Fact 1: Neurons are the structural and functional units of the nervous system.

Fact 2: Glial cells perform critical functions in the nervous system.

Given the two facts above, answer the question "Neurons are the structural and functional units of where what is critical?" with the following options: 
- organs
 - Glial cells
 - nerves
 - Structural units
 - voltage
 - Storage units
 - Critical care
 - A computer


 

  Glial cells       