The Muscular System

I- What is a Muscular System? 

1. The muscular system is an organ system consisting of skeletal, smooth and cardiac muscles. It permits movement of the body, maintains posture, and circulates blood throughout the body. Attached to the bones of the skeletal system are about 700 named muscles that make up roughly half of a person’s body weight. Each of these muscles is a discrete organ constructed of skeletal muscle tissue, blood vessels, tendons, and nerves. Muscle tissue is also found inside of the heart, digestive organs, and blood vessels. In these organs, muscles serve to move substances throughout the body.
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3. This is the link of the video: http://www.teachertube.com/video/muscular-system-video-41621
4. II- Different Types of Muscles:

There are three types of muscle tissue: Visceral, cardiac, and skeletal.

1. Visceral Muscle. Visceral muscle is found inside of organs like the stomach, intestines, and blood vessels. The weakest of all muscle tissues, visceral muscle makes organs contract to move substances through the organ. Because visceral muscle is controlled by the unconscious part of the brain, it is known as involuntary muscle—it cannot be directly controlled by the conscious mind. The term “smooth muscle” is often used to describe visceral muscle because it has a very smooth, uniform appearance when viewed under a microscope. This smooth appearance starkly contrasts with the banded appearance of cardiac and skeletal muscles.
    
2. Cardiac Muscle. Found only in the heart, cardiac muscle is responsible for pumping blood throughout the body. Cardiac muscle tissue cannot be controlled consciously, so it is an involuntary muscle. While hormones and signals from the brain adjust the rate of contraction, cardiac muscle stimulates itself to contract. The natural pacemaker of the heart is made of cardiac muscle tissue that stimulates other cardiac muscle cells to contract. Because of its self-stimulation, cardiac muscle is considered to be autorhythmic or intrinsically controlled. 
   
   The cells of cardiac muscle tissue are striated—that is, they appear to have light and dark stripes when viewed under a light microscope. The arrangement of protein fibers inside of the cells causes these light and dark bands. Striations indicate that a muscle cell is very strong, unlike visceral muscles. 
   
   The cells of cardiac muscle are branched X or Y shaped cells tightly connected together by special junctions called intercalated disks. Intercalated disks are made up of fingerlike projections from two neighboring cells that interlock and provide a strong bond between the cells. The branched structure and intercalated disks allow the muscle cells to resist high blood pressures and the strain of pumping blood throughout a lifetime. These features also help to spread electrochemical signals quickly from cell to cell so that the heart can beat as a unit.
    
3. Skeletal Muscle. Skeletal muscle is the only voluntary muscle tissue in the human body—it is controlled consciously. Every physical action that a person consciously performs (e.g. speaking, walking, or writing) requires skeletal muscle. The function of skeletal muscle is to contract to move parts of the body closer to the bone that the muscle is attached to. Most skeletal muscles are attached to two bones across a joint, so the muscle serves to move parts of those bones closer to each other. 
   
   Skeletal muscle cells form when many smaller progenitor cells lump themselves together to form long, straight, multinucleated fibers. Striated just like cardiac muscle, these skeletal muscle fibers are very strong. Skeletal muscle derives its name from the fact that these muscles always connect to the skeleton in at least one place.

click on the following link for a clearer image: http://coloringpagesjos.net/wp-content/uploads/2015/404021-muscle-muscular-system-diagram.jpg

Fun Facts about the Muscular System

1- The word muscle is derived from the Latin term musculus, meaning "little mouse". This Latin term could be due to the shape of some muscles or because muscles contracting under the skin can look like a mouse moving under a rug.

2- Skeletal muscle can be further divided into two types, slow twitch and fast twitch.

3- Slow twitch (Type I) muscle contain proteins that give it a rich red color. This muscle carries more oxygen efficiently and using fats, proteins or carbs as energy slow twitch muscle fibers contract over a long period of time. 

4- Therefore type I muscle fiber works well for aerobic sports such as long distance running and cycling.

5- Fast twitch (Type II) muscle is whiter in color as it has less myoglobin (a oxygen carrying protein). Fast twitch fibers contract quickly and powerfully, however they fatigue rapidly.

6- Therefore type II muscle fiber is useful for anaerobic exercise such as sprinting or for strength sports like weightlifting.

7- It takes 17 muscles in the face for us to smile and 43 muscles to frown.

8- The tongue has 8 muscles, so is technically not the strongest muscle in the body.