Bundle of nerves totalled old car on short trip (6,4)

I believe the answer is:

spinal cord

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'bundle of nerves' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.

'totalled old car on short trip' is the wordplay.
'totalled' becomes 'spi' (I can't explain this - if you can you should give a lot more credence to this answer).
'short' means to remove the first letter.
'trip' is an anagram indicator.
'old'+'car'+'on'='oldcaron'
'oldcaron' with its first letter removed is 'ldcaron'.
'ldcaron' with letters rearranged gives 'nalcord'.
'spi'+'nalcord'='SPINAL CORD'

Can you help me to learn more?

I've seen this clue in The Telegraph.

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