Victor Forge
The human body has over 600 muscles that help us move, breathe, swallow, and stay alive. There are three types of muscles: skeletal, smooth, and cardiac. Skeletal muscles are voluntary muscles, meaning we can control how and when they move. They make up 30-40% of our body mass and are attached to bones, allowing us to perform a wide range of movements. On the other hand, smooth and cardiac muscles are involuntary, controlled by the autonomic nervous system without conscious thought. Smooth muscles line our organs, while the cardiac muscle, unique to the heart, pumps blood throughout the body. Together, our muscles, bones, and nerves work in harmony as the neuromuscular system, keeping us moving and alive.
| Characteristics | Values |
|---|---|
| Number of muscles in the human body | More than 600 |
| Types of muscles | Skeletal, cardiac, smooth/visceral |
| Skeletal muscle composition | 30% to 40% of total body mass |
| Skeletal muscle control | Voluntary |
| Skeletal muscle functions | Contraction, movement, maintaining body posture and position, maintaining body temperature, storing nutrients, stabilizing joints |
| Skeletal muscle disorders | Muscle weakness, muscular dystrophies, congenital myopathies, inflammatory disorders, neuromuscular junction diseases |
| Cardiac muscle control | Involuntary |
| Cardiac muscle functions | Pumping blood throughout the body |
| Smooth/visceral muscle control | Involuntary |
| Smooth/visceral muscle functions | Moving substances through organs |
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What You'll Learn
Movement
The human body has over 600 muscles that help us do everything from moving our bodies to breathing and staying alive. The three types of muscles in the human body are skeletal, cardiac, and smooth muscle.
Skeletal muscle is the most common type of muscle in the human body and is the only voluntary muscle tissue, meaning that it is controlled consciously. Skeletal muscles are attached to bones and allow us to perform a wide range of movements and functions. They make up around 30% to 40% of our total body mass. When we perform any physical action, such as speaking, walking, or writing, we are using our skeletal muscles. These muscles contract in response to a stimulus, causing movement. Skeletal muscles are also responsible for sustaining body posture and position, maintaining body temperature, storing nutrients, and stabilizing joints.
Cardiac muscle is found only in the heart and is responsible for pumping blood throughout the body. It is an involuntary muscle, meaning it works without conscious control. Cardiac muscle tissue stimulates itself to contract and is considered intrinsically controlled.
Smooth muscle, also known as visceral muscle, is found inside organs like the stomach, intestines, and blood vessels. It is the weakest of all muscle tissues and is also involuntary. Smooth muscle contracts to move substances through the organs.
The brain, nerves, and skeletal muscles work together to cause movement, collectively known as the neuromuscular system. Nerve cells called motor neurons control the skeletal muscles, receiving signals from the brain and stimulating the muscles to contract. The number of muscle fibers in a motor unit depends on the function of the muscle, with muscles requiring fine motor control involving fewer fibers.
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Respiration
The diaphragm is the primary muscle responsible for breathing. It is a thin, dome-shaped muscle that separates the abdominal cavity from the thoracic cavity. During inhalation, the diaphragm contracts, moving caudally (downward) and drawing the edges cranially (upward). This contraction compresses the abdominal cavity, raises the ribs, and expands the thoracic cavity, allowing air to enter the lungs. When the diaphragm relaxes during exhalation, the elastic recoil of the lungs causes the thoracic cavity to contract, forcing air out of the lungs, and returning to its dome shape.
In addition to the diaphragm, the intercostal muscles are another important group of respiratory muscles. These muscles are attached between the ribs and play a crucial role in manipulating the width of the rib cage. There are three layers of intercostal muscles: external, internal, and internal intercostal muscles. The external intercostal muscles are the most important for respiration, with fibres angled obliquely downward and forward from rib to rib. Their contraction raises each rib towards the rib above, elevating the rib cage and assisting in inhalation. The internal intercostal muscles have fibres angled obliquely downward and backward, and they assist in lowering the rib cage during exhalation.
The accessory muscles of respiration are recruited during exercise or respiratory dysfunction to assist in breathing. These include muscles such as the sternocleidomastoid and the scalenes, which help elevate the rib cage. The involvement of these accessory muscles depends on the degree of respiratory effort. During quiet breathing, the scalenes are active, while the sternocleidomastoids become active with increased respiratory volume.
The respiratory process is tightly controlled by the respiratory centre located in the brain stem, specifically in the medulla oblongata and the pons. The dorsal respiratory group within the medulla plays a significant role in the breathing cycle, while the ventral respiratory group in the ventrolateral medulla is responsible for forced exhalation. The pneumotaxic centre in the pons controls the rate and depth of breathing. Sensors in the airways, brain, blood vessels, and joints also contribute to adjusting breathing patterns based on various stimuli.
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Circulation
The human body's circulatory system consists of the heart and blood vessels. Blood vessels contain layers of connective tissue, muscle, and elastic fibres. The muscles in these blood vessels control their width, which in turn affects blood pressure. Vasodilation widens blood vessels and lowers blood pressure, while vasoconstriction tightens them and raises blood pressure. The body's intricate network of arteries and veins moves 2,000 gallons of blood or more per day, delivering oxygen and nutrients to the body's muscles, tissues, and organs. This network also removes waste products, such as carbon dioxide, and returns them to organs that can dispose of them.
During exercise, the body experiences an increase in blood flow to locomotory muscles, which is achieved by decreasing the resistance of the blood vessels leading to this tissue. This process is known as vasodilation, which helps to lower blood pressure. The skeletal muscle pump acts to empty the veins in the lower extremities, where blood pools due to gravity. Additionally, the heart does not have the capacity to fully perfuse all circulations simultaneously, so blood flow to tissues with lower oxygen priority must be reduced at times.
The autonomic nervous system, particularly the sympathetic nerves, plays a crucial role in the neural control of circulation. These nerves increase cardiac rate and contractility, cause the constriction of arteries and veins, and activate the renin-angiotensin-aldosterone system. The activity of these autonomic nerves is determined by a network of neurons located in the medulla oblongata, which receives inputs from various sources, including the hypothalamus and cerebral cortex. The autonomic nervous system also influences the pulmonary circulation, where serotonin, histamine, and norepinephrine cause contraction and increase vascular resistance, while acetylcholine and isoproterenol relax smooth muscle.
To improve circulation, it is recommended to stay hydrated, exercise regularly, and avoid sitting for extended periods. Compression socks can also improve circulation in the legs. Dry brushing and warm baths can be temporary measures to improve blood flow by opening up arteries and veins.
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Posture
The musculoskeletal system maintains our posture. Muscles, ligaments, and tendons work with joints throughout the body to control our position at all times. They adjust our body to hold us in a stable, comfortable shape. The postural muscles are primarily located in the torso. The abdominal muscles are probably the most widely known of the postural muscles, but there are many multitasking muscles in this region, including the iliacus and psoas muscles, which support the lumbar back. The gluteus and hamstring muscles are also important for posture support. During standing and walking, hamstrings work indirectly to maintain an erect posture.
The trapezius muscle is a flat, triangular muscle that anchors the shoulder blades to the spine. Effective posture requires that the trapezius is strengthened equally in the front and back of the body. An imbalance can cause the shoulder blades to pop out like wings, often leading to pain and discomfort. The erector spinae muscles run laterally to the spine and work to extend it. These include the spinalis, longissimus, and iliocostalis. The multifidus muscles, a smaller group, connect the vertebra.
To improve posture, it is recommended to strengthen, stretch, and lengthen the spine and torso. Exercises such as high planks can help develop balance and strength in the core and back, which are important for good posture. It is also important to be conscious of your posture when sitting, standing, or lying down, and to make adjustments to ensure you are supporting your spine. For example, when sitting, your shoulders should be over your hips, with good lower back support, and your feet should be flat on the floor.
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Waste removal
Our body is made up of more than 600 muscles that help us move, breathe, and perform various other functions to keep us alive. There are three types of muscles in our body: skeletal, cardiac, and smooth muscle. Skeletal muscles are voluntary muscles, meaning we can control how and when they move and work. They comprise 30% to 40% of our total body mass and are attached to our bones through tendons. We use our skeletal muscles to breathe, eat, and move our bones, so they play a vital role in our daily lives.
Smooth muscles, on the other hand, are involuntary muscles that line the inside of some organs. They perform essential functions like moving waste through our intestines and helping our lungs expand when we breathe. Smooth muscles are part of the digestive system, helping to push food through the intestines and eliminate waste from the body. They are also present in the urinary system, aiding in the removal of waste and toxins from the body.
Additionally, our muscles produce waste products, such as lactic acid, during normal activities like walking and even more so during intense exercise. This waste can build up within the muscles, causing fatigue, weakness, and increased chances of injury. Efficient removal of waste products is crucial to maintain healthy muscles. Techniques like effleurage and lymphatic drainage massages can help increase blood flow and lymphatic drainage, respectively, thereby promoting the removal of waste products and reducing muscle fatigue.
Furthermore, our body has other natural mechanisms for waste removal. For example, tears help keep our eyes moist and also remove irritants. Sweat, or perspiration, is another way our body eliminates waste, helping to cool us down when we are too hot or nervous. Our body also gets rid of waste through vomiting and the elimination of feces, which contain undigested food particles and excess fat. Overall, waste removal is a critical function of our body, and our muscles play a key role in this process, especially in terms of waste movement and elimination through our digestive and urinary systems.
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Frequently asked questions
Muscles are pieces of soft tissue throughout your body that help you move, breathe, swallow and stay alive. You have more than 600 muscles in your body that you use almost constantly.
There are three types of muscles in the body: skeletal, cardiac and smooth muscle. Skeletal muscles are voluntary muscles, meaning you control how and when they move and work. They make up 30% to 40% of your total body mass. Cardiac and smooth muscle are involuntary muscles that your autonomic nervous system controls.
Skeletal muscles are the muscles that connect to your bones and allow you to perform a wide range of movements and functions. Your shoulder muscles, hamstring muscles and abdominal muscles are all examples of skeletal muscles.
Smooth muscle tissue lines some of your organs. Visceral muscle, a type of smooth muscle, is found inside organs like the stomach, intestines, and blood vessels. The heart is made of cardiac muscle tissue.
