Muscle

Muscles are soft parts in your body.

They help you move around. Tiny parts inside them pull to make movement.

Some muscles work when you tell them to. These help you walk and stand up.

Other muscles work all by themselves. You do not have to think about them.

Your heart has special muscle too.

It works on its own to pump blood.

Smooth muscle is also in your body. It is found in your stomach. It helps move things through your organs.

Muscles are soft tissues in your body. They help you move.

Inside every muscle are tiny proteins. These are named actin and myosin. They work together to make the muscle contract. This means the muscle gets shorter to pull on things.

There are three main types of muscle. First is skeletal muscle. This type is attached to your bones by tendons. You use these to walk or stand. You can control them with your brain.

Second is cardiac muscle. This is found only in the walls of your heart. It is a striated muscle. Striated means it has a striped look. It works on its own to pump blood.

Third is smooth muscle. It is found in organs like your stomach. It is also in your blood vessels. You do not control this muscle. It works without you thinking about it.

In animals, these muscles grow during development. This way of making muscle is called myogenesis. It starts from special parts in an embryo.

Muscle is a special soft tissue found in animals. It is one of four basic types of tissue in the body.

Muscles allow living things to move and function. There are three main types of muscle tissue in vertebrates. These are skeletal, cardiac, and smooth muscle. Each type has a very different job to do. Even though they look different, they all help the body work.

Muscle works through a process of contraction and relaxation. Inside the tissue, there are special proteins called actin and myosin. These proteins interact with each other to create movement.

Other proteins like troponin and tropomyosin help regulate this process. In skeletal muscle, the cells are long and have many nuclei. These cells are called muscle fibers. They are arranged in parallel bundles that look striped under a microscope. This striped look is called being striated.

Long ago, people gave muscles a funny name. The word muscle comes from the Latin word "musculus." This is a small version of the word for mouse.

People thought a flexed muscle looked like the back of a mouse. This same idea is found in Greek words too. Muscles form during a stage called myogenesis. This happens while an embryo is still developing. Special cells called myoblasts move to the right places to build the tissue.

Different muscles have very specific locations and numbers. Skeletal muscle makes up about 42% of an average man's body mass. For an average woman, it is about 36%.

Cardiac muscle is found only in the walls of the heart. This is called the myocardium. Smooth muscle is found in many places like the stomach and bladder. It is also in your blood vessels and even your skin. Smooth muscle cells are much shorter than skeletal muscle cells.

You can think of muscles like different kinds of engines. Skeletal muscles are like engines you drive yourself. You use your central nervous system to move them voluntarily. Cardiac and smooth muscles are like automatic engines. They work involuntarily, which means they work without you thinking.

Your heart pumps blood using cardiac muscle without any help from your mind. Smooth muscle moves food through your intestines using wave-like motions. All these different parts work together to keep you moving and alive.

Muscle is a specialized soft tissue found in animals. It is one of the four basic types of animal tissue.

This tissue is essential because it allows for movement and the maintenance of bodily functions. Muscles function by contracting and relaxing to create force. This ability is what enables everything from running to the beating of a heart.

At the microscopic level, muscle movement is a mechanical process. It relies on the interaction of contractile proteins called actin and myosin. These proteins slide against each other to cause the tissue to shorten. Two regulatory proteins, troponin and tropomyosin, help control this interaction.

This movement happens within organized units called sarcomeres. In striated muscles, these sarcomeres are arranged in parallel bundles of myofibrils. This specific arrangement creates the striped appearance seen under a microscope.

Vertebrates possess three distinct types of muscle tissue. The first is skeletal muscle, which is striated and attached to bones by tendons or aponeuroses. This type is responsible for locomotion and maintaining posture.

The second is cardiac muscle, which is also striated but found only in the heart walls, known as the myocardium. It connects at branching angles called intercalated discs. The third type is smooth muscle, which is non-striated and found in the walls of internal organs.

Smooth muscle can be single-unit, acting as a connected mass, or multiunit, allowing for finer control.

Skeletal muscle is classified by how it produces energy and speed. Type I fibers are known as slow-twitch or red muscles. They are rich in myoglobin and mitochondria, which allows them to sustain aerobic activity.

Type II fibers are fast-twitch muscles. Type IIa fibers are aerobic and appear red when deoxygenated. Type IIx is the fastest muscle type in humans, capable of intense bursts of activity. Finally, Type IIb is an anaerobic, white muscle that is less dense in myoglobin.

Muscle tissue forms during embryonic development through a process called myogenesis. All muscles derive from the paraxial mesoderm. This tissue divides into segments called somites. Each somite contains a division called the myotome, which produces muscle.

Special cells called myoblasts migrate to specific locations to fuse into long muscle cells. This complex migration is guided by chemical signals and connective tissue frameworks.

There are significant differences in how these muscles are controlled. Skeletal muscle is voluntary, meaning it is controlled by the central nervous system. However, reflexes allow for non-conscious activation of skeletal muscles through the nervous system.

In contrast, cardiac and smooth muscles are involuntary. They can be activated by the autonomic nervous system, hormones, or internal pacemaker cells. For example, cardiac muscle relies on a constant blood and electrical supply to function.

Muscle mass and density vary between individuals and species. In an average adult man, skeletal muscle makes up 42% of body mass. In an average adult woman, it accounts for 36%.

Muscle tissue is also denser than fat. Muscle has a density of approximately 1.06 kg/liter, while adipose tissue is about 0.9196 kg/liter. This makes muscle about 15% denser than fat. The word "muscle" itself comes from the Latin "musculus," meaning "little mouse," because a flexing muscle resembles a mouse moving under the skin.