Exam 1 Review:  Chapter 18:  Internal Conduction System

electrical synapse - the specialized type of synapse between two excitable cells, e.g., cardiac muscle cells, some smooth muscle cells, and some neurons, in which the impulse is transmitted from one cell to the next by the depolarization of the sending cell creating a local ionic current flow which destabilizes the voltage gated Na⁺ channels in the adjacent cell so that it also depolarizes; such cells are usually connected by gap junctions; no neurotransmitter is required.

autorhythmicity = automaticity - a property of cardiac muscle cells (and some smooth muscle cells); the ability to depolarize and contract at a set rate on their own with no outside stimulus or regulation necessary because of their leaky ion channels and, as a result, an unstable membrane resting potential.

conduction system - The specialized pacemaker cells of the heart form a communication network to coordinate the heartbeat in a regular and efficient way; the system consist of two large collections of pacemaker cells, the sinoatrial and atrioventricular nodes, and a series of tracts and fibers forming pathways to the cells of the myocardium.

pacemaker - (1)  A part of the body, such as the mass of specialized cardiac muscle fibers of the sinoatrial node, which sets the pace or rhythm of physiological activity.  (2)  An implanted electronic device that takes over the function of the natural cardiac pacemaker, i.e., an artificial pacemaker.

sinoatrial node= SA node - A small mass of specialized conducting cardiac muscle fibers (conduction myofibers) located in the posterior wall of the right atrium of the heart which acts as a pacemaker by generating at regular intervals the electric impulses of the heartbeat; it receives external regulation from nerves from both divisions of the ANS.

sinus rhythm - The normal activity of the pacemaker system of the heart in which the SA node fires at a regular rate, typically between 60 and 100 bpm, and each beat (depolarization event) is conducted normally through to the ventricles; on the ECG a short pause will be present between the P wave and the QRS complex and between the QRS complex and the T wave.

atrioventricular node = AV node - A small mass of specialized conducting cardiac muscle fibers (conduction myofibers), located in the wall of the right atrium of the heart, near the origin of the interventricular septum, which receives heartbeat impulses from the sinoatrial node and directs them through the atrioventricular bundle to the walls of the ventricles.

atrioventricular bundle = bundle of His - A short linear collection of specialized conducting cardiac muscle fibers (conduction myofibers) located in the upper portion of the interventricular septum which transmit the cardiac impulse from the atrioventricular node to the bundle branches and on to the ventricles causing them to contract; it is regulated by the conduction control center of the ventricles, the AV node.

bundle branches - Two short linear collections of specialized conducting cardiac muscle fibers (conduction myofibers) located in the middle portion of the interventricular septum which transmit the cardiac impulse from the atrioventricular bundle to the network of conduction myofibers which stimulate the ventricles to contracts; they are regulated by the conduction control center of the ventricles, the AV node.

conduction myofibers = Purkinje fibers - The specialized large-diameter cardiac muscle fibers which conduct electrical impulses from the AV bundle into the ventricular walls; they have lost the capacity to contract, and therefore, do not have myofibrils; they are regulated by the conduction control centers of the heart, the SA and AV nodes.

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List:

4. the sequence of depolarization through the parts of the conduction system.

         (1) sinoatrial node = SA node → (2) conduction myofibers of the atrial walls and internodal pathway → (3) atrioventricular node = AV node → (4) atrioventricular bundle and bundle branches → (5) conduction myofibers of the ventricular walls and papillary muscles

Sketch and Label:

5. the Conduction System of the heart and list the sequence of depolarization through the parts of the conduction system.

 

(1) sinoatrial node = SA node → (2) conduction myofibers of the atrial walls and internodal pathway → (3) atrioventricular node = AV node → (4) atrioventricular bundle and bundle branches → (5) conduction myofibers of the ventricular walls and papillary muscles