Cardiovascular Two

•Sympathetic nerves from 

• - upper thoracic spinal cord, through sympathetic chain to cardiac nerves
• - directly to ventricular myocardium
• - can raise heart rate to 230 bpm

•Parasympathetic nerves

• - right vagus nerve to SA node
• - left vagus nerve to AV node
• - vagal tone – normally slows heart rate to 70 - 80 bpm
• - No vagal innervation to ventricular myocardium

•myogenic - heartbeat originates within heart

•autorhythmic – regular, spontaneous depolarization

•Sinoatrial (SA) node: pacemaker, modified cells, initiates heartbeat, sets heart rate, located in right atrium

•fibrous skeleton insulates atria from ventricles

•AV node: electrical gateway to ventricles in right atrium

•AV bundle: pathway for signals from AV node into ventricles

•Right and left bundle branches: divisions of AV bundle that enter interventricular septum

•Purkinje fibers: upward from apex spread throughout ventricular myocardium to excite cardiomyocytes

•Short, branched cells, one central nucleus

• •Less Sarcoplasmic reticulum, large T-tubules
• - admit more Ca2+ from ECF

• •Intercalated discs join myocytes end to end
• - interdigitating folds - ­ increase surface area
• - Desmosomes - hold cells together, structural support
• - electrical junctions - gap junctions allow ions to flow between cardiomyocytes

•Aerobic respiration, rich in myoglobin and glycogen, large mitochondria

•Organic fuels: fatty acids, glucose, ketones and lactic acid

•Fatigue resistant