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The human body has over 600 muscles, comprising 30% to 40% of total body mass. These muscles enable us to move and perform a wide range of functions. There are three types of muscles: skeletal, smooth, and cardiac. Skeletal muscles are the only voluntary muscles, meaning we can control how and when they move. They are attached to bones and move by shortening their length, pulling on tendons, and moving bones closer to each other. Smooth and cardiac muscles are involuntary, controlled by the nervous system without conscious thought. They are responsible for essential functions like moving substances through organs and maintaining blood pressure. All muscles move by contracting, using energy from food, and receiving signals from the brain.
| Characteristics | Values |
|---|---|
| Number of muscles in the human body | Over 600 |
| Muscle movement | Contraction and relaxation |
| Muscle contraction | Rapid in striated muscles, gradual in smooth muscles |
| Muscle composition | Skeletal muscle tissue, blood vessels, tendons, and nerves |
| Types of muscle tissue | Visceral, cardiac, and skeletal |
| Types of muscle movement | Voluntary and involuntary |
| Skeletal muscle composition | Skeletal muscle fibres |
| Skeletal muscle movement | Voluntary |
| Involuntary muscle movement | Controlled by the autonomic nervous system |
| Skeletal muscle function | Contract to move parts of the body closer to the bone |
| Skeletal muscle attachment | Two or more places on bones, other muscles, or tissues |
| Muscle fibre covering | Epimysium, perimysium, and endomysium |
| Muscle fibre contraction | Depends on energy generated from food |
| Muscle fibre molecules | Actin and myosin |
| Muscle fibre communication | Sensors in muscles and joints send messages to the cerebellum and brain |
| Muscle fibre repair | Through stem cells |
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What You'll Learn
Skeletal muscle movement
Skeletal muscles are the most common type of muscle in the human body, comprising 30% to 40% of total body mass. They are attached to the bones of the skeletal system and allow a wide range of movements and functions. These muscles are voluntary, meaning individuals have conscious control over how and when they work.
Skeletal muscles are composed of cells collectively referred to as muscle fibres. Each muscle fibre is multinucleated, with its nuclei located along the periphery of the fibre. These muscle fibres further subdivide into myofibrils, which are the basic units of the muscle fibre. The myofibrils are surrounded by the muscle cell membrane (sarcolemma), which forms deep invaginations called transverse tubules (T-tubules) within the myofibril. The muscle fibres are flexible and range from less than half an inch to just over 3 inches in diameter.
The contraction of skeletal muscles in response to a stimulus generates force and movement. This contraction occurs when the muscle fibres shorten, pulling on tendons and moving bones closer to each other. The muscle fibres stretch and press together, resulting in the movement of the body or internal organs. Skeletal muscles rarely work independently but rather in groups to produce precise movements. The muscle responsible for a specific movement is called the agonist or prime mover, and it pairs with an antagonist muscle that produces the opposite effect. For example, the biceps brachii muscle flexes the arm at the elbow, while its antagonist, the triceps brachii muscle, extends the arm.
Skeletal muscles serve various purposes beyond producing movement. They help sustain body posture and position, maintain body temperature, store nutrients, and stabilize joints. Additionally, they contribute to basal energy metabolism by serving as a storage site for essential substrates such as carbohydrates and amino acids.
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Involuntary vs voluntary movements
The human body has over 600 muscles, comprising around 30% to 40% of total body mass. These muscles are responsible for movement, both voluntary and involuntary. Voluntary movements are actions that an individual controls, such as sprinting or scrolling through a phone. These movements are consciously performed and controlled by the somatic nervous system. On the other hand, involuntary movements occur without conscious thought, such as the beating of the heart or breathing. These movements are controlled by the autonomic nervous system.
Voluntary movements are typically associated with skeletal muscles, which are attached to bones and allow for a wide range of movements. Skeletal muscles are the only voluntary muscles in the human body. They contract to move body parts closer to the bones they are attached to. Most skeletal muscles are attached to two bones across a joint, allowing for precise movements. For example, the biceps brachii muscle flexes the arm at the elbow, while its antagonist, the triceps brachii muscle, extends the arm.
In contrast, involuntary movements are often associated with visceral and cardiac muscles. Visceral muscles are found inside organs like the stomach and intestines, and they contract to move substances through the organ. Cardiac muscles, on the other hand, are responsible for the involuntary movement of the heart. These involuntary movements are crucial for maintaining essential bodily functions, such as breathing, digestion, and waste elimination.
While voluntary movements involve conscious decision-making, involuntary movements are reflexive and automatic. Reflexes, a type of involuntary movement, are rapid responses to specific stimuli, such as withdrawing your hand after touching something hot. These reflexes are mediated by circuits of neurons near the spinal cord, ensuring quick reactions without conscious thought.
In summary, voluntary movements are consciously controlled and primarily involve skeletal muscles, enabling various bodily actions. On the other hand, involuntary movements occur without conscious thought and are associated with visceral and cardiac muscles, maintaining essential bodily functions. Both types of movements are integral to the human body's overall functionality and adaptability.
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Agonist and antagonist muscles
The human body has over 600 muscles, which, along with bones, form the musculoskeletal system. These muscles are responsible for all kinds of movements, from holding the body still to performing complex actions like sprinting. There are three types of muscles in the body: skeletal, cardiac, and smooth muscle.
Skeletal muscles are voluntary muscles, meaning we can control how and when they move. They are attached to the bones of the skeletal system and allow us to perform a wide range of movements. When we want to perform an action, the skeletal muscles contract and move the bones they are attached to. These muscles rarely work alone and often work in groups to produce precise movements.
Now, in any group of skeletal muscles working together, there is always a primary mover or 'agonist' muscle. This is the muscle that is tensed or "strained" during an action and is responsible for creating the desired movement. For example, when lifting a cup, the biceps brachii is the agonist or prime mover.
However, the agonist always works in tandem with an 'antagonist' muscle that produces the opposite effect on the same bones. In the case of lifting a cup, the triceps brachii muscle is the antagonist, as it extends the arm at the elbow, opposite to the action of the biceps brachii. When the arm is lowered, the roles reverse, with the triceps becoming the agonist and the biceps the antagonist.
This pairing of agonist and antagonist muscles is crucial for two main reasons. Firstly, it allows for more complex movements by providing the necessary resistance and offsetting the force exerted by the agonist, thus protecting our joints and bones. Secondly, it helps the muscles return to their normal position after moving. For instance, when performing a bicep curl, the triceps relaxes to allow the movement to occur, and when the arm is lowered, the bicep relaxes to allow the movement back to the starting position.
In addition to agonists and antagonists, there are also 'synergist' muscles that assist the agonist by stabilising the origin of the movement or the insertion site of the agonist muscle. For example, when the biceps brachii flexes the lower arm during forearm flexion, the brachialis and brachioradialis act as synergists.
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Smooth muscle movement
Smooth muscles are one of the three major types of vertebrate muscle tissue, the other two being skeletal and cardiac muscle. Smooth muscles are non-striated, meaning they lack the striations or bands characteristic of cardiac and skeletal muscle. They can be found in the walls of hollow organs, including the stomach, intestines, bladder, uterus, and blood vessels. Smooth muscles are also present in the tracts of the respiratory, urinary, and reproductive systems, as well as in the skin and eyes.
Smooth muscle can be divided into two subgroups: single-unit and multi-unit smooth muscle. Single-unit smooth muscle, also known as visceral smooth muscle, is found in the walls of most internal organs and lines blood vessels, the urinary tract, and the digestive tract. It contracts as a whole, allowing for coordinated movement or relaxation. Multi-unit smooth muscle, on the other hand, is found in the trachea, iris of the eye, and lining the large elastic arteries. While the terms single- and multi-unit are commonly used, they represent an oversimplification of smooth muscle function.
Smooth muscle plays a vital role in various bodily functions. For example, in the gastrointestinal tract, smooth muscle cells work together with interstitial cells and growth factors to activate movement. In the urinary system, smooth muscle helps rid the body of toxins and maintains electrolyte balance. Smooth muscle is also essential for vascular development and stability, and its ability to contract and relax helps regulate blood pressure and tissue oxygenation.
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How muscles contract
The human body has over 600 muscles, which can be categorised into three types: skeletal, cardiac and smooth muscle. 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 and allow us to perform a wide range of movements. These are the only voluntary muscles in the body, meaning we can control how and when they work.
Skeletal muscles rarely work alone, instead working in groups to produce precise movements. They contract to move body parts closer to the bone to which the muscle is attached. This is achieved by the muscle shortening its length, pulling on tendons, and moving bones closer together.
The process of muscle contraction involves the interaction of myosin and actin proteins. Myosin binds to actin, and this interaction results in a conformational change that causes the muscle cell to contract. This process is known as the sliding filament theory of muscle contraction.
There are different types of muscle contractions, including isometric, isotonic, concentric, and eccentric contractions. Isometric contractions generate tension without changing the length of the muscle fibre, such as when gripping an object. In isotonic contraction, the tension in the muscle remains constant despite changes in muscle length. Concentric contraction occurs when muscle tension is sufficient to overcome the load, resulting in the muscle shortening. Eccentric contraction involves the muscle fibres lengthening as they contract, which can occur voluntarily or involuntarily.
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Frequently asked questions
Muscles move by contracting and then relaxing. They pull on tendons and move bones closer to each other.
There are three types of muscles in the human body: skeletal, smooth, and cardiac. Skeletal muscles are voluntary, while smooth and cardiac muscles are involuntary.
Skeletal muscles are attached to bones and controlled consciously. They contract to move parts of the body closer to the bone they are attached to. Skeletal muscles also work in groups to produce precise movements.
Smooth muscles are controlled by the nervous system and work without conscious thought. They are found in the walls of the stomach, intestines, and blood vessels. Smooth muscles take longer to contract than skeletal muscles but can stay contracted for longer.
Cardiac muscles are striated and involuntary. They are found in the heart and help to pump blood around the body.
