ACTIVIDAD

Apuntes

ACTIVIDAD ELECTRICA CARDIACA: Los cardiomiocitos Cardiac Muscle and Heart Function • Cardiac muscle fibers (cells, or cardiomyocytes) are striated. Sarcomere is the functional unit • Fibers are connected to one another at intercalated discs . The discs contain several gap junctions (big channels) • Abundant mitochondria • SR (sarcoplasmatic reticulum) is less abundant than in skeletal muscle, but greater in density than smooth muscle • Sarcolemma has specialized voltage-gated Ca2+ channels: types L and T Disco intercalar 1 cardiomiocito (marcapaso) (muy ancho, con meseta) (largos) (c.Krebs) Excitación - Contracción La excitación y la contracción son parecidas en músculo cardiaco y en músculo esquelético: ambas requieren calcio (y ATP) En el músculo cardíaco el Ca 2+ proviene tanto del espacio extracelular como del retículo sarcoplásmico Potencial de acción cardíaco How are cardiac contractions started? Excito- conductor system • Specialized muscle cells “pace” the rest of the heart (pacemaker) • Sinoatrial (SA) node; pace of about 65 bpm • Internodal pathways connect SA node to atrioventricular (AV) node • AV node could act as a secondary pacemaker; autorhythmic at about 45 bpm...