Sunday, May 18, 2008

"Sky-blue place" II: Projections

In reference to: Locus Ceruleus: "Sky-blue place";

Noradrenergic neurons of LC project to:

1. thalamus
-especially anteroventral nucleus

2. hypothalamus nuclei (although most noradrenergic projections in this area come from norepinephrine-containing cells in the medulla)

3. hippocampus
noradrenergic activation of the hippocampus may facilitate long-term memory of distressing events

4. septal area
-basal nucleus of the stria terminalis
-central and basolateral nuclei of amygdala
-olfactory bulb

5. cerebellum

6. neocortex

7. several brainstem nuclei thought to function as primary sensory or association centers

Some features of this projection system

Apparently the arborization is very extensive - very few cells project very widely. This means that this little sky-blue spot has a lot of leverage. It doesn't take very many cells to get a big effect if those cells have a multiply-branched communication system in place.

It must be emphasized that this system is entirely inside the brain and spinal cord. LC directs its messaging only to other brain parts. It stays away from the body department - leaves communication of alerting and alarming to a different system; it does not project much directly to sympathetic preganglionic neurons, and probably participates only indirectly in regulation of sympathoneural outflow. Its job seems to be to "alarm" the hypothalamus which in turn "alarms" the adrenals which then prepare the body for an encounter with danger.

It might seem roundabout to have different systems running different parts differently, but a lot of things in the nervous system work like this. Bits that evolved ahead of other bits kept their operating systems and merely linked up to or completely enclosed other systems. They all still work, in parallel, separately and together. And it's not so bad from an organism point of view. Better for survival to have many systems (in case one should be knocked out) than to rely completely on just one perfected one.

The LC doesn't just magically know what's going on outside - special senses are involved, and must register input which must in turn be relayed to the LC before the LC can perform its alarm bell duty. So, next, I'll address where the LC gets its information from.


*Innervation that travels from one part of the brain to another part or parts.

**"Noradrenergic"refers to a neurotransmitter, noradrenaline, also called norepinephrine, that stimulates a nervous system out of ordinary function into super function. (Here is a wikipedia entry about it.) In the brain it is thought to be recycled out of another neurotransmitter called dopamine. In the body it is secreted by the adrenal glands (which sit on top of the kidneys).


1. Handbook of Clinical Neurology: The Autonomic Nervous System Part I, Elsevier 2000, Appenzeller O., Vinken PJ, Bruyn GW, p. 155

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