Chapter 17 Sex and the Brain. Introduction Influence of brain on sex hormones Sexual and reproductive behaviors Male and female brains.
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Chapter 17 Sex and the Brain
Introduction
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
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 GenderDifferentiation of fetus and development of gonads
The Hormonal Control of SexHormones regulate physiological processes
– Sex hormones: Steroids
– Endocrine glands: Release sex hormones
– Pituitary gland: Regulates endocrine glands
– Structure affects function of hormone
– Primary male hormones: testosterones
– Primary female hormones: estradiols
The Hormonal Control of SexThe Hormonal Control of SexThe Principle Male and Female Hormones
– Men: High concentration of androgens
– Women: High concentration of estrogens
Aromatization Process for Steroid Hormones:
Testosterone (androgen) + aromatase estradiol (estrogen)
The Hormonal Control of SexConcentration of estradiol receptors in sagittal section of rat brain
The Hormonal Control of Sex
– Males: Testes- release androgen
• Testosterones – increase at puberty leads to development of secondary sex characteristics
– Females: Ovaries- secrete estradiol (estrogens) and progesterone (progestins)
• 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 SexThe Hormonal Control of SexPituitary 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
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 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 receptors 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
– Sexually dimorphic nucleus (SDN)
– INAH in humans analogous to rat SDN
Why and How Male and Female Brains Differ
Why and How Male and Female Brains Differ
– Organizational effect of hormones• Tend to be irreversible
– Activational effect of hormones• Tend to be temporary
Why and How Male and Female Brains DifferWhy 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.
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
– See Levay, 1991.
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