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Muscles are pieces of soft tissue that help the body move, breathe, swallow, and stay alive. There are over 600 muscles in the human body, making up over 40% of our weight. They are made of thousands of small elastic fibres, woven together like a quilt, that contract and relax to cause movement. The three main types of muscle tissue are skeletal, smooth, and cardiac. Skeletal muscles are attached to bones and allow movement. Smooth muscles are located in various internal structures, including the digestive tract, uterus, and blood vessels. Cardiac muscles are found in the walls of the heart and are controlled by the autonomic nervous system.
| Characteristics | Values |
|---|---|
| Number of muscles in the human body | 600+ |
| Types of muscles | Skeletal, Smooth, Cardiac |
| Skeletal muscle composition | 30% to 40% of total body mass |
| Skeletal muscle control | Voluntary |
| Smooth muscle control | Involuntary |
| Cardiac muscle control | Involuntary |
| Muscle energy sources | Aerobic respiration, Lactic acid fermentation |
| Muscle fibres | Made of thousands of small fibres |
| Muscle movement | Contraction, Relaxation |
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What You'll Learn
- Skeletal muscles are voluntary and controlled by the somatic nervous system
- Cardiac muscle, or myocardium, is an involuntary muscle that pumps blood
- Smooth muscles are involuntary and control the digestive, reproductive, and urinary systems
- Muscle contractions can be isometric or isotonic, with the former increasing tension without movement
- Muscle fibres are made of myofibrils, which contain myoglobin and other molecules to
Skeletal muscles are voluntary and controlled by the somatic nervous system
The human body has more than 600 muscles, which help us perform a variety of functions, from moving our body to breathing and keeping us alive. There are three types of muscle tissue: skeletal, smooth, and cardiac. Skeletal muscles are voluntary muscles, which means they move when we think about moving a part of our body. They are attached to the skeleton and are under our conscious control.
The somatic nervous system is a component of the peripheral nervous system, which is associated with the voluntary control of body movements via skeletal muscles. It is responsible for all the functions we can consciously influence, such as moving our arms, legs, and other body parts. The somatic nervous system consists of both afferent (sensory) and efferent (motor) nerves. It also includes the reflex arc, which involves using interneurons to perform reflexive actions.
The somatic nervous system allows us to voluntarily control our skeletal muscles. It is responsible for transmitting signals from our brain to our muscles, enabling us to move around. This system is essential for coordinating and regulating our movements and muscle activities. It is also involved in transmitting sensory information from our senses, such as smell, sound, taste, and touch, to our brain.
The somatic nervous system is further divided into two types of nerves: spinal nerves and cranial nerves. Spinal nerves carry somatosensory information and motor instructions out of the spinal cord. They form a web of interconnected nerve roots, which then branch out to create nerve fibers. Cranial nerves, on the other hand, are responsible for carrying information to and from our brain.
In summary, skeletal muscles are voluntary and controlled by the somatic nervous system. This system allows us to consciously control our movements and perform various daily functions. The somatic nervous system plays a crucial role in transmitting signals between our brain and muscles, ensuring our body's smooth and coordinated functioning.
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Cardiac muscle, or myocardium, is an involuntary muscle that pumps blood
The human body contains three kinds of muscle tissue: skeletal, smooth, and cardiac. Cardiac muscle, or myocardium, is an involuntary muscle that pumps blood around the body.
Cardiac muscle is a specialised type of tissue that exists only in the heart. It is responsible for keeping the heart pumping and blood circulating around the body. The heart is made up of three layers: the pericardium, myocardium, and endocardium. The myocardium forms a thick middle layer between the outer layer of the heart wall (the pericardium) and the inner layer (the endocardium). The endocardium is not cardiac muscle, but simple squamous epithelial cells that form the inner lining of the heart chambers and valves.
The myocardium found in the ventricles is thick to allow for forceful contractions, while the myocardium in the atria is much thinner. The sheets of muscle that wrap around the left ventricle closest to the endocardium are oriented perpendicularly to those closest to the epicardium. When these sheets contract in a coordinated manner, they allow the ventricle to squeeze in several directions simultaneously – longitudinally (becoming shorter from apex to base), radially (becoming narrower from side to side), and with a twisting motion (similar to wringing out a wet cloth) to squeeze the maximum possible amount of blood out of the heart with each heartbeat.
Cardiac muscle cells contain mitochondria, which are often referred to as the powerhouses of the cells. They also contain baroreceptors, which detect high blood volume through increased stretch in the atrium wall.
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Smooth muscles are involuntary and control the digestive, reproductive, and urinary systems
Smooth muscles are involuntary muscles that line the inside of some organs. They are found in the walls of blood vessels and structures such as the urinary bladder, the intestines, and the stomach. They play an important role in the digestive, reproductive, and urinary systems.
In the digestive system, smooth muscles help with digestion and nutrient collection in the stomach and intestines. They also aid in moving waste through the intestines. Smooth muscles in the urinary system help rid the body of toxins and maintain electrolyte balance. They are also involved in the regulation of blood pressure and tissue oxygenation in arteries and veins.
Smooth muscles are essential for the reproductive system, including both the female and male reproductive systems. They help with vital functions such as giving birth and expanding the lungs when breathing.
Smooth muscles differ from skeletal muscles in that they can be contracted and controlled involuntarily. They consist of thick and thin filaments that do not arrange into sarcomeres, resulting in a non-striated pattern. Smooth muscles have greater elastic properties than skeletal muscles, which is important for organ systems like the urinary bladder, where maintaining contractile tone is crucial.
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Muscle contractions can be isometric or isotonic, with the former increasing tension without movement
Muscle contractions are an essential part of everyday activities, such as walking, running, and lifting objects. They are the tightening, shortening, or lengthening of muscles when we engage in any physical activity. There are two primary types of muscle contractions: isotonic and isometric.
Isotonic contractions occur when a muscle changes length while the tension remains constant, typically when moving something heavy. These contractions are further divided into two types: concentric and eccentric. Concentric contractions occur when the muscle shortens and generates force to overcome resistance. For example, when lifting a heavy weight, a concentric contraction of the biceps causes the arm to bend at the elbow, lifting the weight towards the shoulder. Eccentric contractions, on the other hand, occur when the muscle lengthens while still under tension, like when lowering a dumbbell back down.
Isometric contractions, in contrast, occur when the muscle length remains unchanged while muscle tension increases. During isometric exercises, the muscle does not noticeably change length, and the affected joint doesn't move, yet the muscle is still working. This type of contraction is exemplified by activities such as holding a plank or carrying an object in a steady position. Isometric contractions are also crucial for maintaining posture and joint stability. They are often used in rehabilitation settings to maintain muscle strength without placing stress on injured or vulnerable joints.
Both isotonic and isometric contractions are integral to the body's complex system of movement and stability. While isotonic contractions contribute to functional strength and movement, isometric contractions help stabilize muscles and joints.
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Muscle fibres are made of myofibrils, which contain myoglobin and other molecules to
The human body has more than 600 muscles that help us perform a variety of tasks, from moving our bodies to breathing and keeping us alive. These muscles are made of thousands of small fibres that are woven together, allowing them to stretch and press together to facilitate movement.
Muscle fibres are composed of myofibrils, which are long, cylindrical structures that run parallel to the muscle fibre. Myofibrils contain sarcomeres, the functional units of skeletal muscle, which are composed of thick and thin myofilaments. These myofilaments are composed of proteins, with the thick filaments made of myosin and the thin filaments of actin, along with the regulatory proteins tropomyosin and troponin. The arrangement of these filaments gives skeletal muscle its striated appearance, with light and dark regions.
Sarcomeres play a crucial role in muscle contraction. When a skeletal muscle fibre is activated by a signal from a motor neuron, cross-bridges form between the thick and thin filaments. The thin filaments slide past the thick filaments within the sarcomeres, causing the sarcomeres to shorten. This, in turn, leads to the contraction of individual muscle fibres and ultimately the whole muscle.
The sarcomere structures within the myofibrils are essential for muscle function and provide the foundation for the complex movements and tasks that our muscles perform on a daily basis.
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