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Voluntary muscles are those that are under conscious control, meaning that they are the muscles we use to make all the movements needed in physical activity and sport. They are also referred to as skeletal muscles because they are attached to the skeleton, and striated muscles because the muscle fibres make them look stripy. Skeletal muscles make up 30-40% of the human body mass and include muscles in the arms, legs, neck, back, and trunk. They are controlled by the somatic nervous system and can be voluntarily contracted and relaxed.
| Characteristics | Values |
|---|---|
| Type of Muscle | Skeletal |
| Controlled By | Conscious thought |
| Composition | Long, multinucleated cells with sarcomeres arranged into bundles |
| Appearance | Striated or stripy |
| Location | Attached to bones and skin |
| Function | Contraction and relaxation |
| Percentage of Body Mass | 30-40% |
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What You'll Learn
Skeletal muscles are voluntary muscles
Skeletal muscles are attached to the bones by tendons, which are tough connective tissues. Examples of skeletal muscles include the muscles in our arms, legs, neck, back, and trunk. These muscles are under our conscious control, and we can move them when we want to. For instance, when we decide to reach for a book on a shelf, we are using the voluntary skeletal muscles in our neck, arm, and shoulder.
Voluntary movements are actions that we consciously control and make happen. Our nervous system, specifically the somatic nervous system, controls these movements. When we decide to move, nerves in our somatic nervous system send signals to the skeletal muscles, making them function. Voluntary muscles require a lot more energy than involuntary muscles and remain relaxed when we are not moving, such as when we are asleep.
Voluntary muscles are typically longer and thicker than involuntary muscles, and they are composed of cells with multiple nuclei. These muscles produce movement by contracting and relaxing. However, it is important to note that sometimes, voluntary muscles can move involuntarily, resulting in muscle spasms or cramps due to various reasons such as poor stretching, muscle overuse, dehydration, or illness.
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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 how and when they move. These muscles are attached to bones and allow us to perform a wide range of movements and functions. Skeletal muscles make up between 30% and 40% of our total body mass.
Cardiac muscles, on the other hand, are involuntary muscles. They are found only in the heart and are responsible for pumping blood throughout the body. The heart is composed of three layers: the pericardium, myocardium, and endocardium. The myocardium, or heart muscle, is composed of a specialized type of muscle cell called cardiac muscle.
Cardiac muscle is striated, like skeletal muscle, but it is controlled by the autonomic nervous system, causing it to contract automatically and rhythmically. 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 (the cardiomyocyte plasma membrane) and into the t-tubules to depolarize the membrane. This triggers the release of calcium, which is necessary for contraction to occur.
Cardiac desmosomes are intercellular structures that anchor cardiac muscle fibers together, maintaining the structural integrity of the heart. The contractility of the heart is essential for pumping blood and supplying the metabolic demands of the entire body. Therefore, cardiac muscles, being responsible for these vital functions, are classified as involuntary muscles.
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Smooth muscles are involuntary muscles
Smooth muscle differs from skeletal muscle in terms of structure, function, and regulation of contraction. Smooth muscle tissue demonstrates greater elasticity and function within a larger length-tension curve than striated skeletal muscle. This ability to stretch and still maintain contractility is important in organs like the intestines and urinary bladder. Smooth muscles are composed of spindle-shaped cells with a wide middle and tapering ends, containing a single nucleus. They are activated by smooth muscle cells (SMCs), interstitial cells of Cajal (ICCs), and platelet-derived growth factor receptor alpha (PDGFRα), which work together as a functional syncytium.
The proteins myosin and actin play a crucial role in smooth muscle contraction. Myosin, predominantly class II in smooth muscle, contains two heavy chains (MHC) that form a coiled-coil structure, holding the chains together. These heavy chains contain the N-terminal head domain, while the C-terminal tails have a coiled morphology. Myosin II also has two heads and four light chains (MLC), with two light chains per head. The MLC20 isoform is the regulatory light chain that actively participates in muscle contraction.
Smooth muscle can be categorized into two types: single-unit smooth muscle, also known as visceral smooth muscle, and multi-unit smooth muscle. However, this distinction may be an oversimplification as smooth muscles are often influenced by a combination of different neural elements, and cell-to-cell communication plays a role in their coordination. Smooth muscles are an essential part of the body's muscular system, working involuntarily to support vital functions and processes.
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Voluntary muscles are longer and thicker
Voluntary muscles are those that are under conscious control, such as the neck and leg muscles that we choose to move. They are also referred to as skeletal muscles, as they are attached to the skeleton, and striated muscles, due to their stripy appearance. Skeletal muscles are the most common type of muscle in the body, comprising 30% to 40% of total body mass. They are attached to bones by tendons, allowing us to perform a wide range of movements and functions. We can consciously control these muscles, deciding to perform an action and using our nervous system to control the movement. For example, when we decide to scratch our nose, our arm, hand and finger move towards it due to the activation of voluntary muscles.
Voluntary muscles include the biceps in the arms and the quadriceps in the legs. They are involved in muscle contraction and signalling pathways. Voluntary muscles are controlled by the somatic nervous system, which sends signals to make them function. If someone wants to reach for a book on a shelf, they are using skeletal muscles in their neck, arm and shoulder.
In contrast to voluntary muscles, involuntary muscles, such as cardiac and smooth muscles, are controlled by the autonomic nervous system. They work without conscious thought, such as the muscles in the urinary system that help rid the body of waste. Involuntary muscles are involved in automatic internal processes needed for survival, controlling the blood vessels and organs like the heart, lungs and digestive system.
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Voluntary muscles are controlled by the somatic nervous system
Voluntary muscles are those that are under conscious control, such as the neck and leg muscles that we choose to move. They are also referred to as skeletal muscles because they are attached to the skeleton, and striated or stripy muscles because of the appearance of their fibres under a microscope. Skeletal muscles are the most common type of muscle in the body, comprising 30% to 40% of total body mass. They are attached to bones by tendons, which are tough connective tissues, and allow us to perform a wide range of movements and functions.
Voluntary muscles won't do anything until the brain tells them to. For example, if you want to scratch your nose, you first have to decide to do it, and then your arm, hand, and finger muscles will move towards your nose. This is in contrast to involuntary muscles, which contract and relax without conscious thought, such as the muscles in your heart and guts.
Voluntary muscles can sometimes move involuntarily, causing muscle spasms or cramps due to poor stretching, overuse, dehydration, or illness. Weakness or an inability to control voluntary muscles can signal a health issue, such as a neuromuscular disorder or electrolyte imbalance.
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Frequently asked questions
Voluntary muscles are those that are consciously controlled. They are also called skeletal muscles because they are attached to the skeleton, and striated muscles because they have a striated or stripy appearance.
Voluntary muscles include the muscles in your neck, arms, back, legs, and shoulders.
Voluntary muscles allow the body to move by contracting and relaxing. They also play a role in metabolism and blood sugar level.
Voluntary muscles produce movement by contracting and relaxing. They require a signal from the brain to initiate movement and are controlled by the somatic nervous system.
