One losing head by Russian river? It's to do with nerves (6)
I believe the answer is:
neural
'to do with nerves' is the definition.
(I've seen this before)
'one losing head by russian river?' is the wordplay.
'losing head' means to remove the first letter.
'by' says to put letters next to each other.
'russian river?' becomes 'ural' (I've seen this in other clues).
'one' with its first letter taken off is 'ne'.
'ne'+'ural'='NEURAL'
'it's' is the link.
(Other definitions for neural that I've seen before include "To do with nerve of unreal kind" , "Nervy" , "Relating to nerves" , "Relating to the nervous system" , "Relating to a nerve" .)