Cardiovascular 2 Flashcards
Mastery
Two types of Myocardial Cells
A.C
each myocardial cell has what?
what are AP initiated by?
depolarization = contraction
repolarization = relaxation
Autorhythmic Cells
- Generates and spreads action potentials
- Pacemaker cells(initiate, SA and AV node)
- Conducting cells(spread impulse)
Contractile cells
- 99% of cardiac cells
- Mechanical work of contraction
Each myocardial cell has a distinct action potential
APs are initiated at the pacemakers
PACEMAKER CELLS
Events
Slow depolarization phase of SA node (first half)
Near midpoint of slow depolarization
Threshold is reached
Repolarization of pacemaker cell
Events
- Na+ influx
- Ca++ and Na+ influx
- K+ efflux
K+ permeability (PK+ )decreases
Na+ permeability (PNa+) increases
* Increased leakiness to Na+
⬧ slow influx of Na+
* Approaches threshold
Near midpoint of slow depolarization
- Ca++ (T-type; transient) channels open – voltage sensitive
* Calcium moves in
* Don’t stay open long
pacemaker potential continues to rise toward threshold. Na and Ca
Threshold is reached
- L-type Ca++ channels open
- Calcium moves in
- rapid depolarization and action potential
sodium, sodium and calcium, calcium in thru L channel
Repolarization
- L-type Ca++ channels close
- K+ (rectifier) channels open
* K+ moves out of SA node cells
SA node is ……
AV node
beats / min
Purkinje fibres
beats / min
Ectopic beats
Both are depolarized by….
SA node is autorhythmic
Self-generated
events repeat (~ 70 times / minute)
AV node
40 beats / min
Purkinje fibres
~20 beats / min
Ectopic beats (extrasystoles, ventricular contraction)
Both are depolarized by SA node before they
depolarize themselves
Action Potential of the MYOCARDIAL CONTRACTILE CELLS
Depolarize
Plateua
Repolarize
CA2+ from where?
Cardiac Muscle
when AP reaches it
Depolarization
Na+ moves in
Plateau
Ca++ moves in
Stays depolarized
Repolarization
K+ moves out
Ca from extracellular and sarcoplasmic reticulum
Cardiac Muscle
Excitation-contraction coupling and
relaxation in cardiac muscle
Myocardial Contractile Cells
what kind of AP and refractory
prevents what?
allows for what?
Long Action potential means long
refractory period
- Prevents tetanus
- Allows for relaxation and diastolic filling each beat
contractile myocardium
Autorhythmic myocardium
TABLE
Modulation of Heart Rate by the
Sympathetic Nervous System
Modulation of Heart Rate by the
Parasympathetic Nervous System
Pacemaker cells are more depolarized
Closer to threshold
Will reach threshold faster
Increased heart rate
Minimum point, DISTANCE TO THRESHOLD IS MUCH CLOSER. LESS TIME TO REACH THRESHOLD
- HYPERPOLARIZES pacemaker
- Further from threshold
- Takes longer to reach threshold
- Slower heart rate (normal resting condition)
Specialized Conduction System of
Heart
Pathway of AP
- SA node
- Internodal pathway
- AV node(delay at AV node)
- Bundle of HIS, Or AV bundle, Bundle branches
- Purkinje Fibres
depolarizations are excitatory
depolarizations are a negative wave
TEST:
they show depolarization and repolarization, NOT CONTRACTION, they initiate contraction
The ECG
P-wave
* Atrial depolarization
* Initiates atrial contraction
QRS complex
* Ventricular depolarization and atrial repolarization
* Initiates ventricular contraction
T-wave
* Ventricular repolarization
* Initiates ventricular relaxation
backwards wave and repolarization
two negatives make a positive
Conduction of Impulses
P-wave
Impulse moves to AV node
QRS Complex
T-wave
P-wave (atrial Depolarization)
- Initiated in SA node
* Spreads via gap junctions and internodal pathway
- throughout atria
- Initiates atrial contraction
AV node
Delay of signal (~100 ms, top of ventricles with blood)
* AV nodal delay means ventricles contract after atrial
contraction and ventricular filling
QRS Complex
- Impulse moves to Bundle of HIS, to Bundle branches and then to Purkinje fibres
- Initiates ventricular contraction
* Includes atrial repolarization
T-wave (Ventricular repolarization)
- Reversed repolarization wave (from apex)
- Initiates ventricular relaxation
ECG Leads
ECG Leads
Simple 3 lead – “Einthoven’s Triangle”
6- lead
12 lead
24 or 72 hour
halters
