Sex- biological characteristics that divide organisms into male and female
-Gender-behavioral characteristics associated with being male or female
Gender Role- set of behaviors society deems appopraite for people of a given biological sex
Gender Identity-persons subjective feeling of being male or female
1. Why has sex evolved?
2. Why sexually reproduce as opposed to on my own?
In order to better fit you offspring for a changing environment. Different genes provide a greater probability that at least one gene combination will aid in survival
The Sex Act
Masters and Johnson (1966)= physiological recordings of 10000 episodes of sexual activity in the lab:
Identified 4 Stages of Sexual Response
1. Excitement=increased HR, respiration, muscle tone, engorgement of sexual tissue
2. Plateau= arousal maintained at high level for minutes, preparation for orgasm
3. Orgasm= rythmic contractions of genital muscles, intense euphoria
4. Resolution= arousal decreases and body regains homeostasis
Male refractory period=unable to become aroused for minutes/hours/days
May begin in the cerebral cortex (erotic thoughts ) but is coordinated (and may begin through stimulation of mechanoreceptors) in spinal Cord
-Genetalia mechanoreceptors send information into dorsal horn of SC- information projects to brain
-Info from genitalia or brain activates PARASYMPATHETIC NS =engorgement, erection, and lubricating secretions
-Parasympathetic axons release ACh, and NO onto erectile tissue (relaxation of smooth muscle= increased blood flow)
-Increased activity of sensory axons and input from the brain excites SYMPATHETIC neurons= orgasm
-Muscle contractions of penis and vaginal walls
Testes Produce androgens:
Androgens= male hormones= because males have more than females
-also produced by adrenals
Ovaries produce Estrogen and Progestins:
E & P= female hormones= because females have more than males
(eg. estradiol, progesterone)
Important for male sexual Motivation
-Castration=removal of testes
(but remember adrenals still produce T)
-loss of sexual interest and function
-may be maintained IF sexually experienced
-Reinstated with T replacement
Androgen antagonists (elected by some criminals )
-80-100% effective in eliminating deviant sexual behavior
Having testosterone is important for sexual motivation and performance, but even men with low testosterone may maintain normal sexual activity
Hormones important for female sexual motivation
-in most species, females will not copulate unless in "heat"= heightened levels of female sex hormones
-human females will copulate throughout hormonal cycle, but show more initiation of sex during ovulation when estrogen levels are highest
-not seen in women taking birth control
-ovulation is also when testerone is high
-testosterone therapy for post-menopausal women
Mediate Preoptic Area of the Hypothalamus (mPOA)
Involved in male and female sexual behavior:
-stimulation increases copulation in rats
-Shows activity during copulation
-May be more responsible for performance than drive:
--Monkeys with lesions of the mPOA no tried to copulate with females, but would masterbate in their presence
-Active during copulation
-Stimulation release Dopamine in mPOA
Receives sensory information about erotic stimuli and sends passage to mPOA
Dopamine is important for sexual motivation in both sexes and sexual performance in males
DA increases in nucleus accumbens during sexual stimulation
-Initially small amounts of DA during sexual stimulation active D1 receptors ->activates parasympathetic NS
-As DA increases-> activates D2 receptors ->shifts the balance to sympathetic activation->orgasm!
-D2 activation inhibits erection which accounts for refractory period
The Coolidge Effect: a quicker return to sexual arousal when a new partner is introduced
This is a dopaminergic effect!
-DA increases in NAcc of males when female is presented
-DA drops back to baseline as interest wanes following penetrations
-introduction of a new female increases DA again
Serotonin contributes to refractory period
-Ejaculation is accompanied by 5-HT release in hypothalamus->contributes further to refractory period :
-Injection of seretonin reuptake inhibitors into hypothalamus increase time until next copulation in male rats and affects ability to ejacualate
- SSRIs impair sexual desire and ability to climax in human users
Seretonin inhibits oxytocin
Important for smooth muscle Contraction
-Released from the posterior pituitary
-In non-humans is important for male sexual performance and females sexual receptivity
-Oxytocin levels increase during masturbation
-Is most likely responsible for smooth muscle contractions that occur during orgasm
....also important in:
-correlation of plasma levels and social bonding, increased trust, and decreased fear-> is this actually what increases sexual performance?
Your Nose as a Sex Organ?
Pheromones=airborne chemicals released by organisms that produce physiological or behavioral effects in another organism of the same species
Vomeronasal Organ=cluster of receptors in nasal cavity which detect pheromones
-sends signals to mPOA and medial amygdala
-Males and females using colognes and perfumes containing pheromones report more sexual activity with a partner
-PET scans show activation of anterior hypothalamus when subjects "smelled" pheromones
-Strippers make more money when ovulating :$70 an hour during their peak period of fertility,versus about $35 while menstruating and $50 in between-strippers on birth control always make $35
Sperm (23 chromosomes) + Egg (23 chromosomes ) =Person (46 chromosomes)
Females:22 pair chromosomes and 2X chromosomes=XX
Male:22 pairs chromosomes and 1X and 1Y chromosomes: XY
For the 1st month XX and XY fetuses are identical!
If fetus has Y chromosome= SRY gene which codes for protein called TDF (testis-determined factor)
-Testes develop and secrete:
--Testosterone=masculinizes internal/external genetalia and NS
--MIH (Mullerian Inhibiting Hormone)=Mullerian system degenerates
If fetus has NO Y chromosome= no SRY gene
-Mullerian ducts develop into internal genetalia and external genetalia feminized
-Wolffian system withers and is absorbed!
Testes produce androgens:
Androgens: male hormones= becuase males have more than females (eg. testosterone)
-also produced by adrenals
Ovaries produce Estrogen and Progestins
E & P= female hormones= because females have more than males
(eg. estradiol, progesterone
Ovaries do NOT produce E and P until puberty, so feminization is a passive process in the fetus
Sex hormones have organizational and activational effects.
Organizational Effects of Hormones- mostly occur prenatally; they affect structure and are lifelong in nature. They are PERMANENT
-development of sex organs
Activational Effects of Hormones- can occur at any time in individuals life and may be transient or long lasting. They are REVERSIBLE
-growth of body hair
-development of breast tissue
Fetal testosterone in circulation affects the developing brain:
Steroid hormones can exert their effects in 2 ways...
1. Bind to enzymes/channels/receptors and alter membrane excitability, sensitivity to NT, or NT release (within seconds)
2. Enter the cell and go to nucleus to modify gene transcription
Testosterone is converted to estradiol by aromatase and works at estrogen receptors in the brain
Fetal hormones have organizational effects on the brain which may cause structures to become sexually dimorphic (different in males and females) leading to differences in male and female behavior...in rats anyway.
SDN-POA 5x larger in male rats:
-Destruction of SDN reduces male sexual activity
-Perinatal aromatase inhibitors block masculinization of structure and function
VMH important for female sexual behavior:
-Active during copulation
-Lesion reduce activity
-Stimulation facilitates lordosis
What about humans? Do they have sexually dimorphic brain regions?...Maybe
Preoptic Area=four clusters of neurons called the interstitial nuclei of the anterior hypothalamus (INAH1-4)
-INAH-1 may be larger in men;may be human analogous of SDN
-INAH-3 is 2x larger in men, but we dont know about functional differences
Corpus Callosum may be larger in men?
Remember these are structurally different and many organizational differences may not be pronounced enough to observe
Because hormones are more important than chromosomes for organizing the nervous system it is possible to have a genetic male with a "female brain" and a genetic female with a "male brain"
-Treatment of females early in development with testosterone=decrease in female sexual behaviors in adulthood
-Female calves exposed to androgens in untero=freematins
Congenital Adrenal Hyperplasia (CAH)
-XX individuals with normal internal genetalia (i.e. uterus, ovaries, fallopian tubes)
-Enzymatic defect causes over-activity of adrenals early in development
-Increased androgens masculinize external genetalia (enlarged clitoris)
-Behavior is "tomboyish" and aggressive
-Higher percentage have erotic contact with women (22% as opposed to %10)
Prenatal exposure to androgens cause "male-like" organization of brain...or environmental factors?
Males excel at spatial tasks requiring rotations of 3D objects (Hyde, 1996)
-Males with low T during development perform poorly-may be organizational
-Males with higher T perform better- to a point
-Females with higher androgen level perform better
-Could be related to genes on X chromosomel because a boy's spatial abilities correlate with mother's?
-May have nothing to do with T, but with larger corpus callosum
Does testosterone have a link to aggression?
-Men kill 30 times as often as women
-Aggression in males partly genetic; moderately correlated in identical twins reared apart.
-Testosterone is higher in males rated as more aggressive-is T the cause or effect?
-Testosterone is increased after winning a sports competition
Females excel at verbal fluency and writing
Activational effect of estrogen?
Transsexual men taking estrogen supplements score higher on verbal tests than transsexual men not taking estrogen.
Estrogens increase dendritic spine density in hippocampal neurons
-Dendritic spines= outcrossings on dendrites that allow neuron to have greater surface area for synapses
-Number of dendritic spines on female rat hippocampal neurons fluctuated with 5 day cycle
-Rise in estrogens correlated with rise in spines
-Increased spines=increased excitatory synapses
-New synapses shown to have more NMDA receptors
Estrogens increase long-term potentiation in hippocampus!!
Peak in spine density coincides with peak in fertility=high estrogens
Perhaps increased spatial abilities facilitate looking for a mate???
Sex hormones also have activational effects on secondary sex characteristics (e.g muscle tone, breast tissue, etc)
5-alpha reductase deficiency:
-Genetic mutation in 5-alpha reductase which causes deficiency in the enzyme
-5alpha H converts testosterone into DHT (dihydrotestosterone) during development
-DHT is super potent T masculinizes external tissue
-XY individuals with deficiency may be born with feminized genetalia (i.e. not masculinized)
-At puberty, testes make enough testosterone to masculinize peripheral tissue further -> now male appearance
Salinas, Dominican Republic=Guevodoces