19.6 Stimulation of the Heart

Question 1

how does the SA nodal cells act as a pacemaker

Answer 1

reaching threshold: charge difference between the inside and outside of the cells by moving sodium and calcium ions
depolarization: stops pumping the ions, lack of difference in charge, no poles (draws electrons across the membrane)
repolarization: calcium channels close and potassium channels open

Question 2

spread of action potential

Answer 2

• initiated in the SA node
• distributed throughout both atrai via the gap junction (starting in the sarcolemma of the atrial walls)
• relayed to the AV node + delayed by 0.1 seconds to allow the atria to contract + force blood into the ventricles (delayed because gap junction of the AV node are smaller than those of the SA node, bottleneck that slows the action potential)
• travels from AV node through right + left AV bundles to the purkinje fibers