5 . In addition to the intrinsic cardiac conduction system, which initiate and distributes the electrical impulses that control cardiac activity, many other factors affect the rate at which the heart contracts. The most important of these effects are exerted by the autonomic nervous sytem (ANS) b. Name two other factors that influence heart rate.
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[CIRCULATORY] The nervous system can influence your heart rate (like right now, your heart rate is likely higher than after relax when this exam is over!). This acceleration or deceleration of heart rate is influenced by... a. Norepinephrine release which then increases the permeability (i.e., the amount of time) of Na+ and Ca2+ channels, shortening the amount of time between depolarization of the SA node cells b. Activation of the medullary cardiovascular control center that then inhibits the activation of the sympathetic nervous system, increasing heart rate c. Acetylcholine release that results in increasing the permeability (i.e., amount of time) that the Na+ channels are open, leading to a longer depolarization of cardiomyocytes d. Decreasing the rate at which the AV node spontaneously depolarizes (this is why the AV node is called the pacemaker of the heart) e. Activation of the parasympathetic nervous system that slows down your heart rate by releasing epinephrine
Adi S.
Modification of Heart Rate: The action potential is also passed from autorhythmic cells to the contractile cells, first in the atria (they contract first) and then in the ventricles (they contract second). The autorhythmic cells of the heart set the intrinsic heart rate. While the heart does not require external stimulation to beat, it can be modified by hormones and neurotransmitters. The autonomic nervous system can increase or decrease heart rate; the (i) sympathetic nervous system, via norepinephrine and epinephrine, increases whereas the (j) parasympathetic nervous system, via acetylcholine, decreases heart rate. Going from Autorhythmic to Contractile Cells: The action potential of contractile cells results in depolarization of the sarcolemma, which spreads down the t-tubules of an individual cell and spreads among cells via the (k) gap junctions. Within a contractile cell, the action potential results in an influx of (l) Calcium ions into the intracellular fluid/sarcoplasm via the opening of the (m) L-type Ca2+ channel. Once in the cell, the calcium from the extracellular fluid aids in the release of (n) calcium from the (o) SR. This creates a calcium spark. Several calcium sparks result in a calcium (p) signal. The Ca2+ ions bind to (q) troponin resulting in a conformational change. This conformational change moves (r) thus exposing the actin binding sites on (s) tropomyosin, the motor protein behind contraction. These intracellular mechanisms are responsible for the mechanical contraction of the heart. In order for relaxation of contractile cells to occur, calcium ions need to be moved across the contractile cell membrane via the (t) or sequestered back into the (u) via the calcium ATPase. Thus, (v) ions and (w) are required for contraction and relaxation of the heart.
Match each of the accompanying ECG tracings with the corresponding description: 1. AV heart block 2. tachycardia 3. atrial fibrillation 4. Ventricular fibrillation Filocarpine pansympathomimetic. What effect does this drug have on heart rate? The intrinsic cardiac conduction system initiates and distributes the electric impulses that control cardiac activity. Many other factors affect heart rate. 1. Autonomic nervous system (ANS) - What are the two divisions of the ANS, and how does each division affect heart rate? 2. Other factors - Name two other factors that influence heart rate. Beta-adrenergic blockers are used to treat high blood pressure. Explain how these drugs affect heart rate.
Sri K.
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