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Myelinated muscles are those that are connected to myelinated nerves. Myelin is a fatty-protein substance that forms a sheath or membrane around nerve axons. This sheath acts as insulation, allowing electrical impulses to travel quickly and efficiently from the brain to the muscles. Myelin is produced by oligodendrocytes in the central nervous system and Schwann cells in the peripheral nervous system. Myelinated nerves are associated with smooth muscle in the airways and are involved in reflex control of breathing and the cough reflex. They also play a role in the reflex actions of organs such as the heart, muscles, and glands. The conduction velocity in myelinated nerves depends on the diameter of the axon, with larger diameters resulting in faster conduction.
| Characteristics | Values |
|---|---|
| Number of muscles in the human body | 600-700 |
| Muscle composition | Skeletal muscle tissue, blood vessels, tendons, nerves |
| Types of muscle tissue | Visceral, cardiac, skeletal |
| Visceral muscle location | Stomach, intestines, blood vessels, liver, pancreas |
| Skeletal muscle composition | Myofibers, myofibrils, actin and myosin filaments, sarcomeres |
| Skeletal muscle function | Producing movement, maintaining body posture, controlling body temperature, stabilising joints |
| Skeletal muscle disorders | Muscular dystrophies, congenital myopathies, inflammatory disorders, diseases affecting the neuromuscular junction |
| Muscle movements | Voluntary, involuntary |
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What You'll Learn
Skeletal muscles are attached to the bones of the skeleton
Skeletal muscles enable the body to move. Each skeletal muscle consists of hundreds or even thousands of muscle fibres. These fibres contract, or tighten, and pull on the bones, causing movement. They can only contract, and cannot actively extend or lengthen. Therefore, to move bones in opposite directions, pairs of muscles must work in opposition. For example, the biceps and triceps in the upper arm work in opposition to bend and extend the arm at the elbow.
The muscle fibres are bundled together and wrapped in connective tissue, which supports and protects the muscle cells. Skeletal muscles vary considerably in size, from tiny muscles inside the middle ear to very large muscles in the upper leg. They are voluntary muscles, meaning we control how and when they work.
The myelin sheath is a protective membrane that wraps around part of certain nerve cells. Myelin is made up of protein and fatty substances and provides protective insulation for nerve cells. It allows electrical impulses to transmit quickly and efficiently along nerve cells.
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There are more than 600 muscles in the human body
The human body is an intricate system, comprising various components that work together to enable our existence. Among these components are muscles, which play a crucial role in our daily lives. When we think of muscles, we often envision physical strength and movement, but they contribute to much more. There are over 600 muscles in the human body, each with its unique purpose and function.
The muscular system is a complex network of muscles that work in harmony to facilitate movement and support our bodies. These muscles can be categorised into three main types: skeletal, smooth, and cardiac. Each type of muscle has distinct characteristics and functions, contributing to the overall efficiency of our bodies.
Skeletal muscles, also known as voluntary muscles, are responsible for movement. They are attached to bones and work in pairs, such as the biceps and triceps, to enable a range of motions. These muscles are under our conscious control, allowing us to perform actions like lifting heavy weights or giving birth. The term "striated muscles" refers to the striped appearance of skeletal muscle tissue under a microscope.
Smooth muscles, on the other hand, are involuntary. They are found in various organ systems, including the digestive tract, uterus, and blood vessels. Unlike skeletal muscles, smooth muscles have a more uniform appearance, lacking the striated pattern. They work without our conscious awareness, contracting in waves to perform essential functions like moving food through the digestive tract.
Cardiac muscle tissue, including the heart, is responsible for pumping blood throughout our bodies. This vital function demonstrates the importance of muscles beyond just physical movement. The heart, with its cardiac muscle, works tirelessly, pumping at least 2,500 gallons of blood in a single day.
The human body's muscular system is a testament to its intricate design, with each muscle playing a specific role. While there are over 600 muscles identified, the exact number remains ambiguous due to varying anatomist opinions and the discovery of novel muscle variations. The science of anatomy continues to evolve, shedding light on the remarkable complexity of our muscular system.
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Muscles are made of thousands of small fibres
Skeletal muscle is one of the three significant muscle tissues in the human body, the others being cardiac and smooth muscle groups. Each skeletal muscle consists of thousands of muscle fibres bundled together and wrapped in a connective tissue covering. Each muscle fibre is a single cylindrical muscle cell, and each is surrounded by a plasma membrane called the sarcolemma, which contains sarcoplasm, the cytoplasm of muscle cells.
Within a muscle fibre, proteins are organised into organelles called myofibrils that run the length of the cell and contain sarcomeres connected in series. Each muscle fibre can contain thousands of sarcomeres, which are the smallest functional unit of a skeletal muscle fibre. When bundled together, all the myofibrils get arranged in a unique striated pattern, forming sarcomeres which are the fundamental contractile unit of a skeletal muscle. The two most significant myofilaments are actin and myosin filaments, which are arranged distinctively to form various bands on the skeletal muscle.
The outermost connective tissue sheath surrounding the entire muscle is known as the epimysium. The connective tissue sheath covering each bundle of muscle fibres is known as the perimysium, and the innermost sheath surrounding individual muscle fibres is known as the endomysium.
The myelin sheath is a protective membrane that wraps around part of certain nerve cells. It is made up of protein and fatty substances, providing protective insulation for nerve cells. Myelin allows electrical impulses to travel quickly and efficiently between nerve cells.
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Smooth muscle is found in visceral organs like the liver
Myelin is an insulating layer or sheath that forms around nerves, including those in the brain and spinal cord. It is made up of proteins and fatty substances.
Smooth muscle, on the other hand, is a type of muscle tissue found in the walls of hollow organs, such as the liver, and in tubular structures like vessels and bile ducts. Smooth muscle is also found in the walls of passageways, including arteries and veins of the cardiovascular system. This type of involuntary non-striated muscle is also found in the tracts of the urinary, respiratory, and reproductive systems. Smooth muscle is derived from both mesoderm and neural crest cells, which play an important role in the development of smooth muscle throughout the body, specifically in the regulation of blood vessels.
Smooth muscle consists of thick and thin filaments that are not arranged into sarcomeres, giving it a non-striated pattern. On microscopic examination, it appears homogeneous. Smooth muscle cytoplasm contains a large amount of actin and myosin, the main proteins involved in muscle contraction. Actin filaments attach to dense bodies spread throughout the cell, which can be observed under an electron microscope and appear dark. Another important structure is the calcium-containing sarcoplasmic reticulum, which aids in sustaining contraction. The shape of the smooth muscle is described as fusiform, which is round in the center and tapers at each end.
Smooth muscle can tense and relax but has greater elastic properties than striated muscle. This is important in organ systems like the urinary bladder, where contractile tone must be preserved. Smooth muscle contraction is initiated when Ca++ binds to intracellular calmodulin, which then activates an enzyme called myosin kinase. This enzyme phosphorylates myosin heads so they can form cross-bridges with actin and then pull on the thin filaments. Smooth muscle can be stimulated by pacesetter cells, the autonomic nervous system, hormones, or stretching.
Smooth muscle is found in the walls of visceral organs like the liver, where it plays a role in regulating blood flow and pressure. The sympathetic, parasympathetic, and enteric nervous systems all work together to affect and contract smooth muscle.
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Skeletal muscle is striated and under voluntary control
Skeletal muscle is the most common type of muscle in the human body, comprising 30% to 40% of total body mass. They are attached to bones by tendons and allow us to perform a wide range of movements and functions. These include everyday tasks such as walking, running, writing, and speaking.
Skeletal muscle is striated, meaning it has a pattern of light and dark bands, formed by the arrangement of actin and myosin filaments. These light bands, called I-bands, are regions consisting only of actin filaments. This structured appearance allows the muscle to contract and generate force. The structured alignment of these filaments is integral to the skeletal muscle's ability to generate force.
Skeletal muscle is also under voluntary control, meaning that one can consciously control these muscles to perform actions. The brain sends signals through the somatic nervous system, instructing muscles to contract for particular actions. Through training and practice, individuals can enhance their voluntary control over these muscles, increasing precision and strength of movements.
Striated muscle fibers contain actin and myosin filaments that power contraction and are organized into repeating arrays, called sarcomeres, with a striated microscopic appearance. These filaments are also present in smooth muscles, but they are not organized into sarcomeres. As a result, smooth muscle does not contain the troponin complex required for skeletal muscle contraction and has a different mechanism for controlling contraction.
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Frequently asked questions
The myelin sheath is a protective membrane that wraps around part of certain nerve cells. Myelin is made up of lipids and proteins and appears white. It is produced by oligodendrocytes in the brain and spinal cord (the central nervous system) and by Schwann cells in the peripheral nervous system.
The myelin sheath allows electrical impulses to transmit quickly and efficiently along nerve cells. It acts as insulation for the electrical signals, similar to the plastic insulation covering an electrical cord.
When the myelin sheath is damaged, the electrical signals slow down or stop. Several diseases and conditions, including multiple sclerosis, damage or destroy myelin.
Myelinated muscles refer to the connection between the myelin sheath and muscles. Myelinated nerve cells transmit electrical signals to target muscles, controlling muscle functions such as breathing and the cough reflex.
