Some behaviors are so automatic that they are almost reflexes. Automatic responses to stimuli are largely controlled by the hypothalamus.
The hypothalamus sits behind eye orbits in a human skull. Looking at a side view of the skull, the hypothalamus is seen nestled inside the center of the brain as if nestled inside an upside down horseshoe. The brain matter envelopes the hypothalamus, creating a helmet of folded brain tissue covering the hypothalamus.
Specifically, the hypothalamus is located behind the eye sockets, superior to the optic chiasm, where the optic tracts run from the eyes to the brain. The hypothalamus extends down behind the mamillary bodies where sensory information is processed, like the olfactory sensation of smell. Reflexes for eating, chewing, licking and swallowing are controlled by motor nuclei in the hypothalamus.
The base of the hypothalamus is connected to the pituitary gland by a stalk called the infundibulum, which extends inferiorly, below the hypothalamus.
The base of the hypothalamus, between the infundibulm and the mamillary bodies, is called the tuberal area. Tuber means "swelling." The tuberal area contain nuclei that help control the function of the pituitary gland.
Functions of the Hypothalamus
1) Contraction of Skeletal Muscle. The hypothalamus is able to stimulate other spots in the brain. It stimulates portions of the brain in response to feelings of rage, pain, pleasure or sexual arousal. The universal expression of rage and the basic ways people move during sex are induced by the hypothalamus.
2) Coordination of Nervous and Endocrine Systems. The hypothalamus produces regulatory hormones that stimulate or inhibit endocrine cells in the pituitary gland. The hormones are produced in the tuberal area and released into capillaries to be taken to the pituitary gland.
3) Secretion of Hormones. Antidiuretic hormone, or ADH, and oxytocin are secreted by the hypothalamus and transported through the infundibulum to the pituitary gland where they are released into the blood for distribution through the body. ADH restricts water loss at the kidneys; and oxytocin stimulates smooth muscle contractions in the uterus and mammary glands of females, and the prostate gland of males.
4) Production of Emotional and Behavioral Drives. The hypothalamus has specific centers that cause sensations leading to either conscious or subconscious behavior. Two of these centers are the feeding center and the thirst center.
5) Control of Autonomic Functions. The hypothalamus helps the medulla oblongata to regulate the heart beat, blood pressure, respiration, and digestive functions.
6) Coordination between Voluntary and Autonomic Functions. In an emergency, this response causes heart rate to increase and respiration to speed up.
7) Regulation of Body Temperature. The hypothalamus is able to signal the vasomotor center in the medulla oblongata, to decrease the blood supply to the skin, reducing the rate of heat loss.
8) Establishes Circadian Rhythms. Cycles of wake and sleep are controlled by adjusting the activities of the pineal gland, reticular formation, and also the activities of nuclei in the hypothalamus.
Role of the Hypothalamus
The role of the hypothalamus is one of higher level autonomic control. Cardiovascular centers, respiratory centers, and centers in the medulla oblongata contain nuclei responsible for salivation, swallowing, digestive secressions, and urination. All of these are regulated by the hypothalamus.
The job of the hypothalamus is to make blood pressure rise and the heart beat faster when a person is angry. The hypothalamus is also responsible for making the stomach rumble when a person remembers their last big meal. The growl of a persons stomach is subconscious and it is the sound of skeletal muscles being signalled to move by the hypothalamus.
The next time you find yourself aroused by someone you find attractive, it may be best to just leave the room. Otherwise the hypothalamus may give you away, the way a growling stomach exposes hunger!