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The human body is made up of over 700 muscles, comprising around 40% of total body weight. These muscles are responsible for movement, posture, and blood circulation. There are three types of muscles: skeletal, cardiac, and smooth muscle. Skeletal muscles are voluntary muscles that can be consciously controlled, such as the muscles in the neck, arms, and legs. They make up 30% to 40% of the body's muscle composition and are responsible for converting chemical energy into mechanical energy to facilitate movement. On the other hand, involuntary muscles, such as those in the heart and blood vessels, are not under conscious control and regulate essential functions like digestion and breathing.
| Characteristics | Values |
|---|---|
| Type of Muscle | Skeletal Muscle |
| Controlled By | Conscious Control |
| Composition | Bundled units of fascicles, made up of muscle fibres or muscle cells |
| Muscle Contraction | Controlled by Somatic Nervous System |
| Muscle Mass | 30% to 40% of Total Body Mass |
| Examples | Muscles of the neck, arms, legs, back, and trunk |
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What You'll Learn
Skeletal muscles are voluntary muscles
Voluntary action is defined as an action that is performed with the participation of thinking. Walking, eating, jumping, and running are all examples of activities that require voluntary muscle movement. These actions are consciously performed, with the brain and spinal cord working together with the PNS to generate the required motions.
The somatic nervous system sends signals to make skeletal muscles function. Skeletal muscles can convert chemical energy into mechanical energy to cause voluntary muscle contraction and movement. Their composition involves bundled units of fascicles, made up of muscle fibers or muscle cells.
Weakness or an inability to control voluntary skeletal muscles can signal a health issue, such as a neuromuscular disorder or electrolyte imbalance. Neuromuscular disorders affect the nerves that send electrical signals to voluntary skeletal muscles to control movement. These disorders can damage the nerves themselves or the neuromuscular junction, where the signal is transmitted from a nerve to a muscle.
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Neuromuscular disorders and voluntary muscles
Skeletal muscles, which attach to bones and allow us to perform a wide range of movements, are voluntary muscles. They make up 30% to 40% of our total body mass and are under our conscious control. These muscles respond to nerve signals from the brain that lead to muscle contraction and movement.
Neuromuscular disorders, also known as skeletal muscle disorders, affect the nerves that send electrical signals to these voluntary skeletal muscles to control movement. These disorders can damage the nerves themselves or the neuromuscular junction, where the signal is transmitted from a nerve to a muscle. As a result, communication between the nerves and muscles becomes disrupted, leading to significant muscle weakness, atrophy, or pain.
There are hundreds of types of neuromuscular disorders, and they can be inherited or caused by a spontaneous gene mutation. Some are also caused by immune system disorders or autoimmune diseases. The most common symptom is muscle weakness, which can lead to twitching, cramps, aches, and pains. Other symptoms include muscle atrophy, disturbance of sensation (such as numbness and tingling), and fatigue.
The treatment for neuromuscular disorders focuses on managing symptoms, delaying disease progression, and enhancing patients' quality of life. This is achieved through medications, physical therapy, occupational therapy, and, when necessary, surgery. While there is currently no cure for most neuromuscular disorders, research is ongoing, particularly in the fields of genetic therapies and new medications.
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Involuntary muscles are not under conscious control
The human body is made up of more than 700 muscles, which can be broadly classified into three types: skeletal, cardiac, and smooth muscle. Skeletal muscles are voluntary muscles that can be consciously controlled. They make up 30% to 40% of human body weight and are attached to bones, allowing for a wide range of movements and functions. These include the muscles in the neck, arms, legs, back, and trunk.
In contrast, involuntary muscles are not under conscious control. Their contraction and relaxation are regulated by the autonomic nervous system, which manages essential daily functions such as digestion and breathing. Involuntary muscles include those involved in automatic internal processes necessary for survival, including the control of blood vessels and organs like the heart, lungs, and digestive system.
Cardiac muscles, found only in the heart, are involuntary. They are responsible for pumping blood throughout the body and maintaining proper blood circulation by regulating the heartbeat. Smooth muscles, another type of involuntary muscle, lack the striated structure of skeletal muscles and instead consist of sheets or layers of smooth muscle cells. These muscles are stimulated by the autonomic nervous system to contract through the release of hormones or other chemical signals.
While voluntary muscles are under the control of the somatic nervous system, involuntary muscles are regulated by the autonomic nervous system. This distinction is crucial in understanding how different types of muscles function and respond to stimuli in the human body.
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Cardiac muscles are involuntary
There are three types of muscles in the human body: skeletal, cardiac, and smooth muscle. Skeletal muscles are voluntary muscles, meaning an individual can control how and when they move and work. On the other hand, cardiac and smooth muscles are involuntary muscles controlled by the autonomic nervous system.
Cardiac muscles, also called the myocardium, are involuntary muscles. They are one of the three major categories of muscles in the human body, along with smooth and skeletal muscles. Cardiac muscles are responsible for the contractility of the heart and, consequently, the pumping action. The heart must contract with enough force to pump blood and supply the metabolic demands of the entire body.
The cardiac muscle cells, or cardiomyocytes, are striated and branched, containing many mitochondria. Each cardiomyocyte contains a single, centrally located nucleus surrounded by a cell membrane known as the sarcolemma. The sarcolemma of cardiac muscle cells contains voltage-gated calcium channels, which are specialized ion channels that skeletal muscles do not possess.
Cardiac muscle cells contain branched fibres connected via intercalated discs that contain gap junctions and desmosomes. These interconnections allow the cardiomyocytes to contract together synchronously to enable the heart to work as a pump. The generation of a cardiac action potential is involuntary and proceeds via a process known as excitation-contraction coupling (ECC). Action potentials travel along the sarcolemma and into the t-tubules to depolarize the membrane.
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Smooth muscles are involuntary
Smooth muscles differ from skeletal muscles, which are voluntary muscles that attach to bones and allow for a wide range of movements and functions. Skeletal muscles make up between 30% and 40% of an individual's total body mass and are controlled by the somatic nervous system. They can be found in the neck, arms, legs, back, and trunk.
In contrast, smooth muscles are regulated by the autonomic nervous system, which controls their contraction and relaxation. This system stimulates smooth muscle cells to contract through the release of hormones or other chemical signals, leading to the shortening of the cells via the movement of actin and myosin myofilaments.
The absence of conscious control over smooth muscles is essential for maintaining vital bodily functions that occur without conscious thought. For example, the muscles in the urinary system help rid the body of waste and toxins, while smooth muscles in the digestive system facilitate digestion through contractions.
In summary, smooth muscles are involuntary muscles that play a crucial role in maintaining essential bodily functions through their automatic contractions and relaxations, all regulated by the autonomic nervous system.
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Frequently asked questions
Voluntary muscles are those that are under conscious control. They are also known as skeletal muscles and are attached to bones, such as the muscles in your arms, legs, neck, back and trunk. They make up 30-40% of human body weight.
Voluntary muscles contract and relax to allow the body to move. They are controlled by the somatic nervous system, which sends signals to the muscles to function.
Weakness or an inability to control voluntary muscles can signal a health issue such as a neuromuscular disorder or an electrolyte imbalance. Neuromuscular disorders can damage the nerves that send signals to the muscles, resulting in muscle weakness, atrophy or pain.
Involuntary muscles are those that are not under conscious control. They include muscles involved in automatic internal processes needed for survival, such as controlling your blood vessels, heart and digestive system.
