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The human body has over 600 muscles, which are made of thousands of small fibres woven together. These fibres stretching and pressing together is what moves your organs or body. There are three types of muscles: skeletal, smooth, and cardiac. Skeletal muscles are attached to the bones by tendons and are under voluntary control. Smooth muscles are involuntary and are usually found in sheets or layers, with one layer of muscle behind the other. Cardiac muscle is also involuntary and makes up the mass of the heart. Muscles can be found all over the body, from the neck, back, and shoulders to the arms, legs, chest, and more.
| Characteristics | Values |
|---|---|
| Number of muscles in the body | More than 600 |
| Muscle types | Skeletal, cardiac, smooth |
| Skeletal muscle other names | Striated muscle |
| Skeletal muscle composition | Located between bones, made of flexible muscle fibres, controlled voluntarily |
| Skeletal muscle function | Allow a wide range of movements and functions |
| Skeletal muscle mass | 30% to 40% of total body mass |
| Cardiac muscle other names | Myocardium |
| Cardiac muscle function | Makes up the heart, responsible for rhythmic contractions |
| Cardiac muscle control | Involuntary |
| Smooth muscle other names | Involuntary muscle |
| Smooth muscle function | Found in walls of blood vessels, urinary bladder, intestines, stomach, eyes |
| Smooth muscle control | Involuntary |
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Skeletal muscles
The primary function of skeletal muscles is contraction, which allows for movement. When skeletal muscles contract, they also function as endocrine organs by secreting myokines, a type of signalling molecule. Skeletal muscles also play a vital role in maintaining posture and balance, protecting vital organs, and producing body heat. Additionally, they act as a storage source for amino acids and glycogen, which can be used for energy during starvation or intense activity.
The health of skeletal muscles is crucial, and maintaining their strength and flexibility is important. Skeletal muscles have nerve fibres and blood vessels that supply oxygen and nutrients and remove waste products. Intense exercise can lead to a buildup of lactic acid, causing soreness that typically resolves within a few days.
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Involuntary muscles
The human body has more than 600 muscles, which help with everything from moving your body to keeping you alive. There are three types of muscles: skeletal, cardiac, and smooth muscle. Skeletal muscles are voluntary muscles, meaning you control how and when they move. Cardiac and smooth muscles are involuntary muscles, which means they work without you having to think about it.
One very important involuntary muscle is the heart, which beats continuously to pump blood around the body. Cardiac muscle, or myocardium, makes up the middle layers of the heart and is responsible for squeezing and relaxing to pump blood through the cardiovascular system. Cardiac muscle is also striated, but it is under involuntary control.
Smooth muscles are also found in the internal walls of the intestines, stomach, uterus, and blood vessels. They help in pushing food molecules along the length of the alimentary canal, controlling the internal diameter of the blood vessels, and contracting the uterus during labour and childbirth. These muscles also play an important role in the female and male reproductive systems, the urinary system, and the respiratory system.
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Voluntary muscles
Skeletal muscles are voluntary muscles that connect to bones and allow a wide range of movements and functions. They make up 30-40% of total body mass and are attached to bones by tendons. Examples of skeletal muscles include shoulder, hamstring, and abdominal muscles.
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Cardiac muscles
The human body has more than 600 muscles, and they can be categorised into three types: skeletal, cardiac, and smooth muscle. Cardiac muscle, also called myocardium, 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 is made up of three layers: the pericardium, myocardium, and endocardium. The endocardium is not cardiac muscle and is comprised of simple squamous epithelial cells that form the inner lining of the heart chambers and valves. The pericardium is a fibrous sac surrounding the heart, consisting of the epicardium, pericardial space, parietal pericardium, and fibrous pericardium. The cardiac muscle is responsible for the contractility of the heart and, therefore, the pumping action.
The primary function of the cardiac muscle is to pump blood into circulation by generating sufficient force. The mechanism behind each coordinated contraction involves the cardiac muscle and electrical impulses. These contractile functions of the heart require ATP, which can be obtained through various substrates, including fatty acids, carbohydrates, proteins, and ketones. The contractile units of the muscle cells are called sarcomeres, which are composed of long proteins that organise 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.
Cardiac muscle cells (cardiomyocytes) are the contractile myocytes of the cardiac muscle. The cells are surrounded by an extracellular matrix produced by supporting fibroblast cells. Cardiomyocytes are tubular structures composed of chains of myofibrils, which are rod-like units within the cell. The cardiomyocytes are joined together at their ends by intercalated discs to create a syncytium of cardiac cells.
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Smooth muscles
In terms of location, smooth muscles can be found in the walls of hollow organs, such as the intestines, uterus, stomach, and bladder. They are also present in the walls of passageways, including arteries and veins of the cardiovascular system. Additionally, smooth muscles are found in the tracts of the urinary, respiratory, and reproductive systems.
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Frequently asked questions
Skeletal muscles are attached to bones by tendons and make up 30% to 40% of your total body mass. Your shoulder muscles, hamstring muscles, and abdominal muscles are all examples of skeletal muscles.
Smooth muscles are usually found in layers with one layer of muscle behind the other. They are located in the walls of blood vessels and structures such as the urinary bladder, intestines, and stomach.
Cardiac muscles make up the mass of the heart and are responsible for its rhythmic contractions.
Muscles in your chest and back move your ribs when you breathe.
