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The human body is made up of hundreds of muscles, which are pieces of soft tissue that help us move, breathe, swallow, and stay alive. There are three types of muscles in the body: skeletal, cardiac, and smooth muscle. Smooth muscle tissue lines some of our organs, while skeletal muscles are attached to bones and allow us to perform a wide range of movements and functions. Cardiac muscle is a special type of muscle tissue that is only found in the heart.
| Characteristics | Values |
|---|---|
| Definition | Muscles are pieces of soft tissue throughout your body that help you move, breathe, swallow and stay alive. |
| Types of muscles | There are three types of muscles in the human body: skeletal, cardiac and smooth muscle. |
| Muscle lining | Smooth muscle tissue lines some of the organs in the body. |
| Muscle mass | Skeletal muscles comprise 30% to 40% of your total body mass. |
| Muscle fibres | Each skeletal muscle fibre is a single cylindrical muscle cell. Each muscle is surrounded by a connective tissue sheath called the epimysium. |
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What You'll Learn
Skeletal muscle
Each skeletal muscle is made up of hundreds or even thousands of muscle fibres bundled together and wrapped in a connective tissue covering. These fibres are long and cylindrical muscle cells, also known as myocytes, that range from 2 to 3 cm in length and 100 micrometers in diameter. The fibres contract, allowing the muscles to move bones and enabling various movements.
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Cardiac muscle
The human body contains three kinds of muscle tissue: skeletal, smooth, and cardiac. Cardiac muscle, also called the myocardium, is a type of muscle tissue that forms the heart. It is an involuntary, striated muscle that constitutes the main tissue of the wall of the heart. The heart is the only place in the body that has cardiac tissue.
The primary function of cardiac muscle is to pump blood into circulation by generating sufficient force. When the cardiac muscle contracts, the myosin filament pulls the actin filaments toward each other, causing the cell to shrink. This contraction allows the ventricle to squeeze in several directions simultaneously, maximising the amount of blood squeezed out of the heart with each heartbeat.
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Smooth muscle
Multi-unit smooth muscle, on the other hand, is neurogenic and requires stimulation from the autonomic nervous system for contraction. It is found in the trachea, iris of the eye, and lining the large elastic arteries. Smooth muscles play a crucial role in various bodily functions, including blood pressure regulation, circulation, vision, and digestion. They are also responsible for goosebumps, pupil dilation, and contractions during labour.
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Muscle tissue
Skeletal muscle is the most common type of muscle in the body, accounting for 30-40% of total body mass. It is a voluntary muscle, meaning we control how and when it moves. Skeletal muscles are attached to bones and allow us to perform a wide range of movements. Each skeletal muscle fibre is a single cylindrical muscle cell, and each muscle is made up of hundreds or thousands of these fibres bundled together and wrapped in a connective tissue covering. Skeletal muscle tissue is striated, consisting of elongated multinucleate muscle cells called muscle fibres, and is responsible for body movements.
Smooth muscle is an involuntary, non-striated muscle that lines some organs such as the liver, pancreas, and intestines. It does essential jobs like moving waste through the intestines and helping the lungs expand during breathing. Smooth muscle plays a role in the female and male reproductive systems, the urinary system, the respiratory system, and the digestive system.
Cardiac muscle is also an involuntary muscle. It is found only in the walls of the heart and is made of a special type of muscle tissue. Cardiac muscle has branching fibres, one nucleus per cell, striations, and intercalated discs.
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Muscle fibres
There are three types of muscle fibres: slow oxidative (SO), fast oxidative (FO), and fast glycolytic (FG). Most skeletal muscles contain all three types, although in varying proportions. Muscle fibres can adapt to changing demands by changing size or fibre type composition. This plasticity serves as the basis for physical therapy interventions designed to increase a patient's force development or endurance.
Skeletal muscle fibres are classified into two types: type 1 and type 2. Type 2 is further divided into subtypes: Type 2A and Type 2B. Type 1 fibres utilise oxygen to generate energy for movement and have a higher density of energy-generating organelles called mitochondria, which makes them appear dark. Type 2A fibres can also use oxygen to generate energy but contain fewer mitochondria, making them lighter in appearance. Type 2B fibres do not use oxygen to generate energy; instead, they store energy for short bursts of movement and have the fewest mitochondria, appearing white.
Slow-twitch and fast-twitch fibres are influenced by training. For example, sprint training can improve the power generated by slow-twitch fibres, while endurance training can increase the endurance level of fast-twitch fibres. The number of slow and fast-twitch fibres in the body is determined by genetics. Age-related loss of muscle mass occurs due to a decrease in the total number of both type I and type II fibres, with a preferential atrophy of type II fibres.
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Frequently asked questions
Muscle lining refers to the smooth muscle tissue that lines some of the organs in the body. Smooth muscle is an involuntary muscle that plays an essential role in keeping you alive.
Smooth muscle fibres line the walls of hollow visceral organs such as the liver, pancreas and intestines.
Muscle lining, or smooth muscle, helps to move waste through the intestines and aids in lung expansion when breathing.
Skeletal muscle is the most common type of muscle in the body and is attached to the bones, allowing for a wide range of movements. Unlike smooth muscle, skeletal muscle is voluntary, meaning you control how and when it moves.
Cardiac muscle is the third type of muscle and is located in the walls of the heart. It is involuntary.
