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The human body has about 600 muscles, which can be categorised into three types of muscle tissue: skeletal, smooth, and cardiac. Skeletal muscles are attached to bones and are under voluntary control, meaning their movement can be consciously controlled. They make up 30% to 40% of human body weight and play a role in metabolism and blood sugar level maintenance. Smooth and cardiac muscles, on the other hand, are involuntary muscles, contracting and relaxing without conscious awareness.
| Characteristics | Values |
|---|---|
| Type of Muscle Tissue | Skeletal Muscle |
| Controlled By | Brain, Nerves |
| Appearance Under Microscope | Striated, Striped |
| Muscle Composition | Bundled Elastic Fibres |
| Muscle Contraction | Respond to Nerve Signals from Brain |
| Muscle Shape | Spindle, Flat, Triangular, Circular |
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What You'll Learn
Skeletal muscles are controlled voluntarily
Skeletal muscles are under voluntary control, meaning that their movement can be consciously controlled. They make up 30% to 40% of human body weight in a healthy person. These muscles are attached to bones and work with the brain and nerves to cause movement, which is known as the neuromuscular system. The brain sends messages to the motor neurons, triggering the release of the chemical acetylcholine, which causes the muscle to contract.
Skeletal muscles are also known as striated muscles because they appear striped when viewed under a microscope. They are bundled units of fascicles, made up of muscle fibres or muscle cells. Each muscle fibre is divided into myofibrils, which contain thick (myosin) and thin (actin) myofilaments. These myofilaments fold together when given the signal to contract, shortening the length of the muscle fibre and, in turn, the entire muscle.
The musculoskeletal system, or locomotor system, includes both skeletal muscles and bones. Skeletal muscles are generally grouped into opposing pairs, such as the biceps and triceps on the front and back of the upper arm. They can be found in the neck, arms, and legs. Skeletal muscles come in four main shapes: spindle, flat, triangular, and circular.
Unlike skeletal muscles, smooth muscles lack the striated structure and are found in the walls of hollow visceral organs, such as the liver, pancreas, and intestines, as well as in blood vessels and airways. Smooth muscles contract involuntarily in response to stimulation from the autonomic nervous system or the release of hormones and other chemical signals. Cardiac muscle, found only in the heart, is also under involuntary control. It contracts and relaxes without our conscious awareness, controlled by both the autonomic nervous system and its own pacemaker cells.
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Cardiac muscles are involuntary
There are three types of muscle tissue: skeletal, smooth, and cardiac. Cardiac muscle cells are located in the walls of the heart and are under involuntary control. They contract and relax without our conscious awareness. Cardiac muscles are striated like skeletal muscles, but they are controlled by both the autonomic nervous system and their own pacemaker cells, causing them to contract automatically and rhythmically. The heart contracts or beats about 100,000 times per day, 36 million times per year, and about 2.5 billion times over a lifetime.
In contrast, skeletal muscles are voluntary muscles that can be consciously controlled. They make up 30-40% of human body weight in a healthy person and are attached to bones, allowing movement. The brain, nerves, and skeletal muscles work together to cause movement through the neuromuscular system. Skeletal muscles respond to nerve signals from the brain that lead to muscle contraction. They can also convert chemical energy into mechanical energy to cause voluntary muscle contraction and movement.
Smooth muscles, on the other hand, are involuntary muscles found in the walls of hollow visceral organs such as the liver, pancreas, and intestines, as well as in the digestive, reproductive, and urinary tracts, blood vessels, airways, and other locations like the inside of the eye. They lack the striped appearance of skeletal and cardiac muscles when viewed under a microscope. Smooth muscles are arranged in layered sheets that contract in waves along the length of the structure. Their contraction is stimulated by the autonomic nervous system through the release of hormones or other chemical signals.
While cardiac muscles are indeed involuntary, they are distinct from smooth muscles in terms of structure and function. Cardiac muscles have a striated appearance similar to skeletal muscles, while smooth muscles lack these stripes or striations. Additionally, cardiac muscles have their own pacemaker cells that contribute to their rhythmic contractions, a characteristic not typically associated with smooth muscles.
In summary, cardiac muscles are involuntary muscles found specifically in the heart, contracting and relaxing without conscious control. They possess unique structural and functional characteristics that differentiate them from other types of muscles in the body, such as skeletal and smooth muscles.
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Smooth muscles are involuntary
Smooth muscles are arranged in sheets or layers of smooth muscle cells that contract in waves along the length of the structure. Unlike skeletal muscles, smooth muscles lack the striated structure observed in skeletal and cardiac muscles, giving them a smooth appearance under a microscope. This distinction is due to differences in cell types and the kinds of health conditions that affect their function.
The contraction of smooth muscles is regulated by the autonomic nervous system, which controls essential daily functions such as digestion and breathing. When stimulated by the autonomic nervous system, smooth muscle cells contract through the movement of actin and myosin myofilaments, resulting in a shortening of the muscle fibre. This process occurs spontaneously without nervous or hormonal stimulation, making it independent of our conscious control.
Smooth muscles play a vital role in maintaining the functions of the organs and structures in which they are found. For example, in the digestive system, smooth muscles contract to propel food through the digestive tract. In the blood vessels, smooth muscles regulate blood flow and pressure by contracting and relaxing. Their involuntary nature ensures that these crucial functions occur automatically, without requiring our conscious effort.
While smooth muscles are generally involuntary, it is worth noting that some limited voluntary control can be exerted over certain smooth muscles, such as those involved in eye movement and urination. However, the majority of smooth muscle functions occur independently of our conscious control, highlighting the importance of these muscles in maintaining our body's essential processes.
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Voluntary muscles are controlled by the neuromuscular system
Voluntary muscles, also known as skeletal muscles, are under conscious control. They are attached to bones and respond to nerve signals from the brain that lead to muscle contraction and relaxation, resulting in movement. This process is known as the neuromuscular system, where the brain, nerves, and skeletal muscles work together.
The neuromuscular system involves the brain sending messages to motor neurons, which are specialized nerve cells that service the muscles. These nerve signals are transmitted to the muscles through the release of neurotransmitters, such as acetylcholine, at the neuromuscular junction—the space between a nerve cell and a muscle fiber.
Skeletal muscles make up 30% to 40% of human body weight and are found in various parts of the body, including the neck, arms, and legs. They are responsible for supporting movement, such as lifting heavy weights, and play a role in metabolism and blood sugar regulation.
Neuromuscular disorders, also known as skeletal muscle disorders, can affect the nerves that transmit electrical signals to voluntary skeletal muscles, disrupting movement control. These disorders can cause muscle weakness, atrophy, or pain. Examples of such disorders include amyotrophic lateral sclerosis (ALS), Charcot-Marie-Tooth disease, and multiple sclerosis (MS).
In contrast to voluntary muscles, involuntary muscles, such as cardiac and smooth muscles, function without conscious control. Cardiac muscles, found in the heart, contract and relax automatically, maintaining a rhythmic heartbeat. Smooth muscles, on the other hand, are located in the walls of hollow visceral organs, such as the liver, pancreas, and intestines, as well as in blood vessels and airways. They contract in waves along the length of the structures they line.
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Involuntary muscles are controlled by the autonomic nervous system
Involuntary muscles, such as those found in the heart, blood vessels, and digestive system, are controlled by the autonomic nervous system. This system is a component of the peripheral nervous system, which includes every part of the nervous system that isn't the brain and spinal cord. The autonomic nervous system regulates involuntary physiological processes, such as heart rate, blood pressure, respiration, digestion, and sexual arousal. It consists of three divisions: sympathetic, parasympathetic, and enteric.
The sympathetic nervous system (SNS) and the parasympathetic nervous system (PNS) contain both afferent and efferent fibers that provide sensory input and motor output to the central nervous system (CNS). The SNS and PNS motor pathways consist of a two-neuron series: a preganglionic neuron with a cell body in the CNS and a postganglionic neuron with a cell body in the periphery that innervates target tissues. Most postganglionic sympathetic neurons release neurotransmitters that regulate blood flow and gastrointestinal motility.
The autonomic nervous system controls the automatic functions of the body that are necessary for survival. It manages essential daily functions such as digestion and breathing. For example, it regulates the release of hormones and other chemical signals that stimulate smooth muscle cells in the intestines and blood vessels to contract. Smooth muscle lacks the striated structure of skeletal muscle and consists of sheets or layers of smooth muscle cells.
The autonomic nervous system also controls the muscles in the eyes, including pupil dilation and the muscles used for focusing. It manages the lacrimal (tear) system, the running of the nose, and salivation in the mouth. Additionally, it controls the body's ability to sweat and the muscles that cause hair to stand up.
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Frequently asked questions
Voluntary muscles are skeletal muscles that can be consciously controlled. They attach to bones and respond to nerve signals from the brain that lead to muscle contraction. They make up 30% to 40% of human body weight in a healthy person.
Voluntary muscles include the muscles in your neck, arms, and legs. Generally, skeletal muscles are grouped into opposing pairs, such as the biceps and triceps on the front and back of the upper arm.
Involuntary muscles, on the other hand, are those that are not under our conscious control. These include smooth muscles, which are found in the walls of hollow organs like the liver, pancreas, intestines, and blood vessels. Cardiac muscles, which are specific to the heart, are also involuntary.
