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Involuntary muscles, also known as white muscles or smooth muscles, are muscles in the human body that cannot be controlled by will or consciousness. 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 found lining the internal organs, such as the oesophagus, stomach, intestines, urinary tract, blood vessels, and intestinal tract. Cardiac muscles, on the other hand, are striated and branched and are only found in the heart, where they are responsible for pumping blood throughout the body.
Characteristics and Values of Involuntary Muscles
| Characteristics | Values |
|---|---|
| Definition | Muscles whose movement cannot be controlled by will or consciousness |
| Types | Cardiac and smooth muscles |
| Cardiac Muscle Structure | Striated or non-striated |
| Smooth Muscle Structure | Non-striated |
| Smooth Muscle Shape | Fusiform |
| Smooth Muscle Composition | Thick and thin filaments, actin, myosin, and calcium-containing sarcoplasmic reticulum |
| Controlled By | Autonomic nervous system |
| Functions | Pumping blood, maintaining heartbeat, pushing food molecules, controlling internal diameter of blood vessels, contracting uterus during labour and childbirth, etc. |
| Location | Heart, internal organs (e.g., stomach, intestine, urinary bladder), blood vessels, urogenital tracts, respiratory tracts, etc. |
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What You'll Learn
Cardiac muscle
Involuntary muscles are those whose movement cannot be controlled by will or conscious control. They are often associated with organs that exhibit slow and regular contractions and relaxation. Involuntary muscles include smooth muscles and cardiac muscles.
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Smooth muscle
An example of single-unit smooth muscle function is the uterine muscles during childbirth, which contract in a coordinated fashion to facilitate labour and childbirth. On the other hand, smooth muscles lining the lungs' airways, ciliary muscles in the eye, and arrector pili muscles in the skin are examples of multi-unit smooth muscles. These muscles show independent contraction and relaxation responses.
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Autonomic nervous system
The autonomic nervous system (ANS) is a division of the nervous system that operates the internal organs, smooth muscle, and glands. It is a control system that acts largely unconsciously and regulates vital bodily functions, such as heart rate, blood pressure, digestion, respiratory rate, pupillary response, urination, and sexual arousal. The ANS is also known as the visceral nervous system and was formerly called the vegetative nervous system. It is a component of the peripheral nervous system, which includes every part of the nervous system that isn't the brain and spinal cord.
The ANS regulates involuntary physiological processes, including heart rate, blood pressure, respiration, digestion, and sexual arousal. It is regulated by integrated reflexes through the brainstem to the spinal cord and organs. Autonomic functions include control of respiration, cardiac regulation, vasomotor activity, and certain reflex actions such as coughing, sneezing, swallowing, and vomiting. The ANS also manages the width of the pupils, regulating how much light enters the eyes, and the muscles the eyes use to focus.
The ANS is classically divided into the sympathetic nervous system and the parasympathetic nervous system. The sympathetic division emerges from the spinal cord in the thoracic and lumbar areas, while the parasympathetic division has craniosacral "outflow", meaning that the neurons begin at the cranial nerves and the sacral spinal cord. The parasympathetic nervous system promotes a "'rest and digest' response, calming the nerves, and enhancing digestion. The ANS also controls the fight-or-flight response, or acute stress response, which diverts blood flow away from the gastrointestinal tract and skin, and towards the skeletal muscles and lungs.
The ANS is involved in a wide range of bodily functions, including the digestive system, liver and pancreas functions, urinary tract functions, and the reproductive system. It also plays a role in the immune system, triggering reactions and managing the tear system around the eyes, the runny nose, and salivation in the mouth.
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Involuntary muscle structure
Involuntary muscles are those whose movement cannot be controlled by will or conscious control and are often associated with organs that exhibit slow and regular contractions and relaxation. They are also known as smooth muscles or non-striated muscles as there are no striations when viewed under a microscope. Smooth muscles are fusiform in shape, i.e., round at the center and tapering at the ends. They are made up of thick and thin filaments that are not arranged into sarcomeres, resulting in a non-striated pattern. The cytoplasm of smooth muscles contains actin and myosin in large amounts. They also have a calcium-containing sarcoplasmic reticulum, which is responsible for prolonged contraction. Smooth muscles can be single-unit or multi-unit muscles. Single-unit smooth muscles contract and relax as a whole, while multi-unit muscles contract and relax separately.
Smooth muscles are found lining the internal organs, such as the esophagus, stomach, intestines, liver, pancreas, urinary tract, blood vessels, intestinal tract, and reproductive organs. They also line the lungs' airways, the ciliary muscle in the eye, and the arrector pili muscles in the skin. Smooth muscles are involved in essential functions, such as moving waste through the intestines, helping the lungs expand during breathing, and controlling the internal diameter of blood vessels.
Another type of involuntary muscle is the cardiac muscle, which is only found in the heart. The cardiac muscle is composed of individual heart muscle cells called cardiomyocytes, which are joined together by intercalated discs. These muscle cells are enclosed by collagen fibers and other substances that form the extracellular matrix. The cardiac muscle contracts involuntarily, pumping blood throughout the body and maintaining proper blood circulation.
In summary, involuntary muscles include smooth and cardiac muscles, which are structurally and functionally distinct from voluntary muscles. Smooth muscles have a non-striated appearance, are found lining various organs, and exhibit slow and steady contractions. In contrast, cardiac muscles are striated, located only in the heart, and have unique contraction patterns to facilitate blood circulation.
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Involuntary muscle functions
Involuntary muscles, also known as "white muscles" or "smooth muscles", are muscles in the human body whose movement is not under conscious control. They are controlled by the autonomic nervous system, which stimulates them to contract through the release of hormones or other chemical signals. Involuntary muscles include smooth muscles and cardiac muscles. Smooth muscles are non-striated and are found lining the internal organs, such as the esophagus, stomach, intestines, urinary tract, blood vessels, and intestinal tract. Cardiac muscles, on the other hand, are striated and are only found in the heart, where they are responsible for pumping blood throughout the body.
Smooth muscles can be further classified into single-unit and multi-unit smooth muscles. Single-unit smooth muscles contract and relax as a whole, while multi-unit smooth muscles contract and relax independently. An example of a single-unit smooth muscle is the digestive tract, which exhibits slow and steady involuntary contractions. Examples of multi-unit smooth muscles include the smooth muscles lining the lungs' airways, ciliary muscles in the eye, and the arrector pili muscles in the skin.
Cardiac muscles, also known as myocardium, are composed of individual heart muscle cells called cardiomyocytes, which are joined together by intercalated discs. These muscle cells are enclosed by collagen fibers and other substances that form the extracellular matrix. The contraction of cardiac muscle differs from that of both skeletal and smooth muscles, as it is controlled by both the autonomic nervous system and its own pacemaker cells, resulting in automatic and rhythmic contractions.
Involuntary muscles play a crucial role in various bodily functions, such as maintaining proper blood circulation by maintaining a steady heartbeat, pushing food molecules along the length of the alimentary canal, controlling the internal diameter of blood vessels, and contracting the uterus during labour and childbirth. They are also involved in the movements of the internal organs and aid in the passage of fluids and food in the digestive system.
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Frequently asked questions
Involuntary muscles are muscles in the human body whose contraction is not controlled by will or conscious control. They are also known as "white muscles" or "smooth muscles".
Examples of involuntary muscles include cardiac muscle and smooth muscle lining the intestinal tracts, blood vessels, urogenital tracts, respiratory tract, etc.
Smooth muscles are non-striated involuntary muscles that line the viscera or the internal hollow organs like the urinary tract, blood vessels, and intestinal tract. They are also found in the walls of the lungs' airways, ciliary muscles in the eye, and the arrector pili muscles in the skin.
Cardiac muscles are striated involuntary muscles found only in the heart. They are composed of individual heart muscle cells called cardiomyocytes, which are joined by intercalated discs.
Voluntary muscles are under conscious control and are associated with the skeleton system. They are attached to bones by tendons and are responsible for the movement of body parts. On the other hand, involuntary muscles are controlled by the autonomic nervous system and are found in the heart, blood vessels, and the digestive system.
