The nervous system, which branches out into the central nervous system and the peripheral nervous system. Nerves that transmit signals from the brain are called motor nerves, while nerves that transmit information from the body to the central nervous system are called sensory(peripheral) nerves.
In the peripheral nervous system there is also the enteric nervous system which functions the gastrointestinal system. It's in here, the gastrointestinal system - where if we feel like something is not right we state that 'I felt something in my stomach'. Or, I feel queezy, like something is not right.
Within the body, the musculoskeletal system is the mechanical interface(MI) to the nervous system.
Nerves should be able to slide and glide freely to reach their destination so as to connect with the end point and come back freely so messages are relayed easily. If the pathway is not moving freely it can interfere with the message relay. Doesn't mean it's not working, just it might not be working as fluently and could be interfering with the messages getting to the tissue/s and muscle/s. If the connections are working, then the body is not working to it's full capacity and restrictions occur.