The Functions of Hypothalamus
The hypothalamus is part of limbic system and just lies below the thalamus. It has widespread connection with the rest of the forebrain and the midbrain. It extends from the area superior to the optic chiasm to the posterior margins of the mamiilary bodies. And, the infundibulum is connecting the floor of the hypothalamus to the pituitary gland. The hypothalamus performs the following functions: the subconscious of skeletal muscle contraction, the control of autonomic function, the coordination of activities of the nervous and endocrine systems, the secretion of ADH and oxytocin, the production of emotions and behavioral drives, coordination between voluntary and autonomic functions, the regulation of body temperature, and the control of circadian rhythms.
The hypothalamus directs somatic motor patterns associated with rage, pleasure, pain and sexual arousal by stimulating centers in other portions of the brain. It also adjusts and coordinates the activities of autonomic centers in the pons and medulla oblongata the regulate heart rate, blood pressure, respiration, and digestive functions.
The hypothalamus was found to exhibit significant second-order modulation of activation when subjects receiving funny and sad stimuli (Karlsson, KA. el. 2010). The hypothalamus has several pathways that influence arousal. One set of axons releases the neurotransmitter histamine, which produced widespread excitatory effects throughout the brain, increasing wakefulness and alertness. Male and female rats will show characteristic sexual responses when one portion of the hypothalamus is stimulated. Another pathway from the hypothalamus release a peptide neurotransmitter called hypocretin. Hypocretins neurons of the hypothalamus are activated following positive emotional arousal. The loss of hypocretin neurons results in the sleep disorder narcolepsy (Karlsson, KA. et al. 2010). The lateral hypothalamus was shown to be influenced by he oral sensory properties of fat. This implicated that the hypothalamus is involved in responsiveness to peripheral hunger and satiety signals (Grabenhorst, F. et al. 2010).
The hypothalamus acts as an endocrine organ. Hypothalamic neurons synthesize hormones, such as ADH and oxytocin, transport them along axons within the infundibulum and release them into the circulation at the neuropophysis. The hypothalamus contains special cells known as osmoreceptors, which monitor the osmotic concentration of the extracellular fluid (ECF). The population of osmoreceptors includes neurons that secrete ADH. These neurons are located in the anterior hypothalamus, and their axons release ADH near fenestrated capillaries in the neuropophysis. The release of ADH can stimulate water conservation at the kidneys, reducing urinary water losses and concentrating the urine. And, it also can stimulate the thirst center, promoting the intake of fluids. The oxytocin is produced by the paraventricular nucleus and stimulates smooth muscle contraction in the uterus and mammary glands of females and the prostate gland of males. The secretion of oxytocin, epinephrine, and norepinephrine involves both neural and hormonal mechanism. And, the ANP neurons located within hypothalamus also plays an important role in the modulation of blood pressure and body fluid volume.
The hypothalamus also controls the pituitary gland, altering its release of hormones. The regulatory hormones released at the hypothalamus are transported directly to the adenohypophysis by the hypophyseal portal system. There are two classes of hypothalamic regulatory hormones exist: releasing hormones and inhibiting hormones. A releasing hormone stimulates the synthesis and secretion of one or more hormones at the adenohypophysis. An inhibiting hormone prevents the synthesis and secretion of hormones from the adenohypophysis. Several hypothalamic and pituitary hormones are released in sudden bursts called pulses. When hormones arrive in pulses, target cells may vary their response with the frequency of the pulses. The rate of the secretion is controlled by negative feedback. The hormones released by the adenohypophysis control the activities of the endocrine cells in the thyroid, suprarenal cortex, and reproductive organs.
The hypothalamic centers may be stimulated by sensory information from the cerebrum, brain stem, and spinal stem, changes in the composition of the CSF and interstitial fluid, or chemical stimuli in the circulating blood that moving rapidly across highly permeable capillaries to enter the hypothalamus. The hypothalamus is important in motivational activities such as drinking, eating, and sexual behavior. Specific hypothalamic centers produce sensations that lead to conscious or subconscious changes in behavior.
The preoptic area of the hypothalamus coordinates the activities of other CNS centers and regulates other physiological systems to maintain normal body temperature. If body temperature falls, the preoptic area sends messages to the vasomotor center, an autonomic center in the medulla oblongata that controls blood flow by regulating the diameter of peripheral blood vessels. Therefore, the vasomotor center can decrease the blood supply to the skin, reducing the rate of heat loss.
In conclusion, hypothalamus plays important role in regulating hormones and body response. Lesion of the hypothalamus can seriously affect eating, drinking, temperature regulation, sexual behavior, fighting, or activity level.
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Karlsson, KA, C. Windischberger, F. Gerstl, W. Mayr, JM Siegel, and E. Moser. "Modulation of Hypothalamus and Amygdalar Activation Levels with Stimulus Valence." NeuroImage 51.1 (2010): 324-28. Print.
Martini, Frederic, and Judi Nath. Fundamentals of Anatomy & Physiology. 8. San Francisco, CA: Benjamin Cummings, 2009. 477-478, 612-616, 1014. Print.
Miyoshi, Michio, and Tatsuo Watanabe. "Role of Anterior Hypothalamic Natriuretic Peptide in Lipopolysaccaride-induced Fever in Rats." European Journal of Applied Physiology 109.1 (2010): 49-57. Print.