Dominic Stone
The human body is made up of hundreds of muscles, each with a specific function. Muscles are tissues that support the body and enable movement. They are broadly classified into three types: skeletal, smooth, and cardiac. Skeletal muscles are attached to bones and are under voluntary control, while smooth and cardiac muscles are involuntary. Skeletal muscles are the most common type, comprising 30-40% of body weight, and are responsible for various functions, including movement, posture, and digestion. Smooth muscles line organs and help move substances through them, while cardiac muscles make up the heart and facilitate blood circulation. Understanding the different parts of muscles and their functions is essential for maintaining overall health and fitness.
| Characteristics | Values |
|---|---|
| Types of muscle tissue | Cardiac, smooth, and skeletal |
| Most common type of muscle | Skeletal muscle |
| Percentage of total body mass | 30% to 40% |
| Function of skeletal muscle | Contract to move parts of the body closer to the bones |
| Skeletal muscle control | Voluntary |
| Cardiac muscle control | Involuntary |
| Smooth muscle control | Involuntary |
| Muscle injuries | Strains, pulls, spasms, cramps, skin discolouration |
| Muscle injury management | RICE method (Rest, Ice, Compression, Elevation) |
| Muscle naming terms | brevis, longus, longissimus, magnus, major, maximus, minor, etc. |
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Skeletal muscle
The tissue of a skeletal muscle is striated, giving it a striped appearance due to the arrangement of the sarcomeres. Skeletal muscles contain multiple fascicles, or bundles of muscle fibres. Each individual fibre and each muscle is surrounded by a type of connective tissue layer of fascia. Skeletal muscle fibres are multinucleated, with the nuclei often referred to as myonuclei. The skeletal muscle cells are the individual contractile cells within a muscle.
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Cardiac muscle
The heart is made up of three layers—pericardium, myocardium, and endocardium. The myocardium forms a thick middle layer between the outer layer of the heart wall (the pericardium) and the inner layer (the endocardium). The endocardium is not cardiac muscle and is comprised of simple squamous epithelial cells and forms the inner lining of the heart chambers and valves. The pericardium is a fibrous sac surrounding the heart, consisting of the epicardium, pericardial space, parietal pericardium, and fibrous pericardium.
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Smooth muscle
One of the key functions of smooth muscle is to control the movement of substances through the body, including food, air, and waste products. For example, smooth muscles in the digestive tract help push food through the system, while smooth muscles in the walls of blood vessels regulate blood pressure and flow by contracting and relaxing to control the diameter of the vessels. Smooth muscles also play a role in the respiratory system, where they help maintain the shape and size of the airways, facilitating breathing.
The contractions of smooth muscle are
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Muscle fibre composition
Skeletal muscles are attached to bones by tendons and work in groups to produce precise movements. They are the only voluntary muscle tissue in the human body, meaning they are controlled consciously. Skeletal muscle fibres are typically classified as Type I (slow-twitch) or Type II (fast-twitch) based on their contraction speed. Slow-twitch fibres contract slowly and use aerobic respiration to produce energy, while fast-twitch fibres contract rapidly and are associated with powerful, quick movements. The composition of skeletal muscle fibres can be influenced by training and environmental factors, and they exhibit plasticity, allowing them to adapt to changing demands.
Smooth muscle tissue, on the other hand, is found in the walls of organs like the stomach, intestines, and blood vessels. It is under involuntary control, meaning it is governed by the unconscious part of the brain. Smooth muscle has a uniform, smooth appearance when viewed under a microscope.
Cardiac muscle, found exclusively in the heart, is responsible for the rhythmic contractions that pump blood throughout the body. Like smooth muscle, cardiac muscle is also involuntary and exhibits a unique banded appearance under microscopic observation.
The composition of muscle fibres within these three types of muscle tissues plays a crucial role in determining their specific functions and characteristics. The arrangement of these muscle fibres contributes to the overall functioning of the human muscular system.
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Muscle movement
The muscular system is responsible for the movement of the human body. There are over 600 muscles in the human body, making up about half of a person's body weight. Each muscle is a discrete organ constructed of skeletal muscle tissue, blood vessels, tendons, and nerves.
Skeletal muscles are the most common type of muscle in the human body. They are attached to the bones of the skeletal system and allow us to perform a wide range of movements and functions. Skeletal muscles rarely work individually to achieve movement in the body; they usually work in groups to produce precise movements. The muscle that produces any particular movement is known as an agonist or prime mover. The agonist always pairs with an antagonist muscle that produces the opposite effect on the same bones. For example, the biceps brachii muscle flexes the arm at the elbow, and its antagonist, the triceps brachii muscle, extends the arm at the elbow.
Muscles contract when stimulated by signals from their motor neurons. Motor neurons contact muscle cells at a point called the Neuromuscular Junction (NMJ). Motor neurons release neurotransmitter chemicals at the NMJ that bond to a special part of the sarcolemma known as the motor end plate. The motor end plate contains many ion channels that open in response to neurotransmitters and allow positive ions to enter the muscle fiber. The positive ions form an electrochemical gradient inside the cell, causing Ca2+ ions to be released and allowed to flow into the myofibrils. Ca2+ ions bind to troponin, which causes the troponin molecule to change shape and move nearby molecules of tropomyosin. Tropomyosin is moved away from myosin binding sites on actin molecules, allowing actin and myosin to bind together. This process of muscles contracting allows us to move our bodies.
In addition to the agonist/antagonist pairing, other muscles work to support the movements of the agonist. Synergists are muscles that help to stabilize a movement and reduce extraneous movements. They are usually found in regions near the agonist and often connect to the same bones. Stabilizers are another type of muscle that acts to keep bones immobile when needed. For example, back muscles are stabilizers when they are keeping your posture sturdy.
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Frequently asked questions
There are three types of muscle tissue in the body: skeletal, smooth, and cardiac. Skeletal muscle is the most common type of muscle in the body and is the only voluntary muscle tissue. Smooth muscle is found inside organs like the stomach, intestines, and blood vessels and is under involuntary control. Cardiac muscle makes up the middle layers of the heart and is also involuntary.
Skeletal muscles are part of the musculoskeletal system and work with bones, tendons, and ligaments to support your weight and move you. They are attached to the bones by tendons and make up 30-40% of your total body mass. They are also responsible for maintaining body posture, controlling body temperature, and stabilizing joints.
Skeletal muscles are named based on various factors, including their location, origin, insertion, shape, size, direction, and function. For example, the rectus abdominis and transverse abdominis are found in the abdominal region. Some muscles are also named after the part of the bone they are attached to, like the tibialis anterior.
