Chapter 13 Diencephalon: Thalamus and Hypothalamus


■ a periventricular nucleus. ■ contains neurons that produce hypothalamic-releasing factors and gives rise to the tuberohypophyseal tract, which terminates in the hypophyseal portal system of the infundibulum. ■ effects, via hypothalamic-releasing factors, the release or nonrelease of adenohy pophyseal hormones into the systemic circulation. ■ contains dopaminergic neurons; dopamine is the prolactin-inhibiting factor ( PIF ). a. Mammillary nuclei ■ lies superior to the mammillary bodies. ■ receive input from the hippocampal formation via the fornix . ■ receive input from the dorsal and ventral tegmental nuclei and the raphe nuclei via the mammillary peduncle. ■ project to the anterior nucleus of the thalamus via the mammillothalamic tract. ■ contain hemorrhagic lesions in Wernicke encephalopathy. b. Posterior nucleus ■ plays a role in thermal regulation (ie, conservation and increased production of heat). ■ lesions result in poikilothermia , the inability to thermoregulate.

4. Mammillary region


■ characterized by mostly reciprocal connections.

A. Afferent connections to the hypothalamus ■ derive from the following structures:

1. Septal area and nuclei and orbitofrontal cortex ■ via the medial forebrain bundle.

Mediodorsal nucleus

Medial forebrain bundle


Orbitofrontal cortex Septal nuclei

Periaqueductal gray

Mammillary peduncle

Septal area

Medial forebrain bundle

Dorsal tegmental nucleus Ventral tegmental nucleus

Corticohypothalamic fibers

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Amygdaloid body

FIGURE 13.6. Major afferent (input) connections of the hypothalamus. The fornix projects from the hippocampal formation to the mammillary bodies. The medial forebrain bundle conducts both afferent and efferent fibers.

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