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)
what do parasympathetic fiber activation do in the heart?
Ach activate M receptors in SA node.
- decrease “funny” Na+ conductance (dec. rate of phase 4 depol)
- inc. K-Ach (hyperpol.)
- dec. Ca2+ conductance
In the SA node the rate is controlled by the _____; in the AV node the rate is controlled by ________ (in terms of axn potential graphs)
SA: slope of phase 4
AV: slope of phase 0 (velocity of the conduction of the axn potential)
ANS on AV node: more Ca+ that enters… the ____ the conduction velocity
more inward current, faster
*sympathetic inc. conduction through AV node
sympathetic vs parasympathetic response on AV node
symp: refractory period is shorter (inc. Ca2+ in)
parasymp: effective refractory period is longer (dec. Ca2+ in, inc. K+ out)
does parasympathetic work on the atria, ventricles or both?
atria only
cardiac cycle: A : what is happening? EKG shows? heart sounds? murmur here would mean?
Atrial Systole (Still Ventricular Diastole): Atria contract, Final phase of ventricular filling
EKG: P wave, PR interval
Heart Sounds: 4th heart sound (S4)
Murmur: Mitral stenosis
cardiac cycle: B: what is happening? EKG shows? heart sounds?
Isovolumetric ventricular contraction (start of systole)
EKG: QRS complex
Heart Sounds: 1st heart sound (S1), AV valves closing
cardiac cycle: C : what is happening? EKG shows? heart sounds? murmur here would mean?
Rapid Ventricular Ejection (systole proper)
EKG: ST segment
Heart Sounds: Systolic click
Murmur: Aortic stenosis OR Mitral regurgitation
cardiac cycle: D : what is happening? EKG shows? heart sounds?
Reduced ventricular ejection: Ventricles slow down their emptying of blood. Aortic pressure begins to fall as blood runs off into arteries. Ventricles starting to repolarize
EKG: T- wave
Heart Sounds: None
cardiac cycle: E : what is happening? EKG shows? heart sounds?
Isovolumetric ventricular relaxation
EKG: Nothing
Heart sounds: 2nd heart sound (S2)
Closing of Aortic and Pulmonary valves
cardiac cycle: F : what is happening? EKG shows? heart sounds? murmur?
Rapid ventricular filling: Mitral valve opens when pressure is A>V. Ventricles fill passively with blood from atria
EKG: Isometric before the P wave
Heart Sounds: Opening snap. 3rd heart sound (S3)
Murmurs: none
cardiac cycle: F : what is happening?
Reduced Ventricular Filling
Ventricles relaxed
Final phase of ventricular filling
murmur vs heart sounds
murmur: turbulent flow
Heart sounds: NOT from blood going through an abnormal opening
-Made from blood flow: S3 and S4
-Made from valves
diastolic vs systolic heart sounds
made from valves…
Diastolic: Opening snap – stenotic mitral valve
Systolic: Early ejection sounds - valve problem. Clicks – MVP (mitral valve prolapse)
systolic left side, forward flow murmur
aortic stenosis
if it was ride side, would be pulmonary stenosis
systolic left side, backward flow murmur
mitral regurg
if it was right side, would be tricuspid regurg
diastolic left side, forward flow murmur
aortic regurg
if it was right side, would be pulmonary regurg
diastolic left side, backward flow murmur
mitral stenosis
if it was right side, would be tricuspid stenosis
The deflections on the ekg represent ______, not ________.
electrical activity, not muscle contraction
