Dominic Stone
The human body has more than 600 muscles that help us do everything from pumping blood around the body to lifting heavy objects. We can control some of our muscles, such as our skeletal muscles, which are voluntary muscles that we can use to kick a football or lift a book. However, other muscles, like our heart muscles, are involuntary and perform essential functions without us having to consciously think about them.
| Characteristics | Values |
|---|---|
| Number of muscles in the human body | More than 600 |
| Types of muscles | Skeletal, Cardiac, Smooth |
| Types of muscle control | Voluntary, Involuntary |
| Voluntary muscles | Skeletal muscles |
| Involuntary muscles | Cardiac, Smooth muscles |
| Muscle functions | Movement, breathing, swallowing, pumping blood, supporting organs |
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What You'll Learn
Skeletal muscles (voluntary)
Skeletal muscles are the most common type of muscle in the human body, comprising 30% to 40% of total body mass. They are attached to bones by tendons and are responsible for producing movements of body parts in relation to each other. These muscles are voluntary, meaning individuals have control over how and when they work. For example, if you reach for a book on a shelf, you are using the skeletal muscles in your neck, arm, and shoulder.
Skeletal muscles are also known as striated muscles because they have a striped appearance due to the light and dark parts of the muscle fibres. These muscles are made up of long, fine fibres, each of which is a bundle of finer myofibrils. Within each myofibril are filaments of the proteins myosin and actin, which slide past each other during muscle contraction and expansion. The dark bands, called Z lines, are formed where the actin and myosin filaments overlap. The region between two Z lines is called a sarcomere, which is considered the primary structural and functional unit of muscle tissue.
Males generally have more skeletal muscle mass than females, and taller or overweight individuals also tend to have higher muscle mass. Skeletal muscle mass decreases with age, so it is important to maintain muscle health to preserve strength and functionality. Skeletal muscles play a vital role in everyday activities such as breathing, eating, and moving bones, so keeping them strong and healthy is crucial for overall well-being.
Skeletal muscles work in conjunction with the bones of the body to provide strength and power. In most cases, a skeletal muscle is attached to one end of a bone and stretches across a joint to attach to another bone. This allows for a wide range of movements and functions, from holding the body still to performing complex physical activities like running or playing sports.
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Cardiac muscles (involuntary)
The human body has more than 600 muscles, and one of the three major categories of muscles is cardiac muscle, also called myocardium. The heart is the only organ in the body made of cardiac tissue and is the only organ that is also a muscle. Cardiac muscle makes up the middle layer of the heart, and it doesn't exist anywhere else in the body. The heart is made up of three layers: the pericardium, myocardium, and endocardium. The endocardium is not cardiac muscle but forms the inner lining of the heart chambers and valves. The pericardium is a fibrous sac surrounding the heart.
Cardiac muscle is under involuntary control, which means it works without conscious thought. The autonomic nervous system controls it. The heart beats on its own without any input from conscious thought, and this is an example of an involuntary movement. The cardiac muscle squeezes and relaxes to pump blood through the cardiovascular system. This pumping action is enabled by the synchronous contraction of cardiomyocytes, which are cardiac muscle cells. The functional unit of cardiomyocyte contraction is the sarcomere, consisting of thick (myosin) and thin (actin) filaments. The interaction between these filaments forms the basis of the sliding filament theory.
Calcium plays a crucial role in the contraction of cardiac muscle cells. Action potentials travel along the sarcolemma (the cardiomyocyte plasma membrane) and into the t-tubules, which are highly branched invaginations of the sarcolemma. These t-tubules allow for the influx of calcium into the cell via voltage-gated calcium channels. This increase in intracellular calcium triggers the release of more calcium through the ryanodine receptor, a process known as calcium-induced calcium release. The released calcium attaches to troponin C, causing tropomyosin to detach from the myosin-binding sites on actin. Actin and myosin then form a cross-bridge, resulting in contraction. This process is known as excitation-contraction coupling (ECC).
Cardiac muscle cells are branched and contain many mitochondria. Each cell contains a single, centrally located nucleus surrounded by the sarcolemma. Cardiac muscle cells also contain intercalated discs that connect the cells and allow them to contract together. These interconnections are vital for maintaining the structural integrity of the heart.
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Smooth muscles (involuntary)
Smooth muscles, also known as involuntary muscles, are not under conscious control. They contract and relax in response to signals from the autonomic nervous system, which regulates essential functions such as digestion, breathing, and blood pressure. Smooth muscles line the walls of hollow visceral organs like the liver, pancreas, stomach, intestines, and blood vessels. They are also found in the urinary system and play a role in toxin removal and electrolyte balance.
The shape of smooth muscle is fusiform, with a round center that tapers at each end. Unlike skeletal muscles, smooth muscles lack a striated structure and instead consist of sheets or layers of smooth muscle cells. These cells contain large amounts of actin and myosin, the proteins responsible for muscle contraction. When stimulated by the nervous system, smooth muscle cells contract through the movement of actin and myosin filaments, allowing for spontaneous regulation of bodily functions.
The unique properties of smooth muscles make them vital in various physiological processes and medical treatments. For example, in the cardiovascular system, smooth muscles help regulate blood flow by controlling the diameter of blood vessels. In the respiratory system, smooth muscle constriction in the lungs can lead to the development of asthma. The relaxation of airway smooth muscle through bronchodilators is a life-saving treatment for asthmatic patients.
Additionally, smooth muscles play a role in gastric emptying by increasing muscle signaling. In the context of disease, changes in smooth muscle lining blood vessels have been linked to atherosclerosis, a condition characterized by plaques that damage and block these vessels. Furthermore, continuous smooth muscle activation in the lungs can contribute to the development of pulmonary hypertension.
Smooth muscles are an essential component of the human body, facilitating involuntary functions that are vital for survival. Their presence in various organ systems highlights their versatility and significance in maintaining overall health and homeostasis.
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Muscle soreness and pain
The human body has over 600 muscles that help us do everything from pumping blood around the body to lifting heavy objects. We are able to control some of our muscles, while others, like the heart, function without us having to think about them.
Skeletal muscles are voluntary muscles, meaning we can control how and when they work. They make up 30-40% of our total body mass and are attached to bones, allowing us to perform a wide range of movements and functions. For example, when we reach for a book on a shelf, we are using the skeletal muscles in our neck, arm, and shoulder.
Smooth and cardiac muscles, on the other hand, are involuntary muscles controlled by the autonomic nervous system. Smooth muscles line our organs and help with functions like digestion and urination.
However, if muscle soreness persists or worsens despite rest, it could be a sign of a more serious issue requiring professional care. Localized muscle pain or soreness in one spot is often related to an injury or recent stress on that muscle group. On the other hand, diffuse, all-over body aches may indicate a disease or condition affecting the whole body. If muscle pain does not improve with rest and home treatments within a week, it is recommended to seek medical advice.
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Muscle contractions
The human body has over 600 muscles that help us do everything from pumping blood around our bodies to lifting heavy objects. We can control some of our muscles, such as our skeletal muscles, while others, like our heart muscles, work without us thinking about them.
Skeletal muscles are voluntary muscles, meaning we can control how and when they move and work. They are the most common type of muscle in our bodies, comprising 30-40% of our total body mass. Skeletal muscles are attached to bones and allow us to perform a wide range of movements and functions. They are made up of thousands of small fibres woven together, and these fibres stretching and pressing together is what moves our bones and body.
The contraction of skeletal muscles is neurogenic, requiring synaptic input from motor neurons. Once innervated, the protein filaments within each skeletal muscle fibre slide past each other to produce a contraction, as explained by the sliding filament theory. This contraction can be described as a twitch, summation, or tetanus, depending on the frequency of action potentials. Skeletal muscle tension is at its greatest when the muscle is stretched to an intermediate length, as per the length-tension relationship.
In contrast, smooth and cardiac muscles have myogenic contractions, meaning they are initiated by the muscle cells themselves rather than being stimulated by an outside event. Smooth muscles, for example, contract and relax in our stomachs and digestive systems to allow food to move through our bodies. They are involuntary muscles, controlled by our autonomic nervous systems.
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Frequently asked questions
Humans have more than 600 muscles, but not all of them are under our control.
The skeletal muscles are under our voluntary control. These muscles help us perform a wide range of movements and functions.
Smooth muscles and cardiac muscles are involuntary muscles that we cannot control. They are controlled by the autonomic nervous system.
Skeletal muscles are attached to the skeleton. They help give our body strength and power. They comprise 30% to 40% of our total body mass.
Smooth muscles are found in our stomach, digestive system, bladder, and blood vessels. They help break down food and maintain blood pressure. Cardiac muscles are found in the heart and are responsible for pumping blood throughout our body.
