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The human body has over 600 muscles, which are pieces of soft tissue that help us move, breathe, swallow, and survive. The muscular system is responsible for the movement of the human body. The three main types of muscle are skeletal, smooth, and cardiac. Skeletal muscles are attached to the bones of the skeletal system and allow movement. They are the most common type of muscle in the body and are under our conscious control, meaning they are also known as voluntary muscles. Smooth muscles are located in various internal structures, including the digestive tract, uterus, and blood vessels. Cardiac muscle is responsible for pumping blood throughout the body and is found only in the heart.
| Characteristics | Values |
|---|---|
| Number of muscles in the human body | 600+ |
| Types of muscles | Skeletal, Smooth, Cardiac |
| Skeletal muscle mass | 30% to 40% of total body mass |
| Muscle composition | Thousands of small fibres |
| Muscle fibre composition | Myofibrils, a specialized protein (myoglobin), molecules to provide oxygen and energy |
| Muscle control | Voluntary (skeletal) and Involuntary (smooth and cardiac) |
| Muscle functions | Movement, posture, balance, breathing, swallowing, supporting organs |
| Muscle groups | Chest, back, leg, neck, shoulder, hamstring, abdominal |
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Skeletal muscles
The muscles are fuelled by glucose from carbohydrates in our diet, as well as specific minerals, electrolytes and other dietary substances such as calcium, magnesium, potassium and sodium. Skeletal muscle also acts as a storage source for amino acids, which different organs of the body can use for synthesising organ-specific proteins. They also play a central role in maintaining thermostasis and act as an energy source during starvation.
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Cardiac muscles
The human body contains three types of muscle tissue: skeletal, smooth, and cardiac. Cardiac muscle tissue is unique to the heart and makes up the thick middle layer of this vital organ, known as the myocardium. The myocardium is surrounded by the thin outer layer epicardium (or visceral pericardium) and an inner endocardium.
Cardiac muscle tissue is responsible for the rhythmic contractions of the heart, which are involuntary and outside of our conscious control. These contractions generate the pressure required to pump blood through the circulatory system. The rapid and coordinated contraction and relaxation of cardiac muscle are vital for pumping blood throughout the body. Cardiomyocytes are the individual cells that make up cardiac muscle, and their primary function is to contract.
Cardiac muscle cells contain many specialised proteins and molecules that provide the energy and oxygen required for muscle contraction. When a cardiac muscle cell contracts, the myosin filament pulls the actin filaments towards each other, causing the cell to shrink. This process is powered by ATP. Intercalated discs connect cardiac muscle cells, and gap junctions inside these discs relay electrical impulses from one cell to another.
Cardiac muscle tissue can be affected by various conditions, such as cardiomyopathy, which can impair the heart's ability to pump blood or relax. Ischemic heart disease, the leading cause of morbidity and mortality worldwide, is characterised by an imbalance between the supply and demand of oxygenated blood for cardiac tissue. Aerobic exercise can help to keep cardiac muscle tissue strong and healthy, reducing the risk of developing cardiomyopathy and improving the efficiency of the heart.
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Smooth muscles
Smooth muscle is one of the three main types of muscles in the human body, the other two being skeletal and cardiac. Smooth muscles are involuntary muscles, meaning they work without conscious thought. They are controlled by the autonomic nervous system and are responsible for handling some of the most important automatic jobs in the body. Smooth muscles are found throughout the body and play a key role in automated self-management processes. They are structurally different from skeletal muscles, with narrow ends, a wider middle, and a shorter length.
The smooth muscles in the ciliary body of the eye control how the eyes focus by pulling on fibers called zonules. Smooth muscles are also found in the uterus, where contractions occur during labor. Additionally, they are present in the walls of blood vessels and structures such as the urinary bladder, intestines, and stomach.
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Muscle fibres
The human body is made up of about 600 muscles. These muscles are broadly categorised into three types: skeletal, smooth, and cardiac. Skeletal muscles are the most common type of muscle in the body, comprising 30% to 40% of total body mass. They are attached to the bones by tendons and are under voluntary control, allowing for a wide range of movements and functions. Skeletal muscle fibres are classified into two types: type 1 and type 2. Type 1 fibres utilise oxygen to generate energy for movement and have a higher density of mitochondria, giving them a darker appearance. Type 2 fibres are further divided into subtypes: Type 2A and Type 2B. Type 2A, which can also use oxygen to generate energy but contain fewer mitochondria, and Type 2B, which does not use oxygen and instead stores energy for short bursts of movement.
Smooth muscles, on the other hand, are involuntary and found in the walls of blood vessels and structures like the urinary bladder, intestines, and stomach. They have a more uniform appearance and an oblong shape, much shorter than skeletal muscle fibres. Cardiac muscles, found only in the heart, are also striated and have their own unique rhythm due to specialised pacemaker cells that generate impulses for contraction.
The different types of muscle fibres, namely slow oxidative (SO), fast oxidative (FO), and fast glycolytic (FG), are present in varying proportions within skeletal muscles. Slow-twitch fibres are associated with endurance capabilities, while fast-twitch fibres are linked to sprinting abilities. The ratio of these fibre types can be influenced by training and is determined by a person's genetics. Additionally, muscle fibres can adapt to changing demands by modifying their size or fibre type composition, forming the basis for physical therapy interventions aimed at improving force development or endurance.
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Muscle groups
The human body has over 600 muscles, which can be categorised into three main types: skeletal, smooth, and cardiac. Skeletal muscles are the most common type, comprising 30% to 40% of your total body mass. They are attached to the bones by tendons and allow you to perform a wide range of movements and functions. Examples of skeletal muscles include shoulder muscles, hamstring muscles, and abdominal muscles.
Smooth muscles, on the other hand, are involuntary muscles found in the walls of blood vessels and structures like the urinary bladder, intestines, and stomach. They work without conscious effort, such as in the process of eliminating waste and toxins from the body.
Cardiac muscles make up the third type and form the mass of the heart. These muscles are also involuntary and are responsible for the rhythmic contractions that pump blood throughout the body.
When it comes to specific muscle groups, some of the major ones include the pectorals or pecs, which are the large chest muscles. They provide bulk to the upper body and support various everyday movements, such as reaching across the body or tucking in a shirt.
The glutes are another major muscle group located in the buttocks. They are the largest muscles in the body and play a key role in moving the legs backward and sideways, as well as maintaining balance while walking or running.
Additionally, the quadriceps or 'quads' form a muscle group in the front of the thigh, consisting of four large muscles: rectus femoris, vastus lateral, vastus intermedius, and vastus medialis.
Lastly, the calves, located in the lower back part of the legs, are essential for walking, running, and climbing stairs, as well as explosive moves like sprinting and jumping.
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Frequently asked questions
Skeletal muscles are attached to the bones of the skeletal system and are located throughout the body. They are the most common type of muscle in the human body. They are also known as voluntary muscles because they are under our conscious control. Examples include shoulder muscles, hamstring muscles, abdominal muscles, biceps, and triceps.
Smooth muscles are involuntary muscles located in the walls of internal structures such as the digestive tract, urinary bladder, uterus, intestines, and blood vessels. They are also found in the heart, where they are known as cardiac muscles.
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.
The back contains the origins of many muscles involved in the movement of the neck and shoulders. Some of these muscles include the erector spinae, semispinalis dorsi, semispinalis capitis, multifidi, rotators, and quadratus lumborum.
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