L3 & L4 - Sex and Differences

Question 1

What are the types of sex differences?

Answer 1

Genetic sex
Gonadal sex
Internal reproductive system
External reproductive system
Pubertal sex changes
Hormonal sex
Brain sex
Behavioural and cognitive sex
Sexual identity

Question 2

What is genetic sex?

Answer 2

22 pairs of chromosomes
1 pair is for sex
Genetic sex is determined by fathers (Y chromosomes)
XX female
XY male

Question 3

What are the organisational effects of sex hormones produced by fetal gonads?

Answer 3

Permanent alterations in body or CNS induced by a hormone at a critical period in development
Happens before birth
Only occurs during critical periods

Question 4

What are the activational effects of sex hormones produced by gonads?

Answer 4

Hormone effects that occur in the fully developed organism; depends on previous organisational effects
Happens after birth
Driving behaviours

Question 5

What is the development of gonads (ovaries and testes) and internal sex organs called?

Answer 5

Mullerian system - female internal sex organs
Wolffian system - male internal sex organs

Question 6

What is the indifferent stage of external sex organs?

Answer 6

Phallus
Urethral fold and slit
Tail
Genital swelling

Question 7

What are the factors determining the development of male sex organs?

Answer 7

1. Primordial gonads develop into testes by binding to DNA
2. Testes produce hormones that have anti-mullerian (defeminising) and androgens (masculinising)

Question 8

What is the testis-determining factor for male sex organ development?

Answer 8

Amino acid long protein coded for by SRY region of Y chromosome
Mutations can prevent development of testes

Question 9

What is the anti-mullerian hormone?

Answer 9

A peptide secreted by the fetal testes that has defeminising effects
Inhibits the mullerian system

Question 10

What are androgens?

Answer 10

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

Question 11

What are the factors determining the development of female sex organs?

Answer 11

Primordial sex organs develop into female, ovaries
Internal and external sex organs develop into female organs without any hormonal influence
Lack of male hormones

Question 12

What is XY sex reversal?

Answer 12

Mutations in the SRY region of the Y chromosome
Resulting in female sex organs in XY individuals

Question 13

What is androgen insensitivity syndrome?

Answer 13

Caused by congenital lack of functioning androgen receptors in XY person
Causes development of female with testes and no internal sex organs

Question 14

What is turner’s syndrome?

Answer 14

The presence of only one chromosome (XO)
Lack of ovaries but otherwise normal

Question 15

What is persistent Mullerian duct syndrome?

Answer 15

In XY congenital lack of anti-mullerian hormone causes the development of both male and female

Question 16

What is sexual maturation (puberty)?

Answer 16

Triggered by hypothalamic secretion of gonadotropin-releasing hormone
Secondary sex characteristics develop (breasts, hips, facial hair, deep voice)

Question 17

What is the organisational hypothesis for sex differences in brain and behaviour?

Answer 17

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

Question 18

What are the neural and behavioural sex differences?

Answer 18

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

Question 19

What are the sex differences in male vs female (organisational/activational theory)?

Answer 19

XX - ovaries - feminisation - oestradiol and progesterone
XY - testes - testosterone and oestradiol - masculinisation and defeminisation - testosterone

Question 20

What are the masculinising effects of oestrogen?

Answer 20

Oestrogen is just as effective as testosterone in masculinising brain and behaviour
Many masculinising effects were mediated by oestrogen receptors
Aromatisation hypothesis
Protection hypothesis

Question 21

What is the aromatisation hypothesis?

Answer 21

Some CNS cells testosterone is converted to oestrogen by an enzyme called aromatase before it acts on oestrogen receptors to create masculinising effects

Question 22

What is the protection hypothesis?

Answer 22

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

Question 23

What is the lordosis response?

Answer 23

Flexing of the back in animals to facilitate mating

Question 24

What are the necessary factors for heterosexual mating behaviour in mammals?

Answer 24

All factors must be met for mating to start
Testosterone is necessary for males
Hormonal menstrual cycle is necessary for females

Question 25

What is the hormonal reproductive cycle in female mammals?

Answer 25

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

Question 26

What are the spinal mechanisms relevant to male copulatory behaviour in rats?

Answer 26

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

Question 27

What are the brain mechanisms relevant to mating behaviour in rodents?

Answer 27

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

Question 28

What are the sex differences in human preopitic area (POA) of the hypothalamus?

Answer 28

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

Question 29

What are the sex differences in aggressive behaviour?

Answer 29

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

Question 30

What are the sex differences in cognitive functions?

Answer 30

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

Question 31

What are the brain differences between males and females?

Answer 31

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

Question 32

What are the sex differences in the incidence of neuropsychiatric diseases?

Answer 32

Affective disorders and anxiety disorders are more prevalent in women
Substance abuse, antisocial, autism disorders are more prevalent in males