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46 Cards in this Set
- Front
- Back
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Why engage in sexual behavior? |
1. Gain pleasure In relation to positive incentive Theory in food = gain pleasure from food 2. Main reasons for sex = to produce offspring, survival of species |
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Is sex necessary to reproduce? |
The whiptail lizard is an all-female species They don’t engage in sex Female develops an egg which forms into an embryo Similarly in plants, they don’t physically engage in sexual reproduction They reproduce asexually If the main method of sex is to reproduce, and asexual reproduction is a method of producing offspring, why do species engage in sex? |
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Reason for sexual reproduction |
For genetic diversity If an offspring comes from only a female parent, then the generic copy from the mother is passed down to the offspring If there’s female and male parents, then half the genetic copy is from female and half from male, so the offspring has a unique genetic copy that isn’t identical to both parents In the circumstance of an environmental condition or genetic mutation which effects female parent in asexual reproduction, it will also effect the offspring If there is female and male, then genetic variation exists and if either parent doesn’t survive due to genetic mutation or environmental condition, at least offspring will survive to pass on genes |
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Why are siblings different? |
Every time female and male engage in sex and the female produces an egg, the genetic copy of the egg differs each time a new egg is produced or new sperm is produced so different genetic copies given to each sibling Despite risks of sexual reproduction (STIs, males engage in aggressive means to mate) it provide genetic variation |
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3 fundamental steps involved in sexual reproduction |
1. Gametogenesis = male and female produce gametes = sperm/egg 2. Mating = female and male come into contact physically, bringing the gametes into same location (uterus) 3. Fertilization = sperm fuses with egg and forms a zygote |
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What structures forms the gametes? |
In males = testes In females = ovaries |
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How many chromosomes do humans have? |
23 pairs of chromosome in all cells in body But in gametes there are only 23 single chromosomes Reason: egg and sperm fuse to produce an embryo. If each gives 23 pairs then the offspring will have 46 pairs of chromosome. And as every generation goes forward, the number of chromosomes will multiply |
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How do sex chromosomes interact to determine sex of the offspring? |
Female egg has XX chromosome Sperm has XY chromosome Sperm determines the sex of offspring because it contains the Y chromosome When egg and sperm fuses: 1. Sperm carries Y chromosome, so the zygote has one X chromosome and one Y chromosome In Y chromosome, contains SRY gene in the short arm of Y chromosome 2. Fetus has X chromosome so no SRY gene
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What does SRY gene do? |
In sixth week of gestation, the SRY gene produces a chemical called Testis Determining Factor (TDS) All feotuses have the primordial gonads It’s a tissue that eventually grows into Testes or Ovaries |
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How do Testes or Ovaries form |
When SRY gene releases TDF stimulates the primordial gonads to develop into Testes in 6th week of gestation In 7th week: when TDF makes gonads develop into Testes, the testes releases 2 types of hormones: 1. Testosterone 2. Anti Mullerian Hormone Testosterone stimulates Wolfian duct to develop into male internal sex organs such as Vas deferens and seminiferous tubules The anti mullerian hormone makes the Müllerian duct to degenerate |
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In 8-12 weeks of gestation |
The testosterone stimulates other tissues in fetus to develop into external sex organs E.g. Penis, scrotum Testosterone itself doesn’t cause these tissues to grow Testosterone is converted into dihydrotestosterone These hormones stimulate the external sex organs to develop of male fetus |
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In the absence of SRY gene |
In 6th week = primordial gonads will not develop into testes Any fetus has a natural tendency for primordial gonads to develop into Ovaries if they remain unstimulated by week 7 If testosterone doesn’t stimulate the gonads by week 7, grows into Ovaries REMEMBER: it is the male hormones that cause the primordial gonads to develop into testes In the absence of anti mullerian hormones and testosterone, the wolfian duct degenerates Müllerian duct grows into internal sex organs of females such as Fallopian tube and Uterus Later other tissues develop into external sex organs of females |
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When are female hormones released? |
Female hormones = oestrogen and progesterone Don’t start being released until week 12 Everything that happens up till week 12 is automatically generated, not hormone stimulated in FEMALES |
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In human males, testosterone stimulates growth of tissues into sex organs. What happens at the cellular level? |
Male sex hormone testosterone diffused through cell membrane Enters cytoplasm of a cell In the cytoplasm, enzyme aromatase in found Aromatase Converts testosterone into estrogen Estrogen can bind to receptor protein inside cytoplasm called ESTROGEN RECEPTORS They form a complex called Estrogen-Receptor Complex This complex enters nucleus of cell and binds to specific sites of DNA to trigger transcription producing mRNA then proteins then different sex organs |
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What are Primary sex characteristics? |
These are the formation of internal and external sex organs |
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During puberty, secondary sex characteristics form in males and females. How is this process stimulated? |
With influence of genetics Around puberty, hypothalamus releases hormone called GnRH (Gonadotropin Releasing Hormone) This hormone stimulates the Anterior Pituitary Gland - master gland in brain (controls other glands in body and other internal organs) When anterior Pituitary Gland is sinutlatdf by GnRH, releases 2 types of hormones in males and females: 1) Follicle stimulating hormone (FSH) 2) Leutinising Hormone (LH) In males: FSH causes seminiferous tubules to release sperm In males LH: causes Leydig cells in testes to produce more testosterone When testosterone levels in males increases causes secondary sexual characteristics In females FHS: triggers Ovaries to develop progesterone In females LH: Ovaries develop oestrogen Both progesterone and oestrogen are involved in men’s trail cycle produce the egg for ovulation |
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Secondary sex characteristics |
Males: increase in mass of skeletons and muscles Deepens voice Ability to produce sperm Females: Growth of breast Curves Further growth to external genitalia (vagina, clitoris) 2 years after this menstruation starts in females A year after menstrual cycle can become pregnant |
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Negative feedback in hypothalamic hormone release |
After secondary sex characteristics have developed, the hormone levels in body send signals to Pituitary gland to stop releasing FSH and LH In turn the Pituitary gland sends signals to hypothalamus to stop releasing GnRH This stops the whole process Called negative feedback because feedbacks to same system to stop releasing substances |
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Behaviours that also differentiate females and males |
There are 3 types of behaviours 1. Appetitive behaviours = appetite for sex These are the sexual drives and motivations an individual has towards having sex, include approaching a female and signaling response that attract females or males 2. Consummatory behavior = acts of sex 3. Sexual orientation/ Gender Preferences = appetitive response to a specific target such as those of the same species and males having preference towards females and females having preference towards other males Some males will also have preference towards other males and females towards other females |
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What in the nervous system triggers consummatory behaviors? |
Phoenix et al: First to report an organization effect of prenatal testosterone exposure on adult female sexual behavior in guinea pigs Before this, no evidence that linked the structures of the brain to sexual behaviours |
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Phoenix et al (1959) |
Studies male and female guinea pigs Males and females had distinct consummatory behaviors from one another Males = involved in mounting Females = lordosis = female has ovulated, so lifts hind quarters, moves tail away to signal to male that it wants to mate Experiment: They injected high levels of sex hormones: oestrogen and then progesterone in the females and found they could stimulate lordosis in adult females Also found: if they manipulated males and females in first few days of life (in the neonatal period), it will effect these sexual behavior Experiment: Exposed the female rats to high levels of testosterone in the early days of its life Found: examined female rats later in adult lives, saw they didn’t display lordosis, instead they mounted other females In male rats... Castrates male rats so can’t produce testosterone Found: in adult life, these male rats were not involved in mounting behavior When the male rats were exposed to oestrogen and progesterone = displayed lordosis towards other males Conclusion: manipulation of hormones in early life can affect the way the neural system is organized and in later life this structural change of neural system can effect sexual behaviors However this is still a hypothetical link - no direct evidence Hormones are manipulated and behaviours are measured and in between fill in the gap by saying that hormones effect neural system |
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Raisman & Field |
Different structures in rats... MPOA = in females this region has more no. of synapses MPOA = in males less synapses Experiment: Took rats in early days of life Wxposed female to high levels of testosterone Found: in adult life, number of synapses had reduced Castrated male rats Found: number of synapses significantly increases to a level that is found in healthy female rats |
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SDN in Preoptic Area of Hypothalamus |
Sexually dimorphism = physical and physiological differences between males and females Structural difference... In males the SDN has a larger volume than in females Experiment: In early days of life, female rats given high levels of testosterone Found: SDN increases in size Castrate male rat Found: size of SDN decreases |
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Why do male rats have larger SDN than female rats? |
In both males and females, the SDN is genetically preprogrammed for cell death soon after birth This genetically preprogrammed process of cell death = APOPTOSIS In males: have high levels of testosterone This facilitates the expression of Anti Apoptic Proteins These proteins inhibits process of Apoptosis In females: higher levels of Pro Apoptic Proteins These protein facilitate cell death This is the reason for larger SDN in male rats than females When female rats are given testosterone, this reduces Apoptosis |
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AVPV Nucleus |
AVPV is larger in female rats than male rats Experiment: Female rats exposed to high levels of testosterone Found: reduces the volume Male rats castrated Found: increases volume |
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MePD = Postrodorsal Medial region of amygdala |
MePD is larger in male rats than female rats Experiment: Female rats given high levels of testosterone Found: Size of structure increases Male rats castrated Found: Size of structure decreases |
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Songbirds have been studied to develop models as to how structural changes in brain promote sexual behaviour |
Zebra finch and canaries:- Makes sing Their singing capabilities is attributed to two nuclei in brain: 1. Higher Vocal Centres (at the top region) 2. Robustus Striatum (bottom region) In males: the two nuclei are larger in structure than in females Believed to be the larger size of nuclei that gives these birds the ability to sing Singing ability also influenced by levels of hormones Found: male songbirds sing more during spring than autumn Measured the levels of testosterone in male birds: during spring higher levels of testosterone and lower levels in spring Correlation between levels of testosterone + size of nuclei with singing abilities |
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Experiment on songbirds |
Female songbirds zebrafinches exposed to higher levels of testosterone Found: Size of these nuclei increased This is also true in canaries When they manipulated levels of testosterone in male songbirds, didn’t effect the size of nuclei not ability to send So manipulation of testosterone only effected females and allowed them to sing Question: is it only levels of hormones that changes structures in the brain or are other factors included in triggering these changes?
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GENES: research looked into genes as a factor that overrides hormones in changing brain structures |
Research: House sparrow Male House sparrows have black throat feathers Female house sparrows have brown throat feathers Experiment: Took male and female hatchlings Took patches of skin from the male and transplanted it onto females When the house sparrows are born, they are either genetically male or female and have internal sex gonads that produce the internal sec hormones and organs Found: skin transplant - the colour of the throat feathers depended on the donor’s genes So females developed black feathers Females have sex gonads that develop the female sex hormones and if the physical characteristics of each sex is determine by HORMONE levels, then ideally should have grown brown feathers Concluded: cells in the tissues have the genetic code of the donor therefore the throat feathers grow into the colors determined by genes |
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2nd evidence for genes overriding influence of hormone Agate et al |
They studied a rare group of zebra finches called Gynandromorphic finches They’re special because: The left hemisphere is genetically female as the cells have genetically female chromosomes The right hemisphere is genetically male as the cells have XY chromosomes Structures of that facilitate the zebra finch to sing are more masculine in the right hemisphere than left This male zebra finch would have gonads that release testosterone Ideally the structures on either side of the brain should have been equally male like because they are equally exposed to the same hormones But the genetic composition of the right hemisphere is different to left hemisphere Researchers compared the male and female Gynandromorphic brains Between males and females, males had more male typical features compared to females Concluded: part of the structural changes five new by genetic changes But the fact that there’s differences between males and females must have been triggered by males and females So these findings show the interactions between genes and hormones Sometimes one is more dominant than the other but usually there is more than one factor that determines sexual behaviours |
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Wagner et al: hormonal influence can override genetic effect |
Took mice with two different genetic compositions One is Genetically male with XY chromosomes The other is genetically female won XX chromosomes Experiment: In males, they deleted the SRY gene so precursor gonads develop into Ovaries In these males found MPOA was not masculinized and structures were not large So mice were genetically male but don’t have hormones to produce male sex organs and this changed the brain structures In females: inserted SRY gene into an autosome (non sex chromosome) Found: female mice developed tested and produced testosterone The brain structures became masculinized in these mice Evidence shows hormonal influences can override genetic influences |
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Vries et al |
Took mice that were genetically female or genetically male Some of them were manipulated: Took male with XY, deleted SRY gene and developed Ovaries In female with XX, inserted SRY gene, developed testes These researchers didn’t just look at structural changes in brain They also looked at sexual behaviours such as mounting behaviors Found: both differences in hypothalamic structures and sexual behaviors later in life were predicted by presence of testes or Ovaries NOT by genetic composition |
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Hines et al: evidence in humans on levels of hormones effecting sexual behaviours |
Studied large population of kids Before these kids were born, measured levels of testosterone in mother’s blood Folllwed the children up at mean age of 3.5 years Have questionnaire to parents and teachers (preschool activities inventory) to measure the type of play Behaviour the children are engaged in They wanted to see how male like the okay behaviours were Found: levels of testosterone exposure prenatally was positively correlated with male like play behaviours Didn’t find correlation for boys |
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Auyeung et al: replicated Hines et Al’s study |
They looked at children between 8-9 years old Found: positive correlation between male like play Behaviors and testosterone levels in both boys and girls Typical play behaviours to be expressed may take time in kids May not have found a correlation in earlier study because they were measured at an earlier time point |
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Sex hormones: Vasopressin, Oxytocin |
Vasopressin In males: higher levels of vasopressin increases sexual drives In females: higher levels of vasopressin reduces sexual drive Females need low levels of vasopressin to engage in sexual behaviors Oxytocin Involved in giving person anticipatory sexual excitement - so when you want to engage in sex you anticipate some excitement from it Drugs that block the chemical oxytocin = impairs ability to anticipate sexual excitement so don’t engage in sex High levels of oxytocin + testosterone + LH found in blood during orgasm |
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Neurotransmitters also play a role in sexual behaviors |
Serotonin (5-HT) Lower levels of serotonin increases sexual behaviours in women How is this maintained in brain? Reuptake mechanisms advised serotonin back into cells This means they don’t activate post synaptic cells so less cells activated This facilitates sexual behaviors SSRI Drugs = inhibit reuptake mechanisms for serotonin This means there are increased levels of serotonin in synaptic cleft and increases activity of post synaptic neurons This reduces sexual behaviors One of these SSRI Drug = Prozac/Fluoxetine If these drugs are inserted into female rats = inhibits lordosis Dopamine = facilitates sex If nitric oxide is injected, stimulates release of dopamine Increases sexual motivation Opioids = controls sexual behaviours Injecting drugs that block activation of opioid NTs, this decreases ability of males to control sex |
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Congenital Adrenal Hyperplasia (How do hormones influence sexual orientation) |
CAH = clinical disorder Occurs in females: 1 in 2000 girls Adrenal Gland located above kidney and produces cortisol Cortisol = metabolizes substances in blood Malfunctioning adrenals gland due to genetic mutation causes adrenal gland to produce androgens (male sex hormones) such as testosterone These females are genetically female so their primordial gonads will develop into Ovaries But due to high levels of testosterone, external sex organs don’t develop They develop small penis and develop structure similar to scrotum The condition can be treated in 2 ways: 1. Restoring hormone levels 2. Surgical treatment to have a vaguely opening Research has found that this condition is related to sexual orientation Females with CAH are more likely to be homosexual or bisexual compared to females without this condition |
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Complete Androgen Insensivity Syndrome |
This clinical condition is found in males Androgens are male sex hormones In this condition males are insensitive to androgens Genetically male so develop testes but there’s a difference in external sex organs Receptors in cells that bind to estrogen (converted form of testosterone) at the cellular level When these Receptors are dysfunctional that means your cells are insensitive to testosterone Males develop external sex organs like that of females Males with CAIS are more likely to be bisexual or homosexual compared to males without this condition |
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Are there physical characteristics in our body that are determined by levels of hormones |
Can measure a physical characteristic in body that are determined by hormones Then can relate this hormone to sexual orientation Somatic marker = 2D:4D digit ratio Males have shorter index finger compared to ring finger = smaller digit ratio Females have index and ring finger of same size = larger digit ratio Manning et al: Comparing digit ratios of males found: higher testosterone related to smaller digit ratios Females: higher levels of estrogen and progesterone = higher digit ratios (positive correlation) Also found:- The same gene that controls digit ratio control development of gonads so found hormonal relationship between hormone levels and digit ration Compared homosexual males and females with heterosexual males and females Found: heterosexual males have lower digit ratios Homosexual males found larger digit ratios similar to that found in women In females there was no difference found |
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2 physiological characteristics that also determines sexual orientation |
These 2 physiology characteristics differ between males and females and also found this difference determined by Hormones 1. Pre pulse inhibition for startle response Startle response = sudden stimulus (loud noise) causes body to undergo startle response But if the loud noise is preceded by weaker noise the startle response to loud noise is less = pre pulse inhibition Found: in males there’s stronger pre pulse inhibition than females Rahman et al:- Looked at differences of pre pulse inhibition between homosexuals and heterosexuals Found... Heterosexual females show weaker pre pulse inhibition Homosexual females show stronger pre pulse inhibition than that if hetero. females and closer to that of males In males found no difference between homo./hetero. This physiological characteristic that distinguishes sexual orientation in females NOT MALES 2. Click evoked otoaccoustic emmisions = when you hear a sound an organ in ear called cochlea generates sound wave that travels to inside of ear Found: the otoaccustic emmisions is higher in amplitude in females than males Compared homosexuals and heterosexuals Found... Heterosexual females have higher levels of otoaccoustic strengths Homosexual females have lower levels of otoaccoustic emissions No difference in males This characteristic determines sexual orientation in females Note: only the digit ratio is deterministic of the sexual orientation in males
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Cognitive measures also predicts sexual orientation |
Mental rotation of images task: Found: heterosexuals males are better at this task than heterosexual females Heterosexual males are better at this task than homosexual males Homosexual females are better at this task than heterosexual females Other cognitive measures also have differences between males and females and predicts sexual orientation |
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Further findings on Digit Ratios |
Digit ratios not only predict sexual orientation but skills on a certain task and clinic mental disorders Found: males who played football had lower digit ratios compared to males who don’t play football Suggested: maybe football players have higher visuospatial skills Another finding: elite musicians had lower digit ratios compared to non-musicians In these studies only predicts skill levels of males High Digit ratio has been correlated with high levels of depression |
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Differences in structural organization of brain may predict sexual orientation |
LeVay: Interstitial Nuclei of Anterior Hypothalamus There are 4 INAHs in the hypothalamus Found: the INAH-3 was 2 times larger in males than females Also found... Homosexual males have a smaller INAH-3 than heterosexual males This has only been found in males so this structure can only predict sexual orientation of male |
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Byne et al replicated the study |
Found: Volume of INAH-3 was found to be highest in heterosexual males Volume of INAH-3 in homosexual males was smaller and similar to that of females ALSO FOUND... There was no difference in the number of neurons or number of synapses they formed Only found difference in volume The volume doesn’t tell you anything about functioning of structure only number of synapses indicate how well it is functioning or not Concluded: structural difference in homosexual male may not predict the male being homosexual But the fact that the male is homosexual may lead to decrease in volume of nucleus |
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Another structure involved in predicting sexual orientation = SCN |
SCN located below frontal lobe found: SCN is smaller in males than females In homosexual males the volume of SCN is larger than in heterosexual males SCN is related to sexual reproduction The size of structure may be deterministic of sexual orientation |
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Roselli et al: Sheep analogue of SDN |
oSDN = ovine sexually dimorphic Nucleus Located in hypothalamus Similar to hypothalamic structure of humans Found: Rams have larger oSDN than females Homosexual rams had oSDN that was 2 times smaller than heterosexual rams (similar findings to that of humans) Also found... Aromatase levels in oSDN of homosexual rams was lower than in heterosexual rams |
