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There are three types of muscle tissue in vertebrates: skeletal, cardiac, and smooth muscle. The muscular system is responsible for the movement of the human body. Skeletal muscles, which are the most common type of muscle in the body, are attached to the bones of the skeletal system and allow us to perform a wide range of movements and functions. Each skeletal muscle may be made up of hundreds or thousands of muscle fibers bundled together and wrapped in connective tissue. These muscle fibers contract and allow the muscles to move bones. Cardiac muscle tissue is found only in the walls of the heart, while visceral muscle is found inside organs like the stomach and intestines.
| Characteristics | Values |
|---|---|
| Number of muscles in the human body | More than 600 |
| Muscle tissue types | Three: skeletal, cardiac, and smooth muscle |
| Skeletal muscle composition | Tendons, perimysium, skeletal muscle tissue, blood vessels, nerves |
| Skeletal muscle mass | 30-40% of total body mass |
| Skeletal muscle fibre length | 0.5-3 inches |
| Skeletal muscle fibre width | 3-8 micrometres |
| Skeletal muscle fibre breadth | 18-200 micrometres |
| Cardiac muscle composition | Branched X or Y-shaped cells with intercalated disks |
| Smooth muscle location | Walls of organs and structures like the oesophagus, stomach, intestines, bronchi, uterus, urethra, bladder, blood vessels |
| Smooth muscle function | Moving substances through organs |
| Abdominal muscle count | Five |
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Skeletal muscle
Each skeletal muscle contains multiple fascicles, or bundles of muscle fibres. These muscle fibres are multinucleated, with the nuclei referred to as myonuclei, which are located along the inside of the cell membrane. The muscle fibres are formed through the fusion of myoblasts, resulting in long multinucleated cells. Skeletal muscle fibres are typically much longer than those of other muscle tissues, measuring between 2 and 3 cm in length and 10 to 100 μm in diameter.
The skeletal muscles are responsible for various functions, including producing movement, maintaining body posture, controlling body temperature, and stabilizing joints. They also play a role in chewing and swallowing, as well as expanding and contracting the chest cavity for breathing. Additionally, skeletal muscles are involved in the generation of body heat through the contraction of muscle fibres.
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Smooth muscle
Additionally, smooth muscle is involved in various specific functions throughout the body. For example, it causes hairs to stand on end, forming goosebumps. In the eyes, smooth muscles control how the eyes focus by pulling on zonule fibres and dilating or constricting the pupils. In the uterus, smooth muscles are responsible for contractions during labour. Smooth muscle is inherently linked to many medical treatments, especially those aimed at modifying signalling pathways that affect smooth muscle function.
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Cardiac muscle
There are three types of muscle in the body: skeletal, smooth, and cardiac. Cardiac muscle, also called the myocardium, is an involuntary, striated muscle that constitutes the main tissue of the wall of the heart. The heart is made up of three layers: the pericardium, the myocardium, and the endocardium. The endocardium is not cardiac muscle, but 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.
Specialised modified cardiomyocytes known as pacemaker cells set the rhythm of the heart contractions. They are only weakly contractile and are connected to neighbouring contractile cells via gap junctions. They are distributed throughout the heart and are responsible for generating and sending out electrical impulses. The Purkinje fibres rapidly conduct these electrical signals. Coronary arteries bring nutrients to the muscle cells, and veins and a capillary network take away waste products.
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Muscle contractions
The human body has more than 600 muscles, which help us move, breathe, swallow, and stay alive. There are three types of muscles: skeletal, smooth, and cardiac. Skeletal muscles are attached to bones and allow us to perform a wide range of movements and functions. They are voluntary muscles, meaning we control how and when they work. Smooth and cardiac muscles, on the other hand, are involuntary and are controlled by the autonomic nervous system.
Muscles contract when stimulated by signals from motor neurons. Motor neurons release neurotransmitter chemicals that bond to a part of the sarcolemma known as the motor end plate. This causes the opening of ion channels, allowing positive ions to enter the muscle fiber and creating an electrochemical gradient. This process leads to the release of Ca2+ ions, which bind to troponin, causing a change in shape and moving nearby molecules of tropomyosin. This movement allows actin and myosin to bind together, resulting in muscle contraction.
There are different types of muscle contractions, including concentric, eccentric, and isometric contractions. Concentric contractions occur when the muscle tension is sufficient to overcome the load, resulting in the muscle shortening as it contracts. An example is lifting a heavy box, where your arm muscles contract to hold the weight, and your leg muscles tighten as you stand up with the additional weight. Eccentric contractions happen when the muscle is actively lengthened, such as when walking or lowering something heavy. Isometric contractions occur when the muscle is held at a set length without lengthening or shortening, like carrying something in front of you without raising or lowering it.
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Muscle fibres
The human body contains more than 600 muscles, which are made up of thousands of small muscle fibres woven together. These fibres stretch and press together to enable movement.
There are three types of muscle tissue: visceral, cardiac, and skeletal. Visceral muscle is the weakest type of muscle tissue and is found inside organs like the stomach, intestines, and blood vessels. It contracts to move substances through the organ and is controlled by the unconscious part of the brain, making it an involuntary muscle.
Cardiac muscle is striated, meaning it appears to have light and dark stripes when viewed under a light microscope. The cells of cardiac muscle are X or Y-shaped and are connected by intercalated discs, which provide a strong bond between the cells. This allows cardiac muscle to resist high blood pressure and the strain of pumping blood. Cardiac muscle is also branched and interconnected, allowing for the beating of the heart.
Skeletal muscle is the most common type of muscle in the body and is attached to bones, allowing for a wide range of movements. Skeletal muscle fibres are classified into two types: type 1 and type 2. Type 1 fibres utilize oxygen to generate energy for movement and have a higher density of mitochondria, making them dark. Type 2 fibres can be further divided into subtypes. Type 2A fibres can use oxygen to generate energy but contain fewer mitochondria, making them light. Type 2B fibres do not use oxygen and instead store energy for short bursts of movement. They have the fewest mitochondria and appear white. Skeletal muscle fibres can also be classified as slow oxidative (SO), fast oxidative (FO), or fast glycolytic (FG).
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Frequently asked questions
Muscles are pieces of soft tissue throughout your body that help you move, breathe, swallow and stay alive. There are more than 600 muscles in the human body.
There are three types of muscles in the body: skeletal, smooth, and cardiac. Skeletal muscles are voluntary muscles that you control consciously. Smooth and cardiac muscles are involuntary and are controlled by the autonomic nervous system.
Skeletal muscles are the most common type of muscle in the body. They are attached to the bones and allow you to perform a wide range of movements and functions. Skeletal muscles make up between 30% and 40% of your total body mass.
Smooth muscles are involuntary muscles that line the inside of some organs. They help with essential functions such as moving waste through your intestines and expanding your lungs when you breathe. Smooth muscles are also found within the walls of organs and structures such as the oesophagus, stomach, intestines, and blood vessels.
