Smooth Muscle - Definition, Function and Location | Biology (2023)

Definition of Smooth Muscle

Smooth muscle is a type of muscle tissue that is used by various systems to apply pressure to vessels and organs. Smooth muscle is composed of sheets or filaments of smooth muscle cells. These cells have actin and myosin fibers that run throughout the cell and are supported by a framework of other proteins. Smooth muscle contracts under certain stimuli as ATP is released for use by myosin. The amount of ATP released depends on the intensity of the stimuli, allowing smooth muscle to have a graded contraction as opposed to the “on-or-off” contraction of skeletal muscle.

Smooth Muscle Structure

Smooth muscle tissue, unlike skeletal or cardiac tissues, does not have clearly defined striations visible in the cells. This is because smooth muscle cells are organized differently than other muscle cells. As seen in the image below, the actin and myosin filaments in smooth muscle are arranged in a stacked pattern throughout the cell. This “ladder” arrangement of actin and myosin is very different from the structure of skeletal and cardiac muscle. Actin filaments (red lines) in smooth muscle run from one side of the cell to the other, connecting in dense bodies and in the cell membrane. In skeletal and cardiac muscle, actin filaments are attached to Z-plates, which contain many actin filaments and appear as dark bands under the microscope. In smooth muscle, actin and myosin fibers are arranged at angles to each other as they travel through the cell. This can be seen in the image below.

smooth muscle function

Like all muscle tissue, the function of smooth muscle is to contract. The image above shows how the actin and myosin fibers shorten, effectively shrinking the cell. However, there are some key differences in how smooth muscle contracts compared to other types of muscle. In skeletal muscle, a signal from thesomatic nervous systemcrosses into the muscle, where it stimulates organelles in the muscle cell to release calcium. Calcium causes a protein to separate from actin, and myosin quickly binds to the gap in actin. Since ATP was always available, myosin uses it to rapidly contract the cell.

(Video) Smooth Muscle Tissue Anatomy - Mnemonic, Structure, Contraction, Single-Unit, Multi-Unit

The same does not occur in smooth muscle tissue. In smooth muscle, contraction is not controlled voluntarily by the somatic nervous system, but by signals from theautonomic nervous system, such as nerve impulses, hormones, and other chemicals released by specialized organs. Smooth muscle is specialized to contract persistently, unlike skeletal muscle, which contracts and relaxes very quickly. Instead of a calcium trigger that triggers a twitch reaction, smooth muscle has more of an accelerator, like in a car.

A nerve impulse or external stimulus reaches the cell, which prompts it to release calcium. Smooth muscle cells lack a special protein in actin that prevents myosin from binding. Instead, actin and myosin are constantly linked. But, myosin can only hold on and crawl forward when given energy. Within smooth muscle cells is a complex pathway that allows the level of calcium to control the amount of ATP available to myosin. So when the stimulus is removed, the cells don't immediately relax. Myosin continues to bind to actin and crawl along the filaments until the calcium level drops.

smooth muscle location

This specialized function of contracting for long periods and maintaining that force is why smooth muscle has been adapted to many areas of the body. Smooth muscle lines many parts of the circulatory system, the digestive system, and is even responsible for raising the hairs on your arms.

In the circulatory system, smooth muscle plays a vital role in maintaining and controlling blood pressure and oxygen flow throughout the body. Although most of the pressure is applied by the heart, all veins and arteries are lined with smooth muscle. These small muscles can contract to apply pressure to the system or relax to allow more blood to flow. Tests have shown that these smooth muscles are stimulated by the presence or absence of oxygen and modify the veins to deliver enough oxygen when it is low.

(Video) Musculoskeletal System | Smooth Muscle

Smooth muscle also lines most of the digestive system, for similar reasons. However, cells in the digestive system have different stimuli than those in the circulatory system. For example, layers of smooth muscle tissue in the intestine react to swallowing. When you swallow, tension is applied to one side of the sheet. Cells on that side contract in reaction, a wave begins to propagate through the digestive tract. This phenomenon is known asperistalsis, and is responsible for moving food through the many twists and turns of the intestine.

Smooth muscle, because of its ability to contract and maintain, is used for many functions in many places in the body. In addition to those listed above, smooth muscle is also responsible for contracting the iris, raising the hairs on the arm, contracting the various sphincters in the body, and even moving fluids through the organs by applying pressure on them. Although smooth muscle does not contract or relax as quickly as skeletal or cardiac muscle, it is much more useful for providing consistent elastic tension.


1. A scientist is instructed to test two samples of unknown muscle and determine which is smooth muscle tissue and which is skeletal. However, the scientist broke his microscope yesterday. Which of the following methods will allow the scientist to identify smooth muscle from skeletal muscle?
A.Place the tissues in a solution containing free ATP
B.Place the tissues in a solution containing calcium ions
C.Whichever looks stronger is skeletal muscle

Answer to question #1

Ais correct. By placing tissues in a free ATP solution, we can distinguish between smooth and skeletal muscle. Skeletal muscle already has access to ATP and does not contract when placed in this solution. Smooth muscle uses a series of proteins to inhibit free ATP and prevent myosin from working. In a solution containing a lot of free ATP, smooth muscle would contract. Both tissues contract in a solution of calcium ions because calcium induces both systems.

(Video) Structure of Smooth Muscle | Types of Smooth Muscle | Muscle Physiology | Myology

2. Smooth muscle cells are connected to each other through regions calledadheres to joints. These regions contain many fibrous proteins for strength when cells pull against each other. Junctions also contain tiny gaps, which allow the cell membranes of two neighboring cells to join together. What is the function of thesegap junctions, what are they called?
A.Holes increase connection strength
B.Nerve impulses and chemicals can be transferred here
C.Cells pass ATP through holes

Answer to question #2

Bis correct. When a contraction occurs in smooth muscle tissue, it is important that the rest of the sheet of cells respond. The gap junctions found between cells allow the passage of the nerve impulse or chemical signal that initiated the contraction. This ensures that many cells contract at the same time, producing the effect desired by the body.

(Video) Skeletal Muscle , Cardiac Muscle and Smooth Muscle | Characteristics and Differences

3. Below are statements about smooth muscle. Select the incorrect statement.
A.Smooth muscle uses the same motor proteins as skeletal muscle
B.Smooth muscle is organized in the same way as skeletal muscle.
C.Smooth muscle does not have striations

Answer to question #3

Bis correct. Smooth muscle does not have striations because it is organized differently than skeletal muscle. The arrangement does not produce dark bands in the cells, but the same motor proteins (actin and myosin) are used.

(Video) Mechanism of Smooth Muscle Relaxation | Role of Nitric Oxide | IP3 Pathway


  • Lodish , H. , Berk , A. , Kaiser , C. A. , Krieger , M. , Scott , M. P. , Bretscher , A. , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Matsudaira , P. ( 2008 ).Cell Molecular Biology 6th. ed.New York: W. H. Freeman and Company.


What is smooth muscle description function and location? ›

Smooth muscle is present throughout the body, where it serves a variety of functions. It is in the stomach and intestines, where it helps with digestion and nutrient collection. It exists throughout the urinary system, where it functions to help rid the body of toxins and works in electrolyte balance.

What is the definition of smooth muscle? ›

At a cellular level, smooth muscle can be described as an involuntary, non-striated muscle. Smooth muscle consists of thick and thin filaments that are not arranged into sarcomeres giving it a non-striated pattern. On microscopic examination, it will appear homogenous.

What is the function of the smooth muscle quizlet? ›

Functional roles of smooth muscle contraction: propels contents through a hollow organ or tube. maintains pressure against the contents within a hollow organ or tube. regulates internal flow of contents by changing tube diameter (resistance).

What is smooth muscle described as quizlet? ›

Smooth muscles — sometimes also called involuntary muscles — are usually in sheets, or layers, with one layer of muscle behind the other. You can't control this type of muscle.

What are the locations of smooth muscle? ›

Smooth muscle fibers are located in walls of hollow visceral organs (such as the liver, pancreas, and intestines), except the heart, appear spindle-shaped, and are also under involuntary control. Skeletal muscle fibers occur in muscles which are attached to the skeleton.

What are the functions of smooth and skeletal muscle? ›

Skeletal muscle is an organ that primarily controls movement and posture. Cardiac muscle encompasses the heart, which keeps the human body alive. Smooth muscle is present throughout the gastrointestinal, reproductive, urinary, vascular, and respiratory systems.

Which statement best describes smooth muscle? ›

Smooth muscles are unstriated involuntary with spindle shape cells.

What words describe smooth muscle? ›

Answer: Smooth muscle is an involuntary, non-striated type of (vertebrate) muscle capable of slow rhythmic involuntary contractions. Smooth muscle, also called an involuntary muscle, displays no cross stripes when examined under a microscope.

What is the function of the skeletal muscle? ›

The main functions of skeletal muscle are to contract to produce movement, sustain body posture and position, maintain body temperature, store nutrients, and stabilize joints.

Which of the following are functions of smooth muscle? ›

They have the following functions,
  • Smooth muscles control involuntary movement, such as peristalsis(wave-like passage of food in the alimentary canal).
  • Smooth muscles help in regulating airflow in the lungs.
  • Smooth muscles are responsible for the contractions in the uterus of women while pushing out her baby.

What is the function of smooth muscle in vessels? ›

The smooth muscle cell directly drives the contraction of the vascular wall and hence regulates the size of the blood vessel lumen.

What is the function of smooth muscle Wikipedia? ›

Function. Vascular smooth muscle contracts or relaxes to change both the volume of blood vessels and the local blood pressure, a mechanism that is responsible for the redistribution of the blood within the body to areas where it is needed (i.e. areas with temporarily enhanced oxygen consumption).

Which description of smooth muscle tissue is most accurate quizlet? ›

Which description of smooth muscle tissue is most accurate? This tissue type, in addition to certain muscle tissues, is capable of generating electrical impulses.

Why is it called smooth muscle? ›

Smooth muscle is so named because it has no visible striations. Its contraction is involuntary. It is found in the walls of hollow organs (e.g., digestive tract, blood vessels, urinary bladder) and other areas (e.g., the iris).

Why is it called smooth muscle tissue? ›

On histology, smooth muscle typically appears as a sheet of interconnected, elongated cells within connective tissue. It is called 'smooth' muscle because it lacks the characteristic striations observed in histological sections of skeletal and cardiac muscle [22].

Which of these is not a function of smooth muscle? ›

Answer and Explanation: The correct answer is option C . Option C is not a function of smooth muscle because forcing blood from the heart to the major arteries is accomplished by cardiac muscles, which is the only muscle type found in the heart.

What is the function of cardiac muscle? ›

The cardiac muscle is responsible for the contractility of the heart and, therefore, the pumping action. The cardiac muscle must contract with enough force and enough blood to supply the metabolic demands of the entire body. This concept is termed cardiac output and is defined as heart rate x stroke volume.

How do smooth muscles move substances through the body? ›

The smooth muscle around these organs also can maintain a muscle tone when the organ empties and shrinks, a feature that prevents “flabbiness” in the empty organ. In general, visceral smooth muscle produces slow, steady contractions that allow substances, such as food in the digestive tract, to move through the body.

What are the functions of smooth and rough? ›

The rough ER, studded with millions of membrane bound ribosomes, is involved with the production, folding, quality control and despatch of some proteins. Smooth ER is largely associated with lipid (fat) manufacture and metabolism and steroid production hormone production. It also has a detoxification function.

Is breathing a smooth muscle? ›

The airways and parenchymal tissues of vertebrate lungs are, nearly without exception, lined with smooth muscle controlled by the autonomic nervous system.

Which of the following is an example of a smooth muscle? ›

Smooth muscle generally forms the supporting tissue of blood vessels and hollow internal organs, such as the stomach, intestine, and bladder.

What are 3 characteristics of smooth muscle? ›

Characteristics of smooth muscles:
  • These are non-striated, involuntary muscles controlled by the Autonomous Nervous System.
  • It stimulates the contractility of the digestive, urinary, reproductive systems, blood vessels, and airways.
  • The actin and myosin filaments are very thin and arranged randomly, hence no striations.

How would you describe smooth movement? ›

Smooth movement is predictable movement, and predictable movement is easy to control. This creates a positive feedback loop: increased predictability makes control easier, which makes movement smoother, which enhances predicability and so forth.

What is the difference between smooth muscle and skeletal muscle? ›

Skeletal muscles are attached to bones. They help for movement of various bones of the skeleton. Smooth muscles are forming the walls of hollow organs like intestines, blood vessels.

What is the function and location of the skeletal muscle? ›

Skeletal muscle includes the tissue fibers attached to your skeleton or bones and is responsible for all your movements. These muscles are also found at the openings of tracts in your body, like your throat, anus, and urethra. They're often called voluntary muscles because you control when and how they work.

What is the location of skeletal muscle? ›

Where are the skeletal muscles located? There are skeletal muscles throughout your body. They're located between bones.

What is the major function of muscle? ›

Their predominant function is contractibility. Muscles, attached to bones or internal organs and blood vessels, are responsible for movement. Nearly all movement in the body is the result of muscle contraction.

What is the structure of skeletal and smooth muscle? ›

Muscle tissues differ in structure. Skeletal muscle fibres are packed into regular parallel bundles. Smooth muscle has bundles of thin and thick filaments. Cardiac muscle bundles are branched but connected.

Where is cardiac muscle located? ›

Cardiac muscle makes up the thick middle layer of the heart and is surrounded by a thin outer layer called the epicardium or visceral pericardium and an inner endocardium.

What is the structure and function of the muscle tissue? ›

Muscle tissue is composed of cells that have the special ability to shorten or contract in order to produce movement of the body parts. The tissue is highly cellular and is well supplied with blood vessels.

What is the function of smooth muscle Quora? ›

smooth muscle tissue (also referred to as involuntary) takes care of movement in any part of your body you usually have no control of. Examples: blood vessels, digestive tract, lymph vessels,… The muscles you can voluntarily move are striated muscles.

What are the 3 types of muscles and examples? ›

The three main types of muscle include:
  • Skeletal muscle – the specialised tissue that is attached to bones and allows movement. ...
  • Smooth muscle – located in various internal structures including the digestive tract, uterus and blood vessels such as arteries. ...
  • Cardiac muscle – the muscle specific to the heart.

What is the more common type of smooth muscle? ›

Termed unitary smooth muscle or visceral muscle, this type of smooth muscle is the most common observed in the human body, forming the walls of hollow organs. Single-unit smooth muscle produces slow, steady contractions that allow substances, such as food in the digestive tract, to move through the body.

How can you tell the difference between smooth muscles? ›

While smooth muscles can be observed in the internal organs, striated muscles can be seen attached to the skeleton. The striated muscles comprise muscle fibres, composed of thin and thick filaments. On the other hand, smooth muscles possess interconnected cells for the formation of layers.

Is the heart a smooth muscle? ›

The cardiac muscle cell has one central nucleus, like smooth muscle, but it also is striated, like skeletal muscle.

What is the size of a smooth muscle cell? ›

The smooth muscle cell is 3-10 µm thick and 20-200 µm long. The cytoplasm is homogeneously eosinophilic and consists mainly of myofilaments. The nucleus is located in the center and takes a cigar-like shape during contraction.

What is the name of smooth muscle movement? ›

Peristalsis is a series of wave-like muscle contractions that move food through the digestive tract. It starts in the esophagus where strong wave-like motions of the smooth muscle move balls of swallowed food to the stomach.

Which description of smooth muscle tissue is most accurate? ›

Which description of smooth muscle tissue is most accurate? This tissue type, in addition to certain muscle tissues, is capable of generating electrical impulses.

What is the function of the muscles? ›

Muscles have a range of functions from pumping blood and supporting movement to lifting heavy weights or giving birth. Muscles work by either contracting or relaxing to cause movement. This movement may be voluntary (meaning the movement is made consciously) or done without our conscious awareness (involuntary).

What is the function of smooth muscle histology? ›

There are many functions of smooth muscle, from moving food along the digestive tract, to pulling hair erect in response to cold or fear. When these cells contract, they squeeze the ducts, helping to extrude the contents. Look at this section of ducts, that are surrounded by myo-epithelial cells.

Where is skeletal muscle located? ›

Skeletal muscle is found throughout the body, attached to bones via tendons. It is also present in the tongue, diaphragm, eye socket, and upper esophagus.

What are the distinguishing characteristics of smooth muscle tissue? ›

Smooth muscle cells are elastic, not striated, spindle-shaped and contain a single central nucleus. Smooth muscle cells are arranged together in sheets and this organisation means that they can contract simultaneously. However, they do contain other normal cell organelles such as sarcosomes but in lower numbers.

What are the 4 main functions of muscles in the body list and describe? ›

Muscles allow a person to move, speak, and chew. They control heartbeat, breathing, and digestion. Other seemingly unrelated functions, including temperature regulation and vision, also rely on the muscular system.

What is the structure and function of the muscle? ›

Muscle is a soft tissue found in both animals and humans. The cells of the muscles comprise protein filaments of actin and myosin that slide past one another, which produces contraction and changes both the length and the shape of the cell.


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