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73 Cards in this Set
- Front
- Back
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does cardiac muscle depend on nervous system events to initiate depolarization?
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No!
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what input do hearts receive from the nervous system?
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autonomic nervous system inputs both cholinergic and adrenergic modulations to the intrinsice mechanisms underlying the basic rhythm
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what does the ANS contribute to the heart?
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cholinergic and adrenergic input
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what does the ANS do to the heart?
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modulates basic rhythm
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what in the intrinsic cardiac conduction system?
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a small population of non-contractile cardiac cels specialized to initiate and conduct impulses throughout the heart
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what does the intrinsic cardiac conduction system do?
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coordinate rhythmicity of the heart
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what coordinates rhythmicity of the heart?
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intrinsic cardiac conduction system
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what do non-contractile cardiac cells do?
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initiate and conduct impulses throughout the heart
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what initiates and conducts impulses throughout the heart?
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non-contractile cardiac cells
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what is unique about autorhythmic cells?
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they do not maintain a stable resting membrane potential
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what do autorhythmic cells do?
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initiate the impulse that is eventually propagated throughout the heart
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what cells initiate the impules that is propagated throughout the heart?
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autorhythmic cells
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what are the spontaneously changing membrane potentials are called what?
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pacing potentials
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what do pacing potentials do?
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initiate complete action potentials that spread throughout the heart, triggering rhythmic contractions at the underlying rate of the pacing potential
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rhythmic contraction rates are set by what?
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rate of pacing potential
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what is the resting membrane potential of pacing cells?
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-60mV
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what is the resting potential of myocardial cells that are not autorhythmic?
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-90mV
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why is the resting membrane potential of pacing cells higher?
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they have a special population of 'funny' Na+ channels in the sarcolemma
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when do 'funny' Na+ channels open?
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after a pacing cell repolarizes and K+ channels close
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in pacing cells, what occurs after repolarization and K+ channels close?
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funny' Na+ channels open
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what does the opening of 'funny' Na+ channels cause?
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an imbalance of K+ loss and Na+ entry, an accumulation of positive charges inside the cell making the RMP less negative, eventually reaching threshold potential of -40mV that enables Ca++ channels to open
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what does RMP stand for?
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resting membrane potential
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in autorhythmic cells, what does Ca++ influx cause?
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the rising phase of the AP and reverses the membrane potential (depolarization)
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in pacing cells, the rising phase of the AP and depolarization is caused by?
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Ca++ influx from the extracellular fluid
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what causes the falling phase of the action potential is pacing cells?
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increasing K+ permeability and efflux when K+ channels open
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in autorhythmic cells, what does increaseing K+ permeability and efflux when K+ channels open cause?
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falling phase of action potential
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What occurs after 'funny' Na+ channels and K+ channels close in autorhythmic cells?
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cell membrane repolarizes and the spontaneous depolarization cycle repeats as the voltage-gated Na+ channels reopen
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where are autorhythmic cells located?
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in order: sinoatrial (SA) node, atrioventricular (AV) node, AV bundle, right and left bundle branches, purkinje fibers (in vesticular walls)
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what does SA stand for?
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sinoatrial node
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what does AV stand for?
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atrioventrcular node
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where is the SA node?
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the right atrial wall at the junction of the cranial and caudal venae cavae
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what is unusual about the SA node?
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has the most rapid intrinsic rate of spontaneous depolarization
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what is the SA node known as?
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the pacemaker for sinus rhythm
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what is the pacemaker of the sinus rhythm?
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the SA node
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which autorhythmic cells have the most rapid intrinsic rate of spontaneous depolarization?
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SA node
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where does the impulse from the SA node go?
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over the atria to the AV node
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where does the AV node receive the impulse from?
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the SA node
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what occurs to the impulse in the AV node?
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the depolarization is delayed to allow the atria to finish contracting before the ventricles are depolarized and contract
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what causes the delay of depolarization in the AV node?
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smaller fiber diameter and fewer gap junctions
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what prevents the impulse from being sent retrograde back up into the atria once the ventricles depolarize?
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differing regions of the AV node have differing refractory periods
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smaller fiber diamtere and fewer gap junctions cause what in the AV node?
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delay of depolarization
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where does delayed depolarization occur in the heart?
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the AV node
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having differeing refractory periods in differing regions of the AV node is important because why?
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keep the impulse from being sent retrograde back up into the atria once the ventricles depolarize
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where does the AV node send an impulse?
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to the AV bundle
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what is another name for the AV bundle?
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Bundle of His
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what is another name for the Bundle of His?
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AV bundle
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where does the AV bundle receive the impulse from?
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the AV node
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what is the AV bundle?
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the only electrical connection between them
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what is the only electrical connection between the atria and ventricles?
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the AV bundle
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are there gap junctions between the atria and ventricles?
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No!
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where does the impulse from the AV bundle go?
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bundle branches
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where do the bundle branches receive the impulse from?
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AV bundle
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what are bundle branches?
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a separation of the AV bundle into right and left bundle branches
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where do the bundle branches carry the depolarization?
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down the interventricular septum ot the right and left ventricles respectively
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what happens to the conduction speed of the impulse at the AV bundle and bundle branches?
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rapid
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where does the impulse from the bundle branches go?
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purkinje fibers
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where do the purkinje fibers receive the impulse from?
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bundle branches
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where are the purkinje fibers?
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penetrating the ventricles
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what do the purkinje fibers do?
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initiate depolarization in the subendocardium & depolarize the papillary muscles that anchor the AV valve leaflets
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what contracts first, papillary muscles or ventricles?
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papillary muscles; thus locking the valve flaps closed against the pressure generated by the ventricle contraction
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what causes the papillary muscles to contract?
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purkinje fibers
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what causes the ventricles to contract?
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purkinje fibers
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how does ventricular contraction occur?
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it follows ventricular depolarization in a wave-like manner that 'wrings' the heart from the apex toward the atria, ejecting blood intothe pulmonary and systemic vasculature
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what does the autonomic nervous system do to the heart?
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modulates the activity of the intrinsic conduction system
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what modulates the activity of the intrinsic conduction system?
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the autonomic nervous system
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where are postganglionic parasympathetic fibers distributed in the heart?
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SA node and AV node
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what type of receptors are stimulated by postganglionic parasympathetic fibers?
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cholinergic
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cholinergic describes what part of the ANS?
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postganglionic parasympathetic
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where are sympathetic fibers distributed in the heart?
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SA node, AV node, and ventricular myocardium, coronary arteries
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what type of receptors are stimulated by sympathetic fibers?
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adrenergic
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adrenergic describes what part of the ANS?
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sympathetic
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what does the cardioacceleratory center affect?
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the sympathetic ANS
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where does the cardioacceleratory center project sympathetic preganglionic fibers?
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T1-T5 level of the spinal cord
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