Victor Forge
Our bodies have over 600 muscles that help us move, breathe, swallow, and stay alive. Muscles produce movement by contracting and relaxing. This movement is powered by energy from our food, which our bodies convert into chemical energy (adenosine triphosphate or ATP). Skeletal muscles, attached to bones, tendons, and ligaments, are responsible for the movement of our body. Smooth muscles, on the other hand, are found in the walls of organs like the bladder, stomach, and intestines, and cardiac muscles make up the walls of the heart.
| Characteristics | Values |
|---|---|
| Number of muscles in the human body | More than 600 |
| Types of muscles | Skeletal, cardiac, smooth |
| Types of muscle fibres | Type I, Type IIa, Type IIb |
| Types of cardiac muscle cells | Autorhythmic, contractile |
| Types of smooth muscle cells | Single-unit, multi-unit |
| Types of skeletal muscle disorders | Muscular dystrophies, congenital myopathies, inflammatory disorders, diseases affecting the neuromuscular junction |
| Skeletal muscle composition | Bundles of muscle fibres called myofibers |
| Skeletal muscle weight percentage | Approximately 40% of human body weight |
| Skeletal muscle protein percentage | 50% to 75% of all body proteins |
| Energy source for muscles | Food |
| Muscle contraction initiator | Action potential (AP) |
| Muscle contraction regulator | Calcium |
| Muscle repair | Self-repair |
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What You'll Learn
Skeletal muscle contraction
The process of skeletal muscle contraction begins at the neuromuscular junction, which is the synapse between a motoneuron and a muscle fibre. An action potential travels along a motor nerve to its endings on muscle fibres, where the nerve secretes acetylcholine (ACh). ACh acts on the muscle fibre membrane to open ACh-gated cation channels, causing an influx of calcium ions (Ca2+). This influx of calcium ions triggers the release of more ACh at the neuromuscular junction, which then binds to receptors on the muscle fibre, initiating muscle contraction.
The contraction of skeletal muscle fibres is powered by the interaction of actin and myosin filaments. These filaments are organised into repeating arrays called sarcomeres, giving skeletal muscle its striated appearance. During contraction, ATP is hydrolysed into ADP and P, causing the myosin heads to change conformation and move towards the positive end of the actin filament. This movement of myosin heads pulls on the actin filament, causing the sarcomere and the muscle fibre to contract.
There are different types of skeletal muscle fibres, including Type I (slow-twitch) and Type II (fast-twitch) fibres. Type I fibres have a low rate of fatigue and are suited for endurance activities like maintaining posture and marathon running. Type II fibres, on the other hand, have a faster contractile speed and are better suited for moderate-movement actions like walking and biking.
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Smooth muscle contraction
Muscle contractions generate movement. There are three types of muscles in mammals: skeletal, cardiac, and smooth. Skeletal muscles are attached to bones and give the body structure and strength. Cardiac muscle comprises the walls of the heart, allowing blood to be pumped through the vasculature. Smooth muscles, on the other hand, do not have striations and we cannot actively control them. They are found throughout the body in the blood vessels, gastrointestinal (GI) tract, bronchioles, uterus, bladder, and other organs.
For smooth muscle contraction to occur, myosin light chain kinase (MLCK) plays a crucial role. MLCK phosphorylates the light chain of myosin, enabling it to interact with actin. The energy released from ATP by myosin ATPase activity powers the cycling of the myosin cross-bridges with actin, resulting in contraction. The contractile activity in smooth muscle is highly regulated and depends primarily on the phosphorylation state of the light chain of myosin.
Smooth muscle can be divided into two subgroups: single-unit and multi-unit. Single-unit smooth muscle, also known as visceral smooth muscle, is found in the walls of most internal organs, blood vessels, the urinary tract, and the digestive tract. It contracts as a functional syncytium, with neighbouring muscle cells connected via gap junctions. Multi-unit smooth muscle, on the other hand, is found in the muscles of the eye, the trachea, and lining the large elastic arteries. It is neurogenic, meaning its contraction is initiated by the autonomic nervous system.
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Muscle relaxation
Muscle movement is facilitated by muscle contraction, which is the primary function of skeletal muscle. Skeletal muscles are attached to bones and give the body structure and strength. They contract in response to a stimulus, generating movement and allowing us to consciously move our limbs.
Progressive muscle relaxation (PMR) is a technique used to control stress and anxiety, relieve insomnia, and reduce symptoms of certain types of chronic pain. It was developed by Edmund Jacobson in the 1920s and 1930s and is based on the theory that physical relaxation leads to mental calmness. PMR involves tightening and relaxing specific muscle groups in a sequential manner, starting from the lower extremities and ending with the face, abdomen, and chest. During the practice, one inhales and tenses a muscle group for 5 to 10 seconds, then exhales and releases the tension, focusing on the subsequent feeling of relaxation in that area. This process is repeated for each muscle group, with the entire practice taking 10 to 20 minutes.
PMR has been found to have therapeutic benefits for various conditions, including headaches, cancer pain, high blood pressure, and digestive issues. It has also been shown to reduce symptoms of depression, anxiety, and stress while improving overall well-being and quality of life. The technique is simple to learn and can be practiced by almost anyone in a quiet, comfortable space.
In summary, muscle relaxation through PMR is an effective way to manage stress and its physical and mental effects. By tensing and relaxing muscle groups in a specific order, individuals can achieve a state of relaxation that promotes mental calmness and relieves tension.
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Muscle repair
Muscles contract to produce movement in the body. There are three types of muscles: skeletal, cardiac, and smooth muscles. Skeletal muscles, which are attached to bones, are responsible for most of the movements in the body. They also provide structural support, maintain body posture, and store nutrients.
Skeletal muscles are further classified into two types: striated and smooth. Striated muscles have regular stripes or striations due to the arrangement of muscle fibers, which form parallel lines. These muscles are responsible for voluntary movements like jumping in the air or chewing food. Smooth muscles, on the other hand, do not have striations and are responsible for involuntary movements like moving food through the digestive system.
Muscles have an incredible ability to repair themselves when damaged. This self-repair process is highly coordinated and involves various cell types and interactions. Skeletal muscle repair, in particular, requires the activation of satellite cells, which are residential muscle stem cells. The repair process can be divided into three phases: destruction, regeneration, and remodelling.
During the destruction phase, muscle injury occurs, leading to rupture and necrosis of the myofibers, formation of a hematoma, and an inflammatory reaction. The regeneration phase involves phagocytosis of damaged tissue, followed by the activation of satellite cells and the regeneration of myofibers. In the remodelling phase, the regenerated myofibers mature, and the muscle's functional capacity is restored. Scar tissue formation also occurs during this phase.
To support muscle repair, adequate rest, hydration, and nutrition are essential. Consuming protein after a workout helps repair muscle damage and maximize muscle growth. Getting enough sleep is crucial, as it is during sleep that the body repairs muscles. Additionally, gentle stretching can aid in muscle recovery by re-establishing the normal length of the muscles.
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Muscle groups
The human body has more than 600 muscles, which account for about 40% of a person's weight. These muscles are responsible for movements such as allowing us to consciously move our limbs, jump in the air, and chew our food. They are also responsible for involuntary movements, such as keeping our hearts pumping, moving food through our guts, and even making us blush.
There are three types of muscles: skeletal, cardiac, and smooth. Skeletal muscles are attached to bones and give the body structure and strength. They also provide stability to joints, maintain body posture, and store nutrients. Skeletal muscle fibres can be further classified into Type I, Type IIa, and Type IIb fibres. Type I fibres are slow-twitching fibres that have a low rate of fatigue and are best suited for endurance types of contraction, such as maintaining posture and marathon running. Type IIa fibres are fast-twitching fibres with a high myosin ATPase activity and an intermediate rate of fatigue, making them suitable for moderate-movement actions like walking and biking. Type IIb fibres are also fast-twitching fibres.
Cardiac muscles comprise the walls of the heart, allowing blood to be pumped throughout the body. Cardiac muscle is the only type of muscle tissue found in the heart.
Smooth muscles do not have striations and are found throughout the blood vessels, gastrointestinal tract, bronchioles, uterus, and bladder. They produce more gradual contractions than striated muscles, such as the slow movement of food through the digestive system.
When creating a strength training routine, it is common to group muscles together by their location (e.g., chest, leg, or back muscles) or the type of movement they perform (e.g., abductors, flexors, or extensors). Many exercises work multiple muscle groups, and these are called multi-joint exercises (MJE). Examples of MJEs include squats, bench presses, deadlifts, and shoulder presses. On the other hand, isolation exercises, or single-joint exercises (SJE), target specific muscles within a muscle group, such as bicep curls for the bicep muscles.
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Frequently asked questions
Muscles are pieces of soft tissue throughout the body that help us move, breathe, swallow, and stay alive.
Muscles produce movement by contracting and relaxing. This process is made possible by the interaction of proteins called myosin and actin. When myosin "grabs" onto actin, the muscle contracts. When myosin releases actin, the muscle relaxes.
Mammals have three types of muscles: skeletal, cardiac, and smooth. Skeletal muscles are attached to bones and give the body structure and strength. Cardiac muscles make up the walls of the heart and power its contraction and relaxation. Smooth muscles make up the inside of organs such as the bladder, stomach, and intestines and play a role in involuntary functions.
There are two types of skeletal muscle contractions: concentric and eccentric. Concentric contractions occur when the muscle pulls a joint in the direction of the contraction. Eccentric contractions occur when the muscle works to decelerate a joint at the end of a movement.
Through various biochemical pathways, our bodies convert the nutrition we consume into chemical energy (adenosine triphosphate or ATP) that powers contraction in all muscle types.
