9.3: Types of Muscle Tissue (2023)

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    Work those eye muscles!

    Roll your eyes - a small movement, considering the visibly large and strong external eye muscles that control eyeball movements. These muscles are called the strongest muscles in the human body in terms of the work they do. However, the outer eye muscles perform a surprising amount of work. Eye movements occur almost constantly during waking hours, especially when examining faces or reading. The eye muscles are also exercised every night during the phase of sleep called rapid eye movement sleep. The outer eye muscles can move the eyes because they are mostly made of muscle tissue.

    What is muscle tissue?

    9.3: Types of Muscle Tissue (3)

    Muscle tissueIt is a soft tissue that makes up most of the muscle tissues of the human muscular system. Other muscle tissues are connective tissues, such as the tendons that attach skeletal muscles to bones and the connective tissue sheaths that cover or line muscle tissues. Only muscle tissue per se, however, has cells capable of contraction.

    There are three main types of muscle tissues in the human body: skeletal, smooth, and cardiac muscle tissues. Figure \(\PageIndex{2}\) shows how the three types of muscle tissue appear under the microscope. As you read about each type below, you'll learn why all three types appear the way they do.

    Skeletal Muscle Tissue

    Skeletal muscleis muscle tissue attached to bones bytendons, which are bundles of collagen fibers. Whether you're moving your eyes or running a marathon, you're using your skeletal muscles. Skeletal muscle contractions are either voluntary or under the conscious control of the central nervous system via the somatic nervous system. Skeletal muscle tissue is the most common type of muscle tissue in the human body. By weight, an average adult male is about 42% skeletal muscle, and an average adult female is about 36% skeletal muscle. Some of the major skeletal muscles in the human body are labeled in Figures \(\PageIndex{3}\) and Figure \(\PageIndex{4}\) and listed in Table \(\PageIndex{1}\).

    Table \(\PageIndex{1}\): Skeletal muscles. Some muscles are visible in anterior and posterior views.
    Muscles visible in Figure \(\PageIndex{3}\) Muscles visible in Figure \(\PageIndex{4}\)
    rotator cuff (several muscles are part of this group) shoulder lifter
    brachial biceps rhomboids
    brachial rotator cuff
    round pronator triceps brachii
    braquiorradial gluteus maximus
    adductor muscles tibial posterior
    tibial anterior fibular longo
    deltoid short fibula
    pectoralis major trapeze
    rectus abdominis deltoid
    abdominal external oblique braquiorradial
    iliopsoas wider back
    quadriceps femoris biceps femoris
    fibular longo semitendinosus
    fibular bravis semimembranoso
    9.3: Types of Muscle Tissue (4)
    9.3: Types of Muscle Tissue (5)

    Skeletal muscle pairs

    To move bones in opposite directions, skeletal muscles usually consist of pairs of muscles that work in opposition to one another. For example, when the biceps muscle (on the front of the arm) contracts, it can cause the elbow joint to flex or bend the arm, as shown in Figure \(\PageIndex{5}\). When the triceps muscle (on the back of the arm) contracts, it can cause the elbow to extend or straighten the arm. The biceps and triceps muscles are examples of muscle pairs where the muscles work in opposition to each other.

    9.3: Types of Muscle Tissue (6)

    Skeletal muscle structure

    Each skeletal muscle consists of hundreds – or eventhousands– from skeletal muscle fibers, which are long thread-like cells. As shown in Figure \(\PageIndex{6}\), skeletal muscle fibers are individually wrapped in connective tissue calledendomysium. Skeletal muscle fibers are grouped into units calledmuscle fascicles, surrounded by connective tissue sheaths calledperimysium. Each fascicle contains between ten and 100 (or even more!) skeletal muscle fibers. The fascicles, in turn, are grouped together to form individual skeletal muscles, which are wrapped in connective tissue calledepimysium. The connective tissues of skeletal muscles have a variety of functions. They support and protect the muscle fibres, allowing them to resist the forces of contraction by distributing the forces applied to the muscle. They also provide pathways for nerves and blood vessels to reach the muscles. In addition, the epimysium anchors muscles to tendons.

    9.3: Types of Muscle Tissue (7)

    The same structure of bundles within bundles is replicated within each muscle fiber. As shown in Figure \(\PageIndex{7}\), a muscle fiber consists of a bundle of myofibrils, which are bundles of protein filaments. These protein filaments consist of thin filaments of the protein actin, anchored in structures called Z disks – and thick filaments of the protein myosin. Filaments are arranged together within a myofibril in repeating units calledsarcomeres,that go from one Z disk to the next. The sarcomere is the basic functional unit of skeletal (and cardiac) muscle. It contracts as the actin and myosin filaments slide past each other. Skeletal muscle tissue is said to be striated because it looks striped. It has this appearance because of regular, alternating bands of A (dark) and I (light) filaments arranged in sarcomeres within muscle fibers. Other components of a skeletal muscle fiber include multiple nuclei and mitochondria.

    9.3: Types of Muscle Tissue (8)

    Slow and fast twitch skeletal muscle fibers

    Skeletal muscle fibers can be divided into two types, called slow-twitch (or type I) muscle fibers and fast-twitch (or type II) muscle fibers.

    • Slow twitch muscle fibersthey are dense in capillaries and rich in mitochondria and myoglobin, a protein that stores oxygen until needed for muscle activity. Relative to fast-twitch fibers, slow-twitch fibers can carry more oxygen and support aerobic (oxygen-using) activity. Slow-twitch fibers can contract for long periods of time, but not very forcefully. They are primarily used in endurance events such as long-distance running or cycling.
    • Fast twitch muscle fiberscontain fewer capillaries and mitochondria and less myoglobin. This type of muscle fiber can contract quickly and powerfully, but it tires very quickly. Fast-twitch fibers can only sustain short bursts of anaerobic activity (one that doesn't use oxygen). Relative to slow-twitch fibers, fast-twitch fibers contribute more to muscle strength and have greater potential to increase mass. They are mainly used in short, strenuous events such as running or weight lifting.

    The proportions of fiber types vary considerably from muscle to muscle and from person to person. Individuals may be genetically predisposed to have a higher percentage of one muscle fiber type than another. Generally, an individual who has more slow-twitch fibers is better suited for activities that require endurance. In contrast, an individual who has more fast-twitch fibers is better suited for activities that require small bursts of energy.

    Smooth muscle

    Smooth muscleis the muscle tissue in the walls of internal organs and other internal structures, such as blood vessels. When smooth muscles contract, they help organs and vessels carry out their functions. When the smooth muscles in the stomach wall contract, they compress the food inside the stomach, helping to mix and churn the food and break it down into smaller pieces. This is an important part of digestion. Smooth muscle contractions are involuntary and therefore not under conscious control. Rather, they are controlled by the autonomic nervous system, hormones, neurotransmitters, and other physiological factors.

    smooth muscle structure

    9.3: Types of Muscle Tissue (9)

    The cells that make up smooth muscle are often calledmyocytes.Unlike the muscle fibers of striated muscle tissue, smooth muscle tissue myocytes do not have their filaments arranged in sarcomeres. Therefore, smooth fabric is not striated. However, smooth muscle myocytes contain myofibrils, which contain bundles of myosin and actin filaments. The filaments cause contractions when they slide over each other, as shown in Figure \(\PageIndex{8}\).

    smooth muscle functions

    9.3: Types of Muscle Tissue (10)

    Unlike striated muscle, smooth muscle can sustain long-term contractions. Smooth muscle can also elongate and still maintain its contractile function, which striated muscle cannot. An extracellular matrix secreted by myocytes increases smooth muscle elasticity. The matrix consists of elastin, collagen and other elastic fibers. The ability to stretch and yet contract is an important attribute of smooth muscle in organs such as the stomach and uterus (Figure \(\PageIndex{9}\)), both of which must stretch considerably as they perform their normal functions.

    The following list indicates where many smooth muscles are located, along with some of their specific functions.

    • Walls of the gastrointestinal tract (such as the esophagus, stomach, and intestines), moving food through the tract by peristalsis.
    • Walls of the air passages of the respiratory tract (such as the bronchi), controlling the diameter of the passages and the volume of air that can pass through them
    • Walls of male and female reproductive organs; in the womb, for example, pushing a baby out of the womb and into the birth canal
    • The walls of structures in the urinary system, including the urinary bladder, allow the bladder to expand so it can hold more urine and then contract as urine is released.
    • Walls of blood vessels, controlling the diameter of the vessels and thereby affecting blood flow and blood pressure
    • Lymphatic vessel walls, squeezing fluid called lymph through the vessels.
    • Irises of the eyes, controlling the size of the pupils and therefore the amount of light that enters the eyes
    • Arrector pili in the skin, raising hairs in hair follicles in the dermis.

    heart muscle

    9.3: Types of Muscle Tissue (11)

    heart muscleit is only found in the heart wall. It is also called myocardium. As shown in Figure \(\PageIndex{10}\), the myocardium is surrounded by connective tissues, including the endocardium on the inside of the heart and the pericardium on the outside of the heart. When the heart muscle contracts, the heart beats and pumps blood. Cardiac muscle contractions are involuntary, like smooth muscle contractions. They are controlled by electrical impulses from specialized heart muscle cells in the area of ​​heart muscle called the SA node.

    Like skeletal muscle, cardiac muscle is striated because its filaments are arranged in sarcomeres within muscle fibers. However, in cardiac muscle, the myofibrils branch at irregular angles rather than arranged in parallel rows (as they do in skeletal muscle). This explains why cardiac and skeletal muscle tissues look different from each other.

    Cardiac muscle tissue cells are arranged in interconnected networks. This arrangement allows the rapid transmission of electrical impulses, which stimulate practically simultaneous contractions of the cells. This allows cells to coordinate heart muscle contractions.

    The heart is the muscle that does the most physical work in a lifetime. Although the power of the heart is much less than the maximum power of some other muscles in the human body, the heart does its work continuously throughout life without rest. Heart muscle contains many mitochondria, which produce ATP for energy and help the heart resist fatigue.

    Feature: Human Body in the News

    The human heart develops in a sequence of events that are controlled by communication between different types of cells, including cells that will become the myocardium (the heart muscle that forms the wall of the heart) and cells that will become the endocardium (the connective tissue covering the inner surface of the myocardium). If the communication between the cells is abnormal, it can cause various heart defects like cardiac hypertrophy or abnormal enlargement of the heart muscle. Cardiac hypertrophy causes the heart to thicken and weaken over time, making it less able to pump blood. Eventually, heart failure can occur, causing fluid to build up in the lungs and extremities.

    Abnormal cell communication is the mechanism by which a mutation called PTPN11 leads to cardiac hypertrophy in a disorder known as NSML (Noonan Syndrome with Multiple Lentigos). New research by scientists at Beth Israel Deaconess Medical Center in Boston has determined what kind of cellular abnormalities occur that lead to NSML. In the research, the scientists developed mouse models to express the PTPN11 mutation as they developed. The researchers manipulated the mouse models so that the mutation was expressed only in the cells that would develop in the myocardium of some mice. In contrast, in other mice, the mutation was only expressed in cells that would develop into the endocardium. Unexpectedly, heart hypertrophy occurred only in mice that expressed the mutation in endocardial cells, and not in myocardial cells, which had long been assumed to be the affected cells. Research results suggest potential targets for the treatment of NSML. They may also help scientists understand the causes of other heart conditions that are far more common than NSML.


    1. What is muscle tissue?

    2. Where is skeletal muscle located and what is its general function?

    3. Why do many skeletal muscles work in pairs?

    4. Describe the structure of a skeletal muscle.

    5. Relate the structure of muscle fibers with the functional units of muscles.

    6. Why is skeletal muscle tissue striated?

    7. Compare and contrast slow-twitch and fast-twitch skeletal muscle fibers.

    8. Where is smooth muscle found? What controls smooth muscle contraction?

    9. Compare and contrast smooth muscle and striated muscle (like skeletal muscle).

    10. Where is the heart muscle located? What controls your contractions?

    11. Cardiac and skeletal muscle tissue are striated but look different from each other. Why?

    12. The heart muscle is smaller and less powerful than some other muscles in the body. Why is the heart the muscle that does the most physical work in a lifetime? How does the heart resist fatigue?

    13. Arrange the following units within a skeletal muscle in order, from smallest to largest:issue; sarcomere; muscle fiber; myofibril

    14. Give an example of connective tissue found in muscles. Describe one of your roles.

    15.True or false:Skeletal muscle fibers are cells with multiple nuclei.

    Explore more


    You can learn more about the three types of muscle tissue by watching this Khan Academy video:


    1. Eyesby the diaper; public domain
    2. Muscle tissuepor Mdunning13,CC POR 3,0via Wikimedia Commons
    3. anterior muscles markedpor Häggström, Mikael (2014). "Galeria médica de Mikael Häggström 2014". WikiJournal of Medicine 1 (2).DOI:10.15347/wjm/2014.008.ISSN 2002-4436.Public domain. . . . via Wikimedia Commons
    4. Posterior muscles labeledpor Häggström, Mikael (2014). "Galeria médica de Mikael Häggström 2014". WikiJournal of Medicine 1 (2).DOI:10.15347/wjm/2014.008.ISSN 2002-4436.Public domain. . . . via Wikimedia Commons
    5. muscle movementbyCK-12licensedCC BY-NC 3.0
    6. muscle structureby the National Cancer Institute, public domain via Wikimedia Commons
    7. muscle fibersbyOpenStax,CC POR 4.0via Wikimedia Commons
    8. actin-myosin filamentpor Boumphreyfr,CC POR 3,0via Wikimedia Commons
    9. Placentaby Gray38, public domain via Wikimedia Commons
    10. heart wallbyOpen Stax High School,CC POR 3,0via Wikimedia Commons
    11. Text adapted fromhuman biologybyCK-12licensedCC BY-NC 3.0


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