PSY 2007 - Sex Differences

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Neurotransmitters

Chemical messengers in the brain

–From one neuron to the next

–Local action

–Effects can be activation or inhibition, depending on the transmitter/receptor combination

Hormones

Chemical messenger in the body

–Through the bloodstream

–Global action

–Effects can be varied, depending on the hormone/receptor combination

SRY Gene

Located on the Y-chromosome

Turns the fetal gonad into a testis (2 testes) - Testis-Determining Factor.

In its absence, the gonad becomes an ovary.

Early testis produces 2 types of hormones

–Anti-Mullerian Hormone (defeminising)

–Androgens (masculinising)

•In the absence of these hormones, female sex organs develop (primary sexual characters)

Organizational Effect (action of hormones)

Effect remains after the hormone has been removed. Often occurs during a sensitive period.

Activational Effect (action of hormones)

Effect is reversible, depending on presence or absence of hormone.

Puberty

•Organizational and activational role of sex hormones

•Development of Secondary Sexual Characters

•Pubic and axillary hair are androgen (androstenedione) sensitive in both males and females

•During childhood, sex hormone levels are almost undetectably low

•Developmental timing mechanism starts puberty

•Sex differences in mechanisms and timing

Gonadotropin-Releasing Hormones (GnRH)

Starts off Puberty

Move from hypothalamus to anterior pituitary gland to trigger sexual maturation

Gonadotropins (FSH & LH) in different sex

Male: Sperm production (FSH) & Testosterone production.(LH)

Female: Cause follicles to ripen (FSH) & Induce ovulation and formation of Corpus Luteum.(LH)

Hypothalamus-Pituitary-Gonadal Axis

negative feedback system, regulation of gondal hormones 

• Keep testostrone at an optimal point 

Androgen insensitivity syndrome

•Gonads develop as testes

•Androgen receptors do not work

•Testosterone cannot do its normal job

•46, XY individuals develop anatomically as female, but without internal female genitalia

Puberty is typically late, sometimes helped with hormone supplements

They typically identify as women

5α-reductase deficiency

•5α-reductase turns testosterone into DHT

•DHT is crucial for prenatal external genital development

•46, XY children are born with female external genitalia, but male internal genitalia

At puberty, the high levels of testosterone can “mimic” DHT

They develop male genitalia (“Guevedoces”)

After puberty, they mostly identify as men

Congenital Adrenal Hyperplasia

•High levels of prenatal testosterone in girls

•Ambiguous external genitalia in girls

•Often treated once diagnosed

•Some 46,XX children assigned male at birth

•5% of CAH girls assigned female at birth have gender dysphoria

•12% of CAH “girls” assigned male at birth have gender dysphoria

Four core genotypes

•By comparing the two rows to each other, you can find those sex differences that are due to the organizational effects (or activationaleffects if later in life) of testosterone ONLY

•By comparing the two columns to each other, you can find those sex differences that are due to genetic differences between males and females (presumably other genes on X and/or Y chromosomes).

Anti-Mullerian Hormone

Hormone produced by the early testis that causes defeminisation.

Male Sex Determination in Mammals (Hormones)

Primordial gonads develop into testes; androgens cause masculinization; Wolffian system develops into vas deferens, seminal vesicles, prostate; primordial external genitalia develop into penis and scrotum.

Female Sex Determination in Mammals (Hormones)

Primordial gonads develop into ovaries; Mullerian system develops into fimbriae, fallopian tubes, uterus, inner vagina; Wolffian system withers away; primordial external genitalia develop into clitoris, labia, outer vagina.

Neurotransmitters

Effects can be activation or inhibition, depending on the transmitter/receptor combination

Sexual Orientation

•One of the most extreme sex differences

•90-95% of human males are attracted to human females exclusively (“gynophile”)

•85-90% of human females are attracted to human males exclusively (“androphile”)

Structural differences (Sex differentiation in the brain)

•Male brains are ~ 10% larger

•Female cortex is thicker (more grey matter)

•Males have larger white matter volume & subcortical structures