The muscular system is an organ system consisting of skeletal, smooth and heart muscles. It enables body movement, maintains posture, and circulates blood throughout the body. The muscular system in the vertebrates is controlled through the nervous system, although some muscles (such as the heart muscle) can be completely autonomous. Together with the skeletal system it forms the musculoskeletal system, which is responsible for the movement of the human body.
Video Muscular system
Otot
There are three different types of muscles: skeletal muscle, heart or heart muscle, and smooth muscle (not striated). Muscles provide strength, balance, posture, movement and heat to keep the body warm.
Skeletal muscle
Skeletal muscles, like other striated muscles, are composed of myocytes, or muscle fibers, which in turn are made up of myofibrils, which are composed of sarcomomes, the basic building blocks of striated muscle tissue. After stimulation by action potential, skeletal muscles perform coordinated contractions by shortening each sarcomomer. The best model proposed for understanding contractions is the shear filament model of muscle contraction. In sarcomas, actin and myosin fibers overlap in contractile motion against each other. The myosin filament has a head-shaped head that leads to the actin filament.
Larger structures along myosin filaments called myosin heads are used to provide attachment points at the binding sites for actin filaments. The myosin heads move in a coordinated fashion; they rotate to the center of the sarcometer, releasing and then reattaching to the nearest active site of actin filaments. This is called ratchet type drive system.
This process consumes a large amount of adenosine triphosphate (ATP), the cell's energy source. ATP binds a cross bridge between the myosin head and actin filaments. The release of energy forces rotates the myosin head. When ATP is used, it becomes adenosine diphosphate (ADP), and since muscles store small ATP, they must continue to replace ADP that is discarded with ATP. Muscle tissue also contains a stored supply of rapid refill chemistry, creatine phosphate, which, when necessary, can help rapid ADP regeneration into ATP.
Calcium ions are required for each sarkomer cycle. Calcium is released from the sarcoplasmic reticulum to the sarcoma when the muscles are stimulated to contract. This calcium exposes the actin binding site. When muscles no longer need to contract, calcium ions are pumped from the sarcoma and back into storage in the sarcoplasmic reticulum.
There are about 639 skeletal muscles in the human body.
Cardiac muscle
The heart muscles are different from the skeletal muscle because the muscle fibers are laterally connected to each other. Furthermore, just like the smooth muscles, their movements are not realized. The heart muscles are controlled by the sinus nodes that are affected by the autonomic nervous system.
Smooth muscle
The delicate muscles are controlled directly by the autonomous and unconscious nervous system, meaning that they are incapable of being moved by the conscious mind. Functions such as heartbeat and lung (which can be controlled voluntarily, either to some extent) are the muscles that are not realized but not the smooth muscles.
Maps Muscular system
Physiology
Contraction
The neuromuscular joint is the focal point in which the motor neuron is attached to the muscle. Acetylcholine, (a neurotransmitter used in skeletal muscle contraction) is released from the axon terminal of the nerve cell when the action potential reaches a microscopic junction, called a synapse. A group of chemical messengers crosses synapses and stimulates the formation of electrical changes, produced in muscle cells when acetylcholine binds to receptors on its surface. Calcium is released from its storage area in the sarcoplasm cell reticulum. The thrust of nerve cells causes calcium release and causes short muscle contractions called muscle twitching. If there is a problem with the neuromuscular junction, very long contractions may occur, such as muscle contraction resulting from tetanus. Also, loss of function at intersections can produce paralysis.
Skeletal muscles are arranged into hundreds of motor units, each involving a motor neuron, attached by a series of fingerlike structures called axon terminals. It attaches and controls the discrete bundle of muscle fibers. Coordinated and refined responses to certain circumstances will involve controlling the exact number of motor units used. While individual muscle units contract as units, all muscles can contract on a predetermined basis due to the structure of the motor unit. Coordination of motor units, balance, and control often come under the direction of the cerebellum of the brain. This allows complex muscle coordination with little conscious effort, such as when a person drives a car without thinking about the process.
Aerobic and anaerobic muscle activity
At rest, the body produces most of the ATP aerobically in the mitochondria without producing lactic acid or other grueling byproducts. During exercise, ATP production methods vary depending on the individual's fitness as well as the duration and intensity of the exercise. At lower activity levels, when exercise continues for long duration (a few minutes or longer), energy is generated aerobically by combining oxygen with carbohydrates and fats stored in the body. During higher intensity activities, with duration likely to decrease with increasing intensity, ATP production may shift to anaerobic pathways, such as the use of phosphate creatin and phosphate systems or anaerobic glycolysis. The production of biochemical aerobic ATP is much slower and can only be used for low-intensity exercise with long duration, but does not produce exhausting waste products that can not be removed immediately from the sarcoma and the body and produces a much larger molecule of ATP per fat or molecule carbohydrate. Aerobic training allows the oxygen delivery system to be more efficient, allowing aerobic metabolism to start faster. Anaerobic ATP production produces ATP much faster and allows near-maximal intensity training, but also produces large amounts of lactic acid that make high-intensity exercise unsustainable for more than a few minutes. The phosphate system is also anaerobic, allowing for the highest level of exercise intensity, but the intramuscular phosphaminestin deposits are very limited and can only provide energy for exercises lasting up to ten seconds. Recovery is very fast, with a full creatine store regenerated within five minutes.
Clinical interests
Many diseases can affect the muscular system.
See also
- The main system of the human body
References
External links
- Online Muscle Tutorial
- GetBody Smart Muscle system tutorial and quiz
- MedBio.info Use and form ATP in muscle
Source of the article : Wikipedia
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