Download Cardiac Muscle Tissue

Cardiac Muscle Tissue
 Forms a thick layer called myocardium.
o Striated like skeletal muscle.
o Contractions pump blood through the heart and into blood vessels.
o Contracts by sliding filament mechanism.
 Cardiac muscle cells
o Short
o Branching
o Have 1 or 2 nuclei and not fused
o Triggered by ionic calcium to contract, like skeletal muscle.
 Cells join at intercalated discs
o Complete junctions
o Form cellular networks
 Cells are separated by the delicate endomysium
o Bind adjacent cardiac fibers
o Contains blood vessels and nerves.
Intercalated Discs – Complex junctions
 Adjacent sarcolemmas intercalate
 Possesses 3 types of cell junctions
o Desmosomes
o Fasciae adherens – long desmosome-like junctions
o Gap junctions.
 Triggered to contract by Ca2+ entering the sarcoplasm
o Signals sarcoplasmic reticulum to release Ca2+ ions.
 Ions diffuse into sarcomeres
 Trigger sliding filament mechanism
 Not all cardiac cells are innervated
o Will contract in rhythmic manner without innervation
o Inherent rhythmicity
 Is the basic for rhythmic heartbeat
Smooth Muscle Tissue
• Found in the walls of visceral organs
• Six major locations
• Walls of circulatory vessels
• Respiratory tubes
• Digestive tubes
• Urinary organs
• Reproductive organs
• Inside the eye
• Cells are spindle-shaped
• Contain one centrally located nucleus
• Separated by endomysium
• Grouped into sheets in walls of hollow organs
• Longitudinal layer – muscle fibers run parallel to organ’s long axis
• Circular layer – muscle fibers run around circumference of the organ
• Both layers participate in peristalsis
• Cells are non-striated and contain no sarcomeres
• Thin and thick filaments are present
• Entry of Ca2+ into the cytoplasm signals contraction of the smooth muscle
fiber
• Caveolae – tiny infoldings of the sarcolemma
• Contraction is slow and sustained
•
• Takes 30 times longer to contract than skeletal muscle fiber
• Maintains contractile force for a long time
Is innervated by autonomic nervous system
• Only a few smooth muscle fibers are innervated in each sheet
• Impulse spreads through gap junctions
• Whole sheet contracts as a unit
• Exceptions – iris of the eye and arrector pili muscles