Functions of the Hypothalamus
The hypothalamus plays an important role in the control of many functions that are vital for the survival of an animal. In exercising such control the hypothalamus acts in close coordination with higher centres including the limbic system and the prefrontal cortex, and with autonomic centres in the brainstem and spinal cord. The main functions attributed to the hypothalamus are as follows.
The hypothalamus is responsible for feelings of hunger and of satiety, and this determines whether the animal will accept or refuse food. It has been observed that stimulation of the lateral zone of the hypothalamus stimulates hunger while stimulation of the medial zone produces satiety. The lateral zone is also responsible for thirst and drinking. Based on such studies a feeding centre has been described in the lateral hypothalamic nucleus, and a satiety centre in the ventromedial nucleus.
Correlate this with the fact that some neurons in the hypothalamus are sensitive to osmolarity (preoptic nucleus), glucose content and fatty acid content of blood.
The hypothalamus controls sexual activity, both in the male and female. It also exerts an effect on gametogenesis, on ovarian and uterine cycles, and on the development of secondary sexual characters. These effects are produced by influencing the secretion of gonadotropic hormones by the hypophysis cerebri.
The hypothalamus exerts an important influence on the activity of the autonomic nervous system, and thus has considerable effect on cardiovascular, respiratory and alimentary functions. Sympathetic activity is said to be controlled, predominantly, by caudal parts of the hypothalamus; and parasympathetic activity by cranial parts, but there is considerable overlap between the regions concerned.
The hypothalamus has an important influence on emotions like fear, anger and pleasure. Stimulation of some areas of the hypothalamus produces sensations of pleasure, while stimulation of other regions produces pain or other unpleasant effects.
The influence of the hypothalamus in the production of hormones by the pars anterior of the hypophysis cerebri, and the elaboration of oxytocin and the antidiuretic hormone by the hypothalamus itself, have been described above. Through control of the adenohypophysis, the hypothalamus indirectly influences the thyroid gland, the adrenal cortex, and the gonads.
Through control over the autonomic nervous system, and hormones, the hypothalamus plays a complex role in the way a person responds to stress.
Some neurons in the preoptic nucleus of the hypothalamus act as a thermostat to control body temperature. When body temperature rises or falls, appropriate mechanisms are brought into play to bring the temperature back to normal.
Several functions of the body show a cyclic variation in activity, over the twenty four hours of a day. The most conspicuous of these is the cycle of sleep and waking. Such cycles (called circadianrhythms) are believed to be controlled by the hypothalamus, which is said to function as abiological clock. The suprachiasmatic nucleus is believed to play an important role in this regard. Lesions of the hypothalamus disturb the sleep-waking cycle.
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