CVS 6 - Lecture notes 1-5 PDF

Preview

Summary

Notes based on prof slides and Human Physiology book by L.Sherwood 9th edition...

Description

Cardiovascular System Physiology Main Ideas Properties of the Cardiac Muscle

Action Potential of Autorhythmic Cells

NOTES  

Excitation of the heart is triggered by electrical impulses rather than neural transmitters. Contraction of the heart is triggered by elevation of intracellular calcium influx. i. Autorhythmic cells:  1% of cardiac muscle cells  Do NOT contract  Generate and conduct action potentials  Unstable membrane potential ii. Contractile cells:  99% of cardiac muscle cells  Perform mechanical work of pumping  Normally do NOT produce action potentials

 

Slow leakage of K+ out and faster leakage of Na+ in > causes slow depolarization Ca2+ channels opening as membrane approaches threshold causing more channels to open > causing rapid depolarization Slow K+ channels open as membrane depolarizes > causing an effluent of K+ and repolarization of membrane



Functional Characteristics of Slow Response Action Potentials (slow channel)

1. 2. 3. 4.

Properties of Cardiac Muscle



 

SA node has the fastest spontaneous rate of all normal cardiac tissues; acts as the cardiac pacemaker (rate varies form 60 ~ 180/min, depending on needs). SA node is intensely innervated by the autonomic NS; so the rate is finely adjusted to the body’s needs over a wide range. AV node has slow conduction; imposes delay between atrial and ventricular contraction to allow efficient ventricular filling. AV node acts as a filter that protects the ventricles when the atria fires very quickly.

Myocytes depend heavily on oxygen and blood supply. o Have a long refractory period in which they do not respond to any electrical impulses (causes AV node delay due to poor electrical impulse coupling???). Refractory period:  prevents summation of contractions  Prevents fatigue  Prevents tetanus Not fatigued Excitability cycle

© templatelab.com...