1. Chapter 17 Sex and the Brain

2. 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

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

4. 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

5. 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

6. Sex and Gender
Differentiation of fetus and development of gonads

7. 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

8. 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

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

10. 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

11. 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

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

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

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

15. 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

16. 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

17. 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

18. 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

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

20. 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