Nervous system
Body system picture:
Body system function: The nervous system helps you sense whether you are in trouble or if you want to do something. This is outside of your body but the nervous system also works inside the body. The nervous system helps start process like the digestive system and if you start to eat the nervous system tells the digestive system process to start. This happens without you even knowing but on the outside you know it happens. The nervous system works with the brain so you would know if something will hit you or so a system can start it's process.
Organs: First is the brain which has a lot of different parts that help it function. The main 5 parts of the brain are the cerebrum, the cerebellum, the brain stem, the pituitary, and the hypothalamus. The cerebrum helps you to do things like move your hands and feet. There are 2 halves of the cerebrum, the left side helps you do your work like math and reading. While the right half is all about what you enjoy and colors. The left half of the cerebrum also controls the right side of your body while the right half of the cerebrum controls the left side of your body. After the cerebrum there's the cerebellum which is below and in the back of the cerebrum. The cerebellum helps you with your movement and how you balance. It also helps with your coordination of how your muscles work together. The cerebellum also helps you move around like when you're surfing on a surf board and if you don't have a cerebellum then you won't be able to balance, move, or surf. After is the brain stem and is under the cerebrum and is in front of the cerebellum. The brain stem connects the brain to the spinal cords that run down your back and throughout your body. The brain stem is also in charge of all the functions in your body like digest your food or to breath. It also helps your involuntary muscles function or the ones that your can't control like the heart and it gives the brain messages from other parts of the body. It does the same thing with the brain, it gives messages from the brain to your body parts. Then there's the pituitary which is only as small as a pea and hormones come from it. Those hormones help you to grow and the pituitary helps a lot in puberty when both girls and boys become men and women. Lastly there's the hypothalamus helps you stay at your temperature. Sweating and shivering are both caused by the hypothalamus so you can either get warmer (shivering) or get cooler/colder (sweating).
One organ function: Do you wonder where your emotions come from because they come from the brain which has little cells called amygdala. The amygdala help you feel emotions such as anger, sadness, happiness, shock, fear, and many others.
Interactions with other systems: The nervous system interacts with all of the other systems because they need to know what to do and since the brain is part of the nervous system along with the brain stem which is connected to the spinal cords your body knows what to do. The nervous system sends signals to your muscles so they know what to do. It also connects with other organs that your don't even know your body has (voluntary muscles).
Analogy:
Analogy image: 
Analogy explantation: A radio tower is like the nervous system because the nervous system tells the body instructions on what to do through the spinal cord. Then a radio station sends radio signals to radios in the world. The broadcast could include ad commercials and the ad commercials tell the people who are listening who to call or where to go to buy their product. This is similar to how the nervous system transports messages through the spinal cord to other organs or systems. Radio towers broadcast a signal which is then picked up by radios around the world and then people can hear what the broadcasters are saying.
Redesign: A way to redesign the nervous system is to make the brain stem stronger so it can support the weight of your brain better. Also if the skeletal system can't protect the brain stem then if the brain stem is stronger it would be able to withstand a hit to the neck/head.
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