Muscular System
Muscles are the key to movement and let’s face facts, movement is pretty cool. You can use complicated muscle combinations to dance, do sports, or play musical instruments. However you can also use muscles for simpler pleasures, such as lying back on the sofa and flicking your thumb over your button (the one on the TV remote control to change channels).
The job of muscle is to contract and in doing so they move. Different types of muscle do different jobs. Visceral muscle (also called smooth muscle) is inside organs like the stomach and intestines (to move food around the digestive system) and also in the blood vessels. Cardiac muscle is in the heart. Skeletal muscle (also called striated muscle) is the type that moves the skeleton (and the body) around. Visceral and cardiac muscle is not consciously controlled, while skeletal muscle can be consciously controlled – allowing singing, dancing and literature and many other wonderful things about being human (in your face jellyfish!).
Skeletal muscle fibres can be either type I (slow twitch) or type II (fast twitch). Type I fibres carry lots of oxygen and so are good for aerobic exercise that doesn't use big bursts of effort, such as long distance running. Type II fibres are opposite to this. This explains why if you watch a long distance runner they do lots of breathing, while a weight lifter holds a deep breath and then lifts. The runner is taking lots of oxygen for aerobic activity by the type I fibres. The weight lifter doesn't use much oxygen for anaerobic activity by the powerful, but easily tired, type II fibres (clearly I must have loads of type II fibres, cause I'm totally hench!).
Muscle fibres are bundled together and surrounded by a membrane called perimysium. This membrane allows nerves and blood to pass through the muscle. The bundles of fibres are called fascicles and these are bundled together and surrounded by a membrane called epimysium, to form muscle.
Muscle fibres are made up of myofibrils, which are made up of sections called sarcomeres, which are made up of proteins called myosin (a thick band) and actin (a thin band). Myosin and actin are arranged in overlapping layers.
The left and right edges of each sarcomere are identifiable (when viewed with an electron microscope) as dark bands, called Z lines. Where the myosin is layered is called the A band and this lies in the middle of the sarcomere, but not the whole length. Between the left (and right) of the A band and the Z line is the I band (not a trademark of apple corp). When muscle contracts, the A band stays the same length, while the I band shortens. This brings the Z lines closer together, contracting the muscle.
The detail of how muscle occurs can get quite complicated (meaning that I'm probably not clever enough to explain it in a simple way), but lets give it a whirl...
Muscle contracts when motor neurons (nerves inside the muscle) release a messenger chemical called acetylcholine. This has an effect that causes the release of calcium within the sarcomere, which removes a protein (called tropomyosin) from the head of the myosin and so allows the myosin to bind to the actin. An energy source chemical called ATP is present on the myosin and as this now breaks down to ADP and other chemicals. As the ADP and other chemicals are released, it caused the myosin to flex (which pulls the actin that the myosin has bound to) in a process called "the power stroke" (yep, I know its pretty cool, sounds like a wrestling move). Another ATP molecule then binds to the myosin, allowing it to detach from the actin and get ready to be used again. Calcium is then pumped out, allowing the tropomyosin to again cover the myosin head.
If you're interested, watching this clip can only help as this guy is really clear and also sounds so smooth that you could spread his voice on toast!
The job of muscle is to contract and in doing so they move. Different types of muscle do different jobs. Visceral muscle (also called smooth muscle) is inside organs like the stomach and intestines (to move food around the digestive system) and also in the blood vessels. Cardiac muscle is in the heart. Skeletal muscle (also called striated muscle) is the type that moves the skeleton (and the body) around. Visceral and cardiac muscle is not consciously controlled, while skeletal muscle can be consciously controlled – allowing singing, dancing and literature and many other wonderful things about being human (in your face jellyfish!).
Skeletal muscle fibres can be either type I (slow twitch) or type II (fast twitch). Type I fibres carry lots of oxygen and so are good for aerobic exercise that doesn't use big bursts of effort, such as long distance running. Type II fibres are opposite to this. This explains why if you watch a long distance runner they do lots of breathing, while a weight lifter holds a deep breath and then lifts. The runner is taking lots of oxygen for aerobic activity by the type I fibres. The weight lifter doesn't use much oxygen for anaerobic activity by the powerful, but easily tired, type II fibres (clearly I must have loads of type II fibres, cause I'm totally hench!).
Muscle fibres are bundled together and surrounded by a membrane called perimysium. This membrane allows nerves and blood to pass through the muscle. The bundles of fibres are called fascicles and these are bundled together and surrounded by a membrane called epimysium, to form muscle.
Muscle fibres are made up of myofibrils, which are made up of sections called sarcomeres, which are made up of proteins called myosin (a thick band) and actin (a thin band). Myosin and actin are arranged in overlapping layers.
The left and right edges of each sarcomere are identifiable (when viewed with an electron microscope) as dark bands, called Z lines. Where the myosin is layered is called the A band and this lies in the middle of the sarcomere, but not the whole length. Between the left (and right) of the A band and the Z line is the I band (not a trademark of apple corp). When muscle contracts, the A band stays the same length, while the I band shortens. This brings the Z lines closer together, contracting the muscle.
The detail of how muscle occurs can get quite complicated (meaning that I'm probably not clever enough to explain it in a simple way), but lets give it a whirl...
Muscle contracts when motor neurons (nerves inside the muscle) release a messenger chemical called acetylcholine. This has an effect that causes the release of calcium within the sarcomere, which removes a protein (called tropomyosin) from the head of the myosin and so allows the myosin to bind to the actin. An energy source chemical called ATP is present on the myosin and as this now breaks down to ADP and other chemicals. As the ADP and other chemicals are released, it caused the myosin to flex (which pulls the actin that the myosin has bound to) in a process called "the power stroke" (yep, I know its pretty cool, sounds like a wrestling move). Another ATP molecule then binds to the myosin, allowing it to detach from the actin and get ready to be used again. Calcium is then pumped out, allowing the tropomyosin to again cover the myosin head.
If you're interested, watching this clip can only help as this guy is really clear and also sounds so smooth that you could spread his voice on toast!