Week 2 Electrical Conduction Flashcards
Relative to the outside of a cell, is the inside positive or negative in charge?
The inside of the cell is negative
Is potassium higher in concentration inside or outside of a cardiac muscle cell?
It higher inside the cell
Intracellular: K = 140mEq/L
Extracellular: K = 4mEq/L
Is sodium higher in concentration inside or outside the cell?
Outside the cell
Intracellular: Na = 14mEq/L
Extracellular: Na = 142mEq/L
What prevents potassium from leaking out of a cell until the concentration is the same on the outside and inside of the cell?
Chemical driving force is eventually balanced by electrical driving force so no further net movement of potassium
What does the Nernst Equation calculate?
*Equilibrium potential
The electrical potential (amount of build-up of negativity on inside of cell membrane) that equals the chemical driving force
What ion makes the major contribution to the resting membrane potential of the cardiac muscle cell?
Potassium
What ion makes a small contribution tot he resting membrane potential?
Sodium
What ion pump returns ion concentrations back to baseline?
Na+ K+ - ATPase Pump
How does the Na+, K+ -ATPase pump contribute to resting membrane potential?
The pump is powered by ATP and moves 3 Na ions out of the cell, and 2 K ions into the cell
What ion mines rapidly into a cell during depolarization?
Sodium
What ion exits the cell to restore the baseline electrical charge in a cell during repolarization?
Potassium
What restores ion concentrations back to their baseline levels?
ATPase pump
In what part fo the heart are fast-response action potentials (non-pacemaker action potentials) found?
They are found in fibers
- atrial myocardial fibers - ventricular myocardial fibers - purkinje fibers
In what part of the heart are slow-response action potentials (pacemaker action potentials) typically found?
Slow response are nodes
- sinoatrial node - atrioventricular node
What are some differences between non-pacemaker and pacemaker action potentials?
Pacemaker (nodes) resting membrane potentials are higher than non-pacemaker (fast)
There is no phase 1 in slow response action potential
-they also start at a higher voltage: -60 or -70, rather than -90
What makes the potassium move intra-cellular to extra-cellular
Concentration gradient
As potassium moves outside the cell, what happens to the charge of the cell?
The cell becomes negatively charged
It’s a membrane potential bc the potassium has left behind a negatively charged anion, and it makes the potassium what to come back into the cell
Concentration gradient is driving K out, and a negative membrane potential drives the potassium to want to be back inside
What is equilibrium potential for potassium
When the amount of K moving out of the cell is equal to the amount of K moving into the cell
Almost no difference of the movement of potassium
What is chemical gradient?
Concentration difference
This exists for K+ to diffuse out of the cell.
The opposite is found for Na+ and Ca++, their chemical gradient favors inward diffusion.
What is equilibrium potential?
The membrane potential that is necessary to oppose the outward movement of K+ down its concentration gradient
What is equilibrium potential?
The potential difference across the membrane required to maintain the concentration gradient across the membrane
*represents the electrical potential necessary to keep K+ from diffusing down its chemical gradient and out of the cell
What is resting membrane potential?
It’s determined by the concentrations of positively and negatively charged ions across the cell membrane, the relative permeability of the cell membrane to those ions, and the ionic pumps that transport ions across the cell membrane
What is depolarization?
When a cell becomes less negative
What is repolarization?
When a cell becomes more negative
What is fast action potential?
Phase 0
Because it happens so rapidly
What are the 5 phases of the non-pacemaker (fast-response) action potential?
- Phase 0: depolarization
- Phase 1: partial repolarization
- Phase 2: plateau
- Phase 3: repolarization
- Phase 4: resting membrane potential
What is phase 0 of fast response action potential?
Sodium channels open, and rapid inward movement of Na+ causes the cell to rapidly depolarize.
What is phase 1 of fast-response action potential?
- inactivation of Na+ channels
- beginning of outward movement of K+ bc too positive inside the cell
- initial repolarization
What is phase 2 of fast-response action potential?
- plateau phase
- the slow inward movement of Ca++ counterbalances the outward K+ current
- this delays repolarization and prolongs the absolute refractory period
- the long plateau produces a long action potential to ensure a forceful contraction of substantial duration
What happens with calcium-induced calcium release?
The small amount of Ca++ that enters the cells when depolarizer is small, but this triggers the release of a large amount of Ca++ into the cytosol from the sarcoplasmic reticulum with results in binding of myosin to actin and contraction of the myocyte
*calcium increases contractility
What is phase 3 of fast-response action potential?
- continued outward current of K+ is responsible for repolarization
- Na+ channel recovery period begins during relative refractory period
What is the relative refractory period?
The period shortly after the firing of a nerve fiber when partial repolarization has occurrred and a greater than normal stimulus can stimulate a second response
What is absolute refractory period?
The period immediately following the firing of a nerve fiber when it cannot be stimulated no matter how great a stimulus is applied
What is phase 4 of fast-response action potential?
- back to baseline
- restoration of ionic gradients
- Na+ K+ ATPase pump helps make this happen
What is another name for phase 2 in non-pacemaker cells?
Plateau phase
Release of a large amount of calcium from the sarcoplasmic reticulum is triggered by the entry of which ion?
Ca++
What is the function of the sarcoplasmic reticulum within a cardiac muscle cell?
Stores Ca++ ions
What ion is the major determinant of the resting membrane potential in cardiac cells?
Potassium
What are the various phases found in pacemaker (slow response) action potentials?
- phase 0
- phase 2
- very brief
- phase 3
- not separated clearly from phase 2
- phase 4
What phase from the fast response action potential is missing in the slow response action potential?
Phase 1
What is phase 0 of slow response action potential?
Depolarization mainly by influx of Ca++
What is automaticity?
The ability of a focal area of the heart to generate pace making stimuli
What is the heart’s dominant pacemaker?
SA node
AKA sinus node
What is diastolic depolarization?
-influx of Ca++
If you decrease the influx of Ca++, it will decrease automaticity
Slow diastolic depolarization requires more time to reach threshold
What effects on aspects of diastolic depolarization will cause changes in heart rate?
If you slow influx of Ca++, you will decrease automaticity
What pacemaker region of the heart is typically dominant?
SA node
What is overdrive suppression?
This mechanism causes the secondary pacemaker to become hyperpolarized when driven at a rate above it’s intrinsic rate?
This is due to Na+ K+ ATPase
What are the intrinsic rates of the various pacer areas of the heart?
SA node: 60-100
Atrial Foci: 60-80
Junctional Foci: 40-60
Ventricular Foci: 20-40
What is a sarcomere?
A bundle of myofilaments
- the basic contractile unit
- Contain:
- thin filaments which contain actin
- thick filaments which contain myosin
Cardiac cells are arranged in a branching network that is known as what?
Functional syncytium
What are T-tubules in a cardiac muscle cell?
- part of the external sarcolemma (cell membrane of a striated muscle fiber cell)
- open to the external environment of the cell which permissions to exchange between extracellular and intracellular compartments
What is the sarcoplasmic reticulum?
- extensive branching, tubular network that surrounds the myofilaments
- primary function is to regulate intracellular calcium concentrations
What is excitation-contraction coupling?
The process by which an influx of CA++ from the interstitial fluid during action potential triggers the release of calcium by the sarcoplasmic reticulum initiating the mechanism of muscle contraction
- Ca++ binds to Troponin-C
- myosin head bind to active
- requires ATP
- reduces sarcomere length
- muscle contracts
What triggers the for release of large amounts of calcium from the sarcoplasmic reticulum?
Influx of CA++ from the interstitial fluid during AP
What is the process called whereby large amounts of calcium are released from the sarcoplasmic reticulum?
Calcium-induced calcium release (CICR)
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
Troponin helps hold tropomyosin on the actin filament. For a muscle contraction to occur, troponin and tropomyosin must be moved to reveal the myosin-binding sites. Calcium triggers movement of these proteins. When calcium binds to troponin, the shape of the troponin molecule changes
What is the sliding filament model?
The myosin muscle fibers slide past the actin filaments during muscle contraction, while the two groups of filaments remain relatively constant in length
Is ATP required for cardiac muscle relaxation?
Yes.
CA++ is removed from troponin-C, and myosin unwinds from actin
*this allows the sarcomere to resume its original relaxed length
