Conclusion

The nervous system is made up of many neurons, each carrying different types of information. The pattern of electrical activity in a neuron has a specific meaning depending on the identity of the neuron. For example, a sensory neuron that receives touch information from a specific part of the body carries that information to the brain, forming a “labelled line.” This principle applies even in a simple animal like the leech. As you have seen, in the leech, three different cell types respond to touch sensation and carry this information to the rest of the nervous system.