Brain and Behavior Sexual Reproduction (Test #3)

Sexual differentiation depends on...

level of testosterone (androgen, not estrogens) during a sensitive period

Human sensitive period for genital formation occurs during...

the first trimester of pregnancy

Exposure to testosterone during sensitive periods in females leads to...

clitoris larger than usual, sexual behavior becomes masculinized

No androgen receptors/castration in males leads to...

female-like anatomy and behavior

Females lacking estradiol during early life do not develop

normal sexual behavior

Estradiol and other estrogens effects on male development

modifies various internal structures, including the prostate gland

Absence of sex hormones leads to...

no development of normal sexual behavior

Sexually dimorphic nucleus

Area in the anterior hypothalamus

Larger in males

Contributes to control of male sexual behavior

Sex hormones early in life influence development in the following brain areas: (2)

hypothalamus, amygdala

Alpha-fetoprotein

found in the blood during early sensitive periods, binds to estradiol, and prevents it from entering developing cells. Testosterone does not bind to alpha-fetoprotein and freely enters the cell

Sex Differences: Boys

play with cars, trains, balls and guns, and play roughly (same for monkeys generally but lesser extent)

Sex Differences: Girls

play with dolls and tea sets, and play cooperatively (same for monkeys generally but lesser extent)

Girls born to women with high testosterone levels while pregnant show...

a slightly elevated preference for typical boys' toys

Boys born to women with high phthalate (similar to estrodile) (found in perfumes, food packaging, etc.) levels while pregnant showed...

more interest in typical girls' toys

Toy preferences are a result of both...

prenatal hormones and child-rearing experiences

Oxytocin (Important for...; stimulates...)

Important for reproductive behavior

Stimulates uterine contractions during delivery and mammary glands in releasing milk

Behavior effects hormone secretions, and hormones effect behavior

Testosterone increases...

touch sensitivity in the penis

Sex hormones bind to receptors in...

the hypothalamus

including the ventromedial nucleus, the medial preoptic area (MPOA), and anterior hypothalamus

Testosterone triggers the release of...

dopamine by the MPOA and other areas

Dopamine stimulation of _____ and ______ receptors is associated with sexual arousal

D1 and D5

Dopamine facilitates...

erection of the penis and sexually receptive postures in females

Higher concentrations of dopamine stimulate ___ receptors and lead to _____

D2; orgasm

Neurotransmitter serotonin decreases sexual activity by...

blocking dopamine release

Married men or those in a committed relationship generally have _______ testosterone levels

lower

Typical reason for impotence:

impaired blood circulation (gain weight)

Testosterone reduction leads to...

Negative side effects such as diabetes, depression, and weight gain

The menstrual cycle

Periodic variation in hormones and fertility over the course of about 28 days

The hypothalamus and pituitary interact with the ovaries to produce the menstrual cycle

After the end of a menstrual period: (3)

Anterior pituitary releases follicle-stimulating hormone (FSH)

FSH promotes growth of follicle in the ovary

Follicle nurtures the ovum and produces estrogen

Towards the middle of the menstrual cycle:

The follicle builds up receptors to FSH

As a result, the follicle produces increasing amounts of estradiol

Increased estradiol causes...

the anterior pituitary to increase release of FSH and luteinizing hormone (LH)

_____ and _____ cause the follicle to release an ovum

FSH; LH

The remnants of the follicle release...

the hormone progesterone

Progesterone Functions (2)

Prepares the uterus for implantation of a fertilized ovum

Inhibits the further release of LH

If woman is pregnant, _________ and __________ levels increase gradually throughout pregnancy

estradiol; progesterone

If not pregnant... (menstruation)

levels of Estradiol and Progesterone decline, and uterine lining is cast off

High levels of estradiol and progesterone produce...

heightened activity in the serotonin receptor (Causes nausea associated with pregnancy)

Birth control pills prevent pregnancy by...

interfering with the usual feedback cycle between the ovaries and pituitary

The combination-pill contains estrogen and progesterone functions:

Prevents the surge of FSH and LH that would release an ovum

Thickens the mucus of the cervix

More difficult for sperm to reach the egg

Prevents egg from implanting in uterus

Women most fertile during middle of cycle and studies suggest...

Studies suggest that women become more sexually responsive during this time

Show increased attention to sex-related stimuli such as erotic videos

Show increased interest in flirting

Lap dancers receive larger tips

Prenatal androgens and estrogens...

Stimulate brain areas important for memory

At least ________ more active in the brains of one sex than the other

85 genes

______ are better at recognizing emotion, and ______ injections makes them worse

women; testosterone

Prolactin (3) gets women's body ready for baby by...

Necessary for milk production

Enables mother to eat more than usual

Responsible for some maternal behavior

Vasopressin

Hormone synthesized by the hypothalamus

Secreted by the posterior pituitary gland

Associated with social behavior in many species

Facilitates olfactory recognition

Mice and humans can adopt normal maternal behaviors without pregnancy hormones

________ replaces _________ as hormonal levels decline

experience; hormonal influences

Correlation between father's hormones and level of interaction with their child:

Fathers with lowest testosterone and prolactin levels spent most time playing with and caring for child

Sexual selection

Genes that make an individual more appealing to the opposite sex will increase the probability of reproduction

Gender identity is a product of... (3)

Rearing, experience, and biological factors, (especially prenatal hormones)

Intersex Causes (2)

Woman released two ova, each fertilized by a different sperm and ova united instead of becoming twins

An atypical hormone pattern occurs before birth

Congenital Adrenal Hyperplasia (CAH)

Overdevelopment of the adrenal glands from birth

Most common cause of the intersex condition

Caused by a genetic defect

Cortisol production leads to overstimulation of the adrenal gland

Leads to extra testosterone production

Female becomes partly masculinized

An estimated 1 out of _____ children is born with some degree of genital ambiguity

1 in _____ has enough genital ambiguity to make the sex uncertain

100; 2,000

Interests/Preferences of CAH Girls (brains exposed to higher levels of testosterone during prenatal/early postnatal):

Toy preference: intermediate between preferences of non-CAH boys and girls

During adolescence, CAH girls showed interests in between those of typical males and females

More physical aggression in adulthood/Preference for rough sports

Testicular Feminization/Androgen Insensitivity

Condition in which individuals with an XY chromosome pattern have smaller than average penis or the genital appearance of a female

Production of androgens is normal but lack the androgen receptor that enables it to activate genes in a cell's nucleus

Some genetic males fail to produce an enzyme that converts testosterone to dihydrotestosterone leading to...

Looking female at birth but a penis develops during adolescence and puberty

Most then accept a male gender identity

Brain is exposed to testosterone during early development

Many who remain female through adolescence feel dissatisfied (hormone exposure plays huge role in gender preferences)

Most _____ discover sexual orientation early

men

Anatomical/Behavioral Differences b/w heterosexual/homosexual men

Heterosexual men slightly taller and heavier

Gay men use landmarks more often when giving directions

Genetics and Homosexuality

If one twin is homosexual, probability that other twin is homosexual is fairly high (for monozygotic twins)

Unlikely that any gene on the X chromosome plays a major role

Hypotheses as to why genes have not been selected out: (3)

Homosexuality may be related to epigenetics

Genes may be maintained by kin selection

Genes that produce homosexuality may produce advantageous effects in relatives

Prenatal Influences to Homosexuality

Prenatal exposure to stress and alcohol may play a role

Stress releases endorphins

Antagonizes the effects of testosterone on the hypothalamus

Male subjects subjected to either prenatal stress or alcohol developed...

male and female sexual behaviors

Male subjects exposed to both stress and alcohol during prenatal development had...

decreased male sexual behavior

Differences in brain anatomy between homosexuals and heterosexuals...

homosexual brain is shifted towards the opposite sex in some (but not all) ways

Homosexual men tend to have:

Larger anterior commissure and suprachiasmatic nucleus

Slightly larger third interstitial nucleus of the anterior hypothalamus (INAH-3)

During early stage of prenatal development, both male and female have... (3)

a set of Müllerian ducts and a set of Wolffian ducts, as well as undifferentiated gonads

Wolffian Ducts

precursors to other male reproductive organs

develop into the vas deferens and seminal vesicles

Müllerian ducts

precursors to the female's oviducts, uterus, and upper vagina

SRY Gene

Located on male Y chromosome

Causes the primitive gonads to develop into testes, the sperm-producing organs

Developing testes produce androgens which increase testes growth

Also produce Müllerian inhibiting hormone (MIH)

Females do not have the SRY gene and their gonads develop into ovaries, the egg-producing organs

Androgens and estrogens are...

steroid hormones

Steroid Hormones (4 Carbon Rings) exert their effects (3 ways)

Bind to membrane receptors like neurotransmitters

Enter cells and activating certain kinds of proteins in the cytoplasm

Bind to chromosomes where they activate or inactivate certain genes

Estrogen

Category of chemicals; Estradiol = most common

Androgens

Category of chemicals; Testosterone = most common

Progesterone (2)

Prepares the uterus for the implantation of a fertilized ovum

Promotes the maintenance of pregnancy

Gene/Sex Differences

At least three genes on the Y chromosome are active in specific brain areas

At least one gene on the X chromosome is active only in the female brain

Activating effects of sex hormones

Occur at any time of life and temporarily activate a particular response

Examples: pregnancy, menstruation