Cardiovascular anatomy & physiology Flashcards
Identify the statements that BEST describe ventricular myocytes. (select 3)
a. hyperkalemia increases threshold potential
b. they contain more mitochondria than skeletal myocytes
c. T-tubules spread the wave of depolarization throughout the myocardium
d. resting membrane potential is -90 mV
e. sodium conductance is greater than potassium conductance at rest
f. hypokalemia decreases resting membrane potential
b. they contain more mitochondria than skeletal myocytes
d. resting membrane potential is -90 mV
f. hypokalemia decreases resting membrane potential
________________ initiate and propagate action potentials that trigger a coordinated myocardial contraction.
Myocardial cells
_______________ is the ability to generate an action potential spontaenously.
Automaticity
______________ is the ability to respond to an electrical stimulus by depolarizing and firing an action potential.
Excitability
Cardiac myocytes contain
contractile elements (actin & myosin myofilaments)
_______________- is the difference in electrical potential between the inside and outside of the cell.
The resting membrane potential (RMP)
__________________ is the voltage change that must occur to initiate depolarization.
Threshold potential
______________ is the movement of a cell’s membrane potential to a more positive value.
Depolarization
______________ is the return of a cell’s membrane potential towards a more negative value after depolarization
Repolarization
_______________ is the movement of a cell’s membrane potential to a more negative value beyond the baseline RMP
Hyperpolarization
When serum K+ decreases, RMP becomes more
negative. making the myocytes more resistant to depolarization
In excitable tissue, the primary job of the sodium-potassium ATPase is to
restore the ionic balance towards resting membrane potential
When serum K+ increases, RMP becomes more
positive, making the myocytes depolarize more easily
Severe hyperkalemia can
block depolarization
What facilitates the spread of a cardiac action potential throughout the myocardium?
gap junctions
__________ describes the situation when there is no net movement of an ion across a cell membrane.
Equilibrium potential
_________ is the ability to transmit electrical current
Conductance
____________ describes the force of myocardial contraction during systole.
Inotropy
_____________ describes the heart rate
Chronotropy
________________describes conduction velocity through the heart
Dromotropy
_________ describes the rate of myocardial relaxation during diastole.
Lusitropy
The primary determinant of threshold potential is
Serum Ca2+
What are the two purposes that the Na-K+ ATPase pump serves?
it removes the Na+ that enters the cell during depolarization
it returns K+ that has left the cell during repolarization
The primary determinant of resting membrane potential is
serum K+
How does hypercalcemia affect the cell?
the threshold potential becomes more positive
the cells become more resistant to depolarization
Resting membrane potential is established by what 3 mechanisms?
- chemical force
- electrostatic counterforce
- sodium/potassium ATPase
Which phase of the ventricular action potential is associated with the GREATEST calcium conductance?
a. 1
b. 2
c. 3
d. 4
b. 2
Unlike neurons, the cardiac myocyte’s action potential has a _____________
plateau phase where depolarization is prolonged
The plateau phase gives the cardiac myocytes time
to contract
The myocyte action potential consists of
5 phases: phase 0, 1, 2, 3, and 4
Describe phase 0.
depolarization: Na+ in
Describe phase 1.
initial repolarization: Cl- in and K+ out
Describe phase 2.
Plateau: Ca2+ in and K+ out
Describe phase 3.
Repolarization: K+ out
Describe phase 4.
maintenance of transmembrane potential: K+ out and Na/K-ATPase function
These parts of the heart do not have a plateau phase
the SA & AV node
Which current is responsible for spontaneous phase four depolarization in the SA node?
a. I-Na
b. I-K
c. I-Ca
d. I-f
d. I-f
Describe the cardiac conduction system.
SA node–> internodal tracts–> AV node–> bundle of His–> left & right bundle branches–> Purkinje fibers
The heart rate is determined by the
intrinsic firing rate of the SA node & autonomic tone
_____________ depress the automaticity of the SA node which explains why these drugs can cause a junctional rhythm.
Volatile anesthetics
________________ of the SA node impairs its function as the dominant pacemenaker
Disease or hypoxia
If disease or hypoxia of the SA node occurs, the cells with __________________________ will assume the pacemaker responsibility.
the next highest rate of spontaneous phase 4 depolarization
The SA & AV node action potential consists of
3 phases
The 3 phases of the SA & AV node AP include
Phase 4= spontaneous depolarization : Na+ in (I-f) and then Ca2+ in (t-type)
Phase 0= depolarization: Ca2+ in (L-type)
Phase 3= repolarization: K+
Physiologically, we can increase the heart rate by
increasing the rate of phase 4 spontaneous depolarization and or/bringing RMP and TP closer together
At rest, ______ tone exceeds __________ tone in the heart
PNS; SNS
The PNS tone for the heart is the
vagus nerve- innervates the SA node (right) and left vagus innervates the AV node
The SNS tone for the heart is the
cardiac accelerator fibers (T1-T4)
