BIOS 213 Lecture Notes - Lecture 25: Endoplasmic Reticulum, Tetany, Sarcolemma
Document Summary
Ca2+ plateau ensures a complete contraction cycle, repolarization almost coincides with relaxation. Refractory period at the end of the myocardial action potential coincides with the relaxation phase of contraction. Depolarization, cation influx, from neighboring cells depolarizes sarcolemma, down t-tubules, Calcium pumps return ca2+ to sarcoplasmic reticulum or ecf. Pacemaker cells are in the sinoatrial node, sa node, trigger cardiac action potentials in myocardial cells. Unstable vm due to net na+ influx through if channels, open when vm is low (-), hyperpolarized. At a threshold, ca2+ voltage gated channels open. Ca2+ from the pacemaker spike spreads through gap junctions nearby contractile or myocardial cells, triggering na+ influx and cardiac action potentials in myocardial cells. Muscarinic achr opens k+ channels slowing rate of depolarization. Catecholamines (ne from neurons, epi from adrenal medulla) stimulate beta-1 adrenergic receptors which use camp 2nd messenger. Camp keeps if channels open longer, na+ influx increases. Dual innervation of the autonomic system allows fast response.
