2 Introduction Influence of brain on sex hormones Sexual and reproductive behaviorsMale and female brains
3 Sex and Gender Concept of Gender Biological characteristics and qualitiesGender-specific behaviorsSelf-assessmentSocietal expectationsGeneticsHormonesGender-identityPerception of gender
4 Sex and Gender The Genetics of Sex Encodes testis-determining factor Location of SRY on Y chromosomeCauses development of testes and testicular hormonesMakes fetus develop as maleDefault pathway, female
5 Sex and GenderDifferentiation of fetus and development of gonads
6 The Hormonal Control of Sex Hormones regulate physiological processesSex hormones: SteroidsEndocrine glands: Release sex hormonesPituitary gland: Regulates endocrine glandsStructure affects function of hormonePrimary male hormones: testosteronesPrimary female hormones: estradiols
7 The Hormonal Control of Sex The Principle Male and Female HormonesMen: High concentration of androgensWomen: High concentration of estrogensAromatization Process for Steroid Hormones:Testosterone (androgen) + aromatase estradiol (estrogen)
8 The Hormonal Control of Sex Concentration of estradiol receptors in sagittal section of rat brain
9 The Hormonal Control of Sex Males: Testes- release androgenTestosterones – increase at puberty leads to development of secondary sex characteristicsFemales: Ovaries- secrete estradiol (estrogens) and progesterone (progestins)Blood concentrations of sex hormones varyMales- levels fluctuate mildly during a 24 hour cycleFemales- levels fluctuate more extensively but on a28-day cycle
10 The Hormonal Control of Sex Pituitary and Hypothalamus Control of Sex HormonesGonadotropins: LH and FSHMales- LH produces testosterone; FSH aids sperm maturationFemales- LH, FSH cause estrogen secretion
11 The Neural Basis of Sexual Behaviors Mammalian Mating Strategies:PolygynyMale mates with many femalesPolyandryFemale mates with many malesMonogamyOne mate
12 The Neural Basis of Sexual Behaviors The Neurochemistry of Reproductive BehaviorPrairie voles: Solidly monogamousMeadow voles: Asocial and promiscuousAffected by oxytocin and vasopressin… Prairie voles exhibit higher levels of vasopressin and oxytocin…. Suggesting a role in the brain
13 The Neural Basis of Sexual Behaviors Role of oxytocin and vasopressin receptors in reproductive behaviorPrairie voles display more oxytocin receptors in females and more vasopressin receptors in malesMeadow voles, fewer receptors in both sexes
14 Why and How Male and Female Brains Differ Sexual Dimorphisms of the CNSSexually dimorphic nucleus (SDN)INAH in humans analogous to rat SDN
15 Why and How Male and Female Brains Differ Organizational effect of hormonesTend to be irreversibleActivational effect of hormonesTend to be temporary
16 Why and How Male and Female Brains Differ An example of the activational effects of hormones… in the somatosensory cortex, the plasticity of the ventral surface for the nipples increases by ~100% to encourage lacation .This increase in sensation is associated also with increases in prolactin, oxytocin, and a variety of birthing, parental care, and reproductive behaviors.
17 Why and How Male and Female Brains Differ Sexual OrientationINAH-3 - twice as large in heterosexual males compared to heterosexual females: Sexually dimorphicINAH-3 in homosexual males: Similar in size to that in heterosexual femalesINAH – 3 in homosexual females does not appear to differ from heterosexual femalesSee Levay, 1991.