Flashcards in Lecture 10 - Myocardial EC Coupling Deck (67)
Which part of the EKG shows atrial depolarization? Which shows the time from start of atrial depolarization to start of ventricular depolarization?
- P-R interval
Which part of EKG show ventricular depolarization? Which show ventricular depolarization, ventricular contract, and ventricular depolarization?
- Q-T interval
What does the T wave on an EKG show? What does an inversion often indicate?
- inversion may indicate recent MI
What is the ST segment show?
What causes the U wave?
What is the order of speed of conduction in the heart? Pacemaker?
What is the conduction pathway??
1. Purkinje> Atria> Ventricles> AV Node
2. SA Node> AV> Bundle of His/Purkinje/ventricles
3. SA Node --> Atria --> AV NODE --> common bundle -> Bundle Branches --> Fascicles --> Purkinje fibers --> Ventricles
What is the function of the sarcolemma?
Plasma membrane of Cardiac cells
1. propagates Action Potentials
2. controls Ca influx by activating SLOW INWARD CALCIUM current
What part of the cardiac cell activates the SLOW inward calcium current?
depolarization of T-tubules from sarcolemma
What is the function of T-Tubules?
Transmits AP from Sarcolemma
- depolarization activates slow Ca influx
Where are T-tubules found?
- connected by RyR receptors to SR
What is the function of the Sarcolemma?
intracellular Calcium storage site
Where are terminal cistern & longitudinal cistern found?
What is the function of Terminal Cisternae?
Site in SR where Ca influx TRIGGERS opening of Calcium release channels to initiate contraction
What is the function of LONGITUDINAL cisternae?
- site of Ca re-uptake to initiate RELAXATION
What is the function of Troponin C?
- binds Calcium to initiate contraction
Calcium receptor on contractile protein (actin)
What is the function of Troponin I?
(phosphorylating it activates it)
- prevents the binding of Calcium to Troponin C
= causes RELAXATION when phosphorylated
Is the contraction mechanism (actin myosin cross bridge) the same in cardiac & skeletal muscle contraction?
What is the mechanism of E-C coupling?
1. AP sent down sarcolemma, enters T-tubule
2. T-tubule depolarization activates slow inward Ca channels
3. Ca influx binds & opens RyR receptors
4. Increase Ca influx from SR --> binds Troponin C
5. Tropomyosin shifts, and actin & myosin can bind
6. CONTRACTION (CICR= calcium induced calcium release)
How can we maintain contraction?
Maintain elevated cytosolic Calcium
What are the mechanisms of relaxation?
1. Ca re-uptake into SR by Ca-ATPase (SERCA) - 80%
2. NA/Ca antiporter (18%)
3. Ca out of CELL via Sarcolemma Ca pump(2%)
What is a mechanism for reducing CYTOSOlIC calcium?
- brings it back to SR
What is a mechanism for reducing CELLULAR calcium?
(3 Na in/1 Ca out)
What occurs if Sodium influx is decreased via Na/Ca antiporter?
- reverse action
- less Na in
- less Ca OUT = increase Ca in cell for CONTRACTION
Which cells, cardiac or skeletal, function by syncytium? How is this achieved?
- coordinated via gap junctions
How are cardiac and skeletal muscles activated?
1. Cardiac = gap junctions
2. Skeletal = NMJ --> via ACh (released into clft & binds to post-synaptic membrane causing Na influx resulting in DEPOLARIZATION
Contraction of skeletal muscle is dependent on what? Cardiac?
1. AP via NMJ!
NOT CICR --> Voltage Sensor of Calcium (DHPR) that allows Calcium to enter cell via RyR receptors
2. Calcium induced Calcium release
How is contraction increased in cardiac cells? Skeletal?
1. INCREASE CALCIUM influx via SLOW CALCIUM CURRENT & SR Ca Content!
2. increase in AP frequency increases amplitude of contraction (& recruitment of muscle fibers)
Which cells, cardiac or skeletal, experiences tetany or summation?
Skeletal (summation of AP & muscle fiber recruitment)
True or false: Cardiac cells utilize primarily anaerobic metabolism
- use Aerobic, have a lot of mitochondria & use a lot of ATP
- skeletal is primarily via Glycolysis