Electrical Activity of the Heart - Quiz 2 Flashcards
The oustide of the cell is _______ charged relative to the inside of the cell which is _______ charged.
Positively, Negatively
Is concentration of Potassium higher inside or outside the cell
Inside
Is sodium concentration higher inside or outside the cell?
Outside
What stops potassium from leaking out of cell when concentration K+ is the same inside and outside?
Electrostatic force - the negativity inside the cell
What does the Nernst Equation calculate?
Equilibrium Potential
Chemical Force = Electrostatic Force
(Of Potassium)
Goldman Equation
Membrane Potential when Na, K, and Cl are involved
What ion contributes the most to the resting membrane potential of the cardiac cell?
Potassium
What ion makes a small contribution of the resting membrane potential?
Sodium
The ion pump that returns ion concentrations back to baseline in resting membrane potential?
Na+, K+ ATPase
Sodium/Potassium-ATP Pump
- Steady inward leak of Na+ would depolarize cell
- Metabolic pump, pumps out Na from cell and pumps in K+
- Pumps OUT 3 Na+ and Pumps IN 2 K+
- Electrogenic Pump
- Partially inhibited by digitalis
What ion moves rapidly into a cell during depolarization?
Sodium
How is the baseline electrical charge restored during cell repolarization?
Potassium channels open and rapid diffusion of potassium to exterior reestablishes normal resting membrane potential
Where are the Fast-Response Action Potentials located?
Atrial Myocardial Fibers
Ventricular Myocardial Fibers
Purkinje Fibers
Where are the Slow-Response Action Potentials?
SA & AV Node
Differences between Fast and Slow Cardiac Action Potentials
- Resting Membrane Potential: Slow > Fast
- Slope of Upstroke: Fast > Slow
- Amplitude of Action Potential: Fast > Slow
- Overshoot of Action Potential: Fast > Slow
Phases of Fast Response Action Potential
Phase 0: Depolarization
Phase 1: Partial Repolarization
Phase 2: Plateau
Phase 3: Repolarization
Phase 4 Resting Membrane Potential
Phase 0 (Fast Response)
Depolarization - fast sodium channels open - rapid influx of sodium (+20 mv)
Phase 1 (Fast Response)
Initial Repolarization - fast sodium channels close - potassium leaves cell through open potassium channels
Phase 2 (Fast Response)
Plateau - L-type calcium channels open. Ca+ entering is equal to K+ leaving
This entry of this small amount of ion into the cell triggers release of a large amount of calcium into the sarco plasmic reticulum.
Calcium through the L-type calcium channels
What happens when a large amount of calcium leave the sarcoplasic reticulum
Calcium binds with Troponin-C
Myosin binds to actin and contraction of the myocyte
Which ion is the major determinant of the Resting Membrane Potential?
Potassium
Phase 3 (Fast Response)
Rapid Repolarization - calcium channels close and potassium channels open.
Potassium exits cell, ending plateau phase and returns cell membrane to resting level.
Phase 4 (Fast Response)
Restoration of Ionic Concentrations
- Na+, K+-ATPase
- Na+-Ca++ Exchanger
- ATP-driven Ca++ Pump
Phases of Slow Response (Pacemaker) Action Potential
Phase 4: Cations from adjacent cell
Phase 0: Calcium Influx
Phase 2: very brief plateau phase
Phase 3: Repolarization: Ca+ channels close and Lots of K+ leaves
Effective Refractory Period
Absolute Refractory Period - impossible for another action potential to triggered
Relative Refractory Period
Period where an action potential can be triggered if the stimulus is large/strong enough
Automaticity
Ablity of a focal area of the heart to generate pacemaking stimuli
What is the heart’s dominate pacemaker
SA Node
Where does the depolarization wave flow from the SA node?
In all directions
Diastolic Depolarization
- Inward Na+ - via funny sodium channels
- Ca++ Influx
- K+ Efflux
What effects on aspects of diastolic depolarization will cause changes in heart rate
Neurotransmitters
Norepi, acetylcholine, succinylcholine, T1-T4 cardiac accelerators
Overdrive Supression
Sinus node controls beat of heart because its discharge is faster than any other part of the heart.
Automaticity of pacemaker cells become depressed after a high frequency of excitation
- Due to Na+, K+-ATPase
- More Na+ is forced out than K+ entering at higher heart rates - hyperpolarize
- Slow diastolic depolarization needs more time to reach threshold
What is a sarcomere?
Structural unit of striated muscle tissue between two Z-lines
The name of the branching network that cardiac cells are arranged in
Intercalated Discs
T-Tubules
Extensions of cell membrane that penetrate into the center of skeletal and cardiac muscle cells
- Open to exterior of muscle fiber - can communicate with fluid surrounding muscle fiber
Sarcoplasmic Reticulum
Membrane bound structure in muscle cells that store and regulate calcium movement
What is the process called when large amounts of calcium are released form the Sarcoplasmic Reticulum into the cell?
Calcium-Induced Calcium Release (CICR)
What ion allows binding between actin and myosin?
Calcium
Function of Troponin
Inhibit Actin and Myosin From Binding
- Calcium binds to Troponin C - conformational change
- Myosin heads bind to actin leading to cross-bridge movement and shortens sarcomere
- Calcium goes back to SR
- Calcium is removed from Troponin-C and myosin unbinds from actin
Function of ATP in the heart
ATP needed for crossbridge movement, muscle shortening (contraction), and muscle relaxation
Excitation Contraction Coupling
Coupling between myocyte actional potentials and contraction
Sliding Filament Model
Mechanism of muscle contraction
Myosin (thick) filaments slide past actin (thin) filaments during muscle contraction
