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The human body is an intricate machine, with over 600 muscles supporting almost every part of it. These muscles are made of thousands of small fibres woven together, allowing us to move, breathe, swallow and survive. There are three types of muscle tissue: skeletal, cardiac, and smooth. Skeletal muscles are voluntary muscles that support our weight and movement and are connected to our bones by tendons. Cardiac muscles are involuntary and exist only in the heart, helping to pump blood throughout our bodies. Smooth muscles are also involuntary and line the insides of some organs. Each muscle is made up of multiple tissues, including blood vessels, lymphatics, contractile muscle fibres, and connective tissue sheaths. The outermost sheath of connective tissue covering each muscle is called the epimysium. But are there layers within our muscles?
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What You'll Learn
- Skeletal muscles are voluntary muscles that support your weight and movement
- Cardiac muscle, or myocardium, is an involuntary muscle that only exists in the heart
- Smooth muscles are involuntary muscles that line the inside of some organs
- Muscles are made of thousands of small fibres woven together
- Muscle strains, or pulled muscles, are the most common muscle injury
Skeletal muscles are voluntary muscles that support your weight and movement
Skeletal muscles are a vital part of the musculoskeletal system. They are voluntary muscles, meaning that you have conscious control over how and when they move and work. They are attached to bones by tendons and help to support your weight and enable movement. Skeletal muscles make up around 30-40% of your total body mass, and there are more than 600 of them in the human body.
These muscles are made up of thousands of small, flexible fibres, woven together and surrounded by connective tissue layers. The fibres contract and tighten, allowing the muscles to move the bones so you can perform a wide range of movements. Each muscle fibre is composed of several hundred to several thousand myofibrils, which are, in turn, made up of actin and myosin filaments called myofilaments. These myofilaments are repeated in units called sarcomeres, which are the basic functional, contractile units of the muscle fibre necessary for muscle contraction.
Skeletal muscles have both mechanical and metabolic functions. Mechanically, the primary function of skeletal muscle is to convert chemical energy into mechanical energy, thus generating force and power. From a metabolic perspective, skeletal muscle contributes to basal energy metabolism, serving as a storage site for essential substrates such as carbohydrates and amino acids. Skeletal muscles also produce body heat, which is a by-product of muscular activity.
Skeletal muscles are susceptible to various conditions and injuries, with muscle strains being the most common type of muscle injury. Strains occur when the strands of muscle fibre are stretched beyond their limit and tear apart. Other common conditions include age-related degeneration and muscle spasms or cramps.
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Cardiac muscle, or myocardium, is an involuntary muscle that only exists in the heart
The human body is made up of three types of muscle tissue: skeletal, smooth, and cardiac. Cardiac muscle, or myocardium, is an involuntary muscle that only exists in the heart. It is responsible for keeping the heart pumping and blood circulating around the body.
Cardiac muscle is a specialized, organized type of muscle tissue that forms the heart. It is made up of sarcomeres that allow for contractility. 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, forming the inner lining of the heart chambers and valves. The pericardium, on the other hand, is a fibrous sac surrounding the heart.
The cardiac muscle contracts and relaxes to pump blood through the cardiovascular system. This involuntary muscle beats on its own without any conscious input, keeping the heart pumping and blood circulating throughout the body. The heart is a hardworking muscle, beating thousands of times a day to keep us alive. It is composed of individual cardiac muscle cells joined by intercalated discs and encased by collagen fibers and other substances that form the extracellular matrix.
The myocardium contains sheets of cardiac muscle cells or cardiomyocytes. These sheets contract in a coordinated manner, allowing the ventricle to squeeze in several directions simultaneously. This includes a longitudinal shortening from apex to base, a radial narrowing from side to side, and a twisting motion similar to wringing out a damp cloth. This complex movement ensures that the maximum amount of blood is squeezed out of the heart with each heartbeat.
Regular aerobic exercise can help strengthen cardiac muscle tissue and lower the risk of cardiovascular conditions such as heart attack and stroke. However, various health conditions can affect the cardiac muscle, including myocarditis (inflammation of the heart muscle), cardiomyopathies, and cardiovascular disease.
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Smooth muscles are involuntary muscles that line the inside of some organs
Smooth muscles are non-striated muscles that consist of thick and thin filaments. They have greater elastic properties than striated muscles, which is important in organ systems like the urinary bladder, where contractile tone must be preserved. Smooth muscles are also important in the disease process throughout the body. For example, the use of bronchodilators to relax airway smooth muscle is a critical treatment for asthmatics.
Smooth muscle tissue lines some organs, but most organs are also made of other types of tissue. The heart is the only organ that is also a muscle, and it is made of a special type of muscle tissue called cardiac muscle. This type of muscle tissue is unique to the heart and does not exist anywhere else in the body.
The muscular layer, or tunica muscularis, is a region of muscle in many organs in the vertebrate body. It is responsible for gut movement, such as peristalsis. The muscular layer consists of an inner layer of circularly arranged muscle fibres covered by an outer layer of longitudinally oriented fibres. The Auerbach's nerve plexus (myenteric nerve plexus) is found between these two layers and starts muscle contractions to initiate peristalsis.
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Muscles are made of thousands of small fibres woven together
The human body is an intricate and complex system, comprising various components that work in harmony to facilitate movement and sustain life. Among these components, muscles play a pivotal role in our physical structure and functionality. Muscles are not just bulky masses that enable us to lift heavy objects or perform athletic feats; they are intricate networks of thousands of minuscule fibres intricately woven together like a delicate tapestry. This intricate weaving of muscle fibres grants us the ability to move, breathe, swallow, and perform a myriad of physical tasks.
At the microscopic level, each skeletal muscle fibre is a single cylindrical muscle cell. These cells unite to form robust muscle fibres, with connective tissue acting as a protective sheath. The connective tissue, known as the endomysium, envelops each individual muscle cell, providing essential support and protection. Bundles of these muscle fibres, known as fasciculi, are encased in another layer of connective tissue called the perimysium. The outermost layer, the epimysium, surrounds the entire muscle, holding the fasciculi securely in place. This hierarchical arrangement of muscle cells, fasciculi, and connective tissue layers forms the foundation of our muscular system.
The arrangement of these muscle fibres is not random but follows a precise pattern. In skeletal muscles, for example, the fibres are crossed with a regular pattern of fine red and white lines, creating a distinctive striated appearance. This unique structure is not only aesthetically intriguing but also serves a vital function in producing the full range of body movements. The skeletal muscles, with their intricate fibre composition, attach to bones through tendons, enabling us to perform various physical tasks with precision and strength.
Beyond skeletal muscles, our bodies also possess cardiac and smooth muscle groups, each with its own distinct characteristics and functions. Cardiac muscles, found exclusively in the heart, perform the vital task of pumping blood through our cardiovascular system. Smooth muscles, on the other hand, line the inside of certain organs, playing a crucial role in organ function and movement, such as peristalsis in the alimentary canal. This diversity in muscle types and their specialised functions underscore the complexity and adaptability of the human muscular system.
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Muscle strains, or pulled muscles, are the most common muscle injury
Muscles are made of thousands of small fibres woven together, and when these fibres are stretched beyond their limit, they can tear. This can happen suddenly or gradually. A muscle strain can be mild, with minimal impact on your muscle's strength or motion, or it can be more severe, with more extensive damage and more muscle fibres involved. In the most serious cases, the muscle tears into two pieces or shears away from the tendon, and surgery may be required to stitch the two ends of the muscle back together.
The severity of a strain can be assessed by how much strength and range of motion a person loses, and this can also provide an idea of how long it will take to recover. There are three grades of muscle strain, based on severity. A Grade 1 strain involves stretching and injury to the muscle fibres, but there is minimal structural damage. A Grade 2 strain involves more extensive damage, with more muscle fibres involved, but the muscle is not completely ruptured. A Grade 3 strain is a severe tear where the muscle has torn all the way through.
To treat a pulled muscle, it is important to rest the muscle and apply ice to the injury as soon as possible to help reduce swelling. After the first few days, you can switch to a heat compress to increase blood flow to the area. It is also important to keep the pulled muscle elevated, ideally above your heart, when sitting or lying down. Anti-inflammatory medications can help during the early stages of recovery, and after a few days, you can start moving the muscle again with some light stretches and easy activities.
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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 located almost everywhere throughout your body.
There are three types of muscle tissue in your body: skeletal, cardiac, and smooth muscles. Skeletal muscles are voluntary muscles that help with movement and make up between 30 to 40% of your total body mass. Cardiac muscles are only found in the heart and are involuntary. Smooth muscles are also involuntary and line the inside of some organs.
The muscular layer (myosalpinx or tunica muscularis) consists of an inner layer of circular muscle fibres and an outer layer of longitudinal fibres. The Auerbach's nerve plexus (myenteric nerve plexus) is found between these two layers and initiates muscle contractions and peristalsis. The thickest muscularis layer is found in the stomach, with three layers, while the thinnest is found in the rectum.
Muscle strains are the most common muscle injury, occurring when the muscle fibres are stretched beyond their limit and tear. Other common conditions include myopathies, myositis, infections, cardiovascular disease, muscle pain and spasms, and skin discolouration. More serious conditions include muscular dystrophies, myasthenia gravis, and rhabdomyolysis, which can cause severe muscle breakdown.
