Final answer:
The true statement about any communication system is that a signal must always be sent and received, involving either electrical or chemical signals for communication within the body.
Step-by-step explanation:
The true statement about any communication system is that a signal must always be sent and received. This is a fundamental aspect of communication in both biological systems and man-made technologies. In biological terms, this involves the use of electrical and chemical signals for communication within the body. Neurons, for example, communicate through electrical and chemical signals, whereas the endocrine system communicates through chemical signals, specifically hormones, which can have a wide range of effects and durations of action.
It's important to note that while neurons are essential for neural communication, they are not involved in all forms of communication. Similarly, the endocrine system is not always involved, especially in non-biological communication systems. Additionally, while electrical signals are a key part of neuronal communication, signals can also be chemical in nature, as seen with hormonal communication in the endocrine system or even non-biological systems like digital signals in technology.