Chapter 9 cardiac muscle

Introduction to Cardiac Muscle

• Overview of cardiac muscle as presented in Chapter 9.

• Comparison with skeletal and smooth muscle.

• Focus on introductory components of cardiac muscle.

Types of Muscle

• Three types of muscle: skeletal, cardiac, and smooth muscle.

• Cardiac and skeletal muscle are both striated, sharing anatomical characteristics.

• Important to understand microanatomy as it resembles that of skeletal muscle.

Characteristics of Cardiac Muscle

• Striated Muscle: Cardiac muscle has a striated appearance, similar to skeletal muscle.

• Involuntary Control: Unlike skeletal muscle, cardiac muscle contractions are not under conscious control.

• Autonomic Nervous System Regulation: Both cardiac and smooth muscle are regulated by the autonomic nervous system (ANS).

Developmental Aspects

• Cardiac myocytes arise from a lineage of cells but diverge from skeletal muscle development.

• Clarification: Myoblasts are specific to skeletal muscle; a different myoblast-like cell gives rise to cardiac muscle.

• Differentiation of terms: "cardiomyocyte" and "cardiac myocyte" refer to the same mature cardiac muscle cell.

Structural Attributes

• Cardiac Myocyte: Smaller size compared to skeletal muscle fibers, typically single or few nuclei.

• Intercalated Discs: Important junctions between cardiac myocytes, containing proteins vital for function.

• Branching: Cardiac myocytes can branch, allowing a different structural organization from skeletal muscle.

Functional Properties

• Automaticity: Cardiac muscle can spontaneously depolarize, enabling contraction without nervous system input.

• Distinction from skeletal muscle: The ANS does not dictate contraction timing for cardiac muscle but influences heart rate.

Cellular Communication

• Gap Junctions: Found within intercalated discs, allowing synchronized contraction between adjacent cardiac myocytes.

• Desmosomes: Provide strength and resistance to mechanical stress at intercalated discs, essential during cardiac contraction.

Microanatomy of Cardiac Muscle

• Similar organization to skeletal muscle, including myofibrils and sarcomeres with thick (myosin) and thin (actin, tropomyosin, troponin) filaments.

• Presence of a sarcoplasmic reticulum for calcium storage and release.

• Striations evident due to organized sarcomeres.

• Absence of neuromuscular junctions in cardiac muscle.

Summary and Comparison

• Preparation for exam three: Review comparisons of skeletal, cardiac, and smooth muscle.

• Refer to the table in the textbook for detailed similarities and differences.

• Emphasis on understanding structure-function relationship across the three muscle types.