University:
Western Sydney University
Course:
MEDI 2003 | Clinical Sciences 2
Academic year:

2024
Views:

204

Pages:

2
Author:

Mariam A. A.

Cardiac Excitation Understand that the specialized cardiac electrical conductor systems are electrical pathways that produce muscle electrical activity and output power, which produces effective pumping. Cardiac Excitation Cellular contraction depends on AP (Action Potential) Coordinated excitation depends on coordinated electrical activity in the conduction system Intracardiac pathways: SA → AV → Bundle of His → Purkinje fibers Refer to tablet mechanisms Describe the regional differences in AP configuration by tissue name. Refer to tablet mechanisms Tissue Name Pacemaker Channels SNS (Sympathetic Nervous System) PSNS (Parasympathetic Nervous System) SA Pacemaker Ca, K, If ↑ pacemaker velocity, ↑ rate ↓ pacemaker velocity, ↓ rate Atrial m. Contraction via Ca, K ↑ contraction strength ↓ little effect Purkinje Pacemaker Ca, K, If ↑ pacemaker velocity, ↑ rate ↓ little effect Ventricular m. Contraction via Na, Ca, K ↑ contractility, ↑ strength ↓ little effect Cardiac Rhythm Set by SA @ 60-100 bpm Adult reset: 70-80 bpm Vagal tone: always active → decreases rate, but always counteracts this AV node: 40-50 bpm, transient outward Purkinje fibers: 20-40 bpm, poorly sustained Understand what the ECG is and how it is measured. Role to mechanism Intercellular recording: single cell, membrane potential, DC coupled Extracellular recording: sum of all cells, records changes when changing only, AC coupled Ventricle Motion Dual motion Constrict circular muscle layers ↓ diameter of progressing from apex-base → power/pressure stroke Constrict spiral muscle long axis ↓ shortening long axis conical shape ↓ smaller SV ratio