Cardiac AP Flashcards
How is cardiac muscle like skeletal muscle? (3)
contains actin and myosin myofilaments
capable of contraction
T-tubule system and the SR work to maintain Ca++ homeostasis for contraction and relaxation
How is cardiac muscle NOT like skeletal muscle? (2)
Tight junctions serve as low resistance pathways that help spread the cardiac action potential throughout the myocardium.
(Tight junctions are also called gap junctions or nexi)
cardiac myocytes contain more mitochondria than skeletal muscle cells.
How is cardiac muscle like neural tissue? (3)
It generates resting membrane potential
It can initiate an action potential.
It can propagate an action potential
What is automaticity?
The ability to spontaneously generate an action potential
What is excitability?
The ability to respond to an electrical stimulus by depolarizing and firing an action potential.
What is conductance?
Ions require an open channel to cross from one side of the membrane to the other. An open ion channel increases the conductance of that ion, while a closed channel reduces conductance of that ion.
What equation can be used to predict an ion’s equilibrium potential?
Nernst equation
When is equilibrium of the cardiac cells reached?
Equilibrium is achieved when there is no concentration gradient and therefore no net flow of ion across the cell membrane. The charge inside the membrane balance the charges on the outside of the membrane.
What is the Nernst equation?
E Ion = -61.5 log ( [Ion] inside / [Ion] outside )
What is RMP?
The difference in electrical potential between the inside and outside of the cell. The inside of the cell is negative relative to the outside.
RMP is established by three mechanisms?
chemical force
electrostatic counterforce
sodium/potassium ATPase
Is the inside or outside of the cardiac cell relatively negative?
Inside
What is threshold potential?
The initial voltage at which the cell depolarizes.
Can depolarization be stopped?
Depolarization is an all or none phenomenon - once it begins, it cannot be stopped.
When is the cell easier to depolarize?
When RMP is closer to threshold potential.
When is the cell harder to depolarize?
When RMP is further from threshold potential.
When does depolarization take place?
When there is a reduced polarity across the membrane. This means there is less of a charge difference between the inside and outside of the cell.
In excitable tissue, depolarization results in what?
action potential
Negative to positive is known as?
depolarization
Positive to negative is known as?
repolarization
What is hyperpolarization?
Hyperpolarization takes place when there is an increased polarity across a membrane, there is a large charge difference between the inside and the outside of the cell.
What is repolarization?
The restoration of membrane potential towards resting membrane potential following depolarization.
Why is the cardiac cell relatively positive on the outside and negative on the inside?
The cell continuously leaks potassium, thus losing positive charge from the inside of the cell.
What electrolyte is the MYOCYTE permeable to?
potassium
What electrolyte is the primary determinant of resting membrane potential in the MYOCYTE?
potassium
When the serum potassium decreases (HYPOKALEMIA) what happens to the RMP?
RMP becomes more negative, and the myocyte becomes more resistant to depolarization.
When the serum potassium increases (HYPERKALEMIA) what happens to the RMP?
RMP becomes more positive and myocyte depolarize more easily
When the cell is at rest what is the sodium to potassium permeability of the cardiac cell?
The cell is very permeable to potassium and very low permeability to sodium
What ultimately depolarizes the cell?
When RMP approaches threshold potential, voltage-gated sodium channels open and sodium conductance increases, this depolarizes the cell.
(depolarizing is becoming more positive)
What two purposes does the sodium potassium pump serve?
- removes sodium that enters the cell - during depolarization.
- Returns potassium that has left the cell - during repolarization.
Na/K-ATPase has another name, what is it?
Na/K pump
What is the exchange rate of sodium and potassium by the Na/K pump?
3 sodium ions are removed from the cell and 2 potassium ions go into the cell.
True or False
The sodium potassium pump turns on and off depending on the resting membrane potential?
False, the sodium potassium pump is ALWAYS on
Does the sodium potassium pump require energy?
Yes, the sodium potassium pump is an active transport mechanism that requires energy in the form of ATP?
Cardiac / Ventricular myocytes normal RMP value?
-90 mV
Cardiac / Ventricular myocytes normal TP value?
-70 mV
Does hypocalcemia or hypercalcemia decreased TP?
hypocalcemia decreases TP
Does hypocalcemia or hypercalcemia increase TP?
hypercalcemia raises TP
What is the intrinsic firing rate of the SA node, AV node, and the Purkinje fibers?
SA node = 70-80
AV node = 40-60
Purkinje Fibers = 15-40
which node of the heart provides the P wave?
SA node, thus if the SA node is diseased or impaired you will lack a P wave
At rest which part of the autonomic nervous system modulates the heart rate?
PNS tone exceeds SNS tone at rest
PNS tone includes which nerve to innervate the heart? (SA node and AV node)
Vagus nerve ( CN X)
the right Vagus innervates the SA node and the left Vagus innervates the AV node
SNS tone is innervated / regulated by what?
Cardiac accelerator fibers (T1-T4)
How many phases are there to a cardiac myocyte?
4,0,1,2,3
How many phases are there to the SA node? (could also be AV node)
4,0,3
no phase 1 or 2
Phase 4 in the nodal cells is known as?
spontaneous depolarization
The membrane of the nodal cells is leaky to which electrolyte?
Na+
RMP for the nodal cells is what?
around -60
TP for the nodal cells is what?
-45
What is “funny” about the funny sodium channels?
they are activated by hyperpolarization and not depolarization
(funny current or funny sodium channels)
In the nodal cell what happens at -50 mV?
transient calcium channels (T-type) open to further depolarize the cell.
What is the equation for 02 carrying capacity?
(Hgb x Sa02 x 1.34) + (Pa02 x 0.003)
What is the equation for D02?
CO x [(Ca02)] x 10
Ca02 = (Hgb x Sa02 x 1.34) + (Pa02 x 0.003)
What is oxygen carrying capacity: Ca02?
What is the normal reference value?
How much 02 is carried in the arterial blood.
20mL/dL
What is Oxygen delivery: DO2?
What is the normal reference value?
How much 02 is carried in the blood and how fast it is being delivered to the tissues.
1000 mL/min
What is oxygen extraction ratio: E02?
what is the normal reference value?
How much 02 is extracted by the tissues.
25% for the whole body
What is oxygen consumption: VO2?
what is the normal reference value?
Ho much oxygen is consumed by the tissues.
250mL/min (this value is at rest)
What is Venous oxygen content: Cv02?
what is the normal reference value?
How much 02 is carried in the venous blood.
15mL/dL