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The human body is an intricate system, with over 600 muscles that work in harmony to facilitate movement, maintain posture, and support vital organs. These muscles are broadly classified into three types: skeletal, smooth, and cardiac. Skeletal muscles, attached to bones by tendons, enable voluntary movements like running or lifting weights. Smooth muscles, found in internal organs and blood vessels, work involuntarily to support essential functions like digestion and breathing. Lastly, cardiac muscle, unique to the heart, contracts and relaxes involuntarily to pump blood throughout our bodies. Together, these muscle types, along with the brain and nerves, comprise the neuromuscular system, demonstrating the complex interplay that allows us to move and function.
| Characteristics | Values |
|---|---|
| Number of muscles in the human body | 600 |
| Muscle composition | Thousands of small fibres woven together |
| Types of movements | Voluntary, Involuntary |
| Types of muscles | Skeletal, Smooth, Cardiac |
| Functions | Pumping blood, Supporting movement, Lifting heavy weights, Giving birth |
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What You'll Learn
Skeletal muscles
The tissue of skeletal muscle is striated, having a striped appearance due to the arrangement of sarcomeres. These sarcomeres are the basic functional, contractile units of the muscle fibre, necessary for muscle contraction. Skeletal muscles comprise about 35% of the body weight of humans, although this can vary from person to person. Men tend to have more skeletal muscle mass than women, and taller or overweight people also tend to have higher muscle mass.
The skeletal muscle also acts as a storage source for amino acids, which different organs of the body can use for synthesising organ-specific proteins. It also plays a role in maintaining thermostasis and acts as an energy source during starvation. Skeletal muscles are susceptible to various conditions, ranging from mild injuries to serious myopathies, such as muscular dystrophies and myasthenia gravis.
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Smooth muscles
Smooth muscle is a type of muscle tissue that works automatically, without conscious thought. It gets its name from its smooth appearance, which differs from most other types of muscles. Smooth muscle cells have a unique structure, with narrow ends, a wider middle, and a shorter length compared to other muscle cells. They are spindle-shaped myocytes with a single nucleus.
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, blood vessels (except large elastic arteries), the urinary tract, and the digestive tract. It is controlled by the autonomic nervous system and can contract regularly without input from a motor neuron. Multi-unit smooth muscle, on the other hand, is neurogenic, meaning its contraction must be initiated by the autonomic nervous system neuron. It is found in the trachea, the iris of the eye, and the lining of large elastic arteries.
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Cardiac muscles
The human body contains three kinds of muscle tissue: skeletal, smooth, and cardiac. Cardiac muscle tissue, also known as myocardium, is only found in the heart. It is responsible for the heart's contractility and pumping action, ensuring blood circulation throughout the body.
Cardiac muscle tissue performs involuntary, coordinated contractions that enable the heart to pump blood through the circulatory system. These contractions are controlled by specialized "pacemaker" cells, which respond to electrical impulses from the nervous system. The pacemaker cells regulate heart rate and determine the speed at which the heart pumps blood.
Cardiac muscle cells, or cardiomyocytes, are highly organized and interconnected. They appear striated or striped under a microscope due to the alternating filaments of myosin and actin proteins. When a cardiac muscle cell contracts, the myosin filament pulls the actin filaments closer together, causing the cell to shrink. This process is powered by ATP, which can be obtained from various substrates such as fatty acids, carbohydrates, proteins, and ketones.
Cardiomyopathy is a group of medical conditions that affect cardiac muscle tissue and impair the heart's ability to pump blood effectively. Different types of cardiomyopathy include hypertrophic cardiomyopathy, dilated cardiomyopathy, restrictive cardiomyopathy, and arrhythmogenic right ventricular dysplasia. Exercise can help reduce the risk of developing cardiomyopathy and improve the efficiency of the cardiac muscle.
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Voluntary movements
Skeletal muscles are composed of fascicles, or bundled units of multiple muscle fibres or muscle cells. Each muscle fibre is controlled by a single alpha motor neuron that originates in the spinal cord or brain. These alpha motor neurons can control multiple muscle fibres, ranging from a few to 100 or more. Together, an alpha motor neuron and the muscle fibres it controls form a motor unit, which is the link between the central nervous system and skeletal muscles.
When a person wants to move a part of their body, the skeletal muscles attached to the relevant bones contract and relax under conscious control. Some muscle fibres contract quickly and use short bursts of energy, while others move slowly, such as back muscles that aid in posture.
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Involuntary movements
In addition to these involuntary movements, the body also has involuntary muscles that are responsible for the movements of internal organs. These involuntary muscles include smooth muscles and cardiac muscles. Smooth muscles line the inside of some organs, such as the intestines, lungs, reproductive organs, and blood vessels. They play a crucial role in moving waste through the intestines, aiding lung expansion during breathing, and supporting various body systems. Cardiac muscles, on the other hand, are striated and branched and are found only in the heart. They help maintain proper blood circulation by controlling the heartbeat.
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Frequently asked questions
The human body has about 600 muscles and the three main types are skeletal, smooth, and cardiac.
Skeletal muscles are attached to bones and allow movement. They are also known as voluntary muscles as they are under our conscious control.
Smooth muscles are involuntary muscles located in various internal structures such as the digestive tract, uterus, bladder, and blood vessels. They help with essential functions like moving waste through the intestines, pushing food back out of the stomach when we vomit, and helping the lungs expand when we breathe.
Cardiac muscles, also known as myocardium, make up the middle layers of the heart and are responsible for pumping blood throughout the body.
Commonly ignored muscles include the hamstrings, rotator cuff, erector spinae, and the Serratus. Neglecting these muscles can lead to injuries, pain, and restricted movement.
