Title: Cardiac Muscle and Electrical Activity | Anatomy and Physiology II
Headings: Cardiac Muscle and Electrical Activity
Cardiac Muscle and Electrical Activity
Learning Objectives
Structure of Cardiac Muscle
Conduction System of the Heart
Sinoatrial (SA) Node
Atrioventricular (AV) Node
Atrioventricular Bundle (Bundle of His), Bundle Branches, and Purkinje Fibers
Membrane Potentials and Ion Movement in Cardiac Conductive Cells
Action Potential Review: What is a Stable resting Membrane Potential?
review of a Neuronal action Potential
Why do SA node cardiocytes lack a stable resting membrane potential?
Membrane Potentials and Ion Movement in Cardiac Contractile Cells
Calcium Ions
Comparative Rates of Conduction System Firing
Electrocardiogram
Everyday Connection: ECG Abnormalities
Everyday Connection: External Automated Defibrillators
Cardiac Muscle Metabolism
Chapter Review
Self Check
19.2 Exercise 11.
Critical Thinking Questions
Glossary

Content: T (transverse) tubules penetrate from the surface plasma membrane, the sarcolemma, to the interior of the cell, allowing the electrical impulse to reach the interior. The T tubules are only found at the Z discs, whereas in skeletal muscle, they are found at the junction of the A and I bands. Therefore, there are one-half as many T tubules in cardiac muscle as in skeletal muscle. In addition, the sarcoplasmic reticulum stores few calcium ions, so most of the calcium ions must come from outside the cells. The result is a slower onset of contraction. Mitochondria are plentiful, providing energy for the contractions of the heart. Typically, cardiomyocytes have a single, central nucleus, but two or more nuclei may be found in some cells. Cardiac muscle cells branch freely. A junction between two adjoining cells is marked by a critical structure called an intercalated disc, which helps support the synchronized contraction of the muscle by allowing ions to travel between the sarcolemmas of neighboring cells. As a result, if one cell has an action potential, enough ions will travel through the intercalated discs to permit all connected cells to also reach threshold and have action potentials.