L3 & L4 - Sex and Differences Flashcards
What are the types of sex differences?
Genetic sex
Gonadal sex
Internal reproductive system
External reproductive system
Pubertal sex changes
Hormonal sex
Brain sex
Behavioural and cognitive sex
Sexual identity
What is genetic sex?
22 pairs of chromosomes
1 pair is for sex
Genetic sex is determined by fathers (Y chromosomes)
XX female
XY male
What are the organisational effects of sex hormones produced by fetal gonads?
Permanent alterations in body or CNS induced by a hormone at a critical period in development
Happens before birth
Only occurs during critical periods
What are the activational effects of sex hormones produced by gonads?
Hormone effects that occur in the fully developed organism; depends on previous organisational effects
Happens after birth
Driving behaviours
What is the development of gonads (ovaries and testes) and internal sex organs called?
Mullerian system - female internal sex organs
Wolffian system - male internal sex organs
What is the indifferent stage of external sex organs?
Phallus
Urethral fold and slit
Tail
Genital swelling
What are the factors determining the development of male sex organs?
- Primordial gonads develop into testes by binding to DNA
- Testes produce hormones that have anti-mullerian (defeminising) and androgens (masculinising)
What is the testis-determining factor for male sex organ development?
Amino acid long protein coded for by SRY region of Y chromosome
Mutations can prevent development of testes
What is the anti-mullerian hormone?
A peptide secreted by the fetal testes that has defeminising effects
Inhibits the mullerian system
What are androgens?
Testosterone - acts on receptors in cells of wolffian system and stimulates development Dihydrotestosterone - produced from testosterone, goes through the cell membrane and acts on androgen receptors in the external genitals
They both have a 5 carbon atomic structure
What are the factors determining the development of female sex organs?
Primordial sex organs develop into female, ovaries
Internal and external sex organs develop into female organs without any hormonal influence
Lack of male hormones
What is XY sex reversal?
Mutations in the SRY region of the Y chromosome
Resulting in female sex organs in XY individuals
What is androgen insensitivity syndrome?
Caused by congenital lack of functioning androgen receptors in XY person
Causes development of female with testes and no internal sex organs
What is turner’s syndrome?
The presence of only one chromosome (XO)
Lack of ovaries but otherwise normal
What is persistent Mullerian duct syndrome?
In XY congenital lack of anti-mullerian hormone causes the development of both male and female
What is sexual maturation (puberty)?
Triggered by hypothalamic secretion of gonadotropin-releasing hormone
Secondary sex characteristics develop (breasts, hips, facial hair, deep voice)
What is the organisational hypothesis for sex differences in brain and behaviour?
Exposing female rats to androgen during critical periods altered their adult behaviour
They organise the developing CNS in a masculine way to result in defeminisation
What are the neural and behavioural sex differences?
Many neural sexual dimorphisms in rodents have demonstrated organising effects of androgens
Neural sexual dimorphisms contribute to sex differences in reproductive behaviour
Can be described without behavioural differences
Evidence for interaction between environment and hormonal influences
What are the sex differences in male vs female (organisational/activational theory)?
XX - ovaries - feminisation - oestradiol and progesterone
XY - testes - testosterone and oestradiol - masculinisation and defeminisation - testosterone
What are the masculinising effects of oestrogen?
Oestrogen is just as effective as testosterone in masculinising brain and behaviour
Many masculinising effects were mediated by oestrogen receptors
Aromatisation hypothesis
Protection hypothesis
What is the aromatisation hypothesis?
Some CNS cells testosterone is converted to oestrogen by an enzyme called aromatase before it acts on oestrogen receptors to create masculinising effects
What is the protection hypothesis?
Brains of rodents are protected from masculinising actions by an oestrogen-binding protein called alpha-fetoprotein in the blood
Testosterone is not bound by the protein so can enter the CNS cells where it is converted into oestrogen
Alpha-fetoprotein mutant mice show masculinised brains and behaviour
What is the lordosis response?
Flexing of the back in animals to facilitate mating
What are the necessary factors for heterosexual mating behaviour in mammals?
All factors must be met for mating to start
Testosterone is necessary for males
Hormonal menstrual cycle is necessary for females
What is the hormonal reproductive cycle in female mammals?
Pregnancy is only possible during ovulation (oestrogen and progesterone is high)
Hormonal cycles influence behaviour, cognitive and affective functions that are not directly linked to reproductive behaviour
Rat oestrous cycle is 4 days long
Humans cycle is a month
What are the spinal mechanisms relevant to male copulatory behaviour in rats?
Spinal nucleus of the bulbocavernosus (SNB)
- collection of motor neurons in the lower spine controls muscles at the base of penis
- necessary for penile reflexes
- they are absent in adult females
Interaction of nature and nurture
- rat mothers are stimulated to lick their male pups more
- contributes to normal sexual behaviour and SNB neurons
What are the brain mechanisms relevant to mating behaviour in rodents?
Sex circuits - contain sex hormone receptors, critical for sex differences, testosterone in males, oestrogen and progesterone in females
Sexually dimorphic nucleus (SDN-POA) and posterodistal medial amygdala (MePD) - masculinised by testosterone during a critical period, volume and cell size depend on testosterone
What are the sex differences in human preopitic area (POA) of the hypothalamus?
One nucleus in the POA was larger in males
Studied 4 nuclei in the POA - 2 and 3 were larger in males but no differences in 1 and 4
What are the sex differences in aggressive behaviour?
Some aspects of aggression are strongly related to reproductive behaviour
In rodents it has been shown that aggression is strongly related to brain regions that overlap with regions of reproductive behaviour
In humans evidence shows some aspects of aggression being sexually dimorphic
What are the sex differences in cognitive functions?
Men are generally better at spatial tasks whereas females are better at memory, fine motor control, fluency and perceptual speed
Male advantage in place learning and navigation - may have developed from ecological advantage and larger hippocampus
What are the brain differences between males and females?
Brain weight seemed to be heavier in males both in absolute terms and relative to body size
If these anatomical sexual dimorphisms contribute to sex differences it is not known
What are the sex differences in the incidence of neuropsychiatric diseases?
Affective disorders and anxiety disorders are more prevalent in women
Substance abuse, antisocial, autism disorders are more prevalent in males
