Cardiac Physiology Flashcards
describe the location of the pacemaker of the heart
SA node is medial to the opening of the superior vena cava
name the five parts of the conducting system of the heart
Sinoatrial Node (SA) atrioventricular node (AV) AV bundle right and left bundle branches purkinje fibers
what are the differences between cardiac muscle cells and the cardiac muscle cells that make up the SA node
they spontaneously generate AP at a greater frequency than that of other cardiac muscle cells
smaller diameter cardiac muscle cells
form a knot or lump
have fewer myofibrils
where do the APs from the SA node travel fastes?
the AV node
what cardiac muscle cells do the SA node affect?
atrial muscle cells and AV node
explain the location of the AV node
medial to the right atrioventricular valve
where within the heart do the cmc’s propogate APs slowest?
AV node
where do the APs travel after the AV node?
AV bundle»_space; right and left bundle branches»_space; purkinje fibers
what specialized conducting cells penetrate the myocardium of the ventricles?
purkinje fibers
how do the specialized conducting fibers of the ventricles receive the AP to cntx?
AV node
to what ions are the CMCs permeable to create the resting membrane potential?
low permeability to Na+ and Ca++ and higher permeability to K+
what phase of CMCs makes APs so much slower?
plateau phases
what happens during the plateau phase of CMCs APs
slow repolarization
_________ passes through a hole in the cardiac skeleton to reach ______________
AV bundle – interventricular septum
right and left bundle branches extend …
beneath endocardium to apices of right and left ventricle
how do purkinje fibers differ from other CMCs
large diameter few myofibrils many gap junctions longer fewer intercalated disks
how does the length and amount of intercalated disks affect the efficacy of the Purkinje fibers?
longer fibers causes less of a delay bc fewer intercalated disks means AP can travel easier path–just down length of sarcolemma
compare and contrast CMCs and SMFs
- Cardiac APs are conducted from cell to cell via gap junctions at the intercalated disk. Skeletal APs travel along the length of a single fiber.
- gap junctions and small diameter fibers cause the rate of AP propagation to be slower in CMCs. Skeletal fibers are larger in diameter and propagation only has to travel the length of a single cell.
- Ca++ induced Ca++ release is unique to CMCs. Ca++ moves through sarcolemma and stimulates release of Ca++ from the sarcoplasmic reticulum
what causes repolarization and plateau phase to move so slowly in APs of CMCs
movement of K+ out of the cell (to begin repolarization) is counteracted by mvmt of Ca++ (and some Na+) through the voltage gated Ca++ channels that are slow to close.
eventually Ca++ channels close and many more voltage gated K+ channels open causing
final repolarization of CMCs
what develops spontaneously in the SA node and what is it?
pacemaker potential: a local action potential that reaches threshold and generates AP in the SA node
what causes the pacemaker potential?
changes in ion movement into and out of the pacemaker cells
what ions cause depolarization in the pacemaker by moving into the cells through a specialized nongated channel?
Na+
mvmt of _____ into the cells and decreased permeability to allowing ___ out of the cells begins depolarization and opens voltage-gated ____
Na+ K+ Ca++
depolarization causes many more ____ to open
voltage-gated Ca+ channels
what is different about the ions that cause depolarization in the pacemaker cells from other CMCs?
pacemaker cells primarily rely on Ca++ movement to cause depolarization and other CMCs rely primarily on Na+
repolarization occurs when voltage-gated ______ channels close and voltage-gated _____ open
Ca++ – K+
how do epinephrin increase heart rate and force of cntx?
by opening voltage gated Ca++ channels
name some calcium channel blockers
nifedipie and verapamil
how would nifedipine or verapmil affect heart rate?
they are Ca++ channel blockers so they slow the pacemaker’s ability to develop an action potential
what are the parasympathetic nerve fibers that connect to the heart?
vagus nerve
where are the terminal ganglia of the parasympathetic vagus nerves?
within the wall of the heart
where do post ganglionic fibers of the parasympathetic nerves innervate the heart?
SA node
AV node
coronary blood vessels
atrial myocardium
_______ is produced by postganglionic parasympathetic neurons and binds to ______________ that cause sarcolemma of the CMC to become _____ permeable to ______, thus ________ the membrane, and ______heart rate
Ach ligand-gated channels more K+ hyperpolarizing decreasing
sympathetic nerve fibers synapse with post______ at the _______
ganglionic
ganglia
which part of the nervous system projects into the heart as cardiac nerves?
sympathetic
How would cutting the paravagus nerve affect the heart rate? What if it was stimulated?
The inhibitory effect of the vagus nerve Ach release would be stopped, hr would increase. If stimulated. Ach release would resume
