Cardiac Muscle Overview and Cells

Cardiac muscle combines features of skeletal and smooth muscle. It's striated, uses sliding filaments for contraction, but fibers are short, branched, and interconnected via gap junctions called intercalated discs.

Cardiac muscle cells contract without direct nerve stimulation. Specialized pacemaker cells initiate the contraction signal.

Specialized cardiac muscle cells that generate spontaneous action potentials, setting the heart's rhythm. They are smaller than contractile cells and lack well-organized sarcomeres.

The main muscle cells of the heart, responsible for contraction. They are striated, have organized sarcomeres, and are responsible for pumping blood.

Specialized junctions between cardiac muscle cells. They contain gap junctions that allow electrical signals to pass directly between cells, coordinating contraction.

A functional unit of cardiac muscle cells connected by gap junctions, acting as a single unit. Each atrium and ventricle forms a separate myocardium.

The gradual, spontaneous depolarization of pacemaker cells, leading to action potentials and heart contractions. It's independent of nerve stimulation.

Calcium ions play a crucial role in cardiac muscle contraction. Calcium influx triggers further calcium release from the sarcoplasmic reticulum, leading to muscle contraction. This is different from skeletal muscle.

The process by which an action potential in a cardiac muscle cell triggers contraction. It involves a chain of events that begins with the opening of voltage-gated L-type calcium channels (DHPR), leading to calcium inflow and the subsequent opening of ryanodine receptors (RyR) in the sarcoplasmic reticulum (SR). This releases a surge of calcium into the cytoplasm, which binds to troponin, initiating the crossbridge cycle and muscle contraction.

The initial release of calcium from the sarcoplasmic reticulum (SR) in response to a small influx of calcium ions through voltage-gated L-type calcium channels (DHPR) in the cell membrane.

The accumulated release of calcium from multiple RyR channels in the sarcoplasmic reticulum (SR) through a series of 'calcium sparks', resulting in a robust calcium signal that triggers muscle contraction.

The process of muscle relaxation in cardiac muscle, involving the removal of calcium from the cytoplasm. This occurs through two mechanisms: the calcium-ATPase pump, which actively transports calcium back into the SR, and the sodium-calcium exchanger (NCX), which moves calcium out of the cell.

A period following an action potential in cardiac muscle during which the cell is completely unresponsive to further stimulation, regardless of the stimulus strength, lasting approximately 250 ms.

A sustained muscle contraction caused by a series of rapid, repetitive stimuli, where individual muscle twitches fuse together.

Cardiac muscle cannot sustain tetanic contractions due to its long absolute refractory period, which prevents the muscle from being stimulated again before it fully relaxes. This ensures proper heart function and blood circulation.

The time it takes for a muscle to contract and relax varies between muscle types: Skeletal muscle contracts and relaxes rapidly, Cardiac muscle has a longer contraction and relaxation time compared to skeletal muscle, and Smooth muscle exhibits the slowest contraction and relaxation times among the three.

The three major types of muscle tissue in the body are Skeletal muscle, Cardiac muscle, and Smooth muscle. These muscle types differ in their anatomy, location, control mechanisms, contraction characteristics, and other features.

A comprehensive comparison of the three muscle types, highlighting their differences in appearance, fiber arrangement, location, tissue morphology, internal structure, fiber proteins, control mechanisms, contraction speed, force of contraction, and initiation of contraction.