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12 Cards in this Set
- Front
- Back
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Objective
Explain how sex hormones activate behavior. |
Sex hormones activate sexual behavior partly by enhancing sensations. For instance, estrogens increase the sensitivity of a nerve that transmits tactile stimulation from the pubic area to the brain. Sex hormones also bind to receptors that increase responses of certain areas of the hypothalamus, including the ventromedial nucleus, the medial preoptic area (MPOA), and the anterior hypothalamus. Testosterone and estradiol prime the MPOA and several other brain areas to release dopamine. MPOA neurons release dopamine strongly during sexual activity, and the more dopamine they release, the more likely the male is to copulate. In moderate concentrations, dopamine stimulates mostly type D1 and D5 receptors, which facilitate erection of the penis in the male and sexually receptive postures in the female. In higher concentrations, dopamine stimulates type D2 receptors, which lead to orgasm. The sudden burst of dopamine in several brain areas at the time of orgasm resembles the “rush” that addictive drugs produce. Whereas dopamine stimulates sexual activity, the neurotransmitter serotonin inhibits it, in part by blocking dopamine release.
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Objective
Compare the sexual motivation of male and female rats. |
Researchers found what appeared to be a major difference between male and female rats in their sexual motivation: if a pair of rats have had sexual relations in a particular cage, the opportunity to return to that cage is strongly reinforcing for males but not for females. Then they tried varying the procedure. The male rat was confined to that cage, but the female was free to enter or leave at any time. She could therefore control the timing of when their sexual activity started, stopped, and started again. Under these conditions, females developed a clear preference for that cage. Evidently, female rats find sex very reinforcing if they can control the timing.
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Objective
List the most common causes of impotence. |
Decreases in testosterone levels generally decrease male sexual activity. For example, castration (removal of the testes) generally decreases a man’s sexual interest and activity. However, low testosterone is not the usual basis for impotence, which is the inability to have an erection. The most common cause is impaired blood circulation, especially in older men. Other common causes include neurological problems, reactions to drugs, and psychological tension. Erection depends partly on the fact that testosterone increases the release of nitric oxide (NO). NO facilitates the hypothalamic neurons important for sexual behavior and increases blood flow to the penis. The drug sildenafil (Viagra) increases male sexual ability by prolonging the effects of NO.
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Objective
Describe the hormonal activity that takes place during the menstrual cycle. |
A woman’s hypothalamus and pituitary interact with the ovaries to produce the menstrual cycle, a periodic variation in hormones and fertility over the course of 28 days. After the end of a menstrual period, the anterior pituitary release follicle-stimulating hormone (FSH), which promotes the growth of a follicle in the ovary. The follicle nurtures the ovum (egg cell) and produces several types of estrogen, including estradiol. Toward the middle of the menstrual cycle, the follicle builds up more and more receptors to FSH; even though the actual concentration of FSH in the blood starts decreasing, its effects on the follicle increase. As a result, the follicle produces increasing amounts of estradiol. The increased release of estradiol causes an increased release of FSH as well as a sudden surge in the release of lutenizing hormone (LH) from the anterior pituitary. FSH and LH combine to cause the follicle to release an ovum. The remnant of the follicle (corpus luteum) secretes the hormone progesterone, which prepares the uterus for the implantation of a fertilized ovum. Progesterone also inhibits the further release of LH. Toward the end of the menstrual cycle, the levels of LH, FSH, estradiol, and progesterone all decline.
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Objective
Identify the hormonal changes that prepare mammals for parenthood. |
In birds and mammals—with the possible exception of humans—hormonal changes prepare the mother for parental behavior. Late in pregnancy, the female secretes large amounts of estradiol, prolactin, and oxytocin. Prolactin is necessary for milk production and also for aspects of maternal behavior such as retrieving any wandering young back to the nest. In those species in which fathers contribute to parental care, prolactin is important for their behavior too. Oyxtocin affects maternal behavior, sexual arousal, social attachment, and learning.
In addition to secreting these hormones, the female also changes her pattern of hormone receptors. For example, late in pregnancy, her brain increases its sensitivity to estradiol in the areas responsible for maternal behavior but not in those responsible for sexual behavior. The hormonal changes increase the mothers’ attention to their young after delivery. Hormones act by increasing activity in the medial preoptic area and anterior hypothalamus, areas that are necessary for rats’ maternal behavior. Another key hormone is vasopressin, synthesized by the hypothalamus and secreted by the posterior pituitary gland. In males, vasopressin helps foster bonding with one’s mate and offspring. |
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Objective
Explain why there are two mechanisms for maternal behavior. |
In the first few days, maternal behavior is dependent on hormones. After that period, bonding is experience-dependent. The reason is that hormones compensate for the mother’s lack of familiarity with offspring in the early phase. Then in the later phase, experience maintains the maternal behavior even though the hormones start to decline.
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impotence
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Inability to have an erection
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menstrual cycle
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A periodic variation in hormones and fertility over the course of 28 days
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follicle-stimulating hormone (FSH)
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Hormone released by the anterior pituitary gland that promotes the growth of the follicle in the ovary
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estradiol
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Type of estrogen; plays an essential role in maturation of female sex organs and female reproduction
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luteinizing hormone (LH)
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Hormone released by the anterior pituitary gland that causes the follicle to release the ovum
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periovulatory period
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When ovulation occurs, is the time of maximum fertility and increased estrogen levels
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