The heart is made up of interlacing bundles of ___ muscle fibers arranged ___ around the circumference of the heart.
Within the intercalated discs there are bridges called ___ ___, where opposing membranes approach each other.
Cardiac m. includes most of the structures seen in skeletal m. including ___ and ___ filaments.
does not , CNS
Unlike skeletal muscle, cardiac muscle ___ ___ require command from ___ for the heart to beat.
___ - the ability of the heart to generate signals that trigger its contractions on a periodic basis.
Contractions of the heart are initiated (triggered) by specialized muscle cells called ___ cells. (also called autorhythmic and conduction system cells)
___ cells of the heart that do not contract --- they're purpose is to send out the signals.
SA, gap junctions
A.P. is initiated in the ___ node and spreads through the myocardium passing through ___ ___ (electrical bridges).
What causes the electrical resistance between the atria and ventricles - ___ tissue there.
bundle of his
Impulse leaves AV node and enters the wall between the ventricles (interventricular septum) through the ___ of ___.
The Bundle of His fibers make contact with ___ ___ which make contact with ventricular myocardium cells (contractile cells of the heart)
Once there is contact with the purkenje fibers the impulse then spreads through the rest of the ___. Both sides simultaneously.
The ___ ___ is the heart's pacemaker because it initiates each wave of excitation with atrial contraction.
The bundle of His and other parts of the conducting system deliver the excitation to the apex of the heart so that ___ contraction occurs in an upward sweep.
Different types of heart cells have different combinations of ___ channels that can produce different "looking" A.P.'s.
These different A.P.'s have different jobs in spreadig ___ currents through the heart muscle. (Fmi -we are not going to get into each one).
K+, Na+, -90
Cardiac (contractile) cell (like neurons) have greater resting permeability to ___ than to ___. Resting membrane potential favors -___mV.
With contractile cells, depolarization is still mainly due to ___ flooding into the cell via voltage-gated ___ channels.
positive, K+, depolarization
(Contractile cells) As ___ feedback system is causing the opening of additional Na+ channels, ___ channels start to close, adding to the ___ effect.
Due to the sudden influx of Na+ in the depolarizing contractile muscle cell, the graph looks like a line that is ___-___
(contractile cell) Membrane remains depolarized during the "plateau phase" because: ___ is still below the resting value (still closed) and permeability to ___ increases substantially.
(contractile cell) These ___ channels open when Na+ depolarizes the cell and remain open for a long time.
(contractile cell) These Ca++ channels open when ___ depolarizes the cell and remain open for a long time (called ___ calcium channels)
(contractile cell) The flow of Ca++ cations in the cells balances the flow of K+ cations out of the cell and keeps the membrane ___
(contractile cell) The flow of ___ cations in the cells balances the flow of ___ cations out of the cell and keeps the membrane depolarized.
(contractile cell) ___ occurs when permeability of Ca++ and K+ return to original state.
one to one
(contractile cell) During the "plateau phase" there is a ___ to ___ exchange of Ca++ coming in and K+ going out.
(contractile cell) Repolarization occurs when permeability of ___ and ___ return to original state.
(contractile cell) The rapid opening of ___-gated ___ channels is responsible for the rapid depolarizaiton phase.
voltage, Ca++, K+
The prolonged "plateau" of depolarization is due to the slow but prolonged opening of ___-gated ___ channels PLUS closure of ___ channels
pacemaker, autorhythmic, conduction system
What are the three other names used for "SA node" cells, ___, ___, and ___ ___.
Pacemaker potential - following an A.P., the membrane slowly ___ (drifts) to ___
(autorhythmic cell) Gradual ___ eventually bring membrane potential to threshold --> A.P. occurs.
A.P., A.P., cycle
(conduction system cells) The tail end of one ___ is the trigger for the next ___ --> stuck in a ___.
The slow depolarization that occurs in early stages of the pacemaker potential is due to: 1) closing of ___ channels 2) and opening of ___ channels.
depolarize, pacemaker, a.p.
An autorhythmic cell has the unique ability to ___ spontaneously, resulting in a ___ potential. Once threshold is reached an ___ is initiated which begins with further depolarization and leads to reversal to the membrane potential.
(pacemaker cells) K+ channels open during ___ of the A.P. and then ___ when the membrane returns to its polarized state.
pacemaker cells) "Funny channels" - termed because of their unusual gating behavior. They ___ when membrane potential is ___ value.
"Funny channels" open ___ the cell repolarizes and allow ___ to cross the plasma membrane.
K+, funny, decreases, increases
With __ channels closed and __ channels open during the early stages of the pacemaker potential, K+ movement out of the cell __, where Na+ into the cell __ --> causes initial depolarization
With ___ cells, after it repolarized, that was it, it stayed resting until something triggered it again. (opposite is true of autorhythmic cells)
quickly, short, A.P.
The funny channels are only open very __, closing about 5mV __ of the threshold needed to generate an __.
depolarization, Na+, voltage, Ca++
(pacemaker cells) The initial __ by __ triggers opening of __-gated __ channels --> depolarizing cell even more.
The "funny" channels are only open very quickly, closing about __mV short of the threshold needed to generate an A.P. This is where this cell differs. In every other cell, it's been __ that has gotten us all the way through depolarization.
T-type, short, second, Ca++, L-type
These channels (__ channels) stay open for a __ time before inactivating, but the resulting depolarization triggers the opening of a __ set of voltag-gated __ channels (__ channels) which stay open longer and inactivate slowly.
The SA node cell does not have a steady resting potential, but instead undergoes a slow depolarizaiton. This gradual depolarization is known as a __ __; it brings the membrane potential to threshold, at which point an A.P. occurs.
funny, T-type, L-type
Three ion channel mechanismis contribute to the pacemaker potential: ___-type sodium channels, __ calcium channels, and __ calcium channels.
This pacemaker channel is a type of Ca++ channel that opens only briefly but contributes an inward Ca++ current and an important final depolarizing boost to the pacemaker potential. These channels are called __ calcium channels.
Once the pacemaker mechanisms have brought the nodal cell to threshold, an AP occurs. The depolarizing phase is caused by Ca++ influx through the __ calcium channels.
These channels open much more slowly than do sodium channels, and, because of the fact that they remain open for a prolonged period, they are often referred to as __ calcium channels.
After the second set of (L-type channels) opens the result is a large increase of __, that produces the rapid upswing of depolarization.
(pacemaker cells) The rapid upswing of depolarization (caused by the L-type channels) triggers the opening of __ channels and rise in __ pulls membrane potential back down.
(autorhythmic cells) The return to __ potential activates the __ mechanisms again and the cycle continues !!!
electrical, depolarization, repolarization
___ currents generated during ___ and ___ spread into the tissue surrounding the heart and are conducted through the bodily fluids.
A small portion of the electrical currents, traveling through the bodily fluids, reaches the bodies surface where it can be ___
___ is a recording of that portion of electrical activity induced in the body fluids that reaches the surface of the body --> NOT a direct recording of the ___.
spread, depolarization, repolarization
EKG is a complex recording of the overall __ of activity throughout the heart during __ and __.
systole, closed, get out, tension, shorten
During ___, ventricles are contracting but all valves are __ so no blood can __ __ --> muscle has __ but cannot __.
pressure, aorta, ventricular
Once rising __ in ventricles exceeds that in __, aortic and pulmonary valves open and __ ejection occurs.
close, closed, no
During diastole, ventricles begin to relax, aortic and pulmonary valves __. Atrialventricular (AV) valves are also __--> __ blood is going in or out.
Eventually __ pressure becomes slightly higher than __ pressure --> AV valve opens
Once ventricle is mostly filled, __ contraction takes place (most of the blood fills into the ventricles __ the atriums even contract)
During diastole, when the ventricles begin to relax, the aortic and pulmonary valves close because of __
During diastole, aortic valve is closed because aortic pressure is __ than the ventricular pressure.
Throughout diastole, aortic pressure is falling (due to blood moving out of __) and ventricular pressure is __ (blood from atrium in).
rises, shuts, atrium
As ventricle contracts, pressure __ and __ AV valve preventing backflow into __
Eventually ventricular pressure __ aortic pressure and __ valve will open and ejection can occur.
Cardiac output measured 2 ways: 1) __ (how fast heart is beating) and 2)__/__ (how much of the fluid you are putting out)
Heart rate: In absence of any nervous or hormonal influence heart will beat at approx. __ bpm (inherent rate of SA node)
threshold, Na+, T-type
Sympathetic system causes SA node to reach __ quicker (by increasing permeability to __ and __ Ca+ channels)
Stimulation of parasympathetic causes threshold to be reached __ (hyperpolarizes by increasing permeability to __+)
__ volume also determines cardiac output. The volume of blood ejected by ventricle during contraction is going to change with how much __ you are putting down on it.
preload, sympathetic, afterload
When determining cardiac output, changes in force can be achieved by: 1. changes in end-diastolic volume (or called __) 2. magnitude of __ input to ventricles 3. __ - the aterial pressure against which the ventricle pumps.
Stroke volume increases as the end-diastolic volume increases: this is called the __ __ mechanism.
volume, stretch, Frank Starling
Greater the end-diastolic __, greater the __ -->more forceful the contraction. (also known as the __ __ mechanism)