Chapter 17: Sex

Sex and the Brain

Genetic Sex

Genetic Sex

Genotype based on chromosomes

Gender Identity

Self-perception of gender

Sexual Orientation

the sex of whom one is physically attracted

Concepts of biological sex and gender

– Biological characteristics and qualities

– Gender-specific behaviors

– Gender identity

def 4 Gender-specific behaviors

1. Introspection

   1. Upbringing

2. Societal expectations

3. Genetics, hormones

X chromosome _____ than Y

larger

X contains ___ genes, and Y contains __ genes.

800, 50

male and female genotype

male: XY

female: XX

X-linked diseases occur more often in… than…

men, women

What makes fetus develop as male

SRY: gene on Y chromosome

• Encodes testis-determining factor (TDF)

• Causes the development of testes and testicular hormones

what causes Sex Chromosome Abnormalities

Rarely, too few, or too many sex chromosomes

def turner syndrome

Partial or complete absence of one X chromosome in a female (XO genotype)

def Klinefelter syndrome

Extra X chromosome in a male (XXY genotype)

Differentiation of Fetus and Development of Gonads

male: wolffian duct

female: Mullerian duct

def sex hormones

steroids

• develop from cholestoral

• made of fatty tissue

male and female sex hormones

male: testosterone

female: estradiol

what releases sex hormones

endocrine glands

what regulates the endocrine glands

Pituitary gland

high concentration of androgens

men

high concentration of estrogens

women

how is estrogen made

Testosterone (androgen) + aromatase → estradiol (estrogen)

what don’t pass through cell membranes,

bind surface receptors.

protein hormones

what do pass through cell membrane, bind to

cytoplasmic receptors.

steroid hormones

Receptor concentrations ___ in different brain regions.

vary

what do testes release

androgen

Testosterone increase at puberty leads to development of…

secondary sex characteristics.

what do ovaries secrete

estradiol (estrogen) and progesterone (progestin)

Estrogen increase at puberty leads to maturation of… and development of…

maturation of female reproductive system and development of breasts.

Blood concentrations of sex hormones vary b/t male and female

male: levels fluctuate rapidly each day

female: levels fluctuate in 28-day cycle

Gonadotropins

LH and FSH

LH and FSH funct. in males

LH stimulates testosterone production; FSH aids sperm maturation

LH and FSH funct. in females

LH and FSH cause estrogen secretion.

def 2 phases of Menstrual cycle

1. follicular phase

2. luteal phase

Sexual response cycle

Arousal, plateau, orgasm, resolution

Cerebral cortex ctr Reproductive Organs

– Neural control of sexual response

Spinal cord ctr Reproductive Organs

– Mediates sexual response of genitals

External genitals

males: penis

females: labia and clitoris

what kind of muscles make up genitals

smooth muscle

what relaxes smooth muscle in penis and

clitoris

Neurotransmitters: Acetylcholine, vasoactive intestinal polypeptide (VIP), and nitric oxide (NO)

Activity from the sympathetic division of the ANS

Male orgasm: muscular contractions → ejaculation

females orgasm: muscular contraction

Polygyny

Male mates with many females.

Polyandry

Female mates with many males.

Monogamy

Male and female mate exclusively.

why are prairie voles social and monogamous

more oxytocin (female) and vasopressin (male)

what are montane voles asocial and promiscuous

fewer receptors for oxytocin and vasopressin

what do human plasma oxytocin levels increase

• During breastfeeding in mothers

• During sexual intercourse in men and women

Brain activation demonstrates…

strong reinforcing nature of partner and parental relationships.

what do fMRI studies show

Oxytocin and vasopressin play roles in human bonding.

who is more verbal and who is more spacial

women, men

*Larger differences between individuals than between sexes*

Steroids funct

• Alter membrane excitability, sensitivity to neurotransmitters, neurotransmitter release

• Modulate functions of various enzymes, channels, and transmitter receptors

• Diffuse across outer cell membrane

• Bind to specific steroid receptors in cytoplasm and nucleus

Organizational effects of hormones

• Development, anatomy

• Tend to be irreversible

Activational effects of hormones

• Behaviors

• Tend to be temporary

what normally determines hormonal funct.

genetic sex

Treatment with testosterone in early development of mammals leads to

reduced female reproductive behaviors

what causes an Androgen-insensitive genetic males

defective androgen gene on X chromosome

what causes Congenital adrenal hyperplasia in genetic females

abnormally large adrenals overproduce androgens → External genitals intermediate between normal clitoris and penis

def Gynandromorph

having both male and female tissues

Gynandromorphic zebra finch - brain differences

Female left side

Male right side

Role of genes in complex sex behaviors in fruit flies

• Sexual behaviors encoded in genes

• The fru and dsx genes

what causes increased sexual interest - male vs female

• male: rise in testosterone

• Women: rise in estrogen

what rises during pregnancy

Rise in leptin levels

how does interaction with offspring may alter male brain structure

• increase density of dendritic spines

• Increased vasopressin receptors

what has dramatic effects on hippocampal neuronal dendrites

Estradiol treatment

what coincides with female rat’s peak fertility

Increase in hippocampal spine numbers

• May play a role in changing reproductive needs

• Estradiol’s protective effect on neurons (in culture)

def 2 benefits of estrogen

• May protect against stroke

• May benefit women with multiple sclerosis

Interstitial nucleus of the anterior hypothalamus (INAH); INAH-3 is Twice as large in… than…

men, women

• INAH-3 in… similar to that in…

gay men, women

Spinal nucleus of the bulbocavernosus (SNB) larger in… during…

men, erections

Corpus callosum: splenium larger in… than…

females, males

dimorphisms are

subtle, few, and functions unknown.