In my life I’m constantly busy doing different things especially at this time of year. From going to school, then cross country, going home quickly eating, come back to school and going to band. Then to go to home eat and then finally crack down on homework. From all this walking and running around we don’t think much of it , other than your muscles felling soar at the end of the day, but really there’s more to a muscle then what I thought. For example we’ll use the calf muscle ( gastrocnemius).
This muscle is connected to the bone by a tendon which is connected to the epimysium. It then breaks down to the fascicles and finally to the muscle fiber ( cell) inside of the muscle fibers of the myofibril, inside of that is the those and thin filements. The thin filament is called actin and the thick filament called myosin. The actin is connected to the z line. the actin and myosin stick up in between each other, the myosin has two separate actin filaments on the ends of it, this whole little section is called sarcomeres. n the muscle fiber these sections of sarcomere pair up next to each other so that the connection takes place. Now to go more in depth. Muscle contractions start when a nerve impulse is initiated. Motor neurons which doesn’t make contact with the muscle but leaves a gap In between called a synaptic cleft. When stimulus reaches the synaptic cleft, a chemical is released. This is called a neurotransmitter,the neurotransmitter used in muscle contractions called, acetylcholine ( Ach).
The Ach diffuses across the synaptic cleft and makes contact with the sarcolemma (muscle cell membrane). When Ach makes contact with the sarcolemma, a contraction wave spreads throughout the muscle cell. A muscle tubes going through it, these tubes are called sarcoplasmic reticulum (SR). The function of the SR is to store and release calcium ions (Ca) into the muscle. This is very crucial to the contraction process. As the wave spreads, the SR becomes permeable to Ca, releasing it into the surrounding myofibrils, actin, and myosin.
The presence of Ca ions causes cross bridge formation meaning the myosin heads attach to the actin filaments. Instantly, in one motion, the myosin heads flex inward, making the sarcomere shorter. In order for a full contraction, the cross bridges must break, with the use ATP, then reattach, flex, and break again and again over and over until the muscle is fully contracted. To be able to relax your muscle and stop the contraction, your body must stop the flow of ACh by using an enzyme called cholinesterase. Ca ions must be actively pumped out, sing even more ATP, back into the sarcoplasmic reticulum. The reason this has to be done is in the presence of Ca ions the cross bridges will remain. So if you take the Ca out then the cross bridges cannot form, causing the muscle can relax. The phenomenal thing about this is your body instantly does this, and in seconds this whole process can be started contracted and then over with. Your body continuously does this whether it be running, marching, or walking you rely on your body to contract your muscles and release them when you expect them to.