Here's why:

* Organ: An organ is a self-contained structure made up of different tissues that work together to perform a specific function. Examples include the heart, lungs, and stomach.

* Tissue: A tissue is a group of similar cells that work together to perform a specific function. Examples include muscle tissue, nervous tissue, and epithelial tissue.

* Neuron: A neuron is a single, specialized cell that transmits electrical and chemical signals throughout the body. It is the basic functional unit of the nervous system.

So, while neurons are found within nervous tissue, they are not tissues themselves.