1. CHAPTER 17 The Hypothalamus: Vegetative and Endocrine Imbalance

2. General Features of Hypothalamic Function
Controls visceral activity
Output of emotions from limbic system
Neural and endocrine functions exerted via axonal pathways and vascular system
Functions include self-preservation (such as eating and drinking) and preservation of the species (reproduction)
Involved in water balance, food intake, endocrine control, reproduction, sleep, behavior, output of endocrine system

3. Hypothalamus: Inferior and Midsagittal Views

4. Coronal Sections Through the Hypothalamus

5. Hypothalamus: General Anatomical Features
Very small area of brain, 4 g or about 0.3% of total
Lamina terminalis rostral border; mamillary bodies at caudal border
Divided into 3 regions in rostral caudal axis:
anterior/supraoptic
middle/tuberal
posterior/mamillary
Preoptic area rostral extends to septal region

6. Hypothalamus Has 3 Sagittal Zones
Lateral Zone
lateral to fornix
diffuse neurons
medial forebrain bundle connecting HT, septum and brainstem
MFB also functions in reward
autonomic functions
Medial and Periventricular Zones are divided up into several nuclei

7. Hypothalamic Nuclei By Region
Anterior region
preoptic
supraoptic
paraventricular
anterior
suprachiasmatic
Middle
dorsomedial
ventromedial
arcuate/tuberal
Posterior
mamillary
posterior

8. Neural Inputs to the Hypothalamus
Most neural inputs from limbic system:
hippocampus via fornix
amygdala via ventral amygdaloid path
orbitofrontal cortex
midline thalamic nuc
retina
medial forebrain bundle connects septal area, lateral HT and brainstem
reticular formation sends sensory info

9. Humoral Inputs to the Hypothalamus
Humoral input via vasculature
glucose, hormones
blood osmolality and temperature
Circumventricular organs detect changes in CSF and relay info to HT

10. Neural Outputs of the Hypothalamus
Mamillary bodies to anterior thalamic nucleus (hippocampus projects to mamillary bodies via fornix)
Midbrain reticular formation from medial forebrain bundle and mamillotegmental tract
Amygdaloid nuclei via ventral amygdaloid path
Brainstem and spinal cord autonomic centers both directly and via reticular formation
in the midbrain and rostral pons near periaqueductal gray and floor of 4th ventricle
lateral part of the reticular formation through the pons and medulla

11. Humoral Outputs of the Hypothalamus
Direct secretion of hormones into the circulation
Indirect by secretion of releasing factors into the hypophysial portal system that travel to the anterior pituitary

12. Direct Hormonal Secretion
Magnocellular neurons in supraoptic and paraventricular nuclei
Axons project to posterior pituitary
Release vasopressin and oxytocin
Vasopressin or anti-diuretic hormone acts on kidney to increase water resorption
Oxytocin stimulates smooth muscle contraction in uterus and mammary gland
Both also thought to be involved in other neural functions such as pair bonding, maternal & sexual behavior, and learning

13. Indirect Hormonal Secretion
Small neurons in mediobasal HT have axons projecting to median eminence
Vessels in ME travel to anterior pituitary
Hypothalamic regulatory hormones (releasing factors) are released into extravascular space, enter vessels and are carried to the anterior pituitary
Control release of ant pit hormones including ACTH, growth hormone, FSH, LH, TSH, and prolactin

14. Hypothalamic Functions 1
Body temperature: heat loss center in anterior HT (preoptic area)stimulates sweating and peripheral vasodilation, lesions cause hyperthermia; heat gain center in posterior HT stimulates cutaneous vasoconstriction, piloerection, shivering; lesions cause poikilothermy
Food intake: ventromedial and paraventricular nuclei are satiety centers, lesion causes obesity; lateral HT stimulates food and water intake

15. Hypothalamic Functions 2
Reproduction and sexual function: preoptic and ventromedial nuclei, estrogen and testosterone sensitive neurons control releasing factor neurons in mediobasal HT
Tuberal and arcuate nuclei also involved in endocrine function
Sleep/wake cycle: suprachiasmatic nuc is biological clock; preoptic nuc can initiate sleep; lat HT can change cortical arousal; post HT lesion can cause coma or impaired arousal

16. Hypothalamus Functions 3
Emotions and behavior: ventromedial lesions can cause viciousness/rage
Posterior HT stimulates sympathetic functions
Anterior HT stimulates parasympathetic functions
Mamillary nuclei: recent memory