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Chapter Ten Sexual Behavior
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CHAPTER 10 SEXUAL BEHAVIOR
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Sexual chromosome abnormalities
Sexual Development Sexual chromosome abnormalities Turner syndrome (XO) Normal female external genitalia but ovaries develop abnormally Normal intelligence, deficits in spatial relationships and memory Klinefelter syndrome (XXY) Male with reduced fertility Require hormone treatment at puberty to develop secondary sex characteristics and inhibit female characteristics Normal intelligence but social awkwardness, delayed or reduced verbal skills XYY Subtle physical and behavioral correlates Controversial association with antisocial behavior
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Figure 10.2 The Human Genome
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Figure 10.3 Turner Syndrome
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Three Stages of Prenatal Development
Sexual Development Three Stages of Prenatal Development The Development of Gonads Sex determining region of Y chromosome expressed at 6 weeks gestation Differentiation of Internal Organs Wolffian system develops into seminal vesicles Müllerian sytem develops into uterus, upper vagina, and fallopian tubes Androgen insensitivity syndrome (AIS) XY genotype, but female appearance and gender identity disrupts normal development of the Wolffian system
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Figure 10.4 Differentiation of Gonads and External Genitals
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Figure 10.5 Androgen Insensitivity Syndrome
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Three Stages of Prenatal Development
Sexual Development Three Stages of Prenatal Development Development of External Genitalia No hormonal activity required for development of female genitalia 5-alpha-dihydrotestosterone needed for development of male genitalia Congenital adrenal hyperplasia (CAH) – genetic females exposed prenatally to excess androgens, leads to masculinized genitalia
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Figure 10.6 Congenital Adrenal Hyperplasia (CAH) Masculinizes Genetic Female
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Development at Puberty
Sexual Development Development at Puberty Secondary sex characteristics Gonadotropin-releasing hormone (GnRH) released by the hypothalamus Follicle-stimulating hormone (FSH) and luteinizing hormone (LH) have different effects in males and females 5-alpha-reductase deficiency and maturation of external genitalia
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Figure 10.7 Female Age at Puberty
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Figure 10.8 5-Alpha-Reductase Deficiency Changes External Appearance at Puberty
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Hormones and Sexual Behavior
Regulation of Sex Hormones by the Hypothalamus and Pituitary Gland Hypothalamus exerts control over release of sex hormones, through release of gonadotropin-releasing hormone (GnRH) Melatonin inhibits release of GnRH GnRH travels to anterior pituitary, which releases gonadotropins, LH, and FSH
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Figure 10.9 The Synthesis of Human Sex Hormones
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Figure 10.10 Hypothalamic Control of the Pituitary Gland
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Hormones and Sexual Behavior
The Menstrual Cycle and Female Fertility Stable and predictable fluctuation in events controlled by LH and FSH Ovulation about 2 weeks after the first day of the last menstruation Correlations Between Mood, Menstruation, and Childbirth Premenstrual syndrome Premenstrual dysphoric disorder Postpartum depression Female Contraception Oral contraceptives interfere with ovulation Use of uninterrupted cycles of birth control to reduce frequency of menstruation is now standard medical practice
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Figure 10.11 The Human Menstrual Cycle
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Hormones and Sexual Behavior
Sex Hormones and Female Behavior Sexual Interest in Human Females Report slightly more interest around ovulation Testosterone has greatest impact on women’s sexuality Estrogens and Cognition Best scores on spatial abilities tests when testosterone levels high and worst when estrogen levels are high Best scores on verbal abilities and manual dexterity tests when estrogen levels are high
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Figure 10.12 Sex Influences Cognition
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Hormones and Sexual Behavior
Sex Hormones and Male Behavior Androgens and Competition Testosterone levels increase in anticipation of competition Androgens and Sexual Interest If in normal range, young men’s testosterone levels don’t predict sexual frequency Married men have lower testosterone than single or recently divorced men Androgens and Cognitive Behavior Spatial abilities advantage may be related to testosterone Male Contraceptives
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Hormones and Sexual Behavior
Anabolic Steroids Synthetic versions of testosterone that build tissue Build strength and muscle mass and improve recovery time following muscle damage Significant side effects Acne Enlargement of clitoris or penis Lower voice Unusual hair loss or growth Psychological disturbances Larger breasts in males High blood pressure and kidney disease
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Sex Differences in the Nervous System
Differences in the brains and nervous systems of males and females Sexually dimorphic structures Sexually dimorphic nucleus of the preoptic area Interstitial nuclei of the anterior hypothalamus Hypothalamus, thalamus, white matter Spinal cords of mammals Masculinization of the brain Aromatization masculinizes brains of many animals Testosterone is transformed into estradiol producing masculinization Androgens play a greater role in the masculinization of the human brain
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Figure 10.14 The SDN-POA of the Hypothalamus is Sexually Dimorphic
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Hormones, Sexual Behavior, and Sexual Orientation
Early exposure to androgens influences adult sexual behavior Development of structures not involved in sexual behavior often reflect the influence of prenatal hormone exposure Otoaccoustic emissions of lesbian and bisexual women Comparative size of ring and index finger of gay men
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Brain Structure and Sexual Orientation
LeVay – INAH-3 different between heterosexual and homosexual men? Two to three times larger in heterosexual men than homosexual men Interpretation of findings limited: INAH-3 is too small to observe in living participants , studied autopsied brains Homosexual men identified by diagnosis of AIDS No one knows effect of AIDS on brain Genes and Sexual Orientation Unknown whether direct effect on orientation or indirect effect on prenatal androgen environment
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Figure 10.16 INAH-3 Size Correlates with Sexual Orientation
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The Importance of Symmetry
Attraction The Importance of Symmetry Degree of similarity of one side of face or body to the other The Beauty of Fertility and a Good Immune System Preference for younger features on female Preference for masculine men (testosterone-related facial features) for casual sexual encounter, less masculine men for long-term partner Smell preference may indicate preference for an immune system different from our own
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Figure 10.17 Beautiful Female Faces Are Symmetrical and Youthful
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Romantic Love, Sexual Desire, and Parenting
Sexually dimorphic pituitary hormones Oxytocin Vasopressin Gender-specific mating pressures Men pressured to be promiscuous Women pressured to be selective
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Figure 10.18 Brain Activity and Love
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Sexual Dysfunction and Treatment
Masters and Johnson estimated half of couples experienced some sexual problem Many sexual dysfunctions are psychological in origin Erectile dysfunction can be treated by enhancing activity of NO
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