Neurons vary in the amount of information they receive and transmit. Some have an extremely large social circle and receive and transmit thousands of messages. Others have only a few connections. All messages, however, are passed to connected neurons in the form of chemicals called neurotransmitters. They flow from a message-sending neuron across a gap called a synapse and onto target neurons.
Many scientists compare the union to a key fitting in a lock.
The signals are in the form of charged particles or ions. A large concentration of positively-charged particles entering a receiving neuron tells it to pass on the message. On the other hand, a large concentration of negatively-charged particles entering the neuron will inhibit it from passing on the message. The brain keeps tight control of this message delivery system to avoid communication chaos. A single receiving neuron has thousands of receptor sites and may receive many different messages and passwords at once.