Chapter 17 Sex and the Brain

Introduction Neural machinery underlying reproduction Reproduction and eating Regulated by subcortical structures Conscious control by cerebral cortex Influence of brain on sex hormones Sexual and reproductive behaviors Male and female brains

Sex and Gender Concept of Gender Biological characteristics and qualities Gender-specific behaviors Self-assessment Societal expectations Genetics Hormones Gender-identity Perception of gender

Sex and Gender X chromosome larger than Y The Genetics of Sex Genotype- Male: XY, Female: XX X chromosome larger than Y X contains 1500 and Y contains 50 genes X-linked diseases Occur more often in men than women SRY: Gene on Y chromosome, encodes TDF

Sex and Gender The Genetics of Sex Encodes testis-determining factor Location of SRY on Y chromosome Causes development of testes and testicular hormones Makes fetus develop as male Default pathway, female

Sex and Gender Differentiation of fetus and development of gonads

The Hormonal Control of Sex Hormones regulate physiological processes Sex hormones: Steroids Endocrine glands: Release sex hormones Pituitary gland: Regulates endocrine glands Structure affects function of hormone Male hormone: testosterone Female hormone: estradiol

The Hormonal Control of Sex The Principle Male and Female Hormones Men: High concentration of androgens Women: High concentration of estrogens Testosterone (androgen) + aromatase  estradiol (estrogen) Protein hormones- do not pass through cell membranes, bind surface receptors Steroid hormones (Such as the sex hormones)- pass through cell membrane, bind cytoplasmic receptors Receptor concentrations vary in different brain regions

The Hormonal Control of Sex Concentration of estradiol receptors in sagittal section of rat brain

The Hormonal Control of Sex The Principle Male and Female Hormones (Cont’d) Males: Testes- release androgen Testosterone – increase at puberty leads to development of secondary sex characteristics Females: Ovaries- secrete estradiol (estrogen) and progesterone (progestin) Blood concentrations of sex hormones vary Males- levels fluctuate mildly during a 24 hour cycle Females- levels fluctuate more extensively but on a 28-day cycle

The Hormonal Control of Sex Pituitary and Hypothalamus Control of Sex Hormones Gonadotropins: LH and FSH Males- LH produces testosterone; FSH aids sperm maturation Females- LH, FSH cause estrogen secretion

The Neural Basis of Sexual Behaviors Neural control of human sex organs

The Neural Basis of Sexual Behaviors Reproductive Organs and Their Control Using Neurotransmitters: Relax smooth muscle Acetylcholine vasoactive intestinal polypeptide (VIP) nitric oxide (NO)

The Neural Basis of Sexual Behaviors Mammalian Mating Strategies Polygyny Male mates with many females Polyandry Female mates with many males Monogamy One mate

The Neural Basis of Sexual Behaviors The Neurochemistry of Reproductive Behavior Prairie voles: Solidly monogamous Meadow voles: Asocial and promiscuous Affected by oxytocin and vasopressin… Prairie voles exhibit higher levels of vasopressin and oxytocin…. Suggesting a role in the brain

The Neural Basis of Sexual Behaviors Role of oxytocin and vasopressin receptors in reproductive behavior Prairie voles display more oxytocin in females and more vasopressin receptors in males Meadow voles, fewer receptors in both sexes

Why and How Male and Female Brains Differ Sexual Dimorphisms of the CNS Onuf’s nucleus Controls motor neuron pool Sexually dimorphic nucleus (SDN) INAH in humans analogous to rat SDN

Why and How Male and Female Brains Differ Sex Hormones, the Brain, and Behavior (Cont'd) Organizational effect of hormones Tend to be irreversible Activational effect of hormones Tend to be temporary

Why and How Male and Female Brains Differ The Activational Effects of Sex Hormones Brain Plasticity and Maternal Behavior

Why and How Male and Female Brains Differ Sexual Orientation INAH-3 - twice as large in heterosexual males compared to heterosexual females: Sexually dimorphic INAH-3 in homosexual males: Similar in size to that in heterosexual females INAH – 3 in homosexual females does not appear to differ from heterosexual females