Dominic Stone
The human body has over 600 muscles, which make up over 40% of our body weight. These muscles are made of thousands of small fibres woven together, allowing them to stretch and press together to move our organs and body. The muscular system is primarily responsible for movement, but it also maintains posture and body position, stabilises joints, and produces body heat. The three types of muscle tissue are skeletal, smooth, and cardiac. Skeletal muscles are attached to the bones by tendons and are under voluntary control. Smooth muscle is found in the walls of hollow visceral organs and is under involuntary control. Cardiac muscle makes up the heart and is also involuntary. All muscles are covered by a thick layer of connective tissue known as perimysium, which forms muscle fascicles. These fascicles are then grouped together by a final outer covering of dense connective tissue called epimysium.
| Characteristics | Values |
|---|---|
| Number of muscles in the human body | More than 600 |
| Muscle composition | Thousands of small fibers woven together |
| Types of muscle tissue | Skeletal, smooth, and cardiac |
| Skeletal muscle composition | Connective tissue, nerve tissue, blood or vascular tissue |
| Connective tissue layers | Endomysium, perimysium, and epimysium |
| Connective tissue function | Provides support and protection, allows contraction, provides pathways for blood vessels and nerves |
| Muscle movement | Contraction of muscle fibers creates tension, which is transferred through connective tissue to tendons and bones |
| Muscle shape | Varies, including broad, narrow, circular, and convergent |
| Muscle function | Movement, breathing, swallowing, supporting organs |
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What You'll Learn
Connective tissue layers
Skeletal muscles are covered by connective tissue, which furnishes support and protection for the muscle cells. This connective tissue covering is made up of three layers: the epimysium, the perimysium, and the endomysium.
The epimysium is the outermost layer of connective tissue that surrounds each skeletal muscle. It is a connective tissue sheath that wraps around the entire muscle. Fascia, another type of connective tissue, is found outside the epimysium and surrounds and separates the muscles from one another.
The perimysium is the second layer of connective tissue. It surrounds and encases each bundle of muscle fibers, known as fascicles or fasciculi. These bundles of muscle fibers are groups of muscle cells bundled together. The perimysium extends beyond the fleshy part of the muscle, along with the epimysium and endomysium, to form a tendon or an aponeurosis, which attaches the muscle to bones or other muscles.
The endomysium is the innermost layer of connective tissue. It surrounds each individual muscle fiber or cell within a fascicle. This thin layer of connective tissue is composed of collagen and reticular fibers, which play a crucial role in transferring force produced by the muscle fibers to the tendons.
These three layers of connective tissue not only provide structural support and protection but also serve as pathways for blood vessels and nerves to reach the muscle cells. The connective tissue layers also help transfer the tension created by the contraction of muscle fibers to the tendons and ultimately to the bones, enabling movement.
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Perimysium
The human body is composed of more than 600 muscles that help us move, breathe, swallow, and perform other vital functions. These muscles are made of thousands of small fibres woven together. Each skeletal muscle fibre is a single cylindrical muscle cell, and an individual skeletal muscle may be made up of hundreds or thousands of muscle fibres bundled together and wrapped in a connective tissue covering.
The perimysium, also known as interfascicular connective tissue, is a connective tissue sheath that surrounds individual muscle fascicles (bundles of muscle fibres) and separates them from other fascicles within the skeletal muscle. The perimysium is made up of dense irregular connective tissue, which contains mainly type I and type III collagen. It is continuous with the endomysium, which wraps around individual muscle fibres, and the epimysium, which encloses the entire muscle. The perimysium contains a rich network of blood vessels and nerves, known as the neurovascular bundles, that branch out to supply muscle fibres of each fascicle with nutrients and oxygen while also facilitating signal transmission.
During muscle contraction, the perimysium transmits the force produced by individual muscle fibres across the fascicles, generating smooth, coordinated muscle contraction and movement. The tensile properties of the perimysium are similar in nature to the endomysium. The perimysium is easily deformed in tension and does not exhibit high tensile stiffness unless it has been stretched far beyond the range of working lengths in living muscle.
The perimysium, intermuscular fat planes, and fascia all appear bright on ultrasound (US) imaging. On longitudinal imaging, the perimysium appears as bright linear areas against the darker background of muscle fibres, while on transverse imaging, it appears as bright dots distributed through the darker background of the muscle fascicles.
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Endomysium
The human body is composed of more than 600 muscles that help us move, breathe, swallow, and stay alive. Each skeletal muscle fibre is a single cylindrical muscle cell. An individual skeletal muscle may be made up of hundreds, or even thousands, of muscle fibres bundled together and wrapped in a connective tissue covering.
The endomysium is a delicate sheath of connective tissue that envelops each individual skeletal muscle fibre. It is formed by fibroblasts and consists primarily of type III and type IV collagen. Endomysium surrounds the individual skeletal muscle fibres within the fascicles and forms their immediate internal environment. The three collagenous sheaths, the epimysium, perimysium, and endomysium unite and fuse where the muscles connect to adjoining structures such as tendons.
The endomysium is the key element that separates single muscle fibres from one another. It allows their autonomous gliding during muscle contraction. The endomysium is also a highly deformable tissue that adapts itself to the changes in volume that occur during muscle fibre contraction. Another important function of the endomysium is to regulate the metabolic exchange between muscle and blood. The endomysium contains capillaries which supply the muscle fibre.
The fibres within the endomysium also have the power to transfer force generated by muscle cells, and they seem to get stronger and thicker when tensional stress is applied. As the endomysium is composed of collagen and elastin fibres, it contributes to the resistance of a muscle to tensile forces.
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Fascia
The fascial system consists of a three-dimensional continuum of soft, collagen-containing, loose and dense fibrous connective tissues that permeate the body. It is designed to stretch as you move, but certain factors can cause fascia to thicken and become sticky. For instance, a lifestyle of limited physical activity or repetitive movement that overworks one part of the body can cause fascia to become gummy and crinkled (called adhesion).
Healthy fascia is smooth, slippery, and flexible. Keeping your fascia healthy has many benefits, such as increased mobility and a better range of motion. To maintain healthy fascia, it is important to stay active throughout the day, stretch regularly, and focus on good posture.
Determining whether pain is due to muscles, joints, or fascia can be difficult. Fascia pain often requires more than one therapy for treatment, including heat therapy, an anti-inflammatory diet, yoga therapy, and guided imagery.
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Aponeurosis
Aponeuroses are similar to tendons in that they both play a role in force transmission from muscle to bone. However, aponeuroses differ from tendons in appearance, as they are thin and delicate, while tendons are tough and rope-like. Aponeuroses are also very rarely injured due to their location under many layers of bone and muscle, whereas tendons are prone to injury as they are present in injury-prone areas.
Aponeuroses can act as fascia, a fibrous tissue that envelopes muscles or organs, binding them together or to other tissues. Examples of aponeuroses that act as fascia include the erector spinae aponeurosis (ESA), which blends with the thoracolumbar fascia, and the rectus sheath, formed by the five muscles of the abdomen.
The primary regions with thick aponeuroses include the ventral abdominal region, the dorsal lumbar region, the palmar (palms) and plantar (soles) regions, and the ventriculus in birds. The anterior abdominal aponeuroses are located just superficial to the rectus abdominis muscle, with borders formed by the external oblique, pectoralis muscles, and the latissimus dorsi.
Pennate muscles, in which the muscle fibres are oriented at an angle to the line of action, typically have two aponeuroses.
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Frequently asked questions
Tendons are tough bands of dense connective tissue that attach muscles to bones and cover the muscles.
Collagen.
Thousands of small fibres woven together.
Visceral, cardiac, and skeletal.
Skeletal muscle is a type of muscle tissue that is attached to bones, usually across a joint. They are under voluntary control.
