Muscular system
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A: What is the muscular system?
B: The muscular system is made of three main muscle types
A: What are those types?
B: First, skeletal muscle, which attaches via tendon to our bones. Second, cardiac muscle, which is only found in the heart. Third, smooth muscle, which lines the blood vessels and certain organs like the intestine and uterus
A: How do these muscle types work?
B: They are made of muscle cells, also known as fibers, bundled tightly together. These bundles receive signals from the nervous system that contract the fibers, which in turn generates force and motion. This produces almost all the movements we make
A: Are all movements similar?
B: No. Muscle contraction can be split into three main types. The first two, shortening muscle fibers and lengthening them, generate opposing forces. The biceps will shorten while the triceps will lengthen or relax, pulling up the arm and making it bend at the elbow. This allows you to, say, pick up a book. If the muscle relationship is reversed, you put it down. This complementary partnership exists throughout the muscular system
A: What is the last contraction type?
B: It creates a stabilizing force. In these cases, the muscle fibers don’t change in length, but instead keep the muscles rigid. This allows you to grip a mug of coffee or lean against the wall. It also maintains the posture by holding you upright
A: How about muscle types? How do they work?
B: Skeletal muscles form the bulk of the muscular system, make up about 30-40% of the body’s weight, and generate most of its motion. You may know some muscles of this type like the pectorals and the biceps. Skeletal muscles are connected to the somatic nervous system, which gives you almost complete control over their movements. This muscle group also contains two types of muscle fibers to refine our motions even further, slow-twitch and fast-twitch
A: What are these two fiber types?
B: Fast-twitch fibers react instantly when triggered, but quickly use up their energy and tire out. Slow-twitch fibers, on the other hand, are endurance cells. They react and use energy slowly, so they can work for longer period
A: Okay, I understand what skeletal muscles are and their fiber types. Are cardiac muscles and smooth muscles also managed by the somatic nervous system like skeletal muscles?
B: No. They are managed by the autonomic nervous system, beyond your direct control. That makes your heart thump roughly 3 billion times over the course of your life, which supplies the body with blood and oxygen. Autonomic control also contracts and relaxes smooth muscle in a rhythmic cycle. That pumps blood through the smooth internal walls of blood vessels, enables the intestine to constrict and push food through the digestive system, and allows the uterus to contract when a person is giving birth
A: That’s interesting
B: Actually, there is one more interesting fact about muscle. Do you want to know?
A: Yes
B: As muscles work, they also use energy and produce an important byproduct, heat. In fact, muscle provides 85% of your warmth, which the heart and blood vessels then spread evenly across the body via the blood. Without that, you couldn’t maintain the temperature necessary for your survival