that may spontaneously depolarize and are capable of pacing the heart. ORDER:
- SA node
- Junctional area of the AV node
- Bundle of His
- Purkinje fibers
- Ventricular muscle
Sinous rhythm
paced by the SA node.
heart is paced by the SA node because it has the highest free potential slope
Av node slows down impulse so that
the atria have time to fill the ventricles before ventricular stimulation
R and L bundle branches
- bundle of Purkinje fibers
- depolarize the ventricle quickly
- do not Innervate every cell. terminate close to endocardium and gap junctions spread rest from muscle cell to muscle cell
- R is uniform
- L gives off septal branch, anterior fascicle, posterior fascicle
