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7 Cards in this Set
- Front
- Back
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List the components of the cardiac conduction system. |
Sino-atrial (SA) node: the cells in this bunch actually initiate the depolarization of the heart muscles. They depolarize at a regular rate, establishing the heart rate. It is located in the upper portion of the right atrium. Atrio-ventricular (AV) node: this node is located in the bottom left corner of the right atrium, and gets depolarized just the like cardiac muscle tissue does. After a slight delay, the action potential travels to the bundle of His and branches off into the right and left bundle branches. They reach the bottom of the ventricles and branch out from there. The specialized tissue that branches off the bundle branches is called purkinje fibers that depolarize the rest of the ventricles. |
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Describe the functions of the intercalated disks and gap junctions in cardiac muscle cells. |
They allow for the unison contraction of both atria at the same times, as well as the bottom to top contraction of the ventricles. They allow for rapid depolarization throughout the cells, making up the term cell to cell conduction. |
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Describe the sequence of activation of the heart beginning at the sino-atrial (SA) node. |
The cells in the SA node activate an action potential causing depolarization of both atria at the same times. This depolarization reaches the bottom of the right atria where the AV node is located. This node is then depolarized, relatively slow causing a delay in the travel of the action potential. The action potential is then sent through the bundle of His, dividing into the right and left bundle branches branching off into the ventricles. Once reaching the ventricles, the branches form into the Purkinje fibers further relaying the action potential up the ventricle. |
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Draw a typical cardiac ventricular action potential, properly labeling the horizontal and vertical axes. Identify the resting membrane potential and label the phases. |
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Describe the sequence of events that generates a typical cardiac action potential including the changes that take place in the membrane conductance for Na, K, and Ca. |
There is a resting membrane potential. Then there is a rapid influx of Na, due to VG Na channels opening (K channels are closed). The plateau phase takes place when 2 things happen: 1. Ca L-type channels open and stay open 2. K channels remain closed Repolarization occurs when Ca channels close and K channels open. All this occurs 300-400ms. |
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Draw a typical pacemaker potential. Properly labeling the horizontal and vertical axes. Show the location of the threshold potential. |
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Describe the sequence of events that generates a typical pacemaker potential including the changes that take place in the membrane conductances for Na, K, and Ca. |
The reason the SA node has no resting membrane potential is because of the opening of the Na channels (different from cardiac muscle depol) and transient Ca T-type channels. Once threshold is reached, it rapidly depolarizes by the opening of L-type Ca channels. The cell depolarizes due to the closing of the L-type Ca channels and opening of K channels. This happens 70 times per minute. The SA node cells, under NO influence of the ANS, will fire at 100 times per min, but because parasympathetic activity does take place, it is reduced to 70/min. |
