Hypothalamic nuclei

The entire hypothalamus contains scattered neurons within which some aggregations can be recognized. These aggregations, termed the hypothalamic nuclei, are as follows (Figs. 13.16 to 13.18).

1. The preoptic nucleus extends through the periventricular, intermediate, and lateral zones of the preoptic part.

2. The mamillary nuclei lie within the mamillary body.

The remaining nuclei of the hypothalamus lie either in the periventricular, intermediate, or lateral zones. As the boundaries of nuclei are ill defined, different authors have allocated nuclei differently to these zones. To lessen confusion on this account we will consider the periventricular and intermediate zones collectively as the medial zone.

It has also been found that groupings of hypothalamic nuclei based on functional considerations do not necessary follow groupings according to the regions they lie in. The classification that follows is based on traditional teaching, and some comments on functional groupings are made below.

Nuclei in the medial zone

3. The paraventricular nucleus, and

4. thesuprachiasmatic nucleus, lie in the supraoptic region.

5. The arcuate (or infundibular) nucleus lies in the tuberal region.

6. The posterior nucleus extends into both the tuberal and mamillary regions.

7. The anterior nucleus occupies the supraoptic region.

8. The dorsimedial nucleus, and

9. the ventrimedial nucleus lie in the tuberal part, which also contains small aggregations of cells that constitute

10. thepremamillary nuclei.

Nuclei in the lateral zone

11. The lateral zone contains a diffuse collection of cells that extend through the supraoptic, tuberal and mamillary regions. These cells constitute the lateral nucleus.The lateral zone also contains the following nuclei.

12. The supraoptic nucleus lies in the supraoptic region (just above the optic tract).

13. The tuberomamillary nucleus extends into the tuberal and mamillary regions.

14. Small aggregations of neurons in the tuberal region constitute the lateral tuberal nuclei

Some additional comments on grouping of hypothalamic nuclei

1. On the basis of functional considerations the supraoptic and tuberomamillary nuclei (of the lateral zone) are grouped along with nuclei in the medial zone.

2. The anterior nucleus is not mentioned in some recent texts. Instead a group of intermediatenuclei is described in this situation.

Neuromediators in the Hypothalamus

As many as 25 neuromediators have been located in the hypothalamus, and their distribution has been mapped out. The details are beyond the scope of this section.