Logan Steele
The human body is made up of around 600 muscles, which are responsible for functions such as pumping blood, supporting movement, and lifting heavy weights. These muscles work by contracting and relaxing, and their movement can be either voluntary or involuntary. Voluntary muscles, also known as skeletal muscles, are those that are consciously controlled. They make up 30-40% of human body weight and include the muscles of the neck, arms, legs, back, and trunk. These muscles are attached to bones and respond to nerve signals from the brain, allowing for voluntary movement. On the other hand, involuntary muscles, such as those in the heart and blood vessels, are regulated by the autonomic nervous system and are responsible for essential functions like digestion and breathing.
| Characteristics | Values |
|---|---|
| Type | Skeletal |
| Controlled by | Brain, nerves |
| Consciously controlled | Yes |
| Composition | Bundled units of fascicles, made up of muscle fibres or muscle cells |
| Muscle contraction | Caused by conversion of chemical energy into mechanical energy |
| Makes up | 30% to 40% of human body weight |
| Examples | Muscles of the neck, arms, legs, back, trunk, shoulders, hamstrings, abdominal muscles |
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What You'll Learn
Skeletal muscles are voluntary muscles
There are three types of muscles in the human body: skeletal, cardiac, and smooth muscle. Skeletal muscles are voluntary muscles, which means that you have control over how and when they move and work. They are attached to bones and allow you to perform a wide range of movements and functions. They make up 30% to 40% of your total body mass and are considered the most common type of muscle in the human body.
Skeletal muscles are under conscious control and adhere to bones, moving them. They are also known as striated muscles due to their striped appearance, which is caused by the arrangement of sarcomeres. These muscles are bundled units of fascicles, made up of muscle fibres or muscle cells. The muscles in your neck, arms, back, and legs are all skeletal muscles, and they are essential for maintaining posture and balance, as well as playing a role in respiratory mechanics and safeguarding the body's vital organs.
The nerves in your somatic nervous system send signals to make skeletal muscles function. For example, when you reach for a book on a shelf, you are using the skeletal muscles in your neck, arm, and shoulder. Neuromuscular disorders can affect the nerves that send electrical signals to voluntary skeletal muscles, disrupting communication between the nerves and muscles and resulting in muscle weakness, atrophy, or pain.
Voluntary action is defined as an action that is performed with conscious participation. Walking, eating, jumping, and running are all examples of voluntary actions. Skeletal muscles are essential for these movements and functions, and it is important to keep them strong and healthy.
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Cardiac muscles are involuntary muscles
There are three types of muscles in the human body: skeletal, cardiac, and smooth muscle. Skeletal muscles are voluntary muscles, which means that we can consciously control them. These muscles are attached to bones and make up 30% to 40% of our total body mass. Examples of skeletal muscles include the muscles in our arms, legs, neck, back, and trunk.
On the other hand, cardiac and smooth muscles are involuntary muscles, which means that they are not under our conscious control. Instead, they are regulated by the autonomic nervous system, which manages essential daily functions such as digestion and breathing.
Cardiac muscles, also known as myocardium, are found in the heart and are responsible for the heart's contractility and pumping action. Each cardiac muscle cell, or cardiomyocyte, contains a single, centrally located nucleus surrounded by a cell membrane called the sarcolemma. The sarcolemma contains voltage-gated calcium channels, which are specialized ion channels that skeletal muscles do not possess.
The contraction of cardiac muscle cells is coordinated through structures called intercalated discs, which contain gap junctions and desmosomes. Gap junctions allow for the propagation of electrical signals from one cell to the next, enabling cardiomyocytes to contract together synchronously. Desmosomes are intercellular structures that anchor cardiac muscle fibers together, maintaining the structural integrity of the heart.
The process by which cardiac muscles contract is known as excitation-contraction coupling (ECC). Action potentials travel along the sarcolemma and into the t-tubules, initiating depolarization. This triggers an influx of calcium into the cell, which stimulates the release of more calcium from the sarcoplasmic reticulum. The increased calcium concentration allows actin and myosin to form a cross-bridge, resulting in muscle contraction.
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Smooth muscles are involuntary muscles
The human body has three types of muscles: skeletal, cardiac, and smooth muscle. While skeletal muscles are voluntary muscles, smooth muscles are involuntary. Involuntary muscles are those that are not under conscious control. Instead, their contraction and relaxation are regulated by the
Smooth muscles make up most involuntary muscles. They differ from skeletal muscles in terms of structure, function, regulation of contraction, and excitation-contraction coupling. Smooth muscles lack the striated structure of skeletal muscles and instead consist of sheets or layers of smooth muscle cells. These cells are spindle-shaped myocytes with a wide middle and tapering ends, and a single nucleus. In the relaxed state, each cell is 30–200 micrometers in length, some thousands of times shorter than a skeletal muscle cell. Smooth muscles also demonstrate greater elasticity and function within a larger length-tension curve than striated muscles. This ability to stretch and still maintain contractility is important in organs like the intestines and urinary bladder.
Smooth muscles are found in the walls of hollow organs, including the stomach, intestines, bladder, and uterus. They are also found in the walls of blood vessels and lymph vessels (excluding blood and lymph capillaries), where they are known as vascular smooth muscle. Additionally, smooth muscles are present in the tracts of the respiratory, urinary, and reproductive systems. For example, the ciliary muscles in the eyes change the shape of the lens to focus on objects, while the iris dilator and sphincter muscles contract to dilate or constrict the pupils. In the skin, smooth muscle cells cause hair to stand erect in response to cold temperatures and fear.
Smooth muscles can be divided into two subgroups: single-unit and multi-unit smooth muscle. Most smooth muscles are of the single-unit type, and they can contract regularly without input from a motor neuron. Single-unit smooth muscles are found in the walls of most internal organs, blood vessels (except large elastic arteries), the urinary tract, and the digestive tract. In contrast, multi-unit smooth muscles are neurogenic, requiring stimulation by the autonomic nervous system to contract. They are found in the trachea, in the iris of the eye, and lining the large elastic arteries.
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Voluntary muscles are under conscious control
Voluntary muscles are those that are under conscious control. They are also known as skeletal muscles, and they attach to bones to enable movement. Skeletal muscles make up 30% to 40% of an individual's body weight and are found in the arms, legs, neck, back, and trunk. They are under the control of the somatic nervous system, which sends signals to make them function. For example, when reaching for a book on a shelf, you are using the skeletal muscles in your neck, arm, and shoulder.
Voluntary muscles are composed of long, multinucleated cells, with sarcomeres arranged into bundles. They are made up of cylindrical fibres and are involved in muscle contraction, signalling pathways, and metabolism. Skeletal muscles are also referred to as striated muscles due to their striped appearance under a microscope.
In contrast, involuntary muscles are those that are not under conscious control. Their contraction and relaxation are regulated by the autonomic nervous system, which controls essential functions such as digestion and breathing. Most involuntary muscles are made up of smooth muscle, which is found in the digestive tract, uterus, and blood vessels. Cardiac muscles, found only in the heart, are also involuntary and are responsible for pumping blood throughout the body.
Disorders affecting voluntary muscles include neuromuscular disorders, which can damage the nerves that control muscles and voluntary movement, leading to significant muscle weakness, atrophy, or pain. Maintaining the health and strength of skeletal muscles is important for overall bodily function.
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Involuntary muscles are controlled by the autonomic nervous system
The human body has 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 human body weight and are responsible for a wide range of movements and functions.
Involuntary muscles, on the other hand, are controlled by the autonomic nervous system (ANS), a division of the nervous system that operates internal organs, smooth muscle, and glands. The ANS regulates involuntary physiological processes necessary for survival, such as heart rate, blood pressure, respiration, digestion, and sexual arousal. It consists of the sympathetic nervous system and the parasympathetic nervous system, which work together to maintain homeostasis in the body.
The sympathetic nervous system promotes a fight-or-flight response, corresponding to arousal and energy generation, while inhibiting digestion. It diverts blood flow away from the gastrointestinal tract and skin, enhancing blood flow to skeletal muscles and the lungs. It also dilates the bronchioles of the lungs, allowing for greater oxygen exchange.
The parasympathetic nervous system, on the other hand, promotes a "rest and digest" response, calming the nerves and enhancing digestion. It dilates blood vessels leading to the gastrointestinal tract, increasing blood flow. Additionally, it constricts the bronchiolar diameter when the need for oxygen has diminished.
The ANS regulates various functions in the body, including pupil dilation, tear production, nasal mucus, saliva production, and organ control. It also controls the body's ability to sweat and the muscles that cause goosebumps.
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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% to 40% of your total body mass.
Involuntary muscles are those that are not under conscious control. Their contraction and relaxation are regulated by the autonomic nervous system, which controls essential functions such as digestion and breathing. Involuntary muscles include those in the heart, blood vessels, lungs, and digestive system.
When you reach for a book on a shelf, you are using voluntary skeletal muscles in your neck, arm, and shoulder.
