Overview
Neurons are the cells which transmit information in the nervous system of an animal so that it can sense stimuli coming from its environment and behave accordingly. Not all animals have neurons; Trichoplax and sponges lack nerve cells altogether.
Neurons may be packed to form structures such as the brain of vertebrates or the neural ganglions of insects.
The number of neurons and their relative abundance in different parts of the brain is a determinant of neural function and, consequently, of behavior.
Read more about this topic: List Of Animals By Number Of Neurons