Sexual Differentiation Flashcards
What chromosomes do females and males have?
Females - 2 X
Males - X and Y
What controls for sexual differentiation?
The genes on the chromosomes and hormones
When does sexual differentiation occur?
Pre-natally
Female and male brain prenatally
It is the same - biopotential
Has tissue which supports either formation
What does bipotential mean?
Both possibilities
What do males and females both carry?
A set of mullein ducts and wolffish ducts as well as primitive gonads (testes or ovaries)
What determines what gender they become?
There is an SRY (sex determining region) on the Y chromosome - causes the primitive gonads to develop into testes - producing testoerone
What does testosterone cause?
The development of the wolffish ducts to develop into seminal vesicles and vs deferent
Mullerian inhibiting hormones causes degeration of the M ducts
What is the default sex?
A female
What is the difference in the gonadal hormones?
Males - have mostly androgens and a few estrogens (it is the androgen which determines the masculinisation of the foetus)
Females - have mostly estrogens and a few androgens
What is the role of androgens in females?
Associated with sexual desire
What does organising effects of gonadal hormones mean?
Occurs a few weeks after conception when the sex glands develop into male testes or female ovaries depending on the presence or absence of testosterone
Long lasting effects, occur before birth and at puberty
When do the organising effects occur?
in rats - shortly before and after birth
in humans - before birth (3rd and 4th month) and at puberty
What does activating effects of sex hormones mean?
These induce sexual function and behaviour - induce secondary sex characteristics that appear at puberty by activating brain circuits previously developed as pat of the organising effects
Can occur at any time in life when a hormone temporarily activates a response - only when the hormone is present
When do activating effects occur?
Only when the hormone is present
Organising effects in female and male rats
Female rats injected with T shortly after birth show male typical behaviour - masculanized (mounting instead of lordosis)
Male rats lacking androgen receptors (or injected with T antagonists) develop female typical behaviour
other substances which interfere with T effects - drugs of abuse, alcoohl
drugs that mimic estrogens - BPA
What are the brain sex differences?
Males have more dendritic branching in visual cortex
Females have more dendritic branching in the motor cortex
Corpus callosum - bundle of fibres from one hemisphere to another - region that is thicker in females than males
Rat-typical sexual behaviour
Male - mounts the famle
Female - ear wiggle, hopping, try to get attention
Female arches her back at the final stage, so male can mount her to create babies
What happens in the absence of androgens?
The foetus will be feminised
Masculization requires the presence of androgens
