Logan Steele
The human body has over 600 muscles, which are pieces of soft tissue that help us move, breathe, swallow, and stay alive. They also play a part in every function of the body, from pumping blood to supporting movement and lifting heavy weights. There are three types of muscles: skeletal, smooth, and cardiac. Skeletal muscles are voluntary muscles that help us perform a wide range of movements and functions. Smooth and cardiac muscles are involuntary and help with essential tasks such as digestion, breathing, and keeping the heart beating.
| Characteristics | Values |
|---|---|
| Number of muscles in the human body | 600-700 |
| Muscle types | Skeletal, Smooth, Cardiac |
| Skeletal muscle composition | 30-40% of total body mass |
| Skeletal muscle control | Voluntary |
| Smooth muscle control | Involuntary |
| Cardiac muscle control | Involuntary |
| Muscle functions | Movement, breathing, swallowing, digestion, heartbeat, giving birth |
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Skeletal muscles
These muscles consist of flexible muscle fibres that range from less than half an inch to just over 3 inches in diameter. Each muscle can contain thousands of fibres, and these fibres contract (tighten) to allow the muscles to move bones, enabling a wide range of movements. Skeletal muscles help with functions such as chewing and swallowing, as well as expanding and contracting the chest cavity to enable breathing. They also play a role in maintaining body temperature, storing nutrients, and stabilising joints.
From a mechanical standpoint, skeletal muscles convert chemical energy into mechanical energy, generating force and power. They are also involved in basal energy metabolism, serving as a storage site for essential substrates such as carbohydrates and amino acids.
It is important to keep skeletal muscles strong and healthy, as muscle mass decreases with age.
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Cardiac muscles
The human body has more than 600 muscles, which help us move, breathe, swallow, and stay alive. There are three types of muscles in the body: skeletal, smooth, and cardiac.
Cardiac muscle, also known as myocardium, is one of the three major categories of muscles in the body. It is an involuntary, striated muscle that constitutes the main tissue of the wall of the heart. The cardiac muscle forms a thick middle layer between the outer layer of the heart wall (the pericardium) and the inner layer (the endocardium). The heart wall is a three-layered structure with a thick layer of myocardium sandwiched between the inner endocardium and the outer epicardium. The endocardium lines the cardiac chambers, covers the cardiac valves, and joins with the endothelium that lines the blood vessels that connect to the heart. The outer aspect of the myocardium is the epicardium, which forms part of the pericardial sac that surrounds, protects, and lubricates the heart.
The primary function of the cardiac muscle is to pump blood into circulation by generating sufficient force. The cardiac muscle contracts in a similar manner to skeletal muscle, although with some important differences. Electrical stimulation in the form of a cardiac action potential triggers the release of calcium from the cell's internal calcium store, the sarcoplasmic reticulum. The rise in calcium causes the cell's myofilaments to slide past each other in a process called excitation-contraction coupling. The sliding of actin and myosin past each other produces the formation of "cross-bridges," which causes contraction of the heart and generation of force. The cardiac muscle must contract with enough force and blood to supply the metabolic demands of the entire body.
Cardiac muscle cells (cardiomyocytes) are the contractile myocytes of the cardiac muscle. They are surrounded by an extracellular matrix produced by supporting fibroblast cells. Cardiomyocytes are tubular structures composed of chains of myofibrils, which are rod-like units within the cell. The myofibrils consist of repeating sections of sarcomeres, which are the fundamental contractile units of the muscle cells. Sarcomeres are composed of long proteins that organize into thick and thin filaments, called myofilaments. Each cardiomyocyte needs to contract in coordination with its neighboring cells, working to efficiently pump blood from the heart.
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Smooth muscles
Smooth muscle is one of the three main types of muscle in the body, the other two being skeletal and cardiac muscle. Smooth muscle is a type of muscle tissue that works automatically and is found throughout the body. It gets its name from its smooth, uniform appearance when viewed under a microscope, which is different from the banded appearance of skeletal and cardiac muscles. Smooth muscle exists in various places inside the body, including the stomach, intestines, urinary system, arteries, veins, skin, eyes, uterus, and more.
Smooth muscle serves a variety of functions, including the regulation of blood pressure and circulation, vision, and digestion. It plays a vital role in the regulation of blood pressure and tissue oxygenation by contracting and relaxing to control the width of blood vessels. This function is essential for maintaining basic bodily functions. Smooth muscle is also involved in transporting substances through the body by flexing together to push contents through tubelike passages, such as in the digestive tract.
Another important function of smooth muscle is gatekeeping. Most muscles stay relaxed and only flex when needed, but smooth muscles in sphincters, such as the bladder or anus, stay flexed and only relax when necessary. Smooth muscle in the skin causes hairs to stand on end, resulting in goosebumps. In the eyes, smooth muscle controls how the eyes focus and how the pupils dilate or constrict.
Smooth muscle differs from skeletal muscle in several ways. Smooth muscle contracts and is controlled involuntarily, whereas skeletal muscle responds to conscious control. Smooth muscle cells have a distinct structure, with narrow ends, a wider middle, and a shorter length compared to skeletal muscle fibres. Smooth muscle also has greater elastic properties than skeletal muscle, which is important in maintaining contractile tone in organ systems like the urinary bladder.
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Muscle movement
The human body has over 600 muscles that help with performing a myriad of functions, from involuntary ones like breathing to voluntary ones like walking. The muscular system is responsible for the movement of the human body. Attached to the bones of the skeletal system are about 700 named muscles that make up roughly half of a person's body weight. Each of these muscles 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 comprise 30% to 40% of total body mass and are attached to the bones, allowing for a wide range of movements and functions. Skeletal muscles are voluntary, meaning an individual controls how and when they work. Tendons, or tough bands of connective tissue, attach skeletal muscle tissue to bones throughout the body. Examples of skeletal muscles include shoulder muscles, hamstring muscles, and abdominal muscles.
Cardiac and smooth muscle are involuntary muscles controlled by the autonomic nervous system. Smooth muscles line the inside of some organs and play an important role in many body systems, including the female and male reproductive systems, the urinary system, the respiratory system, and the digestive system. Cardiac muscle is found only in the heart and is responsible for pumping blood throughout the body.
The primary function of skeletal muscle contraction is to allow for the performance of specific movements. Skeletal muscle contraction also provides structural support, maintains body posture, stores amino acids, and maintains core body temperature via shivering. The physiological concept of muscle contraction is based on two variables: length and tension. Tension within the muscle can be produced without changes in the length of the muscle, as when holding a dumbbell in the same position. Upon termination of muscle contraction, muscle relaxation occurs, which is the return of muscle fibres to a low-tension state.
The movements muscles make are coordinated and controlled by the brain and nervous system. The involuntary muscles are controlled by structures deep within the brain and the upper part of the spinal cord called the brain stem. The voluntary muscles are regulated by the parts of the brain known as the cerebral motor cortex and the cerebellum. When an individual decides to move, the motor cortex sends an electrical signal through the spinal cord and peripheral nerves to the muscles, causing them to contract.
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Muscle disorders
There are many types of neuromuscular disorders, and they can be inherited or caused by a spontaneous gene mutation or immune system disorders. Some neuromuscular disorders have symptoms that begin in infancy, while others may appear in childhood or adulthood. Treatment by an experienced multidisciplinary team is vital, and symptoms can be managed with medications, physical therapy, occupational therapy, and, when necessary, surgery.
Some examples of muscle disorders include congenital myopathy, extra-abdominal desmoid tumors, familial periodic paralyses, and mitochondrial disorders. Muscular dystrophy is another type of muscle disorder that causes weakness and the wasting away of muscle tissue. It is inherited and results in the eventual loss of strength.
In addition to neuromuscular disorders, there are other types of muscle disorders such as rippling muscle disease, STAC3 disorder, tubular aggregate myopathy, and rhabdomyolysis. Muscle strains (pulled muscles) are also common muscle injuries that occur when muscle fibres are stretched beyond their limit and tear apart. While occasional muscle aches or pain are normal, chronic soreness or weakness should not be ignored.
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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. There are about 600 muscles in the human body.
There are three types of muscles in the human body: skeletal, smooth, and cardiac. Skeletal muscles are voluntary muscles that you control consciously. Smooth and cardiac muscles are involuntary muscles that work without conscious awareness.
Skeletal muscles are attached to bones and allow you to perform a wide range of movements and functions. Skeletal muscles make up between 30% and 40% of your total body mass.
Smooth muscles line the inside of some organs and perform essential functions like moving waste through your intestines and helping your lungs expand when you breathe. Cardiac muscles make up the heart and are responsible for pumping blood throughout the body.
