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NROC61 - Ch17 textbook notes

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University of Toronto Scarborough
Le Boutillier

Chapter 17 Sex and the Brain Sex and Gender y Genderspecific behaviours result from complex interactions among selfassessment societal expectations genetics and hormones y These behaviours are related to gender identityour perception of our own gender The Genetics of Sex y Females have two X chromosomes one from each parent y Males have an X chromosome from the mother and Y chromosome from the father o Gender is determined by the X or Y contribution from the father y The X chromosome is significantly larger than the Y chromosome o The X chromosome contains about 1500 genes whereas the Y chromosome contains less than 50 y If a female has a defective X gene there may be no negative consequence if her other X gene is normal However any defect in the single X chromosome of the male can lead to developmental defectso These are called Xlinked diseases y The smaller Y chromosome has fewer genes and less diverse functions o It contains the gene called the sexdetermining region of the Y chromosome SRY which encodes for a protein called testisdetermining factor TDF o A human with a Y chromosome and the SRY gene develops as a male and without it the individual develops as a female Sexual Development and Differentiation y How does genotype of the child lead to the male of female development of the gonads o During the first 6 weeks of pregnancy the gonads are in an indifferent stage that can develop into either ovaries or testes o The uncommitted gonad possesses two key structures the Mullerian duct and the Wolffian duct If the fetus has a Y chromosome and an SRY gene testosterone is produced and the Wolffian duct develops into the male internal reproductive system The Mullerian duct is prevented from developing by a hormone called Mullerianinhibiting factorIf there is no Y chromosome and no upsurge of testosterone the Mullerian duct develops into the female internal reproductive system and the Wolffian duct degenerates The Hormonal Control of Sex y Ovaries and testes release hormones and the pituitary gland regulates this release y Sex hormones are crucial to the development and function of the reproductive system and sexual behaviour These hormones are called steroids o Steroids are molecules synthesized from cholesterol and have four carbon rings The Principal Male and Female Hormones y Men have higher concentrations of androgens and women have more estrogens y Steroids act differently from other hormones Some like vasopressin and oxytocin are proteins cannot cross the lipid bilayer which act at receptors with extracellular binding sites o Steroids however can easily pass through cell membranes and bind to receptors within the cytoplasm giving them direct access to the nucleus and gene expression y The testes are responsible for the release of androgens small amounts are also secreted from the adrenal glands o Testosterone is by far the most abundant androgen o Prenatally elevated testosterone levels are essential for the development of the male reproductive system Increases in this hormone during puberty regulates the development of secondary sex characteristics o Female concentrations of testosterone is roughly 10 of those found in males y The principal female hormones are estradiol and progesterone which are secreted by the ovaries
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