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Skeletal muscles are a vital part of the musculoskeletal system, comprising 30 to 40% of our total body mass. They are the muscles that connect to our bones through tendons, allowing us to perform a wide range of movements and functions. These muscles are under our voluntary control, meaning we decide how and when they work. Skeletal muscles are made up of thousands of small fibres that contract and relax, enabling us to move our bones and perform various tasks. While these muscles are essential for our daily activities, they are also susceptible to injuries and conditions such as strains, ruptures, and age-related degeneration. The question arises: are all skeletal muscles straight?
| Characteristics | Values |
|---|---|
| Definition | Skeletal muscles are one of the three types of vertebrate muscle tissue, the others being cardiac and smooth muscle tissue. |
| Location | Skeletal muscles are located throughout the body, between bones. |
| Function | Skeletal muscles allow you to perform a wide range of movements and functions. They also act as a storage source for amino acids and play a role in maintaining thermostasis and energy during starvation. |
| Composition | Skeletal muscles are made up of muscle fibres or cells, which are surrounded by connective tissue layers. Each muscle can contain thousands of fibres. |
| Type of Contraction | Skeletal muscles are striated muscles, meaning they have a striped appearance due to the arrangement of sarcomeres. |
| Control | Skeletal muscles are voluntary muscles, meaning you control how and when they move. Nerve cells called motor neurons control their movement. |
| Percentage of Body Mass | Skeletal muscles comprise 30 to 40% of total body mass. |
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What You'll Learn
Skeletal muscles are voluntary muscles
Skeletal muscles are indeed voluntary muscles, which means that you can consciously control how and when they move and work. They are attached to bones and respond to neuromuscular signals from the brain that communicate with individual muscle fibres and cause them to contract. Skeletal muscles make up 30 to 40% of your total body mass and are the most common muscles in your body. They are located between bones and allow you to perform a wide range of movements and functions.
Skeletal muscles consist of flexible muscle fibres that range from less than half an inch to just over three inches in diameter. Each muscle can contain thousands of fibres, and these fibres usually span the length of the muscle. The fibres contract (tighten), which allows the muscles to move bones so you can perform lots of different movements.
Different types of sheaths, or coverings, surround the fibres: the outermost layer of tissue surrounding the entire muscle is called the epimysium; the middle layer surrounding bundles of muscle fibres is the perimysium; and the innermost layer surrounding individual muscle fibres is the endomysium. Skeletal muscle fibres are red and white, and they look striated, or striped, so they are often referred to as striated muscles.
Nerve cells called motor neurons control the skeletal muscles. Each motor neuron controls several muscle cells in a group known as a motor unit. When a motor neuron receives a signal from the brain, it stimulates all of the muscle cells in its motor unit at the same time. The size of motor units varies throughout the body, depending on the function of a muscle.
It is important to note that not all muscles in the body are skeletal muscles. Smooth muscles, for example, make up your organs, blood vessels, digestive tract, and skin. Smooth muscles are involuntary, meaning they contract and relax automatically and are not under conscious control. Cardiac muscles are also involuntary and are only found in your heart, helping to pump blood throughout your body.
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Skeletal muscles are controlled by the somatic nervous system
Skeletal muscles are found throughout the body and are located between bones. They are made up of flexible muscle fibres that contract, allowing the muscles to move bones and enabling a wide range of movements. Skeletal muscles are voluntary muscles, meaning that you are in control of how and when they move.
The somatic nervous system is a subdivision of the peripheral nervous system, which is all of your nervous system except your brain and spinal cord. The somatic nervous system allows you to move and control muscles throughout your body. It also feeds information from four of your senses – smell, sound, taste and touch – into your brain.
The somatic nervous system consists of cranial nerves (12 pairs), spinal nerves (31 pairs) and association nerves. It is the consciously controlled part of the peripheral nervous system. The peripheral nervous system connects the central nervous system (CNS) – the brain and spinal cord – with innervated organs, serving as a bidirectional communication platform between the CNS and peripheral organs. The somatic nervous system is responsible for the voluntary movements of the body and it mainly comprises motor neurons that innervate skeletal muscles to activate muscle contraction and relaxation.
The human nervous system is divided into the CNS and the peripheral nervous system (PNS). The PNS is further subdivided into the somatic and autonomic nervous systems. The autonomic nervous system controls the subconscious actions of cardiac muscle, smooth muscle and glands.
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Skeletal muscles are striated
Skeletal muscles are indeed striated, or striped, in appearance. They are also referred to as striated muscles. This striated appearance is due to the arrangement of myofibrils, which form sarcomeres when bundled together. Sarcomeres are the fundamental contractile unit of a skeletal muscle and are visible under a microscope as stripes along muscle fibres. Skeletal muscles are attached to the skeleton and are under voluntary control, meaning an individual can control how and when they move and work. They are the most common type of muscle in the body, comprising 30 to 40% of total body mass. They are connected to bones via tendons, allowing for a wide range of movements and functions.
Skeletal muscles consist of flexible muscle fibres that range from less than half an inch to just over three inches in diameter. Each muscle can contain thousands of fibres, and these fibres contract, enabling movements such as breathing, posture maintenance, and everyday activities like reaching for a book on a shelf. Skeletal muscles are also vital for maintaining thermostasis and act as an energy source during starvation.
The development of skeletal muscles begins during embryogenesis, with the para-axial mesoderm differentiating to form the somites, which then develop into the muscle tissue. The process is stimulated by regulatory factors such as Wnt, Shh, and BMP4 proteins. The differentiation of the myotome, influenced by the Sonic Hedgehog (Shh) signalling molecule, results in the formation of specific skeletal muscles in the body, such as the back and body wall muscles.
Additionally, skeletal muscles have a better regenerative capacity compared to cardiac muscles due to the presence of satellite cells. The regeneration process involves phases such as the inflammatory response, activation and differentiation of satellite cells, and maturation of newly formed myofibrils.
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Skeletal muscles are the most common muscles in the body
The skeletal muscle is an essential component of the musculoskeletal system, working in conjunction with bones, tendons, and ligaments to support an individual's weight and facilitate movement. Tendons, which are tough bands of connective tissue, attach skeletal muscles to bones. Examples of skeletal muscles include shoulder, hamstring, and abdominal muscles, as well as back and thigh muscles.
Skeletal muscles rarely work in isolation to achieve movements. Instead, they often collaborate with other skeletal muscles to produce complex movements. For example, when reaching for a book on a shelf, an individual utilises skeletal muscles in their neck, arm, and shoulder simultaneously. Additionally, skeletal muscles play a crucial role in maintaining body posture, ensuring individuals can hold their body still or engage in physical activities like running.
Furthermore, skeletal muscles serve as a storage source for amino acids, which are utilised by various organs for synthesising organ-specific proteins. They also contribute to maintaining thermostasis and can act as an energy source during starvation. The development of skeletal muscles in the limbs and trunk is influenced by the expression of specific proteins and transcription factors, such as MyoD and Myf5, which impact the differentiation of embryonic myoblasts into primary muscle fibres and eventually secondary myofibers.
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Skeletal muscles are attached to bones by tendons
Skeletal muscles are a vital part of the musculoskeletal system. They are attached to bones by tendons, which are fibrous connective tissues. Tendons come in many shapes and sizes, with some appearing as flattened bands and others as rounded cords. The shape of the tendon often matches that of the enthesis, the tissue present at the skeletal attachment site. For example, the tendons of the pectoralis major and latissimus dorsi are flattened sheets of connective tissue that attach to the upper part of the humerus in a linear fashion. In contrast, the more rounded tendons at the wrist attach to bones in a more precise and circumscribed manner. These tendons are associated with intricate movements that require precise positioning at the site of attachment on the bone.
Skeletal muscles are located between bones and consist of flexible muscle fibres that contract to enable movement. These muscles work in pairs, with one muscle contracting and shortening while the corresponding muscle lengthens. For instance, when the bicep contracts, the tricep lengthens. Skeletal muscles are voluntary, meaning that individuals can control how and when they work. They are responsible for a wide range of movements and functions, such as reaching for a book or performing various sports activities.
Skeletal muscles are composed of striated, or striped, muscle fibres that are typically red and white. These fibres can range from less than half an inch to over three inches in diameter and usually span the length of the muscle. Each muscle can contain thousands of fibres, which are surrounded by different layers of sheaths or coverings. The outermost layer is the epimysium, followed by the perimysium in the middle, and the innermost layer is the endomysium.
Skeletal muscles are also important for maintaining thermostasis and regulating blood sugar (glucose) levels. They can take up glucose from the blood as fuel or store it for later use. Additionally, these muscles serve as a storage source for amino acids, which can be used by different organs for synthesizing organ-specific proteins. During embryogenesis, the para-axial mesoderm differentiates to form the somites, which then develop into the muscle tissue that makes up skeletal muscles.
It is important to note that not all skeletal muscles attach to bones via tendons. Some muscles attach to the skeleton by 'fleshy' fibres, and certain powerful pennate muscles may have multiple small intramuscular tendons rather than a single discrete tendon. Tendons are susceptible to various injuries and conditions, such as tendonitis (inflammation or irritation) and ruptures, which can occur in athletes or recreational sports participants.
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Frequently asked questions
Skeletal muscles are the muscles that connect to your bones and allow you to perform a wide range of movements and functions. They are part of the voluntary muscular system and are controlled by the somatic nervous system. Skeletal muscles make up between 30 to 40% of your total body mass.
No, not all skeletal muscles are straight. For example, in the abdominal region, the rectus abdominis muscles run straight up and down, while the transverse abdominis muscles run transversely (left to right) and the obliques run at an angle.
Straight skeletal muscles, such as the rectus abdominis, help to stabilize and move the body. They work together with bones and joints to form lever systems.
If you experience muscle pain, cramps, or weakness that lasts for more than a week or if you have trouble moving, it is important to visit a healthcare provider for an accurate diagnosis and treatment.
