Cardiac muscle

Your heart has strong muscle.

This muscle makes the heart pump. It works in a special way. It can twist like a wet cloth. This helps squeeze blood out.

Small parts of the heart act like a timer. They send tiny sparks to the muscle. These sparks tell the heart to beat. Special tubes help the sparks move fast. Tiny cells stay joined together. This helps them work as one big team.

The muscle needs food and air to work. Blood brings these things to the heart. This keeps your heart strong.

Your heart has a special kind of muscle. It is called cardiac muscle. This muscle makes up the thick middle layer of your heart wall.

Cardiac muscle is made of tiny cells called cardiomyocytes. These cells are joined at their ends. They use special parts called intercalated discs to stay connected.

These discs help the cells work as one big team. They let tiny electrical signals move fast from cell to cell. This helps the heart beat in a steady rhythm. Special cells called pacemaker cells act like a timer. They send the signals that start each beat.

To pump blood, the muscle must contract. An electrical signal tells the cell to let out calcium. This causes parts inside the cell to slide past each other. This movement is how the muscle squeezes. The muscle can even twist like a wet cloth to squeeze out blood.

Working muscle needs a lot of power. Blood brings oxygen and nutrients through coronary arteries. This keeps the cells from getting tired.

Your heart relies on a very special tissue called cardiac muscle. This muscle is also known as the myocardium. It makes up the thick middle layer of your heart wall.

This layer sits between the inner endocardium and the outer epicardium. The cardiac muscle is an involuntary muscle. This means it works on its own without you thinking about it. It is also a striated muscle. This means it looks striped when you see it under a microscope.

Working together, these muscle cells act like one big team. This team-like behavior is called a functional syncytium. The cells are called cardiomyocytes. They are joined at their ends by structures called intercalated discs. These discs contain gap junctions that let electrical signals pass through easily.

When an electrical signal, called an action potential, hits a cell, it triggers a change. The signal causes the cell to release calcium from a store called the sarcoplasmic reticulum. This calcium makes tiny fibers called myofilaments slide past each other. This process is called excitation-contraction coupling.

Special cells help keep the heart beating in a steady rhythm. These are called pacemaker cells. The main pacemaker is located in the sinoatrial node. This node sits on the wall of the right atrium. There is also a secondary pacemaker in the atrioventricular node. These cells can send out their own electrical impulses. They also respond to signals from your brain. Larger cells in the bundle of His and Purkinje fibers carry these signals very quickly.

Cardiac muscle cells have unique features to help them work hard. Each cell contains many mitochondria. These tiny parts provide energy in a form called ATP. This energy helps the muscle resist getting tired. The cells also have tiny tubes called T-tubules. These tubes run from the cell surface deep into the center. They help the electrical signal reach the inside of the cell quickly.

The cells are roughly 100 to 150 micrometers long. They are held together by a support system called the extracellular matrix. This matrix includes proteins like collagen and elastin.

To pump blood out, the muscle must squeeze in many directions. The sheets of muscle wrap around the heart in different ways. When they contract, they make the heart shorter and narrower. They even use a twisting motion. This is like wringing out a damp cloth to get every drop out.

This motion helps the heart pump the most blood possible. To keep doing this, the muscle needs a constant supply of oxygen. This blood travels through the coronary arteries. These arteries start at the aortic root and sit on the heart's surface.

Cardiac muscle, also known as the myocardium, is a specialized tissue that makes up the heart wall. It is one of three types of vertebrate muscle, alongside skeletal and smooth muscle. This tissue is involuntary, meaning it functions without conscious control. It is also striated, which means it has a striped appearance under a microscope.

The myocardium forms a thick middle layer. It sits between the inner endocardium and the outer epicardium. The endocardium lines the chambers and covers the valves. The epicardium is part of the pericardial sac that protects the heart.

To pump blood effectively, the muscle must contract in a complex way. The heart wall contains sheets of cardiac muscle cells called cardiomyocytes. These sheets are oriented in different directions. Some wrap around the left ventricle near the endocardium. Others are positioned closer to the epicardium. When these sheets contract together, they squeeze the heart in several directions at once. The heart becomes shorter from the apex to the base. It also becomes narrower from side to side. Finally, the muscle uses a twisting motion, similar to wringing out a damp cloth. This coordinated movement maximizes the amount of blood squeezed out during each beat.

At the microscopic level, cardiomyocytes have a very specific structure. Each cell is roughly 100 to 150 micrometers long and 30 to 40 micrometers wide. They are joined at their ends by intercalated discs. These discs contain gap junctions that allow ions to flow easily between cells. This creates a functional syncytium, where cells work together as a single unit.

Inside the cells, protein fibers called myofilaments slide past each other. These are organized into units called sarcomeres. The arrangement of actin and myosin in these sarcomeres creates the striped look.

To maintain this work, cells contain many mitochondria. These provide energy in the form of adenosine triphosphate, or ATP. This high energy supply makes the muscle very resistant to fatigue.

The contraction process begins with an electrical signal called an action potential. This signal travels through T-tubules, which are tiny pouches of cell membrane. These tubes run from the cell surface deep into the center. The T-tubules help transmit the signal quickly to the cell's interior. This signal triggers the release of calcium from the sarcoplasmic reticulum. This internal calcium store is located near the T-tubules. The rise in calcium causes the myofilaments to slide. This specific process is known as excitation-contraction coupling.

Specialized cells called pacemaker cells control the heart's rhythm. These cells can spontaneously generate electrical impulses. They also respond to signals from the brain. The primary pacemaker is the sinoatrial node. It is located on the wall of the right atrium. A secondary pacemaker is found in the atrioventricular node. Other cells, like the Purkinje fibers, are larger and conduct signals very quickly.

If this electrical coordination fails, it can lead to abnormal rhythms like ventricular fibrillation.

Supporting cells called fibroblasts are also vital to the myocardium. They do not contract like cardiomyocytes, but they create the extracellular matrix. This matrix is made of proteins like collagen and elastin. It provides strength, elasticity, and hydration to the muscle cells.

Fibroblasts also help repair the heart after an injury. If a person suffers a myocardial infarction, or heart attack, fibroblasts can become myofibroblasts. These cells can contract gently to pull the edges of an injury together while creating new collagen.

Maintaining the health of the cardiac muscle is essential for survival. The muscle requires a constant flow of oxygen and nutrients. This is provided by the coronary circulation. Coronary arteries originate from the aortic root and lie on the epicardial surface. These arteries bring blood into the myocardium. Afterward, coronary veins drain the blood into the right atrium. If this blood supply is restricted, it can cause ischemic conditions. These include angina or a myocardial infarction. Understanding these systems helps scientists study how to treat heart diseases.