LECTURE NO (-) Neuro-Physiology Kamal Mohammed Lecturer Of Physiology Hypothalamus Faculty Of Medicine Dept.Of Physiology
Hypothalamus Less than 1% of the brain mass Many connect the hypothalamus to the limbic system. The hypothalamus also functions with the limbic system as a unit that regulates emotional and instinctual behavior.
Anatomical Where is the Location: hypothalamus? It consist of group of nuclei present in the floor of third ventricle (which lies between the two thalami) It is a very vascular structure so much so that the nuclei are floating in the blood.
Key concept for hypothalamic function is HOMEOSTASIS Its goal is to maintain internal homeostasis There are both neural and hormonal inputs and outputs from the hypothalamus.
Regulates Mechanisms by:- Receiving sensory information from all areas of the body. Comparing sensory information with biological set points. Adjusting the system to restore the body balance when deviations from biological set points occur.
Stimulation of the anterior hypothalamic centers produces parasympathetic effects While stimulation of the posterior hypothalamic centers produces diffuse sympathetic discharge and increased adrenal medullary secretion.
There are neural connections between the hypothalamus and the posterior lobe of the pituitary gland and vascular connections between the hypothalamus and anterior lobe
Posterior pituitary: displaced hypothalamic axons release vasopressin (ADH) and oxytocin to blood paraventricular nucleus supraoptic nucleus infundibulum post. pituitary Hypothalamic axons
The hypothalamus controls the posterior pituitary by a neural mechanism and the anterior pituitary by a hormonal mechanism ADH hormone and oxytocin are produced in the supraoptic and paraventricular nuclei and transported to the posterior pituitary along the axons of the hypothalamo-hypophyseal tracts.
Also hypothalamus produces groups of hormone, which are carried to the anterior pituitary by the hypothalamo-hypophyseal portal system. Most of these release anterior pituitary hormones, while others inhibit the release of anterior pituitary hormones
through influence of hypothalamus on the anterior pituitary, it regulate sexual function Oestrus, maternal behavior and care of young animals are under direct hypothalamic control
Regulation of Body Water The hypothalamus regulates body water in two ways: (1) by creating the sensation of thirst, which makes the animal or person drink water, thirst center is located in the lateral hypothalamus. (2) by controlling the excretion of water into the urine.
regulation of uterine contractility and milk ejection Stimulation of the paraventricular nuclei causes their neuronal cells to secrete the hormone oxytocin. This in turn causes increased contractility of the uterus as well as contraction of the myoepithelial cells surrounding the alveoli of the breasts lead to milk ejection
Wakefulness and sleep The hypothalamus is part of the reticular activating system, which is indispensable to the initiation and maintenance of the alert wakefulness of the healthy animal. Also stimulation of the some portion of the hypothalamus is found to promote sleep, and lesion in the same area sometimes cause such intense wakefulness that animal actually dies of exhaustion.
As a component of the limbic system, the thalamus is part of the effector mechanism of emotional expression. It is involved in the expression of rage and fear Stimulation of certain regions of hypothalamus pleases, whereas stimulation of other parts causes terror, pain, fear
In mammals, including humans, most of the cells in the body have circadian rhythms. the rhythms are entrained by the paired suprachiasmatic nuclei (SCN), above the optic chiasma These nuclei receive information about the light dark cycle via a special neural pathway, the retinohypothalamic fibers that pass from the optic chiasm to the SCN. Efferent from the SCN initiate neural and humoral signals that entrain a wide variety of well-known circadian rhythms
HUNGER:- Feeding & Satiety Body weight depends on the balance between caloric intake and utilization of calories. Food intake is regulated by a balance between two centers: 1- Feeding center is located in the lateral hypothalamus, - when stimulated leads to extreme hunger, appetite and an intense desire to search for food. - continuous stimulation leads to obesity 2- satiety center is located in the ventromedial nucleus - when stimulated cause anorexia.
Hypothalamus acts as a thermostat and receives information from sensory receptors(warm and cold thermo receptors) Thermal sensation, including both warm and cold sensation Reflex responses activated by cold are controlled from posterior hypothalamus Reflex responses activated by warmth are controlled from anterior hypothalamus
Hypothalamic Function 1. Autonomic control 2. Hypothalamic pituitary relationship 3. Sexual behavior 4. Thirst control 5. Regulation of uterine contractility and milk ejection 6. Control of sleep 7. Control fear and rage 8. Control of body rhythm (circadian) 9. Control of hunger, feeding and satiety 10. Temperature regulation