Cardiac Muscle Tissue Overview http://www.unm.edu

Much of the text material is from, “Principles of Anatomy and Physiology (12th edition)” by Gerald J. Tortora and Bryan Derrickson (2009). I don’t claim authorship. Other sources are noted when they are used. Mapping of the lecture slides to the 13th edition is provided in the supplement.

Structure The most predominant tissue in the wall of the heart is cardiac muscle. Sheets of connective tissue are located between the layers of cardiac muscle fibers. The sheets contain blood vessels, nerves, and a conduction system for propagating electrical activity from the heart’s pacemaker cells. Chapter 10, page 327

Structure (continued) Cardiac muscle fibers have the same arrangement of actin and myosin molecules, and the same bands, zones, and Z discs as skeletal muscle fibers. Intercalated discs, which are unique to cardiac muscle fibers, hold the heart muscle together during its billions of forceful contractions during a full lifetime. These discs are irregular transverse thickenings of the sarcolemma con-necting the ends of cardiac muscle to one another. Chapter 10, page 327

Physiology Skeletal muscle contracts when stimulated by ACh at neuromus-cular junctions in response to action potentials from motor neurons. In comparison, cardiac muscle tissue contracts when stimulated by its autorhythmic muscle fibers—under resting conditions, about 75 times per minute. The autonomic nervous system controls changes in cardiac muscle activity in response to exercise, stress, and other physiological and behavioral conditions. The sympathetic and parasympathetic divisions exert antagonistic actions on cardiac activity (including heart rate, as we discussed). Chapter 10, page 327

Physiology (continued) The mitochondria in cardiac muscle are larger and more numerous than in skeletal muscle fibers. This finding indicates that aerobic respiration is the principal source for generating ATP in cardiac muscle. Cardiac muscle can also use lactic acid from skeletal muscle to pro-duce ATP, a benefit of physical exercise. Chapter 10, page 327

Cardiac Tissue Response Cardiac muscle contractions are 10-to-15 times longer in duration than the contractions of skeletal muscle fibers. The longer contraction time is due to the prolonged delivery of Ca2+ into the sarcoplasm of cardiac muscle fibers Chapter 10, page 327