Describe how the muscle work in the human body
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The human body has over 600 skeletal muscles, which are responsible for various movements and functions. To understand how muscles work, it is important to know their structure and the process of muscle contraction.
The structure of a muscle begins with individual muscle fibers. These fibers are organized into bundles called fascicles, which are then surrounded by a layer of connective tissue called the perimysium. Multiple fascicles together form the whole muscle, which is surrounded by another layer of connective tissue called the epimysium.
Muscles are attached to bones via tendons, which allow for movement when muscles contract and relax. When a muscle contracts, it generates tension and pulls on the bones, causing movement around the joints.
Muscle contraction occurs through a process called the sliding filament theory. Within each muscle fiber, there are smaller units called myofibrils, composed of even smaller units called sarcomeres. Sarcomeres contain two types of protein filaments: thick filaments, made of myosin, and thin filaments, made of actin.
During muscle contraction, the myosin heads of the thick filaments attach to the actin filaments, forming cross-bridges. This process is driven by the release of stored energy in adenosine triphosphate (ATP), which is converted into adenosine diphosphate (ADP) and inorganic phosphate (Pi). The myosin heads pull on the actin filaments, causing them to slide past each other, which shortens the sarcomere.
To trigger muscle contraction, a signal is sent from the brain or spinal cord to the muscle fibers via motor neurons. These neurons release a neurotransmitter called acetylcholine at the neuromuscular junction, which stimulates the muscle fibers to contract.
Muscle contraction continues as long as there is sufficient ATP available. Once the stimulation ceases, the calcium ions responsible for triggering the contraction are reabsorbed into the sarcoplasmic reticulum, and the actin and myosin filaments slide back to their original positions, leading to muscle relaxation.
In summary, muscles work by contracting and relaxing through the interaction between actin and myosin filaments within the sarcomeres. The process of muscle contraction is regulated by signals from motor neurons and dependent on the availability of ATP.