Victor Forge
The human body is an intricate system, with over 600 muscles that work to keep us alive and facilitate movement. These muscles are made up of thousands of small fibres that stretch and press together to move our organs and body. They also help us perform a wide range of movements and functions, from holding our bodies still to running marathons. Skeletal muscles, which are attached to bones, are under our conscious control and are therefore known as voluntary muscles. However, not all muscles are under our conscious control, such as the heart muscle, which beats on its own without our input. The muscles surrounding external body openings, such as the mouth and eyes, have a unique structure that allows them to control the opening and closing of these passages. This structure is known as a circular fascicle arrangement, where muscle fibres are positioned in concentric circles. When these muscles contract, they reduce the size of the opening, and when they relax, the opening increases.
| Characteristics | Values |
|---|---|
| Number of muscles in the body | More than 600 |
| Types of movements | Voluntary, Involuntary |
| Types of muscles | Skeletal, Smooth, Cardiac |
| Muscle disorders | Myopathy, Myasthenia gravis, Rhabdomyolysis, Sarcopenia, Strains, Sprains, Cramps, Tendonitis, Bruising, Metabolic disorders, Endocrine disorders, Toxic disorders, Cancers |
| Muscle control | Controlled by the brain and nerves |
| Muscle shape | Triangular, Circular |
| Muscle composition | Made up of thousands of small fibres woven together |
| Muscle fibres | Composed of blocks of proteins called myofibrils |
| Muscle function | Allow the body to move, help internal organs function |
| Muscle openings | Muscles surrounding external body openings have a circular fascicle arrangement, allowing for control over the opening and closing of these body openings |
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What You'll Learn
Circular fascicle arrangement
The orbicularis oculi is an example of a circular fascicle arrangement. This muscle surrounds the eye and allows it to close. Another example is the orbicularis oris, which goes around the mouth. When this muscle contracts, the oral opening becomes smaller, as when puckering the lips for whistling.
The arrangement of a muscle's fascicles determines its range of motion and power. Circular muscles, in particular, control openings by contracting to close them. They are crucial for regulating the passage of substances through openings.
The design of circular fascicle arrangements facilitates precise control over various physiological functions, such as swallowing, blinking, and maintaining proper oral functions. Understanding the structure of these muscles is essential for studying muscle function and movement in the body, highlighting the significance of the circular arrangement in muscle mechanics.
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Voluntary vs involuntary movement
Human movements can be broadly classified into two types: voluntary and involuntary. Voluntary movements are self-generated, willed actions performed as a result of cognitive processes. They are controlled by the motor cortex, the zone of the cerebrum located behind the frontal lobe. The motor cortex sends a neural message that moves through the brain stem along the spinal cord and into the neural network to the muscle being commanded. We can deliberately order the skeletal muscles to contract, which enables us to perform movements.
Voluntary movements are a fundamental component of human functioning. The capacity for voluntary control is seen as essential to human movements. The sense that one intended to move (willing) and that those actions were self-generated (self-agency) gives the sense of voluntariness and of being in control. The brain, nerves, and skeletal muscles work together to cause movement. This is collectively known as the neuromuscular system.
In contrast, involuntary movements are non-intentional and include normal non-intentional movements, reflexes, and pathological non-intentional movements. They are produced by a non-intentional, pathological activation anywhere within the final common pathways or the two loops (basal ganglia loop and cerebellar loop). Involuntary movements are controlled by other regions of the brain, such as the hypothalamus. The heart, for example, is an involuntary muscle that beats on its own without any external input. Smooth muscles, which line the inside of some organs, are also involuntary muscles. They play an essential role in many body systems, including the digestive, respiratory, and reproductive systems.
It is important to note that dysfunction in certain brain areas can result in semi-voluntary movements, which lie in the borderland between voluntary and involuntary movements. In such cases, a person may experience a disordered sense of will or agency, and the movement may be experienced as unexpected and involuntary, even though it appears voluntary.
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Skeletal muscles
These muscles also play a crucial role in stabilising the body and maintaining posture. They make constant slight adjustments to keep bones stable and help prevent skeletal damage and joint dislocation. Additionally, skeletal muscles help regulate body temperature. When the body detects a lower-than-normal temperature, it tenses and relaxes these muscles to generate heat.
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Smooth muscles
Smooth muscle is one of the three major types of vertebrate muscle tissue, the other two being skeletal and cardiac muscle. Smooth muscle is found in the walls of several hollow organs, including the stomach, intestines, bladder, and uterus. It is also present in the urinary and reproductive systems, as well as the walls of blood vessels and lymph vessels. Smooth muscle is an involuntary muscle, meaning it contracts and relaxes without conscious thought. This type of muscle is responsible for several vital functions in the body, such as blood pressure regulation, circulation, vision, and digestion.
Smooth muscle cells are spindle-shaped with a wide middle and tapering ends, and they contain the proteins actin and myosin, which enable contraction. Unlike skeletal muscle, smooth muscle has no striations as it lacks sarcomeres. Smooth muscle can be divided into two subgroups: single-unit and multi-unit. Single-unit smooth muscle, also known as visceral smooth muscle, is found in the walls of most internal organs and lines blood vessels, the urinary tract, and the digestive tract. It can contract regularly without input from a motor neuron, and most smooth muscle falls into this category. Multi-unit smooth muscle, on the other hand, is neurogenic, meaning its contraction is initiated by the autonomic nervous system.
Smooth muscle plays a crucial role in passage width control within the body. It can flex together to push substances through tubelike passages, such as in the digestive tract. Smooth muscle is also responsible for gatekeeping functions, such as in the bladder and anus, where it stays flexed and only relaxes when needed. In the skin, smooth muscle causes goosebumps by making hairs stand on end. In the eyes, smooth muscle controls how the pupils dilate or constrict and helps with focusing by pulling on fibers called zonules.
Smooth muscle is susceptible to various conditions, including anti-smooth muscle autoantibodies, where the immune system attacks and damages the smooth muscle. Muscular dystrophies can also affect smooth muscle, causing it to stop working properly. Spasms are another issue, where the smooth muscle twitches or contracts uncontrollably, potentially leading to vasospasm or asthma. Additionally, visceral myopathies are a group of smooth muscle diseases that can interfere with their function and may prove fatal when affecting organs like the bladder or large intestine.
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Cardiac muscles
The human body contains three kinds of muscle tissue: skeletal, smooth, and cardiac. Cardiac muscle tissue, or myocardium, is a type of muscle tissue that forms the heart. It is located in the walls of the heart and makes up the middle layers of the heart. It is the only type of muscle tissue that is found in the heart and does not exist anywhere else in the body.
Cardiac muscle tissue produces involuntary movements, meaning they are automatic and a person cannot control them. The heart also contains specialized types of cardiac tissue containing "pacemaker" cells. These contract and expand in response to electrical impulses from the nervous system. The pacemaker cells generate electrical impulses, or action potentials, that tell cardiac muscle cells to contract and relax. The cardiac muscle cells also contain mitochondria, which are often referred to as the powerhouses of the cells. The interconnected cardiac muscle cells give the cardiac muscle tissue its strength and flexibility.
Cardiac muscle tissue contracts and releases involuntarily to keep the heart pumping blood around the body. It squeezes and relaxes to pump blood through the cardiovascular system. Cardiac muscle tissue is highly organized and contains many types of cells, including fibroblasts, smooth muscle cells, and cardiomyocytes. Cardiomyocytes are specialized cardiac muscle cells that perform highly coordinated actions to keep the heart pumping and blood circulating throughout the body.
Regular aerobic exercise can help strengthen cardiac muscle tissue and keep the heart and lungs healthy. Engaging in aerobic activities can train the heart to become more efficient.
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Frequently asked questions
Muscles are pieces of soft tissue throughout your body that help you perform a wide range of movements and functions. There are more than 600 muscles in the human body.
Muscles that surround external body openings, such as the mouth and eyes, typically have a circular fascicle arrangement. This pattern, also known as orbicular, allows these muscles to control the opening and closing of these bodily passages. For example, the orbicularis oculi muscle contracts when we blink, closing the eyelid.
There are two types of muscle movements: voluntary and involuntary. Voluntary movements are actions you choose to perform and control. Involuntary movements are done without conscious awareness.
Muscle disorders may cause weakness, pain, loss of movement, and even paralysis. Common muscle problems include injury or overuse, cramps, tendonitis, and bruising.
