In order for a computer to work, it needs to be plugged into a power source. Not only this, but the power source has to input actual power into the computer. Otherwise it may be plugged in, but it is still incapable of operating because there is nothing giving it life.
The human body is the same. The body needs to be plugged into the brain in order to function. As well, the body needs to breathe and take in food so it has the proper nutrients and oxygen. This ensures that the brain functions properly and thus can ensure the rest of the body works properly. The spinal chord and arteries may attach the brain to the rest of the body, but without these things there will still be no power for it to function. There must be a connection as well as an input of energy.
A branch cannot live apart from the tree. You cannot take a broken branch and plant it in the ground and expect it to grow. It must be attached to the root, which in turn must be attached to the ground. Being attached to the root gives the branch the input connection it needs, and being attached to the ground allows this input to take in the nutrients the branch needs to grow and thrive.
Finally, our minds work likewise. The fact that you are reading this proves that you have the input connection needed for your mind to function. But what are you taking into your mind? If you take in things that are worthwhile and edifying, your mind will be expanded and grow. If you take in nothing but junk, your mind will be poisoned. It will not prosper, but wither into dysfunction and uselessness.