How can a nucleus of a few tens of thousands of neurons supply noradrenaline to the whole cortex? · Grey Matter

Stereological counts find about 16,000 neurons on each side of the human locus coeruleus (roughly 12,000 to 25,000 per side), and counts of the pigmented cells give totals of about 22,000 to 51,000.

How can a nucleus of a few tens of thousands of neurons supply noradrenaline to the whole cortex?

Stereological counts find about 16,000 neurons on each side of the human locus coeruleus (roughly 12,000 to 25,000 per side), and counts of the pigmented cells give totals of about 22,000 to 51,000. Each of these neurons has an axon that branches enormously, running through the forebrain and cerebellum and releasing noradrenaline from swellings (varicosities) all along its length, often away from classical synapses. Noradrenaline then diffuses and acts on receptors over a wide volume. The design suits a state signal: a small, internally coupled population can switch the whole brain toward alertness at once, at the cost of saying little about any specific place.