BIOL 3402 Lecture 2: Human Physiology Heart Notes 2
Document Summary
Myogenic: upward drift to reach threshold, due to: Slow leakage of k out and faster leakage of na in. I"f" channels that open at negative membrane potential and start to close towards threshold. Ca channels open as membrane approaches threshold. Threshold reached = spike of action potential. No hyperpolarization with pacemaker cells: altering activity of pacemaker cells. Ne (norepinephrine) & e (epinephrine) channel activity: neurotransmitters, change pacemaker physiology, reaches threshold faster, causes faster heartbeat, leads to opening of ca channels faster (uses b1 adrenergic receptors. Sa node is the primary pacemaker: chronotropic (rate) effects of autonomic nervous system. Increased ca accelerates depolarization of sa node camp speeds uptake of ca by sarcoplasmic reticulum: allows cardiocytes to relax faster the heart has intrinsic firing rate of 100 bpm. Holds down the heart rate to 70-80 bpm at rest. Steady background firing rate of vagus nerves.
