Cardiac Muscle Structure and Function

A specialized structure in cardiac muscle cells, formed by the fusion of T-tubules and terminal cisternae of the sarcoplasmic reticulum, responsible for regulating calcium release and muscle contraction.

The movement of calcium ions into the cardiac muscle cell initiates muscle contraction, triggering a cascade that leads to filament interaction and shortening.

The T-tubule carries the electrical impulse into the cell's interior, triggering the release of calcium from the sarcoplasmic reticulum, leading to muscle contraction.

The terminal cisternae are specialized regions of the sarcoplasmic reticulum that store calcium, which is released upon receiving an electrical signal, initiating muscle contraction.

The heart is located in the middle mediastinum, between the lungs, and sits at the level of thoracic vertebrae T5-T8.

The human heart has four chambers: two atria and two ventricles, divided into left and right sides by the interatrial and interventricular septa

The interventricular septum is thicker than the interatrial septum because it needs to generate more pressure during ventricular contraction.

Heart valves are one-way structures that regulate blood flow through the heart, preventing backflow and ensuring efficient circulation. There are two main types: atrioventricular valves and semilunar valves.

The stage in the cardiac cycle where the ventricles are relaxed and expanding, allowing blood to flow into the heart.

The period of time during which the heart fills with blood.

The stage in the cardiac cycle where the ventricles contract and force blood out of the heart.

The stage in the cardiac cycle where the ventricles contract and eject blood into the pulmonary and systemic circulation.

The number of heartbeats per minute.

A high heart rate, defined as above 100 bpm at rest.

A low heart rate, defined as below 60 bpm at rest.

An irregular heartbeat pattern.

The middle layer of the heart wall, composed of striated muscle tissue that functions involuntarily like smooth muscle. It contains cardiomyocytes responsible for heart contractions.

Specialized cells within the myocardium responsible for initiating and transmitting electrical signals that cause the heart to contract.

Junctions between cardiomyocytes that facilitate rapid signal transmission across the entire heart, leading to synchronized contractions.

The ability of cardiac tissue to transmit electrical impulses rapidly and uniformly, allowing the heart to contract as a single unit.

The specialized electrical conducting cells of the heart, including the SA and AV nodes, that generate spontaneous electrical impulses to regulate heart rhythm.

The primary pacemaker of the heart, located in the right atrium near the superior vena cava. It initiates 60-80 electrical impulses per minute.

Located in the interatrial septum, the AV node receives electrical signals from the SA node and transmits them to the ventricles. It has a slower conduction speed and a slower firing frequency.

The heart's electrical conduction system consists of a series of components that transmit electrical impulses from the SA node through the atria and ventricles, orchestrating heart contractions.

Valves in veins prevent blood from flowing back, ensuring it moves towards the heart. Their function is crucial for proper blood circulation.

The contraction of leg muscles during walking or standing compresses veins, pushing blood upward towards the heart. This mechanism assists venous return.

Varicose veins occur when weakened valves in surface veins allow blood to pool, causing bulging and distorted veins.

The sympathetic nervous system prepares the body for 'fight or flight' responses, increasing heart rate, blood pressure, and blood flow to muscles.

The parasympathetic nervous system promotes 'rest and digest' functions, slowing heart rate, lowering blood pressure, and diverting blood to digestive organs.

The amount of blood pumped out of the heart per beat.

The volume of blood pumped by the heart per minute. Calculated as: Stroke Volume x Heart Rate.

The period of time between the closure of the atrioventricular (AV) valves and the closure of the semilunar valves.

The period of time between the closure of the semilunar valves and the opening of the atrioventricular (AV) valves.

The first heart sound, heard at the beginning of ventricular systole, caused by the closure of the atrioventricular (AV) valves.

The second heart sound, heard at the beginning of ventricular diastole, caused by the closure of the semilunar valves.

Supply of oxygen and nutrients to the heart muscle.

The resting phase of a cardiomyocyte cell.

The initial phase of the cardiac action potential, where sodium ions rapidly flow into the cell, making it positively charged.

A brief repolarization phase where potassium ions start flowing out of the cell, but it's quickly followed by the plateau phase.

A prolonged phase where calcium ions flow into the cell, keeping the cell slightly depolarized and preventing premature contractions. This allows for effective blood pumping and time for neighboring cells to depolarize.

The final phase of the action potential where potassium ions continue to flow out of the cell, restoring the cell to its resting potential.

The specialized heart cells responsible for initiating the heartbeat. They have a resting membrane potential closer to zero than regular cardiomyocytes, making them more easily stimulated.

Leak channels in SA node cells that allow sodium ions to slowly leak into the cell, bringing the resting membrane potential closer to the threshold value, leading to spontaneous depolarization. They are crucial for intrinsic heart rhythm generation.

Veins have the ability to expand and contract to store and hold blood.

The venous system functions to collect blood from all parts of the body and deliver it to the right atrium of the heart.