Cardiac muscle is specialized to contract repeatedly, reliably, and in a coordinated way throughout life. This lesson introduces its distinctive cells, the structures that connect them, and the properties that make sustained pumping possible.
Cardiac muscle shares striations and contractile machinery with skeletal muscle, but it also has specialized properties that neither skeletal nor smooth muscle shares in the same way. Its most notable property is autorhythmicity: the ability to generate electrical impulses spontaneously at a regular rate. These impulses spread through the heart and trigger contraction. The nervous and endocrine systems can modify heart rate, but the heart can generate its own rhythm.
All flashcards
What is cardiac autorhythmicity?
It is the ability of cardiac tissue to generate electrical impulses spontaneously. The nervous and endocrine systems can adjust the heart's rate without being required to initiate every beat.
How do contractile and conducting myocardial cells differ?
Contractile cells form most of the myocardium and generate the force that pumps blood. Conducting cells specialize in initiating and spreading electrical impulses through the heart.
What are intercalated discs?
They are specialized junctions connecting adjacent cardiomyocytes. Desmosomes and related structures hold cells together, while gap junctions allow ions and electrical excitation to pass between them.
Why do cardiac muscle cells need a long refractory period?
The long refractory period prevents tetany and ensures the muscle can relax so the heart chambers can refill before the next contraction.
What typically replaces cardiac muscle cells lost after an MI?
Damaged areas are often replaced by scar tissue. Because scar tissue does not contract like healthy myocardium, cardiac function may be reduced.
Quiz questions
Why does the atrioventricular (AV) node briefly delay an impulse before it reaches the ventricles?Answer: To let atrial contraction finish and the ventricles fill before they contract.
After passing through the AV node, what is the normal route of the impulse into the ventricular myocardium?Answer: AV bundle, bundle branches, then Purkinje fibers.
What causes the gradual prepotential in cardiac conducting cells?Answer: Slow inward leakage of sodium ions.
What electrical event does the QRS complex represent on an ECG?Answer: Ventricular depolarization.
What is the immediate treatment used to stop ventricular fibrillation?Answer: Defibrillation with an electrical shock.
Based on Anatomy and Physiology 2e by J. Gordon Betts, Kelly A. Young, James A. Wise, Eddie Johnson, Brandon Poe, Dean H. Kruse, Oksana Korol, Jody E. Johnson, Mark Womble, Peter DeSaix (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.