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Voluntary muscles, also known as skeletal muscles, are those that humans can consciously control. They include the muscles of the neck, arms, legs, back, and trunk, and they respond to nerve signals from the brain that lead to muscle contraction. These muscles can convert chemical energy into mechanical energy to cause voluntary movement. Weakness or an inability to control voluntary muscles can indicate health issues such as neuromuscular disorders or electrolyte imbalances. On the other hand, involuntary muscles are involved in automatic internal processes necessary for survival, including controlling blood vessels and organs like the heart, lungs, and digestive system.
| Characteristics | Values |
|---|---|
| Type | Skeletal muscles |
| Controlled by | Brain |
| Controlled through | Nerve signals |
| Composition | Bundled units of fascicles, made up of muscle fibres or muscle cells |
| Function | Convert chemical energy into mechanical energy to cause muscle contraction and movement |
| Part of metabolism | Yes |
| Part of blood sugar level maintenance | Yes |
| Percentage of body weight | 30% to 40% |
| Percentage of body proteins | 50% to 75% |
| Diseases | Skeletal muscle diseases, neuromuscular disorders |
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What You'll Learn
Skeletal muscles are voluntary muscles
The tissue of skeletal muscle is striated, giving it a striped appearance due to the arrangement of sarcomeres. Skeletal muscles contain multiple fascicles, or bundles of muscle fibres, which are much longer than those in other types of muscle tissue. Each muscle fibre and each muscle are surrounded by a type of connective tissue layer called fascia. Skeletal muscles can convert chemical energy into mechanical energy to cause voluntary muscle contraction and movement.
The action potential of a skeletal muscle can be measured using EMG, which stands for electromyography. This measures the hyperpolarization of motor axons from nerve impulses sent to the muscle. EMG is used in research to determine the amount of force generated by a skeletal muscle and as an indicator of muscle fatigue. It can also be used to measure the activation of a skeletal muscle, although this technique is less effective for smaller and deeper skeletal muscles.
Neuromuscular disorders, also known as skeletal muscle disorders, affect the nerves that send electrical signals to control voluntary skeletal muscles. These disorders can cause significant muscle weakness, atrophy, or pain. Charcot-Marie-Tooth disease, a peripheral nerve disorder, causes muscle weakness and atrophy, as well as loss of sensation, most commonly in the legs and feet. Multiple sclerosis (MS) is another disorder that can result in muscle weakness, often more severely on the dominant side of the body.
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Cardiac muscles are involuntary
There are over 600 muscles in the human body, and they can be categorised as either voluntary or involuntary. Voluntary movements are actions that an individual can consciously control. Examples of voluntary movements include flicking your thumb or sprinting around a track.
In contrast, involuntary movements happen automatically without conscious thought. The muscles in and around organs like the heart, lungs, and digestive system move involuntarily to keep the body functioning properly.
Cardiac muscles, which are found only in the heart, are involuntary. They make up the middle layers of the heart and are responsible for pumping blood through the cardiovascular system. While cardiac muscles are striated like skeletal muscles, they possess a unique structure, with a single, centrally located nucleus.
Cardiac muscles are controlled by the autonomic nervous system and their own pacemaker cells, causing them to contract automatically and rhythmically. This automatic contraction ensures the continuous beating of the heart, a vital process for human survival.
The autonomic nervous system can influence the speed of contraction in cardiac muscles, allowing the body to adjust the heart rate as needed. This regulatory mechanism is essential for maintaining homeostasis and responding to changes in the internal and external environment.
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Neuromuscular disorders
Voluntary muscles, also known as skeletal muscles, are those that can be consciously controlled. These include muscles in the neck, arms, legs, back, and trunk. They attach to bones and respond to nerve signals from the brain, resulting in muscle contraction and movement.
In contrast, neuromuscular disorders, or skeletal muscle disorders, are conditions that affect the nerves responsible for transmitting electrical signals to control voluntary skeletal muscles. These disorders can be caused by damage to the nerves themselves or the neuromuscular junction, where signals are transmitted from nerves to muscles. As a result, individuals may experience significant muscle weakness, atrophy, and pain.
- Amyotrophic lateral sclerosis (ALS), or Lou Gehrig's disease, which damages nerves controlling voluntary movement.
- Charcot-Marie-Tooth disease, a peripheral nerve disorder causing muscle weakness, atrophy, and loss of sensation, often in the legs and feet.
- Multiple sclerosis (MS), which leads to degeneration of the myelin sheath surrounding nerves, resulting in reduced impulses and muscle weakness.
Currently, there is no cure for neuromuscular disorders. However, treatments such as medications, physical therapy, occupational therapy, and surgery can help manage symptoms, delay progression, and improve patients' quality of life.
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Weakness or inability to control voluntary muscles
Skeletal muscles are voluntary muscles that can be consciously controlled. These include muscles in the neck, arms, and legs, which attach to bones. Weakness or an inability to control voluntary muscles can be a symptom of a neuromuscular disorder or an electrolyte imbalance. Neuromuscular disorders affect the nerves that control voluntary muscles and the nerves that communicate sensory information back to the brain. When neurons become unhealthy or die, communication between the nervous system and muscles breaks down, resulting in muscle weakness and atrophy.
There are many types of neuromuscular disorders, including genetic myopathies and those caused by problems with the immune system. Amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig's disease, is a neuromuscular disorder that damages the nerves controlling muscles and voluntary movement. Charcot-Marie-Tooth disease is another neuromuscular disorder that causes muscle weakness and atrophy, as well as loss of sensation, typically in the legs and feet. It is caused by a gene mutation that damages myelin, an insulating sheath surrounding nerves. Multiple sclerosis (MS) is a progressive disorder that causes degeneration of the myelin sheath, reducing nerve impulses and resulting in muscle weakness.
Muscular dystrophy (MD) is a group of genetic diseases that cause progressive weakness and degeneration of skeletal muscles. Limb-girdle muscular dystrophy (LGMD) is a type of MD characterised by progressive loss of muscle and the symmetrical weakening of voluntary muscles around the shoulders and hips. Congenital muscular dystrophy refers to MD that is present at birth or becomes evident before age two. It is marked by muscle weakness and degeneration, with some individuals unable to sit or stand without support.
While neuromuscular disorders are a common cause of muscle weakness, electrolyte imbalances can also lead to similar issues. Electrolytes such as sodium, potassium, calcium, and magnesium play a crucial role in muscle function, and altered levels of these electrolytes can result in weakness.
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Involuntary muscles and survival
Involuntary muscles are those that are not under conscious control. They manage functions that happen automatically, such as controlling heartbeats, breathing, and digestion. These processes are essential for survival and occur without our conscious involvement. Involuntary muscles allow the body to maintain these vital functions continuously, ensuring that things like the circulatory and digestive systems work properly.
Involuntary muscles include those involved in automatic internal processes needed for survival that control your blood vessels and organs like your heart, lungs, and digestive system. The heart is a hard-working muscle that beats thousands of times a day to keep you alive. Cardiac muscle, or myocardium, makes up the middle layers of your heart and is composed of a specialized type of muscle cell. Cardiac muscle is striated like skeletal muscle, but is controlled by both the autonomic nervous system and its own pacemaker cells, causing it to contract automatically and rhythmically.
In contrast, voluntary muscles are those under conscious control, like neck and leg muscles that you choose to move. They are also called skeletal muscles because they are attached to the skeleton. 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.
Most involuntary muscles are made up of smooth muscle, which lacks the striated structure of skeletal muscle and instead consists of sheets or layers of smooth muscle cells. Smooth muscles play an important role in many body systems, including the reproductive, urinary, respiratory, and digestive systems.
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Frequently asked questions
Voluntary muscles are skeletal muscles that can be consciously controlled. They make up 30% to 40% of human body weight and include muscles in the neck, arms, legs, back, and trunk.
Voluntary muscles receive nerve signals from the brain, leading to muscle contraction and movement. They can convert chemical energy into mechanical energy to enable voluntary movement.
Neuromuscular disorders, also known as skeletal muscle disorders, impact the nerves that transmit electrical signals to voluntary muscles. Examples include amyotrophic lateral sclerosis (ALS) and Charcot-Marie-Tooth disease, which cause muscle weakness and atrophy.
