Unit 3 Cardiac 1: Anatomy & Physiology Flashcards
Cardiac myocytes have skeletal muscle properties as well as neural tissue properties:
Like skeletal muscle:
Like Neural tissue:
Just cardiac myocytes:
Like skeletal muscle:
-actin and myosin myofilaments
-capable of contraction
-T-tubule system and SR work to maintain Ca+2 homeostasis for contraction and relaxation
Like Neural tissue:
-generates a RMP
-can initiate an action potential
-can propagate an action potential
Just cardiac myocytes:
-tight junctions serve as low resistance pathways to help spread cardiac potential
-cardiac myocytes contain more mitochondria than skeletal muscle
Define automaticity
The ability to spontaneously generate an action potential
Define excitability
The ability to respond to an electrical stimulus by depolarizing and firing an action potential
What is conductance?
Because of their charge, ions do not freely pass through cell membrane. Instead, an ion requires an open channel to cross from one side of the membrane to the other. An open channel increases the conductance of that ion, while a closed channel reduces conductance of that ion.
Define chronotropy
Heart rate
Define inotropy
Strength of contraction (contractility)
Define dromotropy
Conduction velocity (how fast the action potential travels per time)
Define lusitropy
Rate of myocardial relaxation (during diastole)
What is equilibrium potential?
Equilibrium is achieved when there is no concentration gradient and therefore no net flow of ion across the cell membrane.
What equation can be used to calculate an ion’s equilibrium potential?
Nernst equation
E ion = -61.5 log ([Ion] inside / [ion] outside)
What is resting membrane potential? What 3 mechanisms establish RMP?
The difference in electrical potential between the inside and outside of the cell. The inside is negative relative to the outside.
- Chemical force
- Electrostatic counterforce
- Sodium/potassium ATPase
What is threshold potential?
The internal voltage at which the cell depolarizes
What is depolarization?
Depolarization takes place when there is a reduced polarity across the membrane. In excitable tissue, it results in an action potential
What is hyperpolarization?
Hyperpolarization takes place when there is an increased polarity across a membrane.
What is repolarization?
The restoration of a membrane potential towards resting membrane potential following depolarization
What ion is the myocyte permeable to? What does this mean?
Potassium.
The cell continuously leaks potassium losing positives charges, why inside the cell is negative.
Explains why K+ is the primary determinant of RMP
What happens to RMP when K+ decreases? Increases?
Decreases: RMP becomes more negative, and the myocytes become more resistant to depolarization.
Increases: RMP becomes more positive and myocytes depolarize more easily.
Explain what happens to Na+ permeability with RMP approaches threshold potential
Voltage-gated sodium channels open and sodium conductance increases, this depolarizes the cell.
How much Na and K are exchanged by the Na/K pump?
For every 3 Na+ ions it removes it brings 2 K+ ions into the cell
What type of mechanism is the Na/K pump? What does it require?
An active transport mechanism
It requires ATP
What makes the action potential for ventricular muscle unique?
A plateau phase where depolarization is prolonged, giving cardiac myocytes more time to contract, so the heart has enough time to eject its SV.
What are the 2 purposes of the Na/K pump?
- Remove the Na+ that enters the cell during depolarization
2. Return the K+ that left the cell during repolarization
List the 5 phases of the ventricular action potential and describe the ionic movement during each phase.
Phase 0: depolarization -> Na+ influx Phase 1: initial repolarization -> K+ efflux & Cl- influx Phase 2: Plateau -> Ca+2 influx Phase 3: Repolarization -> K+ efflux Phase 4: Na+/K+ pump restores RMP
Events in phase 0 of ventricular action potential
Phase 0: Upstroke
Threshold potential at -70 mV -> depolarization
Activation of fast voltage-gated Na+ channels -> Na+ in
Slope indicates conduction velocity
Events in phase 1 of ventricular action potential
Phase 1: Initial Repolarization Inactivation of Na+ channels Cell becomes slightly less positive -K+ channels open -> K+ out -Cl- channels open -> Cl- in
Events of Phase 2 of ventricular action potential
Phase 2: plateau
Activation of slow voltage-gated Ca+ channels counters loss of K+ ions to maintain the depolarized state. -> Ca+ in
Delays repolarization
Maintains fast Na+ channels in inactivated state
Prolongs the absolute refractory period
Sustained contraction is necessary for the heart’s pumping action
Events of phase 3 of ventricular action potential
Phase 3: Final Repolarization K+ channels open -> K+ out K+ leaves the cell faster than Ca+ enters -> repolarization Slow Ca+ channel deactivate Restores transmembrane potential to RMP
