The Male vs. Female Brain Flashcards
1
Q
What is sexual dimorphism?
A
- Refers to each sex having a different “form” of the brain
- Brain regions that look different or that have different functionalities between sexes
- Motor systems look different: Different body parts to control
- Sensory systems look different: Different body shapes and sizes
- In humans, differences are relatively few, subtle, and of unknown functional consequence. Sexual dimorphic nuclei exist on a continuum, meaning that there are differences on average.
- Fish species: same body length, shape, and weight but different brains between males and females: males have bigger brains and more advanced behaviours
2
Q
Where is the most distinct sexual dimorphism in the mammalian brain located?
A
- Within the preoptic area of the anterior hypothalamus
- Region contains sexually dimorphic nucleus (5-8 x larger in males than females)
3
Q
What are the cluster of nuclei in the preoptic area called that are sexually dimorphic? How many nuclei are there and what evidence do we have that they are sexually dimorphic?
A
- Interstitial nuclei of the anterior hypothalamus
- 4 nuclei
- Debatable evidence that they are larger in males than females
- Areas are activated during sexual behaviour but exact function is unknown. If areas are stimulated, females will begin to display lordosis and darting around the cage.
- Early and very controversial evidence suggest that there could be differences in nuclei that are related to sexual orientation in people – very variable data
- Much larger for heterosexual male than homosexual male in INAH 3
4
Q
Explain how hormones and lesions to the SDN do / do not seem to change sexual orientation in rats.
A
- Hormones do not appear to influence sexual orientation. Injecting androgens or estrogens or removing gonads has no effect.
- Lesions to the male SDN appear to change sex behaviours. Male rats begin spending more time with sexually active males than sexually receptive females (reversal from pre-surgery)
- Lesion studies change sexual behaviour, but we cannot say that it changes sexual orientation
5
Q
What was found about male Rocky Mountain sheeps’ sexual behaviour?
A
- 8% of males prefer to mount and mate with other male sheep
- SDN is half the size in male oriented sheep compared to female oriented sheep
- However, no cause and effect relationship has been established
6
Q
What cognitive tasks are performed better by each sex, on average? What is an evolutionary explanation for this finding?
A
- Girls: comprehension and writing tasks
- Boys: reading, maze learning, mathematical reasoning, mental manipulation of objects
- Throughout evolutionary history, men were required to navigate their environment while women were required to have more social and verbal skills for raising children and families
7
Q
Explain what cognitive tasks are performed better by increases in estrogens and androgens.
A
- Increased estrogens: performance on verbal tasks increase while performance on spatial tasks decrease
- Increased androgens: Better performance on spatial tasks in both men and women
8
Q
Explain the two pathways that allow steroids to influence neurons.
A
- Fast / direct: steroids bind to receptors and modulate channels, enzymes, and receptors. Act like diffuse modulatory systems or neurotransmitters. Alter membrane excitability, sensitivity to neurotransmitters, and neurotransmitter release. This process happens fast and the response is determined by which receptors are expressed in each neuron.
- Example: metabolites of progesterone act as GABA-A agonists and behave like benzodiazepines - Slow / indirect: Diffuse across membranes (lipophilic) and bind to intracellular receptors (cytoplasmic / intranuclear receptors). Promote or inhibit the transcription of specific genes, thus influencing the organization of a cell. Receptors exist for each sex hormone, but the distribution of these receptors varies across the brain.
9
Q
What are the 2 timing effects that are important for steroids’ influence on neurons?
A
- Organizational effects: Early in development, steroids have irreversible changes to perinatal tissue. Widespread and permanent effects on phenotype.
- Activational effects: During later stages of life / during sexual activity, steroids have transient effects that are usually temporary. These effects can elicit male / female sexual behaviour.
10
Q
Explain how estrogen results in masculinization of the brain.
A
- Surge in testosterone during prenatal develoment
- Aromatase converts testosterone to estradiol in the cytoplasm of neurons
- Activation of estradiol receptors triggers masculinization of male tissues
- Female brains do not produce an early surge of testosterone or estrogen
11
Q
Explain how the female fetus is protected against female hormones that masculinize the brain.
A
- Estrogens can be seen in circulation of developing fetus
- alpha fetoprotein is a highly concentrated protein in fetal blood that binds to estrogens and protects the female fetus from masculinization
12
Q
What effects does testosterone have on the XX genotype in animals?
A
- Testosterone exposure to XX rats around birth will abolish female mating behaviours, such as lordosis. These rats will mount and attempt to mate with other estrous XX rats.
- In cows, XX and XY twins result in XX being exposed to testosterone produced by the twin, so the female cow begins to behave like a bull
13
Q
What is the cause and effects of androgen insensitivity?
A
- Cause: mutated androgen receptors
- Testes develop but never descend from abdomen
- Testes produce testosterone but no masculinization occurs, causing an outwardly female appearance
- Tissues cannot respond to testosterone so they develop vagina, clitoris, labia, breasts, and a female body shape
- Testes produce Mullerian inhibiting factor, so the female reproductive system does not develop, they do not menstruate, ad they are infertile
14
Q
What is congenital adrenal hyperplasia?
A
- Occurs in human females
- Overgrown adrenal glands cause overproduction of androgens
- Leads to high exposure to androgens throughout development
- External sex organs are an intermediate between a penis and clitoris
- Demonstrate aggressive behaviour and a higher prevalence of homosexuality (many declare heterosexuality)
15
Q
Who was John (Joan) Reimer?
A
- David Reimer born as a male with twin brother Brian
- During circumcision, accident with electrocautery device burned his entire penis
- Parents decided to castrate him, got him cosmetic surgery, and put him on estrogen supplements
- Grew up as a boy trapped in a girl’s body. He behaved like other boys, rebelled against wearing girls clothes, and was more attracted to other girls than boys.
- At 14, he learned about his circumcision and surgeries and began a sex change and eventually married a girl and adopted some kids.
- At age 38, committed suicide
- Demonstrates that genetically determined sex could not be suppressed even with sex change, surgeries, hormonal therapy, female upbringing, etc.
