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The human body is made up of more than 600 muscles that work to pump blood, support movement, and lift heavy weights. These muscles are made of thousands of small fibres woven together, and they come in three types: skeletal, smooth, and cardiac. Skeletal muscles are voluntary muscles that you can control consciously, and they make up 30-40% of your total body mass. Smooth muscles are involuntary and are usually found in sheets or layers, with muscles contracting in waves along the length of the structure. Cardiac muscles are also involuntary and make up the mass of the heart, contracting and relaxing to pump blood.
| Characteristics | Values |
|---|---|
| Number of muscles in the human body | 600 |
| Types of muscles | Skeletal, Smooth, Cardiac |
| Skeletal muscle mass | 30-40% of total body mass |
| Skeletal muscle composition | Thousands of muscle fibres |
| Types of muscle fibres | Type I, Type II A, Type II B |
| Muscle injuries | Strains, pulls, tears |
| Muscle soreness | Delayed Onset Muscle Soreness (DOMS) |
| Muscle-building supplements | Magnesium, HMB, Amino acids |
| Muscle layers | Epimysium, Perimysium, Endomysium |
| Muscle movement | Voluntary, Involuntary |
| Muscle functions | Movement, posture, balance, breathing, digestion |
| Smooth muscle functions | Female/Male reproductive system, Urinary system, Respiratory system, Digestive system |
| Cardiac muscle function | Heart contractions and pumping of blood |
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What You'll Learn
- Skeletal muscles are attached to bones by tendons and are controlled voluntarily
- Cardiac muscles are involuntary and make up the heart
- Smooth muscles are involuntary and found in the bladder, uterus, eyes, and digestive system
- Type I and Type II muscle fibres have different functions and properties
- Muscles control facial expressions, chewing, and eye movements
Skeletal muscles are attached to bones by tendons and are controlled voluntarily
Skeletal muscles are voluntary muscles, meaning you control how and when they move and work. They are the most common type of muscle in the human body, comprising 30% to 40% of total body mass. They are made of thousands of small fibres woven together. These fibres contract and relax, pulling bones towards each other across joints to enable movement. When you decide to move, the motor cortex sends an electrical signal through the spinal cord and peripheral nerves to the muscles, causing them to contract.
There are three types of muscle tissue in the body: skeletal, cardiac, and smooth muscle. Skeletal muscles are attached to bones by tendons, whereas smooth muscles are found in the walls of organs and blood vessels. Cardiac muscle is found in the heart. Smooth and cardiac muscles are involuntary muscles controlled by the autonomic nervous system.
Skeletal muscles can be further categorised into Type I and Type II fibres. Type I fibres are slow and deliberate in their contractions and are very resistant to fatigue. Type II fibres are stronger and faster than Type I fibres but do not have as much endurance. Type II fibres are further divided into Type II A and Type II B fibres. Type II A fibres are found throughout the body, especially in the legs, while Type II B fibres are faster and stronger but have even less endurance.
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Cardiac muscles are involuntary and make up the heart
The human body has more than 600 muscles, which help with everything from pumping blood around the body to lifting a heavy backpack. There are three types of muscles: skeletal, smooth, and cardiac. Cardiac muscle, also called myocardium, is an involuntary muscle that constitutes the main tissue of the wall of the heart.
The heart is made up of three layers: the pericardium, myocardium, and endocardium. The myocardium forms a thick middle layer between the outer layer of the heart wall (the pericardium) and the inner layer (the 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.
Cardiac muscle is composed of individual cardiac muscle cells, or cardiomyocytes, joined by intercalated discs and encased by collagen fibres and other substances that form the extracellular matrix. These cells are surrounded by an extracellular matrix produced by supporting fibroblast cells. The intercalated discs allow the cardiomyocytes to contract together synchronously to enable the heart to work as a pump. The cardiac muscle cells contain branched fibres, and each cell contains a single, centrally located nucleus surrounded by a cell membrane known as the sarcolemma.
The sarcolemma of cardiac muscle cells contains voltage-gated calcium channels, specialised ion channels that skeletal muscle does not possess. The rise in calcium causes the cell's myofilaments to slide past each other in a process called excitation-contraction coupling. This contraction of the heart muscle uses a lot of energy and requires a constant flow of blood to provide oxygen and nutrients.
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Smooth muscles are involuntary and found in the bladder, uterus, eyes, and digestive system
There are three types of muscles in the human body: skeletal, cardiac, and smooth muscle. Skeletal muscles are voluntary muscles, meaning that you are in control of how and when they move. Cardiac and smooth muscles, on the other hand, are involuntary muscles controlled by the autonomic nervous system. Smooth muscles line the inside of some organs and are responsible for essential tasks such as moving waste through the intestines and helping the lungs expand during breathing.
Smooth muscles are involuntary muscles that are indeed found in the bladder, uterus, eyes, and digestive system. In the urinary system, smooth muscles help to regulate the body's electrolyte balance and rid the body of toxins. They are also responsible for maintaining the contractile tone in the bladder, which is necessary for proper urinary function.
In the digestive system, smooth muscles are present in the stomach and intestines, where they play a crucial role in digestion and nutrient collection. They help move waste through the intestines and facilitate the expansion of the lungs during breathing. Smooth muscles are also found in the female reproductive system, where they line the uterus and create the contractile force during childbirth.
Smooth muscles are also present in the eyes, where they may contribute to eye movement and focus. Additionally, they play a vital role in the regulation of blood pressure and tissue oxygenation by contracting and relaxing the arteries and veins. This function is essential for maintaining the body's basic functions.
Smooth muscles have unique structural characteristics, including thick and thin filaments that do not form sarcomeres, resulting in a non-striated appearance. They contain high levels of actin and myosin, which are essential for muscle contraction. The shape of smooth muscle is fusiform, with a rounded centre tapering at each end, and it possesses greater elastic properties than striated muscle.
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Type I and Type II muscle fibres have different functions and properties
Type I and Type II muscle fibres have distinct functions and properties. Type I muscle fibres are slow-twitch fibres, contracting relatively slowly and using aerobic respiration (oxygen and glucose) to produce ATP. Type I fibres are useful for maintaining posture, producing isometric contractions, and stabilising bones and joints. They do not produce high tension and are not used for powerful, fast movements.
Type II muscle fibres, on the other hand, are fast-twitch fibres with faster contraction speeds. They can be further divided into Type IIA (fast oxidative) and Type IIX (fast glycolytic) fibres. Type IIA fibres primarily use aerobic respiration but can switch to anaerobic respiration, making them more susceptible to fatigue compared to Type I fibres. Type IIX fibres rely on anaerobic glycolysis, which leads to rapid ATP production but also causes them to fatigue quickly.
The proportion of Type I and Type II fibres in an individual's muscles varies and is influenced by genetics. Endurance and resistance training can also impact the distribution and properties of these muscle fibres. Type IIA fibres, in particular, are associated with athletic performance as they can produce high force and are relatively fatigue-resistant.
The different properties of Type I and Type II fibres are utilised in various physical activities. Type I fibres are suited for endurance exercises like long-distance running, while Type II fibres are more involved in high-intensity, short-duration activities such as sprinting or weight lifting.
Understanding the characteristics of these muscle fibres is important for optimising training regimens and can also provide insights into muscle diseases and the ageing process. The ability to maintain motor control and movement in older age may be linked to the continued recruitment of Type II fibres.
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Muscles control facial expressions, chewing, and eye movements
The human face has about 20 facial muscles that are essential for chewing and making facial expressions. These muscles are part of the skeletal system (musculoskeletal system) and are located around the facial openings of the mouth, eyes, nose, and ears, stretching across the skull and neck. They are typically paired, with one on the left side of the face and one on the right.
Facial muscles involved in chewing (muscles of mastication) include the lateral pterygoid, masseter, medial pterygoid, and temporalis. The lateral pterygoid is a fan-shaped muscle that helps open the jaw, while the masseter runs from the cheek to the side of the jaw and helps close it. The medial pterygoid is a thick muscle that also assists in jaw closure, and the temporalis is another fan-shaped muscle that contributes to jaw closure.
The muscles that control facial expressions can be divided into groups based on their location. For example, the corrugator supercilii, located near the eyebrow, enables frowning. The procerus, a small pyramidal muscle between the eyebrows, depresses the medial ends of the eyebrows and wrinkles the skin, creating an expression of anger or sorrow. The orbicularis oculi sphincter muscles close the eyes, depress the brows, and produce "crow's feet" wrinkles at the eyes' corners. The nasalis muscle is involved in creating facial expressions of anger and enhancing deep breathing.
In addition to their role in facial expressions and chewing, the facial muscles also serve a crucial function in eye movements. The orbitalis muscle, for instance, is a sphincter-like muscle that encircles the orbit and the periorbital area. It consists of three parts: the orbital, palpebral, and deep palpebral (lacrimal) parts. The palpebral part, arising from the medial palpebral ligament, is responsible for the movement of the eyelids.
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Frequently asked questions
Muscles are pieces of soft tissue made of thousands of small fibres woven together. They help your body perform a wide range of movements and functions.
There are over 600 muscles in the human body.
There are three types of muscles: skeletal, smooth, and cardiac.
Skeletal muscles are voluntary muscles that you can control. They are attached to bones and help with movement, posture, and balance.
Smooth muscles are involuntary muscles that you cannot control. They are found in the walls of blood vessels and organs like the bladder, intestines, and stomach.
