Cardio- Airey (electrophys) Flashcards
K+ wants to ___ the cell, while Na+ and Ca+ want to ___ the cell
K+ wants to LEAVE, Na+ and Ca+ want to ENTER
at resting membrane potential (-70mV) …K+ and Cl- conductance is ____ due to ______ while Na+ conductance is _____ due to _____
K+ and Cl- : high, conc. gradient and open channels
Na+: low, no open gates, no inward current
______remain closed until the membrane is repolarized back to the resting membrane potential (responsible for the refractory period).
inactivation gates
inner side of the cell membrane- gate
At the end of the depolarization the ___ channels ____ which causes an outward current of _____ (makes the inside more negative). This in combination with the _____ ends the upstroke of the action potential.
K + , open
K+
closure of the inactivation gate
what is accommodation in terms of membrane potential?
when the usual threshold level is passed but no action potential is produced
Happens when depolarization closes Na channel inactivation gates.
Example: hyperkalemia.
contractile vs conducting cells of the heart
Contractile cells:
Muscle of atria and ventricle
Axn potentials in these cause contraction
Conducting cells:
Tissue of the SA node, atrial internodal tracts, AV node, bundle of His, and the Perkinje system
Function to rapidly spread action potentials over the entire myocardium
Can generate spontaneous action potentials
what is the sequence of electric energy through the heart? starting at the SA node…
SA node–>atrial internodal tract–>AV node–>Bundle of His/Purkinje system
SA node vs AV node function
SA node- pacemaker
AV node- slows impulse before bundle of his
Neuro vs Cardiac axn potential
cardio: need sustained force to move blood (need Ca+ )
- Ca+ will bind to troponin to remove inhibition from tropo-myosin of sarcoplasmic reticulum (stored and released for excitation)
cardio axn potential sequence: phase 0 - 4
for atria, ventricles and purkingje system
0: upstroke: Na+ in to depolarize
1: initial repol: inactive gates close, K+ out
2: plateau: stable depol (Ca+ in balancing K+ out)
3: repol: Ca+ channels close, K+ works harder
4: resting membrane potential: NET zero current flow (all balanced, K+ out, Ca+ and Na+ in)
what is Ca+ induce Ca+ release?
inward current of Ca+ in cardiac action potential initiates MORE Ca+ release from storage for MORE muscle contraction
characteristics of axn potential for atria, purkinje and ventricles
axn potential:
- long duration
- plataeu
- STABLE resting membrane potential
- use Ca+
characteristics of axn potential for SA and AV nodes
axn potential:
- automaticity
- UNSTABLE resting membrane potential
- use Ca+
cardio axn potential sequence for SA: 0-4
0: upstroke: Ca+ inward
3: repol: net ouward current by K+ outward
4: spontaneous depol: opening of “funny” Na+ channels
the rate of phase 4 of SA node axn potential sets….
the HR
2 types of refractory periods
- absolute refractory period: no stimulus can activate another action potential (channels SHUT)
- effectory refractory period: Na open but not enough to make conductive axn potential
- relative refractory: phase 3, when fall below threshold but not to normal- bigger than normal stimulus = signal!
when is the supranormal excitatory period?
after relative refractory period and before the next absolute RP – a short period when a weak stimulus can evoke a response. Many arrhythmias develop here.
what is excitation-contraction coupling?
(Ca+ induced Ca+ release)
= is the process by which an electrical stimulus triggers the release of Ca+ by the sarcoplasmic reticulum, initiating muscle contraction by sarcomere shortening
when does relaxation occur in the cardiac cell ?
when Ca2+ is reaccumulated in SR by Ca2+ -ATPase
what does Ca+/Na+ exchanger do in cardiac muscle for excitation-contraction coupling?
uses energy from inward Na gradient to send calcium back out of the cell, to account for the inward flow during plateau phase.
contractility relates to the ______ concentration. therefore the larger ____ current…
Contractility relates to the intracellular Ca2+ concentration
Therefore, the larger the inward Ca2+ current the greater the contractility.
Cross-bridge cycling continues as long as intracellular____ concentration is high enough to occupy the ____ binding sites.
Ca2+
ANS effect on the nodes…. chronotropic vs dromotropic vs inotropic effects..
Chronotropic = change heart rate- SA node Dromotropic = change velocity- AV node Inotropic = change contractility
sympathetic effect on the SA node: what receptor is on the SA node? what effects occur? what meds to counteract?
pos. chronotropic effects (inc. HR)
-B1 receptor on SA node
-increase funny (If) conductance of Na+ (inc. rate of depol)
-increase Ca2+
(BB or CCB to slow HR)
