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Smooth muscle is one of the three major types of vertebrate muscle tissue, the other two being skeletal and cardiac muscle. Smooth muscle is non-striated, meaning it has no sarcomeres and therefore no striations (bands or stripes). It is found throughout the body and serves a variety of functions, including blood circulation, digestion, eyesight, and more. Smooth muscle can be found in the stomach, intestines, urinary system, arteries, veins, skin, eyes, and various other organs and systems. It is controlled by the autonomic nervous system and can be divided into two subgroups: single-unit and multi-unit smooth muscle.
| Characteristics | Values |
|---|---|
| Type | One of the three major types of vertebrate muscle tissue |
| Other names | Non-striated muscle |
| Control | Controlled by the autonomic nervous system |
| Shape | Fusiform (round in the center and tapering at each end) |
| Location | Walls of hollow visceral organs (except the heart), arteries, veins, tracts of the urinary, respiratory and reproductive systems, skin, eyes, etc. |
| Function | Blood circulation, digestion, eyesight, etc. |
| Structure | Thick and thin filaments that do not arrange into sarcomeres, resulting in a non-striated pattern |
| Contraction | Contract uniformly |
| Proteins | Calmodulin, caldesmon, calponin, tropomyosin, actin, and myosin |
| Actin-to-myosin ratio | Between 2:1 and 10:1 |
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What You'll Learn
Smooth muscle is one of three types of muscle tissue
Single-unit smooth muscle refers to a bundle or sheet of smooth muscle cells that contract as a syncytium. In contrast, multi-unit smooth muscle is influenced by a combination of different neural elements, with some degree of cell-to-cell communication and local production of activators/inhibitors resulting in a coordinated response. Smooth muscle tissue demonstrates greater elasticity than striated muscle, which is important for its function in organs like the intestines and urinary bladder.
Smooth muscle contributes to many vital functions in the body, including blood circulation, digestion, eyesight, and more. It plays a role in regulating blood pressure and tissue oxygenation by contracting and relaxing involuntarily. This is controlled by the nervous system, which can tightly regulate many of the body's subsystems without conscious thought. For example, smooth muscle in the gastrointestinal tract works with interstitial cells of Cajal (ICCs) and platelet-derived growth factor receptor alpha (PDGFRα) to form an electrically coupled functional syncytium.
Smooth muscle cells are spindle-shaped with a wide middle and tapering ends, and they do not contain the protein troponin. Instead, significant proteins expressed within smooth muscle include calmodulin, caldesmon, and calponin. Smooth muscle is derived from both mesoderm and neural crest cells, with neural crest cells playing a crucial role in its development throughout the body, especially in the regulation of blood vessels.
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It is controlled by the autonomic nervous system
Smooth muscle is one of the three major types of vertebrate muscle tissue, the others being skeletal and cardiac muscle. Smooth muscle is non-striated, meaning it has no sarcomeres and therefore no bands or stripes. It is found throughout the body, serving a variety of functions. Smooth muscle is controlled by the autonomic nervous system and can be divided into two subgroups: single-unit and multi-unit smooth muscle.
Single-unit smooth muscle refers to when a bundle or sheet of smooth muscle cells contracts as a syncytium. This type of smooth muscle is found in the walls of internal organs and blood vessels, also known as visceral smooth musculature. The smooth muscle cells of the single-unit type are electrically connected by gap junctions and contract uniformly.
Multi-unit smooth muscle cells, on the other hand, are independent of each other and require individual innervation, allowing for more precise muscle control. They are found in the iris and hair erector muscles, among other locations. While the terms single- and multi-unit smooth muscle are useful distinctions, they oversimplify the complexity of smooth muscle control. Smooth muscles are influenced by a combination of different neural elements, and cell-to-cell communication and local activators/inhibitors contribute to a coordinated response even in multiunit smooth muscle.
Smooth muscle is key to many of the body's vital functions, including blood circulation, digestion, eyesight, and more. It is found in the walls of hollow visceral organs, such as the liver, pancreas, and intestines, and appears spindle-shaped. Smooth muscle contributes to the regulation of blood vessels and plays a vital role in maintaining blood pressure and tissue oxygenation.
Smooth muscle is also involved in the digestive process, helping with digestion and nutrient collection in the stomach and intestines. Additionally, it is present in the urinary system, where it aids in toxin removal and electrolyte balance. Smooth muscle has greater elastic properties than striated muscle, which is important for preserving contractile tone in organ systems like the urinary bladder.
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It has greater elastic properties than striated muscle
Smooth muscle is one of the three major types of vertebrate muscle tissue, the others being skeletal (striated) and cardiac muscle. Smooth muscle is non-striated, meaning it has no sarcomeres and therefore no striations (bands or stripes). It is found throughout the body and serves a variety of functions, including blood circulation, digestion, eyesight, and more.
Smooth muscle differs from skeletal and cardiac muscle in terms of structure, function, regulation of contraction, and excitation-contraction coupling. One key difference is that smooth muscle demonstrates greater elasticity and function within a larger length-tension curve than striated muscle. This ability to stretch and still maintain contractility is important in organs like the intestines and urinary bladder.
The elasticity of smooth muscle is due to the presence of actin and myosin, which form continuous chains within the smooth muscle cell. These chains can stretch to dense bodies located on adjacent smooth muscle cells, forming a mesh-like network. This allows the smooth muscle cells to contract uniformly in a spiral corkscrew fashion. The actin and myosin in smooth muscle also have a higher ratio of actin to myosin compared to striated muscle, which may contribute to its greater elasticity.
The shape of smooth muscle is described as fusiform, which is round in the center and tapering at each end. This shape may also contribute to the greater elastic properties of smooth muscle compared to striated muscle, which has a different shape with striations. The unique properties of smooth muscle, including its greater elasticity, make it imperative for medical professionals to have an in-depth understanding of its anatomy and physiology.
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Smooth muscle is found in the walls of hollow organs
Smooth muscle is one of three major types of vertebrate muscle tissue, the others being skeletal and cardiac muscle. It is non-striated, meaning it has no sarcomeres and therefore no bands or stripes. Smooth muscle is found in the walls of hollow organs, including the stomach, intestines, bladder, and uterus.
Smooth muscle is derived from both mesoderm and neural crest cells. This is because smooth muscle contributes to many different tissues throughout the body. Smooth muscle is found throughout the body, serving a variety of functions. It is present in the stomach and intestines, where it helps with digestion and nutrient collection. It is also found throughout the urinary system, where it helps rid the body of toxins and works in electrolyte balance.
Smooth muscle is also found in the walls of blood vessels and lymph vessels (excluding blood and lymph capillaries), where it is known as vascular smooth muscle. It plays a vital role in the regulation of blood pressure and tissue oxygenation. In the gastrointestinal tract, smooth muscle helps with the propulsion of the food bolus. Smooth muscle in the ciliary body of the eye controls how the eyes focus by pulling on fibers called zonules.
Smooth muscle is further divided into two subgroups: single-unit and multi-unit smooth muscle. Single-unit smooth muscle consists of multiple cells connected through connexins that can be stimulated in a synchronous pattern from a single synaptic input. Multi-unit smooth muscle, on the other hand, has independent cells that need to be innervated individually, allowing for more precise control. Single-unit smooth muscle is typically found in the walls of hollow organs, while multi-unit smooth muscle is found in the airways to the lungs and large arteries.
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It is key to many of the body's vital functions
Smooth muscle is a type of muscle that is key to many of the body's vital functions. It is one of the three major types of vertebrate muscle tissue, the others being skeletal and cardiac muscle. Smooth muscle is found throughout the body and serves a variety of functions. It is present in the stomach and intestines, where it helps with digestion and nutrient collection.
Smooth muscle is also found throughout the urinary system, where it helps to rid the body of toxins and maintain electrolyte balance. It is present in the walls of passageways, including arteries and veins of the cardiovascular system, where it plays a vital role in regulating blood pressure and tissue oxygenation. Smooth muscle is also involved in the regulation of blood flow and blood circulation. Without these vital functions, the body would not be able to maintain its most basic functions.
Smooth muscle is also found in the skin, where it causes hairs to stand on end, such as with goosebumps. In the eyes, smooth muscle pulls on fibers called zonules to control how the eyes focus. It is also present in the ciliary muscles, iris dilator muscle, and iris sphincter muscle. Smooth muscle can be further divided into two subgroups: single-unit and multi-unit smooth muscle.
Single-unit smooth muscle refers to when the entire bundle or sheet of smooth muscle cells contracts as a syncytium. In contrast, multi-unit smooth muscle cells are independent and require individual innervation, allowing for more precise muscle control. They are found in the iris and hair erector muscles. Smooth muscle is also present in the male reproductive system, where it plays a role in fertility by facilitating the contractions of the epididymis and vas deferens.
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