Presentation on theme: "Topic 18 Sex and the Brain Lange"— Presentation transcript:
1 Topic 18 Sex and the Brain Lange Biology NeurobiologyTopic 18Sex and the BrainLange
2 IntroductionInfluence of brain on sex hormones…. and the influence of the sex hormones back on the brain.Sexual and reproductive behaviorsMale and female brains
3 Sex and GenderConcepts of Gender are very much inter-realated, but will involve specifics of:Biological characteristics of gender associated with architecture:MorphologyOrganization of the brainGender features associated with psychology and perception:Self-assessmentSocietal expectationsGender-identityPerception of genderGender features associated with biochemistry:GeneticsHormones
4 Some chromosomal systems of sex determination 44 +XYXX22 +XYParentsOvaSpermZygotes(offspring)(a) The X-Y system(b) The X-0 system(c) The Z-W system76 +ZWZZ32(Diploid)16(Haploid)(d) The haplo-diploid systemFemale = default sexMale = default sex
5 Sex and Gender The Genetics of Sexual Determination Y Chromosome encodes testis-determining factor (Tdf)Tdf is produced from the SRY gene on Y chromosomeGuides development of testes and production of testicular hormonesPromotes fetal development as male
6 Sex and GenderDifferentiation of fetus and development of gonads
7 The Hormonal Control of Sex Hormones regulate physiological processesSex hormones: Steroidal hormonesEndocrine glands: Gonads release sex hormonesPituitary gland: Regulates endocrine glands (LH & FSH)Small structural differences affects function of hormonePrimary “male” hormones: androgens (testosterones)Primary “female” hormones: estradiols and progestins
8 The Hormonal Control of Sex The Principle Male and Female Hormones in adulthoodMen: High concentration of androgensWomen: High concentration of estrogens & progestinsAromatization Process for Steroid Hormones:Testosterone (androgen) + aromatase estradiol (estrogen)
9 The Hormonal Control of Sex Concentration of estradiol receptors in sagittal section of rat brain
10 The Hormonal Control of Sex Males: Testes- release androgensAndrogens (testosterones) – increase at puberty leads to development of secondary sex characteristicsFemales: Ovaries- secrete estradiol (estrogens) and progesterone (progestins)For both sexes, blood concentrations of sex hormones vary:Males- levels fluctuate mildly during a 24 hour cycleFemales- levels fluctuate more extensively but on a28-day cycle
11 The Hormonal Control of Sex Pituitary and Hypothalamus Control of Sex HormonesGonadotropins: LH and FSHMales- LH stimulates testosterone; FSH aids sperm maturationFemales- LH, FSH cause estrogen secretion
12 The Neural Basis of Sexual Behaviors Mammalian Mating Strategies:PolygynyMale mates with many femalesPolyandryFemale mates with many malesMonogamyOne mate
13 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
14 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
15 Why and How Male and Female Brains Differ Sexual Dimorphisms of the CNSSexually dimorphic nucleus (SDN)INAH in humans analogous to rat SDN
16 Why and How Male and Female Brains Differ Organizational effect of hormonesTend to be irreversibleActivational effect of hormonesTend to be temporary
17 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.
18 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.
Your consent to our cookies if you continue to use this website.