2 - Cardiac Contraction Flashcards
Na+
sodium
extracellular = 135-145 mEq/L
RMP intracellular = 14 mEq/L
K+
potassium
extracellular = 3.5 - 5.0 mEq/L
RMP intracellular = higher than extracellular, 140?
What does the positive ion concentration gradient result in (RMP)?
positive ion concentration gradient frominsidethe membrane to theoutside causes electronegativity inside the membrane
*nondiffusable, negative ions left inside
Most important ions involved in membrane potentials of nerve and muscle cells…
Na+, K+ & Cl-
-determines voltage of membrane potential
Cl-
chloride
96-106 mEq/L
during RMP, more extracellularly than intracellularly
What prevents all potassium from leaving intracellular compartment during RMP?
electrostatic force
-as more K+ leaves (chemical force), negative forces on inside increase and trap K+ (electrostatic)
Nernst Equation
- The diffusion potential level across a membrane that exactly opposes the net diffusion of a particular ion through the membrane is called theNernst potentialfor that ion-
- electric potential vs. chemical potential
Does any Na+ enter cell during RMP?
yes, small but finite leakage, depolarizing effect
Goldman Equation
- calculates membrane potential
- need Na+, K+ and Cl- involved
Normal nerve fiber permeability to K+ vs Na+
-the permeability of the membrane to potassium is about 100 times as great as to sodium
Action Potential: Activation Gate
- activated at -70, -50 mV
- flips open, allows Na+ to rapidly flow inward
- same conformational change will close gates, just not as quickly
Depolarization Stage
- sudden permeability of Na+ ions
- polarity is neutralized as positive ions rush inwards
Repolarization Stage
- 10,000th of a second
- Na+ channels begin to close and K+ channels open, reestablishing resting membrane potential
Fast Response Action Potentials
Atrial myocardial fibers
Ventricular myocardial fibers
Purkinje fibers
Slow-Response Action Potentials
Sinoatrial node
Atrioventricular node
*generated by pacemaker cells - automaticity
Autoarhythmic Cell
pacemaker cell, slow-response AP
Fast Response Cells
- not automaticity cells
- other cardiac myocytes
Channels of Action Potential in Cardiac Muscle Cells
- ) Voltage activated, fast sodium channels
2. ) L-type calcium channels (slow calcium channels)
(RMP) Relative to the outside of a cell is the inside positive or negative in charge?
negative charge
(RMP)2. Is potassium higher in concentration inside or outside of a cardiac muscle cell?
inside the cell
(RMP) Is sodium higher in concentration inside or outside of a cell?
outside the cell
(RMP) What prevents potassium from leaking out of a cell until the concentration is the same on the outside and inside of the cell?
electrostatic force
-chemical force makes k want to leave, but electrostatic prevents
(RMP) What ion makes the major contribution to the resting membrane of the cardiac muscle cell?
Potassium
(RMP) What ion makes a small contribution to the resting membrane potential?
Sodium
(RMP) What ion pump returns ion concentrations back to baseline?
Na+, K+ ATPase pump
(RMP) How does the Na+-K+ - ATPase pump contribute to the resting membrane potential?
3 Na+ to outside of cell
2 K+ into cell
ATP –> ADP
-electrogenic active transport
(AP) What ion moves rapidly into a cell during depolarization?
Sodium
(AP) What ion exits the cell to restore the baseline electrical charge in a cell during repolarization?
Potassium
(AP) What restores ion concentrations back to their baseline levels?
Na+, K+, ATPase pump
(EA) In what part of the heart are Fast-Response Action Potentials (non-pacemaker action potentials) found?
Atrial myocardial fibers, ventricular myocardial fibers, purkinje fibers
(EA) In what part of the heart are Slow-Response Action Potentials (pacemaker action potentials) typically found?
SA
AV
Bundle of His
(EA) What are some of the differences between Non-pacemaker and Pacemaker action potentials
non-pacemakers: 5 phases
RMP = -90 mV --> 20 mV
depolarize quicker
pacemaker: 3 phases
RMP = -65 mV --> 10 mV(EA) Describe Phase 0 for fast-response/non-pacemaker cells…
Phase 0: depolarization (sodium channels open and change the resting potential of membrane from negative to positive +20 pretty fast
(EA) Describe Phase 1 for fast-response/non-pacemaker cells…
Phase 1: Partial Repolarization, sodium channels close, potassium channels open and potassium goes out, making the inner membrane negative
(EA) Describe Phase 2 for fast-response/non-pacemaker cells…
Phase 2: Plateau; fast potassium channels close, calcium channels open allowing for some repolarization and the action potential then plateaus due to permeability to sodium and decreased permeability to potassium
(EA) Describe Phase 3 for fast-response/non-pacemaker cells…
Phase 3: rapid repolarization: calcium channels close and slow potassium channels open, potassium leaves the cell and membrane potential goes back to negative resting level
(EA) Describe Phase 4 for fast-response/non-pacemaker cells…
Phase 4: restoration of ionic gradients, return to resting membrane potential
Release of a large amount of calcium from the Sarcoplasmic Reticulum is triggered by entry of which ion?
calcium
-blocks tropomysin, allows myosin head to meat with actin
What is the function of the Sarcoplasmic Reticulum within a cardiac muscle cell?
regulated intracellular calcium concentration
Which ion is the major determinant of the Resting Membrane Potential in Cardiac cells?
potassium
What are the phases of Slow Response (Pacemaker) Cells?
Phase 4
Phase 0
Phase 3
Slow Response (Pacemaker) Phase 4
Phase 4: Sodium channels open, slow influx of sodium comes in membrane potential slowly starts to depolarize
Slow Response (Pacemaker) Phase 0
Phase 0: depolarization calcium channels open, calcium comes in so membrane potential is +10
Slow Response (Pacemaker) Phase 3
Phase 3 repolarization: calcium channels close, potassium channels open (sodium channels are still open but there is more k leaving than sodium coming in)
What are the different refractory periods associated with the cardiac action potentials
(ERP) Effective Relative period (no action potential can happen)
(RRP) refractory relative period
Automaticity
ability that pacemaker cells have to launch their own action potential stimuli
What is diastolic depolarization?
- atrial-nodal action potential is slower to develop than ventricular muscle action potential.
- d/t movement of oins
What effects on aspects of diastolic depolarization will cause changes in heart rate?
autonomic nervous system
Which pacemaker region of the heart is typically dominant
SA node
What is Overdrive Suppression
SA node fires quickest, other pacemaker cells do not fire as well
What is a sarcomere?
Segment between the two Z lines represents the contractile unit, the sarcomere.
Cardiac cells are arranged in a branching network that is known as what
Functional syncytium
What are T-tubules in a cardiac muscle cell?
T- tubules are deep invaginations in the sarcolemma membrane
Permits ion exchange between extracellular and intracellular compartments to occur deep in the myocyte during depolarization and repolarization.
What is the Sarcoplasmic Reticulum?
Extensive branching network that surrounds the myofilaments, activated by influx of calcium from interstitial fluid during action potential and releases more calcium.
What is this process called whereby large amounts of calcium are released from the Sarcoplasmic Reticulum into the cell
CICR
Calcium Induced Calcium Release
The presence of what ion allows binding between actin and myosin
Calcium
What is the function of Troponin in the binding between actin and myosin
At resting state, inhibits binding of actin and myosin
