Specific Learning Objectives
Cardiac muscle
Structure
Features
Properties
- Automaticity
- Rhythmicity (Chronotropism)
- Conductivity (Dromotropism)
- Excitablity (Bathmotropism)
- Contractility (Ionotropism)
General features of cardiac muscle
- Striated like skeletal muscle, but involuntary
- 100 μm long and 15 μm wide
- Fibers branched and attached with each other closely
- Intercalated discs between two muscle fibers.
- Numerous gap junctions present in the intercalated disc that make cardiac tissue functional syncytium.
- 2 separate syncytia in heart: atrial and ventricular syncytia, connected with each other by A-V bundle
- Each syncytium obeys all-or-none law.
- The cardiac muscle fibers are highly vascular, i.e. surrounded by a very rich capillary network.
- They show well-developed sarcoplasmic reticulum with plenty of cytoplasm, mitochondria and rich in glycogen.
Properties of Cardiac Muscle
- Automaticity
- Rhythmicity
- Conductivity
- Contractility
- Excitability
- Distensibility
- Long refractory period
- Functional syncytium
- Extrasystole and Compensatory pause
- All or none Law
- Staircase phenomenon
- Length-tension relationship
- Frequency-force relationship
- Load-velocity relationship
Automaticity
- It is the ability to contract regularly even without the nerve supply.
- It is possible due to the spontaneous generation of impulses by the SA node (primary pacemaker of the heart), AV node, His-Purkinje system and ventricular muscle.
Rhythmicity