Sinoatrial node
The sinoatrial node (the SA node) is one of the major elements in the cardiac conduction system, the system that controls the heart rate. This stunningly designed system generates electrical impulses and conducts them throughout the muscle of the heart, stimulating the heart to contract and pump blood. The SA node is the heart's natural pacemaker. The SA node consists of a cluster of cells that are situated in the upper part of the wall of the right atrium (the right upper chamber of the heart). The electrical impulses are generated there. The SA node is also called the sinus node. The electrical signal generated by the SA node moves from cell to cell down through the heart until it reaches the atrioventricular node (AV node), a cluster of cells situated in the center of the heart between the atria and ventricles. The AV node serves as a gate that slows the electrical current before the signal is permitted to pass down through to the ventricles. This delay ensures that the atria have a chance to fully contract before the ventricles are stimulated. After passing the AV node, the electrical current travels to the ventricles along special fibers embedded in the walls of the lower part of the heart. The autonomic nervous system, the same part of the nervous system as controls the blood pressure, controls the firing of the SA node to trigger the start of the cardiac cycle. The autonomic nervous system can transmit a message quickly to the SA node so it in turn can increase the heart rate to twice normal within only 3 to 5 seconds. This quick response is important during exercise when the heart has to increase its beating speed to keep up with the body's increased demand for oxygen.

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sinoatrial node n a small mass of tissue that is made up of Purkinje fibers, ganglion cells, and nerve fibers, that is embedded in the musculature of the right atrium of higher vertebrates, and that originates the impulses stimulating the heartbeat called also S-A node, sinus node

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the pacemaker of the heart: a microscopic area of specialized cardiac muscle located in the upper wall of the right atrium near the entry of the vena cava. Fibres of the SA node are self-excitatory, contracting rhythmically at around 70 times per minute. Following each contraction, the impulse spreads throughout the atrial muscle and into fibres connecting the SA node with the atrioventricular node. The SA node is supplied by fibres of the autonomic nervous system; impulses arriving at the node accelerate or decrease the heart rate.

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sinuatrial node, sinus node nodus sinuatrialis.

Medical dictionary. 2011.

Look at other dictionaries:

  • sinoatrial node — [sī΄nōô rik′yə lərsī΄nō ā′trē əl] n. PACEMAKER (sense 2a): sometimes called sinoauricular node [sī΄nōô rik′yə lər] …   English World dictionary

  • Sinoatrial node — Infobox Anatomy Name = Sinoatrial or (el) node Latin = nodus sinuatrialis GraySubject = GrayPage = Caption = Interior of right side of heart. (SA node not labeled, but region visible at left, near crista terminalis. Caption2 = Schematic… …   Wikipedia

  • sinoatrial node — SA node the pacemaker of the heart: a microscopic area of specialized cardiac muscle located in the upper wall of the right atrium near the entry of the vena cava. Fibres of the SA node are self excitatory, contracting rhythmically at around 70… …   The new mediacal dictionary

  • sinoatrial node — noun Date: 1913 sinus node …   New Collegiate Dictionary

  • sinoatrial node — /suy noh ay tree euhl, suy /, Anat. a small mass of tissue in the right atrium functioning as pacemaker of the heart by giving rise to the electric impulses that initiate heart contractions. Also called sinus node. [1920 25; SINO + ATRIAL] * * * …   Universalium

  • sinoatrial node — si′no•a′tri•al node′ [[t]ˈsaɪ noʊˈeɪ tri əl, ˌsaɪ [/t]] n. anat. a small mass of tissue in the right atrium functioning as pacemaker of the heart by giving rise to the electric impulses that initiate heart contractions • Etymology: 1920–25; sin… …   From formal English to slang

  • sinoatrial node — noun a specialized bit of heart tissue that controls the heartbeat • Syn: ↑pacemaker, ↑cardiac pacemaker, ↑SA node • Hypernyms: ↑cardiac muscle, ↑heart muscle …   Useful english dictionary

  • sinoatrial node — [ˌsʌɪnəʊ eɪtrɪəl] noun Anatomy a small body of specialized muscle tissue in the wall of the heart whose contractions regulate the heartbeat. Origin early 20th cent.: from sinus + atrial (see atrium) …   English new terms dictionary

  • Узел Синусно-Предсердный (Sinoatrial Node, Sa Node) — пейсмейкер (водитель ритма) сердца: специфический микроучасток в сердечной мышце, расположенный в верхней стенке правого предсердия вблизи впадения в него полой вены. Волокна синусно предсердного узла являются самовозбуждающимися; они ритмично… …   Медицинские термины

  • Sinoatrial arrest — or sinus arrest is a medical condition wherin the sinoatrial node of the heart transiently ceases to generate the electrical impulses that normally stimulate the myocardial tissues to contract and thus the heart to beat. Since the heart contains… …   Wikipedia

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