BIO 336 - 3.1

The Menstrual Cycle

• The hypothalamus and pituitary gland work together with the ovaries to regulate the menstrual cycle.
• Follicle-stimulating hormone (FSH) stimulates the growth of a follicle in the ovary, which contains an immature egg.
• The follicle produces estrogen (estradiol), which increases as the cycle progresses.
• Increased estradiol triggers the release of both FSH and luteinizing hormone (LH), leading to ovulation.
• Birth control pills prevent the surge of FSH and LH, preventing ovulation.
• Progesterone, released from the remnants of the follicle, prepares the uterus for implantation and inhibits further LH release.

The Periovulatory Period

• This period, around the middle of the menstrual cycle, marks the time of highest fertility.
• Women experience increased sexual responsiveness during this period, including heightened interest in erotic content and flirting, as well as attraction to more masculine men.

Parental Behavior

• Oxytocin and prolactin, released after childbirth, promote milk production and maternal behavior.
• Oxytocin, a hormone released by the pituitary gland, plays a role in various aspects of reproduction and social behavior.
• Oxytocin stimulates uterine contractions during childbirth and milk release, is released during orgasm, and is involved in establishing social bonds, promoting generosity, trust, and reducing anxiety.

Sexual Arousal in Males

• Testosterone is crucial for male sexual arousal and triggers the release of dopamine in the hypothalamus, stimulating erection.
• Dopamine promotes sexual activity, while serotonin inhibits it by blocking dopamine release.
• Antidepressants, which increase serotonin levels, can decrease sexual arousal as a result.

Testosterone Levels & Behavior

• Testosterone levels correlate with sexual arousal and the desire for multiple sexual partners.
• Married or committed men generally have lower testosterone levels than single men.
• High testosterone levels can drive the desire for additional sexual partners, even within committed relationships.
• Women also experience higher testosterone levels when single compared to married women.
• Phthalates, a group of chemicals found in cosmetics and other products, can inhibit testosterone production.

Genes & Sex Differences

• Sex differences are not solely explained by hormones.
• Genes on the X and Y chromosomes also contribute to biological differences between males and females.

Organizing and Activating Effects of Sex Hormones

• Organizing Effects: occur during sensitive periods of development, influencing the development of sex organs (prenatally) and secondary sexual characteristics (puberty).
• Activating Effects: can occur at any time in life and temporarily activate specific responses, such as increased sex drive or menstruation.
• Current hormone levels influence the strength of activating effects.

Sex Differences in the Hypothalamus

• Early sex hormone exposure influences the development of the hypothalamus, amygdala, and other brain regions.
• The sexually dimorphic nucleus, located in the anterior hypothalamus, is larger in males and is involved in controlling male sexual behavior.
• The female hypothalamus exhibits a cyclical pattern of hormone release, regulating the menstrual cycle.

Sex Differences in Childhood Behavior: Toy Preferences

• The second largest observed sex difference in behavior is toy preference (after sexual preference).
• Boys typically exhibit preferences for cars, trains, and balls, engaging in rough play, while girls prefer dolls, tea sets, and cooperative play.
• This difference is partly due to socialization but also reflects inherent preferences observed even in monkeys raised without human influence.
• Prenatal testosterone exposure influences toy preferences, as girls exposed to higher levels often display more male-typical preferences.

Activating Effects of Sex Hormones on Behavior

• Sex hormones can temporarily modify behavior through activating effects, influencing sexual behavior within minutes.
• A bidirectional relationship exists between behavior and hormone secretion, as seen with aggression and testosterone.