Temperature found in nerve cell particle (7)
I believe the answer is:
neutron
'particle' is the definition.
(neutron is a kind of particle)
'temperature found in nerve cell' is the wordplay.
'temperature' becomes 't' (abbreviation).
'found in' means one lot of letters goes inside another.
'nerve cell' becomes 'neuron' ('neuron' can be a synonym of 'nerve cell').
't' going into 'neuron' is 'NEUTRON'.
(Other definitions for neutron that I've seen before include "one's not charged" , "On tuner (anag.)" , "Uncharged subatomic particle" , "Uncharged particle in a nucleus" , "tiny amount" .)