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The human body is an intricate system, housing over 600 muscles that help us move, breathe, and perform a multitude of other functions. These muscles can be broadly categorized into three types: skeletal, smooth, and cardiac. Skeletal muscles are attached to bones and are responsible for our movements and posture. Smooth muscles, as the name suggests, have a smooth appearance and are found in the walls of organs like the lungs, intestines, and blood vessels. Cardiac muscles are located in the heart and play a vital role in pumping blood throughout our bodies. Each type of muscle has unique characteristics, and together they enable us to perform a wide range of physical activities, from the subtle eye movements when reading a book to more strenuous exercises like running a marathon. Understanding the different types of muscles and their functions is essential for maintaining our overall health and well-being.
| Characteristics | Values |
|---|---|
| Number of muscles in the human body | More than 600 |
| Types of muscles | 3: Skeletal, Smooth, and Cardiac |
| Skeletal muscle composition | Thousands of muscle fibres bundled together |
| Skeletal muscle appearance | Striated |
| Skeletal muscle function | Controls voluntary movement and supports bones to maintain posture |
| Skeletal muscle control | Voluntary |
| Smooth muscle appearance | Smooth |
| Smooth muscle location | Walls of many organs, including the lungs, gastrointestinal tract, reproductive organs, blood vessels, and skin |
| Smooth muscle function | Uses contractile force for shortening and propelling various contents across the lumen of multiple organ systems |
| Smooth muscle control | Involuntary |
| Cardiac muscle location | Walls of the heart |
| Cardiac muscle appearance | Striated |
| Cardiac muscle function | Propels blood and leads to proper oxygenation and maintenance of each cell in the body |
| Cardiac muscle control | Involuntary |
| Muscle injuries | Strains, spasms, cramps, skin discolouration, etc. |
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What You'll Learn
Humans have over 600 muscles
The human body has over 600 muscles that help us perform a wide range of functions, from moving our bodies to breathing and even digesting food. These muscles are made up of thousands of small fibres woven together, allowing us to move our organs and body parts.
There are three main types of muscle tissue in the human body: skeletal, cardiac, and visceral or smooth muscle. Skeletal muscles are the most common type, comprising 30% to 40% of our total body mass. They are attached to bones by tendons and are under our voluntary control, allowing us to perform various movements and maintain our posture and balance. Skeletal muscles are responsible for conscious movements like speaking, writing, and walking. They are also categorized as striated muscles due to their striped appearance under a microscope.
Cardiac muscles, on the other hand, are responsible for the rhythmic contractions of the heart, which is a vital pumping organ. Cardiac muscles are also striated and make up the mass of the heart. Smooth or visceral muscles are found in the walls of blood vessels and organs like the urinary bladder, intestines, and stomach. They are the weakest of all muscle tissues and are controlled by the unconscious part of the brain, making them involuntary muscles.
Additionally, muscles can be categorized based on their function into agonist, antagonist, and synergist muscles. Agonist muscles are the prime movers in a particular movement, while antagonist muscles work in opposition to the agonists to provide stability and control. Synergist muscles assist in movement by stabilizing and reducing unnecessary motions, often working near the agonist muscles.
Muscles play a crucial role in our daily lives, and maintaining their health is essential for overall well-being.
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Skeletal muscles
Skeletal muscle is one of the three types of vertebrate muscle tissue, the others being cardiac muscle and smooth muscle. Skeletal muscle is commonly referred to as 'muscle' and is part of the voluntary muscular system. They are typically attached by tendons to the bones of a skeleton. Skeletal muscle cells are much longer than other types of muscle tissue and are also known as muscle fibres.
The tissue of skeletal muscle is striated, having a striped appearance due to the arrangement of the sarcomeres. Skeletal muscles contain multiple fascicles, or bundles of muscle fibres. Each individual fibre and each muscle is surrounded by a type of connective tissue layer of fascia. Skeletal muscles comprise about 35% of the body of humans by weight, and in healthy young adults, they can make up around 40% of body weight.
Muscle fibres are composed of myofibrils, which are made up of actin and myosin filaments called myofilaments. These are repeated in units called sarcomeres, which are the basic functional, contractile units of the muscle fibre necessary for muscle contraction. Skeletal muscle myocytes are usually very large, measuring about 2-3cm long and 100 μm in diameter.
The functions of skeletal muscle include producing movement, maintaining body posture, controlling body temperature, and stabilizing joints. Skeletal muscle is also an endocrine organ and acts as a storage source for amino acids that different organs of the body can use for synthesizing organ-specific proteins.
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Cardiac muscles
The human body is made up of hundreds of muscles, with each type serving a unique function. One such type is cardiac muscle, also known as myocardium, which is one of the three major categories of muscles in the body, alongside smooth muscle and skeletal muscle.
Cardiac muscle is a type of muscle tissue that forms the heart. It is involuntary, meaning a person cannot control it. This tissue is responsible for the contractility of the heart, or the pumping action, which keeps blood circulating throughout the body. The heart is made up of three layers: the pericardium, the myocardium, and the endocardium. The myocardium is the thick middle layer of the heart, surrounded by a thin outer layer called the epicardium (or visceral pericardium) and an inner endocardium.
Cardiac muscle cells, or cardiomyocytes, are striated, branched, and contain many mitochondria. They 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. The thick filaments contain the protein myosin, while the thin filaments contain the protein actin. When a cardiac muscle cell contracts, the myosin filament pulls the actin filaments toward each other, causing the cell to shrink and generating the pressure needed to pump blood.
The outside of the cardiomyocyte is surrounded by a plasma membrane called the sarcolemma, which acts as a barrier between extracellular and intracellular contents. The sarcolemma contains voltage-gated calcium channels, which are specialized ion channels that skeletal muscle does not possess. Cardiac muscle cells are connected via intercalated discs, which contain gap junctions and desmosomes. These interconnections allow the cardiomyocytes to contract together synchronously, producing a coordinated contraction of the cardiomyocytes in unison.
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Smooth muscles
Smooth muscle is one of the three main types of muscle tissue in the human body, the other two being skeletal and cardiac muscle. Smooth muscle is found in the walls of hollow visceral organs such as the liver, pancreas, stomach, intestines, bladder, and uterus. It is also present in the walls of blood vessels and lymph vessels, where it is known as vascular smooth muscle. Smooth muscle is controlled by the autonomic nervous system and works involuntarily, without conscious thought.
Smooth muscle cells are spindle-shaped with a wide middle and tapering ends, and a single nucleus. They have a different structure from skeletal muscle cells, which are long and cylindrical and form bundles of fibres that give the muscle a grooved appearance. Smooth muscle does not have myofibrils, but its cytoplasm contains large amounts of the proteins myosin and actin, which enable the muscle to contract. Myosin is primarily class II in smooth muscle, with two heavy chains that form a coiled-coil structure.
Smooth muscle serves a variety of functions in the body, including digestion and nutrient collection in the gastrointestinal tract, toxin removal and electrolyte balance in the urinary system, and blood pressure regulation and tissue oxygenation in arteries and veins. It also plays a role in vision by controlling the dilation and constriction of the pupils and the shape of the lens to focus on objects. In the skin, smooth muscle causes hairs to stand on end, resulting in goosebumps.
Smooth muscle can be divided into two subgroups: single-unit and multi-unit smooth muscle. Most smooth muscle is of the single-unit type, which is found in the walls of internal organs, blood vessels, the urinary tract, and the digestive tract. Single-unit smooth muscle contracts as a whole, allowing for coordinated movement. Multi-unit smooth muscle, on the other hand, is found in the trachea, iris of the eye, and lining the large elastic arteries. It is neurogenic, meaning its contraction is initiated by the autonomic nervous system.
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Muscle injuries and conditions
Muscle injuries are a broad term for many pathologies that are common in both athletes and the general population. Muscle strains (pulled muscles) are among the most common muscle injuries. They occur when muscle fibres are stretched beyond their limit and tear apart, causing pain and soreness. This can happen suddenly or gradually, and the severity of the strain can range from mild to severe. A severe tear might require medical care or even surgery.
Muscle soreness after exercise is known as delayed onset muscle soreness (DOMS) and is classified as a grade 1 muscle strain injury. It typically peaks between 24 to 72 hours after exercise and disappears within five to seven days. DOMS is common in individuals who engage in strenuous and unaccustomed physical activity.
Other types of muscle injuries include lacerations, contusions, and degenerative diseases such as muscular dystrophies. Lacerations occur when the muscle is cut by an external object during traumatic accidents. Contusions, on the other hand, are caused by a compressive force to the muscle, often seen in contact sports.
Muscle injuries can also be caused by overuse or repetitive strain. This can happen in athletes who repeatedly perform specific movements or in individuals with certain occupations requiring repetitive tasks. Specific biomechanical or physiological factors may predispose an athlete to injury. Additionally, certain health conditions can affect the muscles, including fibromyalgia, myopathies, myositis, infections, and cardiovascular disease.
It is important to seek medical attention for muscle injuries, especially if there is severe pain, bruising, swelling, or nerve-related symptoms. Proper diagnosis and treatment are crucial for a successful recovery. A healthcare provider may use various tests, such as blood tests, electromyography (EMG), magnetic resonance imaging (MRI), ultrasound, and muscle biopsy, to diagnose and determine the appropriate treatment for muscle conditions or injuries.
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Frequently asked questions
The human body has over 600 muscles.
There are three types of muscles: skeletal, smooth, and cardiac.
Skeletal muscles are attached to bones via tendons and are responsible for movement and posture. They are the only type of muscles that can be controlled voluntarily.
Smooth muscles are found in the walls of many organs, such as the lungs, gastrointestinal tract, reproductive organs, and blood vessels. They are responsible for moving food through the digestive tract and propelling various contents across multiple organ systems.
Cardiac muscles encompass the heart and are responsible for pumping blood and oxygenating the cells of the human body. They are under involuntary control.
