Section 48.3.4 (Exam 4) Pacemakers Flashcards
Heart Function Depends on Properties of Cardiac Muscle
How does the autonomic nervous system control the heart rate?
By influencing rate at which resting potentials of pacemaker cells drift upward
How does the autonomic nervous system increase the rate at which resting potential of the pacemaker drift upwards?
Norepinephrine from sympathetic nerves increases permeability of Na+/K+ and Ca2+ channels, causing the resting potential to rise more rapidly
How does the autonomic nervous system decrease the rate at which resting potential of the pacemaker drift upwards?
Acetylcholine from parasympathetic nerves increases permeability of K+ and decreases that of Ca2+ channels decreasing the rate at which the resting potential rises
What are the two ways the autonomic nervous system influence the rate at which resting potential of the pacemaker drift upwards?
Norepinephrine from sympathetic nerves
Acetylcholine from parasympathetic nerves
How is heart muscle contraction coordinated?
An action potential is generated in the sinoatrial node
It spreads through gap junctions in the atria and they contract together, but does not spread to the ventricles
Why does the action potential not spread from the atria to the ventricles? Why is this ideal?
No gap junctions
Delay between the contraction of atria and ventricles ensures that blood will flow from the contracting atria into the relaxed ventricles fully
How does the AP in the atria cause the ventricles to contract if there is a delay and no direct electrical contact through gap junctions?
The action potential in the atria stimulates the atrioventricular node (secondary pacemaker)
How does the atrioventricular (AV) node conduct action potentials to the ventricles?
AV node cells conduct action potentials to the ventricles via the bundle of His, which divides into right and left branches that run to the tips of the ventricles
From the tip, Purkinje fibers spread throughout the ventricles
What is the bundle of His?
A bundle of specialized cardiac conduction cells that divides into two branches that line the ventricle walls
What are Purkinje fibers?
Specialized cardiac conduction cells that branch off of the two major branches that are part of the bundle of His to reach every part of the ventricles to ensure they contract
Ventricle muscle fibers contract for a much longer time than skeletal muscle fibers due to longer opening of voltage-gated Ca2+ channels and increased Ca2+ availability to stimulate contraction. How is Ca2+ cleared from the inside of the muscle cells?
Ca2+ pumps in the cell membrane
What does an electrocardiogram (ECG or EKG) do?
An EKG uses electrodes to record events in the cardiac cycle
How does an EKG record events in the cardiac cycle without being in contact with the pacemakers?
Large action potentials in the heart cause electrical current to flow outward to all parts of the body
Electrodes register the voltage difference at different times
