The Hypothalamus

  • It forms the lateral wall and floor of third ventricle.
  • Parts of the hypothalamus visible on the base of the brain include the infundibulum, tuber cinerium and mamillary bodies.
  • Tuber cinerium is the floor between the the infundibulum and mamillary.
  • The hypothalamus is divided by fibers of the fornix into medial and lateral nuclear groups.
  • Three rostrocaudal regions: Supraoptic, Tuberal and Mamillary are described.
  • The zone forming the floor of the third ventricle is the median eminence.

Connections of hypothalamus

  • Medial forebrain bundle
  • Hippocampal-hypothalamic fibres.
  • Commissural fibers of fornix.
  • Amygdalo-hypothalmic fibers (striae terminalis)
  • Brainstem recicular afferents.
  • Retinohypothalamic fibers.
  • Mamillary efferents.
  • Descending hypothamic fibres.
  • Efferents to suprachiasmatic.
  • Supraoptic-hypophysial.

 

 

Functions of hypothalamus:
  • Control of involuntary actions, expressions, behaviour associated with emotions, rage, pain, sexual arousal, feeding.
  • Coordination of parasympathetic autonomic function.
  • Coordination of sympathetic autonomic function.
  • Control of temperature (mechanisms for this include dissipation and production of heat, in anterior and posterior regions).
  • Body water balance.
  • Coordination of activities of anterior pituitary gland.
  • Secrete hormones e.g. ADH, oxytocin, releasing hormones.
  • Regulation of satiety destruction may be associated with hyperphagia and obesity.

Connections of the hypothalamus

Input: Output
Neural
  Neural
  1. From the hippocampal formation via the formix.
  2. Amygdaloid nucleus (ventral amygdaloid path)
  3. Orbitalfrontal cortex
  4. Mid-line thalamic nuclei
  5. Retina
  6. Basal fore brain and septal region (via medial fore brain bundle)
  7. Reticular formation
  8. Cerebellum

    ii)     


  1. The anterior thalamic neuclei (mamillothalamic tract)
  2. Mid brain reticular formation (Mamillotegmental tract)
  3. Amygdaloid nucleus (the ventral amygdaloid path)
  4. Brain stem and spinal cord autonomic centres (hypothalamo-bulbar/spinal)
  5. Cerebellum.

 

 

   Humoral
Humoral
This is vascular.  Through this, various hypothalamic neurons get stimulated chemically (e.g. by glucose or hormones) or physically (e.g. by temperature)
This influences the endocrine system directly, by secretion into the general circulation, and indirectly by secretion into the hypophyseal portal system.
   

 
 

Functions of specific nuclei:
Nucleus
Function

Supraoptic

Production of ADH

Paraventricular

Production of Oxytocin

Medial/anterior

Coordination of parasympathetic activity.

Lateral/posterior

Body temperature regulation.

Preoptic

Production of releasing hormones to pituitary

Tuberal

Control of heart rate and blood pressure.

Autonomic center

Control of feeding, continues with grey regions of basal olfactory.

Mamillary

Region, septal region and substantia innominata.

Suprachiasmatic

Receives inputs from retina

 


Reproduction and sexual functions are influenced by preoptic and ventro medial nuclei.
Eestrogen – sensitive and androgen – sensitive neurons in these areas elicit the production of appropriate hormones that regulate production and release of pituitary gonado tropins.  Hypothalamic lesions can cause menstrual cycle disturbances or precocious puberty.

Sleep and the sleep-wake cycle are influenced by several areas.  The suprachiasmatic nucleus, which receives input from the retina is the biological clock that plays a role in circadian rhythms of approximately 24 hours.  The pre-optic area can induce sleep and lateral hypothalamic area is involved in cortical arousal.

The expression of emotions such as anger, fear, embarrassment, occurs through hypothalamic connections with appropriate brain stem and spinal cord centres.The hypothalamus has reciprocal connections with the nuclei associated with behaviour such as the amygdaloid nuclei and the medial dorsal thalamic necleus.