Dominic Stone
Muscles are fibrous by nature, with connective tissue layers of fascia surrounding each muscle fiber. Fascia is a thin casing of connective tissue that surrounds and holds every organ, blood vessel, bone, nerve fiber, and muscle in place. However, excessive fibrous connective tissue buildup in muscles can lead to fibrosis, a medical condition characterized by scar tissue accumulation. Fibrosis can cause reduced mobility, pain, stiffness, and impaired muscle function. It can occur in skeletal muscles, which are the most common type of muscle in the body, enabling movement, maintaining posture, controlling body temperature, and stabilizing joints.
| Characteristics | Values |
|---|---|
| Definition | Excessive buildup of fibrous connective tissue or scar tissue in a muscle |
| Causes | Chronic inflammation, injury, or disease |
| Effects | Loss of strength and flexibility, pain, stiffness, reduced mobility, impaired blood flow |
| Treatment | Dry needling, physical therapy, exercises, stretches, strengthening exercises, TECAR therapy, acupuncture, medication, yoga therapy, massage therapy |
| Prevention | Maintaining muscle strength and health, regular exercise, varied movement throughout the day |
| Research | Studying the role of fibro-adipogenic progenitors (FAPs) and collagen production in fibrosis development |
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What You'll Learn
- Skeletal muscle fibres are multinucleated and have a striped appearance
- Smooth muscle fibres are involuntary and control functions like digestion and pupil size
- Cardiac muscle fibres are striated, branched and interconnected, and have their own rhythm
- Muscle strains occur when muscle fibres are stretched beyond their limit and tear
- Muscle fibres are made of myofibrils, which are composed of actin and myosin filaments
Skeletal muscle fibres are multinucleated and have a striped appearance
Skeletal muscles are one of the three types of vertebrate muscle tissue, the others being cardiac and smooth muscle. They are part of the voluntary muscular system and are attached to bones, allowing for a wide range of movements and functions. Skeletal muscles make up around 30-40% of our total body mass.
Skeletal muscle fibres are multinucleated, with the nuclei often referred to as myonuclei. This occurs during myogenesis, with the fusion of myoblasts each contributing a nucleus. The fusion depends on muscle-specific proteins called fusogens, such as myomaker and myomerger. Skeletal muscle cells require many nuclei to produce the large amounts of proteins and enzymes needed for normal functioning. A single muscle fibre can contain hundreds to thousands of nuclei.
Skeletal muscle fibres have a striped appearance due to the arrangement of sarcomeres. Sarcomeres are functional units created by the arrangement of actin and myosin, which give skeletal muscle its microscopic striated appearance. When viewed under electron microscopy, sarcomeres are arranged longitudinally and include the M line, Z disk, H band, A band, and I band.
The skeletal muscle cells are long, ranging from 10 to 100 micrometers in diameter and several centimetres long. The nuclei are located in the cell's periphery, close to the sarcolemma. The sarcolemma is a tubular sheath that encases and defines each muscle fibre, forming a barrier between extracellular and intracellular compartments.
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Smooth muscle fibres are involuntary and control functions like digestion and pupil size
There are three types of muscles in the human body: skeletal, cardiac, and smooth muscle. Skeletal muscles are voluntary muscles, meaning an individual has control over how and when they move and work. On the other hand, smooth muscles are involuntary muscles that the autonomic nervous system controls. This means that smooth muscles work without conscious thought.
Smooth muscle is present throughout the body and serves a variety of functions. Smooth muscle is found in the stomach and intestines, where it helps with digestion and nutrient collection. It is also present in the urinary system, where it helps to rid the body of toxins and maintain electrolyte balance. Smooth muscle is integral to the human body and is present in almost every organ system. It is also found in arteries and veins, where it plays a vital role in regulating blood pressure and tissue oxygenation.
Smooth muscle differs from skeletal muscle in several ways, including its ability to contract and be controlled involuntarily. The nervous system uses smooth muscle to tightly regulate many of the body's subsystems for life without conscious thought. For example, smooth muscle helps regulate blood pressure without a person needing to think about it.
Smooth muscle fibres are also responsible for controlling functions like pupil size. The autonomic nervous system controls the pupil size by regulating the amount of light that enters the eye through the iris. The iris is a circular muscle that controls the size of the pupil, and it is composed of both smooth and striated muscle fibres. The smooth muscle fibres in the iris help to dilate the pupil in low-light conditions, while the striated muscle fibres help to constrict the pupil in bright-light conditions.
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Cardiac muscle fibres are striated, branched and interconnected, and have their own rhythm
Your muscles are made up of thousands of small fibres woven together. These fibres stretching and pressing together allow your body to move. Your heart is a muscle that beats thousands of times a day to keep you alive.
There are three types of muscles in the body: skeletal, cardiac, and smooth muscle. Skeletal muscles are voluntary muscles, meaning you control how and when they move. Cardiac and smooth muscle are involuntary muscles controlled by the autonomic nervous system.
Cardiac muscle, also called heart muscle or myocardium, is an involuntary, striated muscle that forms the main tissue of the heart wall. It is composed of individual cardiac muscle cells, or cardiomyocytes, joined by intercalated discs. These cardiomyocytes are striated, branched, and interconnected. The striated appearance comes from the regular organisation of myofibrils into sarcomeres, the fundamental contractile units of muscle cells.
Cardiac muscle cells are also connected via intercalated discs that contain gap junctions and desmosomes. These interconnections allow the cardiomyocytes to contract together synchronously, enabling the heart to work as a pump. The electrical impulses that trigger these contractions are carried by specialised modified cardiomyocytes known as pacemaker cells. These pacemaker cells are only weakly contractile and are distributed throughout the heart. They are responsible for generating and sending out electrical impulses that cause the beating of the heart.
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Muscle strains occur when muscle fibres are stretched beyond their limit and tear
Muscle strains, or pulled muscles, are common yet painful injuries. They occur when muscle fibres are stretched beyond their limit and tear. This can happen suddenly or gradually. Muscle strains are often sports injuries, caused by sudden sprinting, twisting, or jumping. However, accidental muscle strains are also common in everyday life. Repeating the same movement over and over, whether at work or during recreational activities, can strain your muscles over time.
There are several risk factors that can contribute to muscle strains:
- Muscle stiffness: Inflexible muscles are more prone to tearing.
- Muscle imbalances: Favouring some muscles over others can make the others too weak.
- Previous injuries: Muscles that have been torn before are more likely to tear again.
- Lack of flexibility and strength: Low flexibility and strength can cause muscles to strain with ordinary use.
- Not stretching or warming up before exercise: Muscles can become overstressed if they are not properly prepared for physical activity.
Doctors classify muscle strains into three grades, depending on the severity of muscle fibre damage:
- Grade I strain: In this mild strain, only a few muscle fibres are stretched or torn. The injured muscle is tender and painful, but has normal strength.
- Grade II strain: This is a moderate strain, with a greater number of injured fibres and more severe muscle pain and tenderness. There is mild swelling, noticeable loss of strength, and sometimes a bruise.
- Grade III strain: For a complete rupture, surgery is the preferred treatment option.
Most muscle strains can heal with time and rest. Doctors often recommend following the RICE rule for Grade I and Grade II strains:
- Rest the injured muscle and take a temporary break from sports activities.
- Ice the injured area to reduce swelling.
- Compress the muscle with an elastic bandage.
- Elevate the injured area.
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Muscle fibres are made of myofibrils, which are composed of actin and myosin filaments
Skeletal muscles are composed of muscle fibres, which are single large cells formed by the fusion of many individual cells. These muscle fibres are made up of myofibrils, which are cylindrical bundles of two types of filaments: thick filaments of myosin and thin filaments of actin. Each myofibril is a chain of contractile units called sarcomeres, which are responsible for the striated appearance of skeletal and cardiac muscle. The sarcomeres are composed of actin and myosin filaments, which are organised into repeated subunits along the length of the myofibril. These subunits are around three micrometres in length and give the cell its striped or striated appearance.
The thick myosin filaments are about 15 nanometres in diameter, while the thin actin filaments are about 7 nanometres in diameter. During muscle contraction, the actin is pulled along the myosin towards the centre of the sarcomere, causing the filaments to slide past each other and overlap. This sliding and overlapping of the actin and myosin filaments result in the shortening of the sarcomeres and the muscle cell as a whole. The thick and thin filaments do not change length during contraction, but their sliding movement causes the distance between the Z-discs to shorten, resulting in the overall shortening of the muscle fibre.
The contraction of skeletal muscle is triggered by nerve impulses that stimulate the release of calcium ions from the sarcoplasmic reticulum, a specialised network of internal membranes. The increased concentration of calcium ions signals muscle contraction via the action of two accessory proteins bound to the actin filaments: tropomyosin and troponin. Tropomyosin is a fibrous protein that binds lengthwise along the groove of actin filaments. Troponin, on the other hand, consists of three polypeptides: troponin I, which binds to actin; troponin T, which binds to tropomyosin; and troponin C, which binds to calcium ions. These proteins control when the actin-binding sites will be exposed for binding to myosin.
In addition to actin and myosin, other proteins contribute to the structure and stability of the sarcomere. Titin, the largest known protein, helps align the thick filaments and adds an elastic element to the sarcomere. It is anchored at the M-line, runs the length of the myosin filament, and extends to the Z-disc. Nebulin, another stabilising protein, is associated with actin filaments and is thought to regulate their assembly by determining their length. These proteins work together to maintain the structural integrity and functionality of the sarcomeres within the myofibrils, ultimately contributing to the overall structure and function of skeletal muscles.
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Frequently asked questions
Muscles are fibrous because they contain connective tissue, which is essential for their structure and function. This connective tissue is called fascia and is present in all muscles.
Fascia is a thin casing of connective tissue that surrounds and holds muscles in place. It is designed to stretch as you move, but it can become thickened, sticky, and tight around muscles, limiting mobility and causing pain.
A sedentary lifestyle with limited physical activity can cause fascia to thicken and become sticky. Repetitive movements that overwork one part of the body can also contribute to this issue.
In general, muscle injuries and joint problems tend to feel worse with movement. Fascia adhesions, on the other hand, often feel better with movement and respond well to heat therapy, which helps restore tissue elasticity.
Dry needling is a technique used by physical therapists to treat fibrotic muscles. This involves inserting thin needles into trigger points to break up scar tissue, promote healing, and improve blood flow and oxygen delivery to the affected area. Physical therapy exercises, stretches, and strengthening exercises are also recommended to improve flexibility, reduce stiffness, and rebuild muscle mass.
