Anatomy & Physiology I and II

Anatomy & Physiology Study Guide swallowing. A narrow stalk called the infundibulum extends inferiorly and connects the floor of the hypothalamus to the pituitary gland. The hypothalamus contains vital integrative and control centers, in addition to those associated with the limbic system. Hypothalamic centers may be stimulated by sensory information from the spinal cord, brain stem, and cerebrum; changes in the compositions of the CSF and interstitial fluid; or chemical stimuli in the circulating blood that move across permeable capillaries to enter the hypothalamus (where there is no blood–brain barrier). The hypothalamus performs several functions: • The subconscious control of skeletal muscle contractions: The hypothalamus directs somatic motor patterns associated with rage, pleasure, pain, and sexual arousal by stimulating centers in other portions of the brain. For example, the changes in facial expression that accompany rage and the basic movements associated with sexual activity are controlled by hypothalamic centers. • The control of autonomic function: The hypothalamus controls, coordinates, and adjusts the activities of autonomic centers in the pons and medulla oblongata that regulate respiration, heart rate, blood pressure, and digestive functions. • The coordination of activities of the nervous and endocrine systems: The hypothalamus coordinates endocrine and neural activities by stimulating or inhibiting endocrine cells in the pituitary through producing regulatory hormones. These hormones are produced at the tuberal area and are released into local capillaries for transport to the adenohypophysis. • The secretion of two hormones: The hypothalamus secretes two hormones: antidiuretic hormone (ADH) and oxytocin (OT). Antidiuretic hormone (ADH, also called vasopressin) is produced by the supraoptic nucleus and restricts water loss at the kidneys, and oxytocin (OT) stimulates smooth muscle contractions in the prostate gland in males and the uterus and mammary glands of females. It is produced by the paraventricular nucleus. These hormones are transported along axons that pass through the infundibulum to the neurohypophysis. There the hormones are released into the blood for distribution throughout the body. • The production of emotions and behavioral drives: Specific hypothalamic centers produce sensations that lead to conscious or subconscious changes in behavior. For example, stimulation of the feeding center produces the sensation of hunger, and stimulation of the thirst center produces the sensation of thirst. These unfocused “impressions” originating in the hypothalamus are called drives. The conscious sensations are only part of the hypothalamic response. For instance, the thirst center also orders the release of ADH by neurons in the supraoptic nucleus. • Coordination between voluntary and autonomic functions: When a dangerous or stressful situation arises, the heart rate and respiratory rate go up, and the body prepares for an emergency. These autonomic adjustments are made by the hypothalamus. • The regulation of body temperature: 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 instructions to the vasomotor center. It affects blood flow by regulating the diameter of peripheral blood vessels. ©2018 Achieve Test Prep Page 134 of 367