The hypothalamus-Subdivision-Connections-Applied anatomy-NotesMed

What is the hypothalamus?

The hypothalamus is a part of the diencephalon located below the thalamus. It settled the sidewalls and floor of the third ventricle in the brain. The hypothalamus is a paired and bilateral structure weighing about 4 gm.

Boundaries of the hypothalamus

The boundaries of the Hypothalamus:

• Superiorly: It bounded by the hypothalamic sulcus from the thalamus.
• Inferiorly: It is bounded by the floor of the third ventricle such as optic chiasma, tuber cinereum, and mamillary bodies, median eminence-a small swelling immediately behind the infundibulum.
• Anteriorly bounded by lamina terminalis (extends from the optic chiasma to the anterior commissure).
• Posteriorly bounded by the tegmentum of the midbrain.
• Medially bounded by the third ventricle.
• Laterally bounded by the internal capsule.

The floor and lateral wall of the third ventricle below the hypothalamic sulcus. It expands anteriorly to the lamina terminalis and posterolaterally to the subthalamus. The column of the fornix traverses through the hypothalamus in the sagittal plane –medial and lateral zones.

Subdivisions and nuclei 

• In the sagittal plane: three regions
  • Anterior(supraoptic)
  • Middle (tuberal)
  • Posterior(mamillary)
• In the coronal plane: three regions
  • Lateral
  • Medial
  • Periventricular
• The medial zone subdivided into
  • Suprachiasmatic region
  • Tuberal and mammillary regions.
• Lateral zone –Few nerve cells and many nerve fibers, most of them running in the longitudinal direction.

Connections in the hypothalamus

Afferent connections

• Dorsal longitudinal fasciculus,  medial forebrain bundle both containing efferents also, stria terminalis from the amygdala,  fornix.
  • Dorsal longitudinal fasciculus: contains both ascending and descending fibers connecting the brain stem reticular formation with the hypothalamus.
  • Medial forebrain bundle: contains ascending and descending fibers from the septal area and olfactory area-emotional drive and sense of smell.
  • Stria terminalis: Amygdaloid nucleus—preoptic and anterior hypothalamic nuclei
  • Fornix –the hippocampus—mammillary bodies of the hypothalamus.

Efferent connections

• Two main descending pathways from the hypothalamus
  • Medial longitudinal fasciculus
    • Originate mainly from the paraventricular nucleus to
    • Dorsal motor nucleus of the vagus
    • Salivatory and lacrimal nuclei
    • Autonomic nuclei in the spinal cord.
  • Mammilotegmental  fasciculus
    • Collateral branches from mamillothalamic fasciculus to the Reticular formation of midbrain and pons.

Functions of the hypothalamus

• Autonomic control
• Endocrine control
• Neurosecretion: (oxytocin and vasopressin)
• Regulation of food and water intake
• Emotional expression
• Sexual behavior and reproduction
• Temperature regulation
• Biological clock

Applied anatomy

• Diabetes insipidus
• Obesity
• Somnolence
• Loss of  temperature  regulation
• Loss of sexual desire
• Disorders of fat and carbohydrate  metabolism

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