Dominic Stone
The human body is home to more than 600 muscles, which help us do everything from breathing and swallowing to pumping blood around our bodies and lifting heavy objects. Muscles are pieces of soft tissue that line some of our organs and allow us to move our bodies and stay alive. They can be broadly divided into three types: striated or skeletal muscle, smooth muscle, and cardiac muscle. Skeletal muscles are the most common type, comprising 30% to 40% of our total body mass, and they are attached to our bones by tendons, allowing us to perform a wide range of movements. Smooth muscle lines some of our organs, while the heart is made of cardiac muscle, which works independently of our conscious control.
| Characteristics | Values |
|---|---|
| Number of muscles in the body | Over 600 |
| Types of muscles | Skeletal, Cardiac, Smooth |
| Skeletal muscle composition | 30-40% of total body mass |
| Skeletal muscle function | Voluntary, controlled movement |
| Cardiac muscle location | Middle layer of the heart |
| Cardiac muscle function | Involuntary, pumps blood |
| Smooth muscle function | Involuntary, lines organs, moves waste |
| Muscle fibres | Type I, Type II (A and B) |
| Muscle injuries | Strain, spasm, weakness, DOMS |
| Muscle treatments | RICE, rest, compression |
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What You'll Learn
- Skeletal muscles are the most common type, comprising 30-40% of body mass
- Cardiac muscle is striated, involuntary, and only found in the heart
- Smooth muscle is involuntary, non-striated, and found in blood vessels
- Facial muscles are unique, attaching under the skin rather than to bone
- Muscles in the neck and back are powerful, allowing for head rotation
Skeletal muscles are the most common type, comprising 30-40% of body mass
Skeletal muscles are the most common type of muscle in the human body, comprising 30-40% of total body mass. They are attached to bones by tendons, which are cords of tough connective tissue. These muscles work with the bones and tendons to support the body and enable movement.
Skeletal muscles are voluntary, meaning they can be controlled consciously. They contract under the influence of the central nervous system, allowing for a wide range of movements. Each muscle can contain thousands of flexible fibres, which contract and relax to facilitate movement. These fibres can be further broken down into Type I and Type II fibres. Type I fibres are slow and deliberate in their contractions, providing stamina and posture. Type II fibres are stronger and faster but have less endurance.
The skeletal muscles in the neck, for example, allow for rotation of the head and neck, as well as assisting in forced inhalation. The deltoid muscles in the shoulders enable a wide range of movements, from swinging a softball bat to shrugging. The pectoralis muscles in the upper chest are commonly known as "pecs", and they are usually larger in males.
The musculoskeletal system, formed by the combination of skeletal muscles and bones, gives the body its power and strength. Skeletal muscles are essential for health and everyday functions, and it is important to keep them strong and healthy.
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Cardiac muscle is striated, involuntary, and only found in the heart
The human body has three major categories of muscles: cardiac, smooth, and skeletal. Cardiac muscle, also known as myocardium or heart muscle, is one of these three types of muscle tissues. It is an involuntary, striated muscle that constitutes the main tissue of the wall of the heart.
The heart is made up of three layers: the pericardium, myocardium, and endocardium. The endocardium is not cardiac muscle, whereas the myocardium is composed of cardiac muscle cells. The cardiac muscle is responsible for the contractility of the heart and, therefore, the pumping action. The heart wall is a three-layered structure with a thick layer of myocardium sandwiched between the inner endocardium and the outer epicardium.
Cardiac muscle cells are striated, branched, and contain many mitochondria. They are under involuntary control. Each myocyte contains a single, centrally located nucleus surrounded by a cell membrane known as the sarcolemma. The sarcolemma of cardiac muscle cells contains voltage-gated calcium channels, which skeletal muscles do not possess. The striations are caused by lighter I bands composed mainly of actin and darker A bands composed mainly of myosin.
Cardiac muscle is only found in the heart. It does not exist anywhere else in the human body.
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Smooth muscle is involuntary, non-striated, and found in blood vessels
Smooth muscle is one of the three major types of vertebrate muscle tissue, the other two being skeletal and cardiac muscle. Smooth muscle is involuntary, meaning it is not under a person's conscious control. It is also non-striated, meaning it has no sarcomeres and therefore no stripes or bands. It is derived from both mesoderm and neural crest cells, which play an important role in the development of smooth muscle throughout the body.
Smooth muscle is found in the walls of most internal organs, including the stomach, intestines, bladder, uterus, and liver, as well as the urinary, reproductive, and respiratory tracts. It is also found in the eyes, where the ciliary muscles, iris dilator muscle, and iris sphincter muscle are types of smooth muscles.
One of the key functions of smooth muscle is to regulate blood pressure and tissue oxygenation. It is found in arteries, veins, and capillaries, where it plays a vital role in maintaining basic bodily functions. Smooth muscle, also known as vascular smooth muscle, wraps around larger vessels and is essential for vascular development, stability, and the regulation of blood flow.
Smooth muscle is capable of maintaining tone for extended periods and often contracts involuntarily. It consists of thick and thin filaments that are not arranged into sarcomeres, giving it a non-striated pattern. Smooth muscle cytoplasm contains large amounts of actin and myosin, the main proteins involved in muscle contraction.
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Facial muscles are unique, attaching under the skin rather than to bone
The human face has about 20 to 30 muscles on each side, which are responsible for facial expressions and chewing. These muscles are part of the skeletal system (musculoskeletal system) and are also known as craniofacial muscles. Unlike other skeletal muscles, which attach to bones and are responsible for skeletal movement, facial muscles are unique in that they attach under the skin and manipulate the skin and soft tissues. Facial muscles have a higher concentration of fast-twitch fibres and fewer mitochondria than other muscles. This allows them to be the fastest-moving muscles in the human body, as seen in the orbicularis oculi and zygomaticus major muscles.
Facial muscles are striated muscles, meaning they appear striped when viewed under a microscope. They are some of the only striated muscles in the body that attach on one side to bone and on the other to skin. These muscles receive signals from the brain via the facial nerve (cranial nerve or CN VII) and the trigeminal nerve's mandibular division (CN V3). The facial nerve provides motor function to the face, allowing for various facial expressions such as smiling, frowning, and raising eyebrows.
The muscles of facial expression are considered extensions of the face's superficial musculoaponeurotic system (SMAS). The SMAS runs from the neck platysma up to the galea aponeurotica and temporoparietal fascia under the scalp. For example, the frontalis muscle, connected to the occipitalis, can raise the eyebrows and produce forehead wrinkles. In contrast, the corrugator supercilii depresses the eyebrows and causes vertical frown lines.
The unique anatomy of facial muscles, with their soft tissue attachments, allows for the movement of the overlying skin and enables us to communicate and express emotional states through facial behaviours and expressions.
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Muscles in the neck and back are powerful, allowing for head rotation
The human body is made up of many muscles, including skeletal muscles, cardiac muscles, and smooth muscles. Skeletal muscles are the most common type of muscle in the body, comprising 30% to 40% of total body mass. They are attached to bones by tendons and help with a wide range of movements and functions.
The neck and back muscles are a vital part of the musculoskeletal system. These muscles are powerful and enable head rotation, as well as other movements like swallowing, chewing, and breathing. The neck muscles are skeletal muscles, meaning they are under voluntary control. They are located at the front, sides, and back of the neck, extending from the base of the skull down to the middle back and around the shoulder blades.
The posterior neck muscles, specifically the superficial muscles, are strap-like muscles that help extend and rotate the head. The suboccipital muscles, located just below the occipital bone at the skull's base, also assist in extending the head in different directions. The transversospinalis muscles enable head movement forward and backward, as well as side-to-side tilting, while also stabilizing the spine.
The splenius muscles, including the splenius capitis and splenius cervicis, are responsible for extending, laterally flexing, and rotating the head. Additionally, the major muscle that laterally flexes and rotates the head is the sternocleidomastoid. The back muscles, such as the erector spinae group, stabilize and move the vertebral column, controlling flexion, lateral flexion, and rotation.
The neck and back muscles work together to provide powerful support and a wide range of movements for the head, including rotation, extension, and flexion.
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Frequently asked questions
Muscles are found throughout the human body. They are pieces of soft tissue that help us move, breathe, swallow, and stay alive.
Broadly, human muscles can be divided into three types: striated or skeletal muscle, smooth muscle, and cardiac muscle. Skeletal muscles are the most common type, comprising 30% to 40% of our total body mass. They are attached to bones by tendons and are under our voluntary control. Smooth muscles line some of our organs, while the heart is made of cardiac muscle.
Skeletal muscles are located between the bones throughout your body. Some examples include the deltoid muscles in your shoulders, the pectoralis muscles in your upper chest, and the hamstring and abdominal muscles. Even your face has plenty of muscles!
Muscles are responsible for various functions in our body. They help us move, maintain posture, and perform voluntary and involuntary actions. For example, skeletal muscles allow us to perform a wide range of movements, while smooth muscles in our organs and cardiac muscles in our heart help with essential functions like digestion and blood circulation.
