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The human body is made up of more than 600 muscles, which help us move, breathe, swallow, and stay alive. There are three types of muscles: skeletal, smooth, and cardiac. Skeletal muscles are voluntary muscles that we can consciously control, such as the muscles in our arms, legs, neck, back, and trunk. Involuntary muscles, on the other hand, are those whose contraction is controlled by the autonomic nervous system and are not under conscious control. These include cardiac muscles, which are found only in the heart, and smooth muscles, which line the inside of some organs and play essential roles in various bodily functions.
| Characteristics | Values |
|---|---|
| Definition | Muscles that contract without conscious control |
| Control | Not under the control of the will (volition) |
| Types | Cardiac and smooth muscles |
| Location | Walls of visceral organs (e.g. liver, pancreas, intestines), heart, internal organs (e.g. oesophagus, stomach, intestines), blood vessels |
| Appearance | Smooth muscles lack striations when viewed under a microscope; cardiac muscles have striations |
| Function | Regular, slow contractions and involuntary actions; essential daily functions like digestion and breathing |
| Regulation | Autonomic nervous system, hormones, local factors |
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What You'll Learn
Cardiac Muscle
The human body contains over 600 muscles that help us move, breathe, swallow, and stay alive. These muscles can be categorised into three types: skeletal, smooth, and cardiac.
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Smooth Muscle
Blood Pressure and Circulation
Digestion
Vision
Reproduction
Respiration
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Involuntary Muscle Functions
Involuntary muscles are those that function without conscious input. They are controlled by the autonomic nervous system and include smooth muscles and cardiac muscles. Smooth muscles are found in the walls of the digestive system, blood vessels, bronchi, uterus, and bladder. They play an important role in the female and male reproductive systems, the urinary system, the respiratory system, and the digestive system. Smooth muscles help with essential functions such as moving waste through the intestines and aiding lung expansion during breathing.
Cardiac muscles, on the other hand, are found only in the heart. These muscles contract and relax to pump blood through the cardiovascular system. The heart beats involuntarily, maintaining proper blood circulation throughout the body.
Involuntary muscles also contribute to variations in the shape or inner diameter of organs. When the involuntary muscles of hollow organs, such as blood vessels and intestines, contract, it results in a reduction in the wall surfaces. This mechanism is vital for regulating blood vessel tone and intestinal peristalsis, ensuring the well-being of the organism.
In summary, involuntary muscles are essential for maintaining vital bodily functions, including digestion, respiration, and circulation. They work alongside voluntary muscles to support movement, posture, and the overall functioning of various organ systems in the body.
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Involuntary Muscle Disorders
Involuntary muscles are those that are not under conscious control. Their contraction and relaxation are regulated by the autonomic nervous system, which controls the activity of organs and blood vessels needed for essential daily functions, such as digestion and breathing. Smooth muscles are involuntary muscles that line the inside of some organs. They play an important role in many body systems, including the reproductive and urinary systems.
Some common involuntary movements associated with hyperkinetic movement disorders include tremors, tics, myoclonus, athetosis, dystonia, hemiballismus, and chorea. Tourette's Syndrome (TS), for example, is a neurobehavioral disorder characterised by multiple motor tics and vocalisations. TS is often associated with anxiety, depression, ADHD, and OCD. Dystonia, another hyperkinetic movement disorder, is initiated by voluntary motion but may later become sustained and extend to other body regions.
Myoclonus, or myoclonic jerks, are shock-like, arrhythmic twitches that may occur with voluntary movement or as a result of a stimulus. Myoclonus is often associated with CNS pathology, hypoxic damage, neurodegenerative disorders, and encephalopathy. It can also be symptomatic of other diseases, such as Alzheimer's, Huntington's, Lewy body dementia, and Creutzfeldt-Jacob disease.
Neuromuscular disorders affect the nerves that control voluntary muscles and those 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 atrophy. Symptoms of neuromuscular disorders include muscle weakness, twitching, cramps, aches, and pains. While there is currently no cure for neuromuscular disorders, treatments aim to manage symptoms, delay disease progression, and improve patients' quality of life.
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Involuntary Muscles vs. Voluntary Muscles
The human body has more than 600 muscles, which help us move, breathe, swallow, and stay alive. These muscles are attached to bones, blood vessels, and other internal organs. They are classified as either voluntary or involuntary based on their movements and structures.
Voluntary muscles are long, multinucleated cells, containing sarcomeres arranged into bundles. These muscles are composed of cylindrical fibers and are usually attached to bones and the skin. They play an important role in allowing the body to move by contracting and relaxing and their actions are mainly under the control of the somatosensory nervous system. These voluntary muscles include skeletal muscles, such as the muscles in our neck, arms, and legs. They move when we think about moving that part of the body. Some muscle fibers contract quickly and use short bursts of energy (fast-twitch muscles). Others move slowly, like our back muscles that help with posture.
Involuntary muscles, on the other hand, are not under conscious control. Their contraction and relaxation are regulated by the autonomic nervous system, which controls the activity of organs and blood vessels needed for essential daily functions, such as digestion and breathing. Most involuntary muscles are made up of smooth muscle, which lines the inside of some organs. These muscles help in pushing food molecules along the length of the alimentary canal, controlling the internal diameter of the blood vessels, and contracting the uterus during labor and childbirth.
The heart, which is composed of cardiac muscle, is also an involuntary muscle. 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 to pump blood throughout the body.
While voluntary muscles are responsible for voluntary movements, such as flicking a thumb or sprinting, involuntary muscles are responsible for involuntary movements, such as the beating of our heart and the movement of our ribs when we breathe.
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Frequently asked questions
Involuntary muscles are muscles that are not under conscious control. Their contraction and relaxation are regulated by the autonomic nervous system.
Involuntary muscles include the heart, respiratory and digestive systems, blood vessels, bronchi, uterus, and bladder.
Involuntary muscles are smooth muscles that lack the striated structure of skeletal muscles. They are composed of sheets or layers of smooth muscle cells.
The contraction of involuntary muscles is triggered by nerves and stimulated by complex chemical fluids such as acetylcholine and norepinephrine.
Involuntary muscles help with essential daily functions such as digestion, breathing, maintaining blood circulation, and controlling the internal diameter of organs.
