Close what's caught up in mixed nerve (3)
I believe the answer is:
end
'close' is the definition.
(thesaurus)
'up in mixed nerve' is the wordplay.
'up' shows that the letters should be reversed in order (in down clue: letters go upwards).
'in' indicates the answer is hidden within the clue.
'dne' is hidden within 'mixed nerve'.
'dne' backwards is 'END'.
'what's caught' is the link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for end that I've seen before include "Butt" , "Purpose, objective" , "Bring to a conclusion" , "border?" , "Finish; goal" .)