CVS2 Flashcards
(18 cards)
What are the gap junctions in cardiac muscle cells called
Intercalated discs
What is the area of the heart that contracts from one stimulation event called
Myocardium or functional synctium
What separates the atria and ventricles
Fibrous skeleton
How does the automatic rhythmicity of the sinus fibers occur
The SA node exhibits the degree of self excitation and inherent discharge rate
How does conduction of the heart occur
Action potential spread via intercalated discs
SA node to AV node to stimulate atrial contraction
AV node at base of right atrium and bundle of His(collection of heart muscle cells specialized for electrical conduction) conduct stimulation to ventricles
In the nterventricular septum , the bundle of His divides into right and left bundle branches
Branch bundles become Purkinje fibers , which stimulate ventricular contraction
Explain the excitation of nodal fibers
Sodium ions naturally tend to leak into sinus nodal fibers- multiple membrane channels
Membrane potential rises to a threshold voltage of -40mV the Ca2+ Na+ channels open
Ca2+ and Ana+ rapidly enter leading to the action potential
It is this inherent leakings to Na+ that causes their self excitation
What is the pacemaker potential
This slow depolarization is due to both opening of Na+ channels and closing of K+ channels. Notice that the membrane potential is never a flat line
What causes depolarization
It the influx of Ca2+ through calcium channels . Action potential begins when the pacemaker reaches threshold
What causes depolarization
It caused by inactivation of Ca2+ and Openning of K+ channels causing effluent of K+ , brings membrane potential back to its most negative voltage
How ask the sinoatrial node depolarize
Spontaneously , at a rate at which they do so can be modulated
Which hormones perform the sympathetic activity
Epinephrine and norepinephrine
Give the names of the two types of receptors that play a role in sympathetic activity
Chronotropic and ionotropic
What the function of chronotropic
Increases rate of SA node discharge via Beta 1 receptor and decreases delay of AV node - speeds up signal
What the function of ionotropic receptor
Increases in force of cardiac contractility - mainly via Beta 2 receptor increases the production of cAMP , which keeps cardiac pacemaker channels open
Speeds heart rate due to Na+ inflow
What do parasympathetic neurons secrete
Acetylcholine
What does the secretion of acetylcholine do
Open K+ channels
What are the reasons for prolonged action potential
Cardiac muscle fast sodium channels as well as slow calcium channels open
The calcium-sodium channel open slower but remain open for longer . Both sodium and calcium flow in for a prolonged period causing the extended plateau phase
How does action potential in cardiac muscles take place
Resting membrane potential of cardiac muscle is -85 and -90 millivolts
Ventricular membrane potential moves from -85 to +20 millivolts (over shoot
