How do we view unobservables like our brains which are composed of matter and particles which have a Quantum constituent

 Terms such as ‘sub-atomic particle’ and ‘particle too small to see’ are perfectly meaningful and should be taken literally 

On the other hand,  it is perfectly rational to remain agnostic about whether there are any such particles because it is  argued that to accept the best scientific theories we have only requires believing that they are empirically adequate, in the sense of correctly describing the observable world, rather than believing that they are true simpliciter. (unconditionally)

How do we view  unobservables (our BRAINS are composed of quantm type (matter) unobservables) 

and if so,,,operate in a Quantum manner.