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37 Cards in this Set
- Front
- Back
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True or False: A cardiac muscle cell has a greater extracellular than intracellular concentration of Na+, whereas the intracellular K+ concentration is much greater than the extracellular concentration. |
TRUE |
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what do ions have a natural tendency to do? |
diffuse across the membrane to create equal concentrations on the two sides. |
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is the cell membrane freely permeable to Na+ and K+? |
no |
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what does the separation of ion pairs create? |
electrical force |
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electrochemical equilibrium potential (Em) |
the balance between the electrical and chemical forces. This potential can be described by the Nernst equation: Em= -61.5 X log inracellular [ion]/extracellular [ion] |
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membrane potential |
the difference between electrical charge inside the cell membrane and the outside of it. |
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what is the rate of ion transfer across a cell membrane dependent on? |
1. concentration difference 2. permeability of the membrane to each specific ion |
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what is the permeability to an ion determined by? |
the opening and closing of ion gates or channels. gates specific to each ion under normal circumstances there is always some "leakages" of ions across a cell membrane |
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how are ions moved outside the cell? |
active transport -sodium-potassium pump ATP is used to fuel this pump |
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what is the resting membrane potential? |
-90 mV |
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what must happen for myocardial muscle fiber to contract? |
action potential must be generated |
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how many stages are involved in an action potential? |
five -labeled as phases 0-4 |
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describe the five phases of an action potential. |
0: rapid deplolarization 1: slight overshoot 2: delay or plateau in membrane potential 3: rapid repolarization 4: return to resting membrane potential |
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true or false: the action potential of skeletal muscle lasts much longer than that of cardiac muscle. |
false -cardiac muscle action potential lasts longer |
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What happens during the Depolarization phase of cardiac muscle?
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*threshold is reached and Voltage Gated Sodium Channels open which rapidly depolarizes the membrane to +20mv (therefore, it's a positive inside the cell)
*sodium channels close |
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What happens in the plateau phase?
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*calcium channels open and inflow of calcium is balanced by inflow of potassium
*this maintains membrane potential at 0mv for 0.2 seconds |
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What happens in the Repolarization
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Potassium channels open and there is a rapid repolarization of the membrane
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What does the plateau phase mean?
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That after a cardiac cell contracts it cannot contract again for 0.2 seconds
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What is the maximum rate of contraction of the heart?
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One beat every 0.2 or 0.3 seconds or ~200 beats per minute
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What does the P Wave indicate on an EKG?
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The depolarization of the atria from -90 to 0mv and therefore contraction of the atria
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What does the QRS wave indicate on the EKG?
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The depolarization of the ventricle and therefore contraction of the ventricles
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What does the T Wave indicate on the EKG?
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The repolarization of the ventricles from 0 to -90 and therefore the ventricles are relaxed.
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Where is the bicuspid valve aka mitral valve?
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Between the LEFT Atria and the LEFT Ventricle
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Where is the Tricuspid Valve?
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Between the RIGHT Atria and the RIGHT ventricle
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What is special about Nodal Cells in the heart?
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They have autorhythmicity, they contract on their own (with no neurological input)
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How does excitation spread throughout the heart?
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*SA node is where impulse originates (located in right atrium) *Impulse travels to AV node. AV node excites, then signal send through atria and Atria contract to AV Bundle*AV bundle brings the signal across the AV septum to the R and L Bundle Branches bringing excitiation to the apex *Perkinje fibres excite the ventricles so they contract |
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what is the pacemaker of the heart |
sinoatrial node (SA node) |
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what is the major function of the AV node? |
delay the signal to prevent the impulse from traveling to the ventricles too rapidly. |
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the SA node set a rate of what? |
60-100 bpm -AV node: 40-60 bpm -Purkinji fibers: 15-40 bpm *If SA node fails, AV node will take over |
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ectopic pacemaker |
happens when some part of the heart develops a discharge more rapid than the SA node -results in dysrhytmia, and the pumping action of the heart, decreasing cardiac output. |
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What innervates the SA and AV nodes through the vagus nerves? |
parasympathetic nervous system |
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what system is distributed to most parts of the heart? |
sympathetic system -rich innervation of ventricles |
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true of false: under normal circumstances the SA node is under tonic influence of both parasympathetic and sympathetic systems |
true |
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Sympathetic stimulation |
- results in release of norepinephrine causing increased permeability - increased heart rate - increased fore of contraction |
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how to cortical centers in brain effect heart rate |
-increase heart rate in response to emotional and physical stress |
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baroreceptors |
-located in carotid sinuses and aortic arch -effect heart rate in response to changes in blood pressure -main job is to control blood pressure through changes in heart rate |
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heart rate variability (HRV) |
the beat to beat variability of the R-R interval. -long or short term measurements via ECG -can provide insight regarding autonomic control of the heart |
