Logan Steele
The human body has over 600 muscles that help us do everything from pumping blood around our bodies to helping us lift heavy objects. Muscles are pieces of soft tissue that help us move, breathe, swallow, and stay alive. They attach to bones, tendons, other muscles, and sometimes under the skin. Tendons are fibrous connective tissues that attach muscle to bone or eyeballs. They can also attach muscles to other muscles or connective tissues. The musculoskeletal system is formed by bones, muscles, and joints, enabling us to do everyday physical activities.
| Characteristics | Values |
|---|---|
| Number of muscles in the human body | Over 600 |
| Muscle attachments | Bones, eyeballs, skin |
| Types of muscles | Skeletal, smooth, involuntary, cardiac |
| Muscle functions | Moving the body, pumping blood, lifting heavy objects, digesting food, breathing, swallowing |
| Muscle movements | Flexion, extension, abduction, adduction, elevation, depression, supination, pronation, dorsiflexion, plantar flexion |
| Muscle structure | Muscle fibres, connective tissue, epimysium, perimysium, endomysium, tendon, aponeurosis |
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What You'll Learn
Muscles attach to bones via tendons
The human body has more than 600 muscles that help us perform a wide range of tasks, from pumping blood throughout the body to helping us lift heavy objects. These muscles are made of thousands of small fibres woven together, forming skeletal, smooth, and cardiac muscle types.
Skeletal muscles are part of the musculoskeletal system, which includes bones, tendons, and ligaments. They are attached to bones by cord-like tendons, with one bone remaining relatively fixed while the other end moves due to muscle contraction. Tendons are fibrous connective tissues that connect muscles to bones or other structures like the eyeball. They are essential for moving the attached bone or structure.
The shape and arrangement of skeletal muscles vary, with some being broad and others narrow. Each skeletal muscle fibre is a single cylindrical muscle cell, and they are bundled together and wrapped in a connective tissue covering called the epimysium. The tendon, an extension of the epimysium, forms indirect attachments from muscles to bones or other muscles.
Smooth muscles, on the other hand, are involuntary and found in sheets or layers. They are commonly found in the stomach, intestines, bladder, and blood vessels, where they aid in digestion, maintaining blood pressure, and controlling urine release. Smooth muscles cannot be consciously controlled; instead, they are directed by the nervous system.
Cardiac muscle, found in the heart, is another type of involuntary muscle. It contracts and relaxes to pump blood through the cardiovascular system.
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Facial muscles attach under the skin
The human face has about 20 skeletal muscles, also known as craniofacial muscles, that lie underneath the skin and are essential to chewing and making facial expressions. They originate from the bones or fibrous structures of the skull and insert into the skin. Facial muscles are not surrounded by fascia, with the exception of the buccinator muscle, which prevents the molars from being bitten during mastication.
Facial muscles are innervated by the facial nerve (CN VII) and vascularised by the facial artery. They are supplied with blood by the ophthalmic and superficial temporal arteries, and vascularised by the posterior auricular and occipital arteries. The facial muscles are attached to the periosteum of bones or to the connective tissue of other muscles by tendons or aponeurosis. Tendons are fibrous connective tissue that attaches muscle to bone or other structures such as the eyeball.
The procerus is a muscle between the eyebrows that pulls the brows downward and flares the nostrils. The orbicularis oculi muscles close the eyes, depress the brows, and cause "crow's feet" wrinkles at the corners of the eyes. The frontalis muscle, connected to the occipitalis, raises the eyebrows and produces transverse forehead rhytides. The corrugator supercilii depresses the eyebrows and causes "frown lines".
Facial muscles may also play a role in reconstructive surgery, particularly in rehabilitating paralyzed areas.
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Smooth muscles are involuntary
There are three types of muscle tissue: cardiac, smooth, and skeletal. Smooth muscles are involuntary muscles, meaning they are not under our conscious control. They are found in the walls of hollow visceral organs, such as the stomach, intestines, bladder, liver, pancreas, and uterus, as well as in the eyes and skin. Smooth muscles are also present in the tracts of the respiratory, urinary, and reproductive systems.
Smooth muscles differ from skeletal muscles in terms of structure, function, and regulation of contraction. They are spindle-shaped and have a single nucleus. They can tense and relax, and in a relaxed state, each cell is 30-200 micrometers in length, thousands of times shorter than a skeletal muscle cell. Smooth muscles do not have myofibrils, but they contain the proteins myosin and actin, which enable them to contract. Myosin, primarily class II in smooth muscle, contains two heavy chains (MHC) that form the head and tail domains. These heavy chains coil together, giving myosin II two heads.
The heavy chains in smooth muscle are coded by a single gene (MYH11), which can produce four distinct isoforms through alternative splicing. Additionally, smooth muscle may contain MHC that does not participate in contraction and arises from multiple genes. Myosin II also contains four light chains (MLC), with two light chains per head. The MLC20, also known as the regulatory light chain, actively contributes to muscle contraction. Two MLC20 isoforms are found in smooth muscle, but only one isoform is involved in contraction.
The thin filaments in the contractile machinery of smooth muscle are primarily composed of alpha-actin and gamma-actin. Smooth muscle alpha-actin is the predominant isoform within this muscle type. Additionally, there is a significant amount of beta-actin, which does not directly contribute to contraction but assists in creating mechanical tension. Different combinations of heavy and light chains can result in various myosin structures, although only a select few combinations are likely to be utilized within a specific smooth muscle bed.
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Prime movers and antagonists work in pairs
The human body has over 600 muscles, each with its own attachment points and functions. Skeletal muscles, for example, have an origin and an insertion. The origin is the end of the muscle attached to a fixed or stabilized bone, while the insertion is the end of the muscle that attaches to the bone being pulled.
The prime mover, also known as the agonist, is the muscle that generates the primary force behind an action. It works in conjunction with the antagonist muscle, which resists or reverses the prime mover's action. These two types of muscles often come in pairs and are connected to opposite sides of a joint. As the direction of movement changes, their roles as prime mover and antagonist also reverse.
For example, the triceps brachii is a prime mover muscle that plays a significant role in extending the elbow joint from a bent to a straight position. It has four attachment points: one insertion on the ulna and three origins on the scapula, humerus, and ulna. The biceps brachii, brachialis, and brachioradialis, on the other hand, are antagonist muscles that flex the elbow.
Additionally, synergists are muscles that assist the prime mover in its function. They can also act as fixators, stabilizing the insertion site. Stabilizers are another type of muscle that maintains bone immobility when necessary, such as when they keep your posture sturdy.
The musculoskeletal system functions similarly to a hammer being used to remove a nail from wood. The bones act as stiff levers, while the articular endings encased in synovial joints serve as fulcrums. The muscles, through their attachments to the bones, determine the force, speed, and range of movement in the body.
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Muscles are soft tissue
The human body has more than 600 muscles that help us do everything from pumping blood around our bodies to helping us lift heavy objects. Muscles are pieces of soft tissue that help us move, breathe, swallow, and stay alive. They also move and support our organs.
Skeletal muscles are part of the musculoskeletal system, which includes bones, muscles, tendons, and ligaments. These muscles are attached by cord-like tendons to bones, such as in the legs, arms, and face. Tendons are fibrous connective tissues that attach muscles to bone or other structures like the eyeball. They also form indirect attachments from muscles to the periosteum of bones or to the connective tissue of other muscles.
Skeletal muscles have an abundant supply of blood vessels and nerves. Each skeletal muscle fiber is a single cylindrical muscle cell, and an individual skeletal muscle may be made up of hundreds or even thousands of muscle fibers bundled together and wrapped in a connective tissue covering. Each muscle is surrounded by a connective tissue sheath called the epimysium, which projects inward to divide the muscle into compartments. Each compartment contains a bundle of muscle fibers called a fasciculus, which is surrounded by a layer of connective tissue called the perimysium. Within the fasciculus, each individual muscle cell, or muscle fiber, is surrounded by connective tissue called the endomysium.
Smooth muscles, on the other hand, are involuntary muscles that we cannot control. They are usually in sheets or layers, with one layer of muscle behind the other. These muscles are found in the stomach, digestive system, bladder, and blood vessels, and they help with essential functions such as breaking up food, moving waste through the intestines, and regulating blood pressure.
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Frequently asked questions
Muscles are pieces of soft tissue that help us move, breathe, swallow, and stay alive.
Muscles attach to bones via cord-like tendons, which are fibrous connective tissues.
Apart from bones, muscles also attach to other muscles via tendons or broad, flat sheet-like aponeuroses.
Unlike muscles in the rest of the body, facial muscles do not attach directly to bone. Instead, they attach under the skin, allowing us to make various facial expressions.
Skeletal muscles are attached by tendons to bones in the legs, arms, and face. Tendons and aponeuroses also attach muscles to other muscles.
