Muscular System

 The muscular system is important in many ways. It contains tissues, controls movement, provides mass, and gives us strength. Without it, other functions would not work.

The earthworm's muscular system is special. It has two kinds: longitutinal, and circular. 

-Circular and longitutinal muscles help the worm move itself. It does this by squeezing all of its muscles forward. 

-As mentioned before, it also uses bristles (satae) to move. 

-Compared to other organisms, a worm has less muscles. We, for example, have muscles in our arms, and legs, while worms do not.
-A worm has an advantage when it comes to muscles because as the circular muscles move, the diameter of the worm's body is reduced, making its body thinner. A human, for example, cannot do this. When the worm does this, it becomes smaller, which is good to fit into smaller places, and to not be seen. 

The crayfish has muscles everywhere. 

-The telson or urapod help the crayfish swim backwards. This is advantageful because without this muscle, the crayfish wouldn't be able to look at its predator, behind it. Also, it can escape quickly. 

-Unlike the worm, the crayfish has muscles everywhere; in its legs, tail, and body. This helps with locomotion. 

-Muscles fill up the entire abdomen of the crayfish. The extensor is what makes the tail straight, and the flexor is what curls it up.

-Having lots of muscle in its legs is an advantage. This is because it can walk, or crawl, faster. This is helpful when running from prey. This is similar in swimming. With more muscles in the tail, it can swim away faster.
-An advantage to having a lot of muscles is that it can be damaged easily. They can be used for defense, but can be damaged while trying to fight. 

The frog is next. 

frog's abdominal muscles

-Like humans, the frog's muscles are attached to its bones. This makes a full range of motion, controlled by our skeleton.

-In order to move, the muscles must contract, shorten, and relax.

-The strongest muscles in the frog's body are in its legs, and abdomen, just like a crayfish. The legs have a lot of muscle because they are needed to jump long distances.

-The abdomen has strong muscles because when a frog jumps, it lands on its abdomen. If it wasn't strong, bones would break as it lands. This was probably different before. Before, the frog probably had a weaker abdomen, and as time passed, frogs evolved stronger abdomens because of
its use.
-One disadvantage to the frog's muscles is that the lower back legs aren't meant to bend the way a human's is. This means it can't walk, or run, or skip. That's right: you can't play hop scotch with it. Anyways, this is bad because it can't get very far in a short amount of time. This makes it easier to get caught.

The rat's muscles are simple. 

-The rat's muscles work in groups. Some move in and some move out.

-The rat is flexible. This means less injury. This is an advantage. The less injury you have, the less risk of dying you'll have.

-The rat has a group of muscles that are on its shoulder. Unlike the human, who has one.

-The rat's muscles are similar to ours and the frog's because they need oxygen to contract, and move. The rat's thigh muscle (biceps femoris) is similar to ours. They both form knee flexion. 

Finally, the human.

taken from the Holt, Rinehart, and Winston biology textbook

-The human obviously has some differences compared to the other organisms. 

-Us humans have a gluteus maximus. This is not only your butt, but a strong, hip extening muscle. This is essential in running, and walking. 

-We also have arms to move, unlike the worm. This is all thanks to the deltoid muscle. The deltoid is our shoulder muscle, which control the movement in our shoulder, and also lets our arms move in rotation. 

-Lastly, we have a muscle called vastus lateralis. This muscle is just above our knee. It allows us to move our knee. Most animals *cough cough worm cough* don't have knees. An advantage to having them would be running. Running can help you escape from prey, and get you places faster. A disadvantage is that like other muscles, it can get injured easily.