Nomadic tribesman controlling vital area? (9)

I believe the answer is:

brainstem

I'm a little stuck... Click here to teach me more about this clue!

'controlling vital area?' is the definition.
The answer and definition can be both body parts as well as being singular nouns.
Perhaps they are linked in a way I don't understand?

'nomadic tribesman' is the wordplay.
'nomadic' indicates anagramming the letters.
'tribesman' is an anagram of 'BRAINSTEM'.

Can you help me to learn more?

I've seen this clue in The Independent.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.