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65 Cards in this Set

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  • Back
heart beats in the absence of any nervous connection b/c
specialized cells called pacemaker cells 9which have pacemaker activity have auto-rhythmicity
electrical (pacemaker) activity is generated by the heart itself and leads to:
cardiac muscle contraction
pacemaker cells in heart have specialized ____ that conducts electrical activity
conduction tissue
cardiac muscle ____ allow rapid spread of electrical activity.
syncitia
cardiac muscle cells = _____ cells
contractile
cardiac muscle cells perform:
mechanical work of pumping blood flow thru cardiovascular system
excitation - __________ pumping allows coordinated contraction of heart
contraction
the conduction system within the heart allows rapid, organized near-synchronous depolarization and contraction of ventricles. this is essential to:
1. allow sufficient rest time for filling of ventricles.(so they dont get overworked)
2. generate pressure efficiently during ventricular contraction and pumping of blood into arterial system.
electrical activity of the heart begins with the pacemaker cells of the:
SA node.
(sinoatrial node)
_______________ in the heart is essential tos timulate the heart to contract
treansmission of electrical activity
the heart cannot contract and pump unless a(n):_____ occurs first
electrical stimulus
pacemaker cells possess the ability to produce a:______ initiating an impulse. they have automaticity
spontaneous electrical stimulus
automaticity of pacemaker cells are altered by _____ and ______
sympathetic and parasympathetic nervous system
electrical activity= impulses=
action potentials
sympathetic stimulation of pacemaker cells ___ heart rate
increases
parasympathetic stimulation of pacemaker cells ___ heart rate
decreases
each group of autorhythmic cells has its own _____
rate of action potential initiation
the heart cells with the fastest rate of action potentials are localized in the:______. thus the ___ drives the rest of the heart at its rate (~70-80 APs/min)= pacemaker of heart
SA node
Latent pacemakers:
1. AV node: APs initiated at 40 Ap/min
2. Purjinje fibers: APs initiated at 20- 40 APs/min

*each of these sets their own rate of AP potential. if SA node stopped, the next highest would take over
electrical activity/ impulses are conducted in :
an orderly sequence throughout the heart
as electrical activity is conducted, cardiac cells undergo a cycle of :
depolarization and repolarization
as waves of depolarization and repolarization are transmitted thru ______ it causes sequential ____ and ___ of heart chambers
myocardium. contraction and relaxation.
pathway of impulse conduction:
SA node(causes upper atria to contract)-Bachmanns bundle-internodal pathways-AV node-Bundle of His-Purkinje fibers(either in right or left ventricle)
pacemaker cells have:
conductivity
depolarization =
contraction
repolarization =
relaxation
as the electrical impulse teavels thry purkinje fibers, causes:
ventricles to contract
_____ have the highest conduction velocity
purkinje fibers
purkinje fibers:
-connect with ventricular myocytes (muscle cells)
-allows for efficient contraction and emptying of ventricles
AV node:
-lowest conduction velocity
-only electrical bridge between atria and ventricle
-allows time for complete atrial depolarization, contracting and emptying of atrial blood into ventricles prior to ventricular depolarization and contraction
the electrical impulse has different speeds at different parts of the heart
ischemia = lack of blood flow
conduction velocities can be altered:
can increase or decrease conduction velocities.
______ can increase conduction velocity within the heart:
sympathetic stimulation, muscarinic receptor antagonists, beta-1-adrenoceptor agonists, circulating catecholamines, and hyperthyroidism
____ can decrease conduction velocities within the heart:
parasympathetic stimulation, muscarinic receptor agonists, beta blockers, ischemia, hypoxia, and sodium & calcium channel blockers
as impulses are transmitted and cardiac cells undergo a cycle of depolarization and repolarization, characteristic ___s are generated in different heart regions
APs
an action potential generated during the depolarization-repolarization cycle has:
unique phases
each phase of APs is the result of specific___moving thru unique ion channels
ions
ion movement creates a ____ and alters membrane potential of the cardiac cell
current
pacemaker action potentials:SA, AV-node, bundle of his, purkinje:
do not have a resting membrane potential- they always trend toward depolarization
non-pacemaker action potentials: atria and ventricles
have a true resting membrane potential ~90 mV, which is maintained by potassium channels
SA node action potential is self induced
ventricle action potential is triggered by depolarizing currents from adjacent cells
the duration of cardiac action potentials(pacemaker and nonpacemaker) is ____ than neuron and skeletal muscle
longer. (b/c you dont want the contractions to occur too close together)
Phase 4--->Phase 0 ---->Phase 3
Diastole(resting)--->depolarization--->repolarization
Phase 4= diastole (relaxation):
pacemaker current (If) = slow

sodium ion channels open slowly into SA node
Phase 0 = depolarization:
(in SA node)
voltage dependent calcium channels open ( l-type, T-type) and calcium moves into cell
Phase 3 = repolarization:
(in SA node)
voltage gated potassium channels open - delayed recifier current

potassium moves out of cell
Phase 0 = depolarization
(in purkinje fibers):
voltage dependent sodium channels open fast
Phase 1 = early repolarization in purkinje fibers:
sodium channels close-transient outward potassium channels open and potassium flows out rapidly
Phase 2= plateau in purkinje fibers:
voltage dependent L-type calcium channels open and calcium moves into the cell. also, potassium rectifying channels open and potassium flows out.
Phase 3 = repolarizatoin in purkinje fibers:
calcium channels close, potassium flows out rapidly
Phase 4 = diastole in purkinje fibers
negative potential maintained via potassium channels (inward recifying)
how does the cardiac cell get ready to generate another action potential?
ion pumps and exchangers return the ions that have moved in and out of the cardiac cell during the AP and maintains the concentration gradients for each of tese ions and returns membrane potential back to baseline (resting)
APs for all cardiac cells have 3 refractory periods.
ARP, ERP, RRP.
ARP=
Absolute Refractory Period. this is when it is unexcitable to stimulation
ERP=
Effective Refractory period. this is the brief period beyond ARP where stimulation produces weak depolarization that does not propogate. (it would just dissipate)
RRP=
Relative Refractory Period. here, stimulation produces a weak PA ( a weak contraction) that does propogate but more slowly than usual.
on an EKG, the P wave =
atrial depolarization (contraction)
on an EKG, the QRS wave =
ventricle depolarization (contracting)
on an EKG, the T wave =
ventricle repolarization (relax)
on an EKG, the P-R interval is:
the time from atrial depolarization (contraction) to spread of impulses thru AV node
on an EKG, the QT interval is:
the time from ventricular depolarization (contraction) to repolarization (relax)
on an EKG, the ST segment is:
the end of ventricular depolarization (contraction) and beginning of ventricular repolarization (relax)
Q =
beginning of ventricular depolarization
S=
end of ventricular depolarization
electrical activity goes in 1 direction only:
SA node --> Atrium --> AV node--> purkinje fiber --> ventricle