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The human body has over 600 muscles that help us move, breathe, and stay alive. Muscles are pieces of soft tissue that are attached to bones or internal organs and blood vessels. The muscular system is composed of specialized cells called muscle fibres, which are bundled together to form sarcomeres, the fundamental contractile unit of a skeletal muscle. Skeletal muscles are the most common type of muscle in the body, comprising 30-40% of total body mass. They are attached to the bones by tendons and are under voluntary control. There are two other types of muscles in the body: smooth muscle and cardiac muscle. Smooth muscle tissue lines some of our organs and cardiac muscle is found only in the heart.
| Characteristics | Values |
|---|---|
| Number of muscles in the human body | More than 600 |
| Muscle tissue | Soft |
| Muscle function | Help with movement, breathing, swallowing, and staying alive |
| Types of muscles | Skeletal, cardiac, and smooth muscle |
| Skeletal muscle composition | Flexible muscle fibers ranging from less than 0.5 inches to over 3 inches in diameter |
| Skeletal muscle function | Allow a wide range of movements and functions, provide structural support, and help maintain posture |
| Skeletal muscle mass | 30%-40% of total body mass |
| Cardiac muscle tissue | Striated, strong, autorhythmic, intrinsically controlled, and involuntary |
| Smooth muscle | Visceral, weakest muscle tissue, involuntary |
| Muscles with unique names | Sternocleidomastoid, tibialis anterior, splenius capitis, splenius cervicis, erector spinae (iliocostalis, longissimus, spinalis) |
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Skeletal muscles
Skeletal muscle cells are much longer than other types of muscle tissue and are also known as muscle fibres. These muscle fibres are composed of myofibrils, which are made up of actin and myosin filaments called myofilaments. These filaments repeat in units called sarcomeres, which are the basic functional, contractile units of the muscle fibre necessary for muscle contraction. Skeletal muscle fibres are red and white and have a striped appearance due to the arrangement of sarcomeres, so they are often referred to as striated muscles.
The skeletal muscle plays a crucial role in maintaining thermostasis and acts as an energy source during starvation. It also serves as a storage source for amino acids, which organs use to synthesise organ-specific proteins. The health and strength of skeletal muscles are important, as they are susceptible to various conditions, from mild injuries to serious or life-threatening myopathies.
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Smooth muscles
The human body has three types of muscles: skeletal, cardiac, and smooth. Smooth muscles are involuntary muscles that work automatically and are found throughout the body. They get their name from their smooth, uniform appearance under a microscope, which is different from the banded appearance of skeletal and cardiac muscles. Smooth muscles are involved in a variety of functions, including digestion, nutrient collection, toxin removal, electrolyte balance, blood pressure regulation, and tissue oxygenation. They are also responsible for controlling the width of passages inside the body, such as in the digestive tract, bladder, and butthole.
At a cellular level, smooth muscles function involuntarily and are controlled by the nervous system through hormones, neurotransmitters, and other receptors. They play a significant role in the disease process and are targeted by various medical treatments. For example, bronchodilators are used to relax airway smooth muscle in asthma, and nitrates are used in combination with ACE inhibitors to treat ischemic heart disease.
Overall, smooth muscles are an integral part of the human body, facilitating essential functions and demonstrating unique structural and functional characteristics that distinguish them from other types of muscles.
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Cardiac muscles
Muscle anatomy is the study of the structure and function of muscles in the body. There are over 600 muscles in the human body, and they are all made of soft tissue. The heart is the only organ in the body that is also a muscle. This muscle, called the myocardium, is made of a special type of muscle tissue called cardiac muscle.
Cardiac muscle is one of three major categories of muscles found in the human body, the other two being smooth muscle and skeletal muscle. It is an involuntary, striated muscle that constitutes the main tissue of the wall of the heart. The cardiac muscle forms a thick middle layer between the outer layer of the heart wall (the pericardium) and the inner layer (the endocardium). The heart wall is a three-layered structure, with the myocardium making up the thickest layer.
The individual cardiac muscle cells are called cardiomyocytes. These cells are tubular structures composed of chains of myofibrils, which are rod-like units within the cell. The myofibrils consist of repeating sections of sarcomeres, which are the fundamental contractile units of the muscle cells. Sarcomeres are composed of long proteins that organize into thick and thin filaments, called myofilaments. Thin myofilaments contain the protein actin, and thick myofilaments contain the protein myosin. The myofilaments slide past each other as the muscle contracts and relaxes. This process is activated by the release of calcium from the sarcoplasmic reticulum (SR) when delivering an action potential to the muscle, in a process called excitation-contraction coupling. The sliding of actin and myosin past each other produces the formation of “cross-bridges”, which causes contraction of the heart and generation of force.
Cardiac muscle cells are joined by intercalated discs, which contain gap junctions and desmosomes. These interconnections allow the cardiomyocytes to contract together synchronously to enable the heart to work as a pump. The intercalated discs provide a strong bond between the cells, allowing the muscle cells to resist high blood pressures and the strain of pumping blood throughout a lifetime. These features also help to spread electrochemical signals quickly from cell to cell so that the heart can beat as a unit.
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Muscle contractions
The human body has more than 600 muscles that help us move, breathe, swallow, and stay alive. Muscles are pieces of soft tissue that are found throughout the body. They help us do everything from holding our body still to running a marathon.
Muscles are classified into three types: skeletal, smooth, and cardiac. Skeletal muscles are attached to bones and give the body structure and strength. They are under voluntary control and are concerned with movement, posture, and balance. The skeletal muscle tissue is composed of cells called muscle fibers. When a nervous system signal reaches the neuromuscular junction, a chemical message is released by the motor neuron. This starts a chemical reaction within the muscle, leading to the contraction and relaxation of muscles.
Smooth muscle tissue lines some of the organs in our body and is controlled by the unconscious part of the brain. It is, therefore, an involuntary muscle. Smooth muscle is found throughout the blood vessels, gastrointestinal (GI) tract, bronchioles, uterus, and bladder.
Cardiac muscle is found only in the heart and is responsible for pumping blood throughout the body. It is also an involuntary muscle. The cells of cardiac muscle tissue are striated and appear to have light and dark stripes when viewed under a light microscope.
The mechanism of muscle contraction can be explained by the sliding filament theory. Muscle contraction is the activation of tension-generating sites within muscle cells. Muscle shortening and contraction are not synonymous. Tension within the muscle can be produced without changes in the length of the muscle, as when holding a heavy object in the same position.
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Muscle groups
The human body has more than 600 muscles, which are pieces of soft tissue that help us move, breathe, swallow and stay alive. The muscular system can be considered one anatomical group, but muscles can also be grouped by their location or the type of movement they perform.
Muscles are considered the only tissue in the body that can contract and move other body parts. They are made of thousands of small fibres woven together, and their names are derived from a variety of factors, including location, origin and insertion, number of origins, shape, size, direction, and function.
There are five major muscle groups in the body: pectorals, quadriceps, calves, glutes, and the sternocleidomastoid muscles. The pectorals, or pecs, are the large chest muscles composed of thick muscle fibres. They add bulk to the upper body and are activated by everyday movements, mainly at the shoulder joint. The four muscles that make up the front of the thigh are called the quadriceps or quads, the second-largest muscle structure in the human body. The calves are located in the lower back part of the legs and are essential for lifting the heels, as well as explosive moves such as sprinting, jumping, and climbing. The glutes are the muscles of the buttocks and the largest muscles in the body. They are crucial for the movement of the legs backward and sideways and help maintain balance while walking or running. The sternocleidomastoid muscles are located on the sides of the neck and are responsible for neck flexion and rotation, as well as assisting in forced inhalation.
Additionally, there are three types of muscle tissue in the body: striated or skeletal muscle, smooth muscle, and cardiac muscle. Smooth muscle lines some organs, and skeletal muscles are attached to bones by tendons. The heart is the only organ that is also a muscle, composed of cardiac muscle tissue.
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Frequently asked questions
Muscles are pieces of soft tissue that help humans move, breathe, stay alive, and swallow. There are more than 600 muscles in the human body.
There are three types of muscles in the human body: skeletal, smooth, and cardiac. Skeletal muscles are the most common type and they are attached to the bones, allowing for a wide range of movements and functions. Smooth muscles line some of the organs and cardiac muscles are found only in the heart.
Skeletal muscles are voluntary muscles that are attached to the bones and controlled by the somatic nervous system. They make up between 30% and 40% of the human body's total mass. Skeletal muscles are responsible for movements such as walking and running, as well as more subtle movements like facial expressions and eye movements.
Smooth and cardiac muscles are involuntary muscles controlled by the autonomic nervous system. Smooth muscles are found in some organs and help facilitate body functions like digestion. Cardiac muscles are responsible for pumping blood throughout the body and stimulating heartbeats.
