Sex and Sex Differences

Question 1

What determines the baby’s sex?

Answer 1

Presence or absence of the Y chromosome

Question 2

Gene SRY

Answer 2

Located on the Y chromosome.
Turns the fetal gonad into a testis (2 testes) –> testis-determining factor.
In its absence, the gonad becomes an ovary.

Question 3

What hormones do early testes produce?

Answer 3

Anti-Mullerian Hormone (defeminising) and Androgens (masculising). In the absence of these hormones, female sex organs develop primary sexual characters.

Question 4

What hormones make external sex hormones?

Answer 4

Dihydrotestosterone (DHT)

Question 5

Sex chromosome effects:

Answer 5

Habit formation, alcohol preference, aggression, nociception.

Question 6

Gonadal (XY-Sry, XY-) effects:

Answer 6

Sex behaviour
LH Secretion
Aggression
Nociception

Question 7

Actions of hormones

Answer 7

Organisational: Hormone makes a permanent change, often during a sensitive period, even if the hormone goes away.
Activational: Effect is reversible, depending on presence or absence of hormone

Question 8

Puberty

Answer 8

Organisational and activation role of sex hormones.
Development of Secondary Sexual Characters.
Pubic and axillary hair are androgen sensitive in both males and females.

Question 9

Onset of puberty

Answer 9

During childhood sex hormone levels are almost undetectably low.
Developmental timing mechanism starts puberty.
Sex differences in mechanisms and timing.

Question 10

The Hypothalamus-Pituitary-Gonadal Axis part 1

Answer 10

GABAergic neurons in the hypothalamus strongly inhibit kisspeptin neurons. This means GnRH isn’t released.
On the onset on puberty kisspeptin neurons release GnRH

Question 11

The Hypothalamus-Pituitary-Gonadal Axis part 2

Answer 11

GnRH is released into the bloodstream, into the pituitary gland.
The anterior pituitary gland is made up of hormone making cells. This releases FSH and LH.
The posterior pituitary gland releases vasopressin and oxytocin

Question 12

Gonadotropins (FSH and LH)

Answer 12

In males these hormones cause sperm production (FSH) and testosterone production (LH).

Question 13

Follicular Menstual Stage

Answer 13

FSH - Small rise and fall to activate the ovary to start producing an egg cell.
Estradiol - Increase in the blood stream produced by ripening follicle. Detected in the pituitary gland which triggers the release of LH and FSH.

Question 14

Luteal Menstrual Stage

Answer 14

Corpus Luteum (old ovum) is active to produce progesterone and estradiol before whitening away in the next stage.

Question 15

Sexual orientation

Answer 15

One of the most extreme sex differences. 90-95% of men are attracted to women exclusively (‘gynophile’) and 85-90% of women are attracted to men exclusively (‘adrophile’)

Question 16

Sex differences in the brain (Swaab and Hofman, 1988)

Answer 16

SCN larger in male-orientated individuals

Question 17

Sex differences in the brain (Levay, 1991)

Answer 17

INAH-3 smaller in male orientated individuals

Question 18

Sex differences in the brain (Allen and Gorski, 1992)

Answer 18

Anterior commissure larger in male orientated individuals

Question 19

What’s wrong with looking at brain differences for sexual orientation?

Answer 19

Could be causal to sexual orientation.
Could also be purely correlation, as indicators of other mechanisms (hormonal, genetic).
Could be consequence of sexual orientation.

Question 20

Cultural Effects

Answer 20

Influences on brain development (eg what you’re exposed to in childhood)
Effects of practice (eg you are better at what you spend more time doing)
Social effects (expectations, stereotypes,…)
HOWEVER- Little to no evidence that this effects sexual orientation

Question 21

Activational Hormonal Effects

Answer 21

Would be found by variations with varying testosterone levels, estradiol levels and menstrual cycle.

No differences detected in adulthood between different sexual orientations.
Hormone fluctuations, manipulations, or treatments affect sexual motivation, but not orientation.

Question 22

Development of testosterone in boys.

Answer 22

Weeks 8-24 of pregnancy
Early: external genitalia.
Late: brain differentiation.

First 3 months after birth
Potential further brain differentiation.

Question 23

Organisational Hormone Effects

Answer 23

Correlations with measured prenatal hormones.

Correlations with adult correlates of prenatal hormones

Conditions with abnormal prenatal hormone levels

1. Congenital Adrenal Hyperplasia (CAH)
2. Androgen Insensitivity Syndrome

CAH women are also more likely to identify as female-orientated

Question 24

Genetic Effects

Answer 24

Higher concordance in monozygotic than dizygotic twins.
Estimates from 30-100%
Possibility higher concordance for women than men

Question 25

Appetitive Behaviour

Answer 25

Behaviour aimed at finding and obtaining a sexual partner

Question 26

Consummatory behaviour

Answer 26

Behaviour of the actual sexual act

Question 27

What controls sexual motivation?

Answer 27

External

1. Usually related to opposite-sex conspecifics
2. Can be chemical stimuli we’re not consciously aware of (pheromones or smells)
3. Can also be learned and of different sensory modalities.

Internal motivations are usually hormones.

Question 28

Male hormones in sexual interest

Answer 28

Suppression of testosterone (T) reduces sexual interest (but not performance)
Anticipation of sexual encounter increases testosterone
No correlation with individual differences in testosterone

Question 29

Female hormones in sexual interest

Answer 29

Sexual interest fluctuates with the menstrual cycle (especially with estradiol)
Androgens (testosterone from ovaries and androstenedione from adrenal gland) increase effect of estradiol up to 3 times
Increase in testosterone in females also with anticipation of sexual activity

Question 30

4 stages of arousal

Answer 30

Excitement
Plateau
Orgasm
Resolution

Question 31

Excitement and Plateau

Answer 31

Getting an erection or vaginal secretion.
Controlled by the parasympathetic nervous system.
The smooth muscle relaxes when astylcoline is released and blood pressure goes down.
More blood enters the genitals
Penile/clitoral erection
Engorgement of labia
Vaginal lubrication

Question 32

Parasympathetic nervous system

Answer 32

Peripheral nerves are either at the end of the spinal cord or in the brain. Pre ganglionic have cell bodies in the CNS, with the synapse close or in the neurons.
Tends to control our state of relaxation and digestion.
The neurotransmitters being used by the pre-ganglionic neurons is asytacoline, and they bind to nicotinic receptors. In the organs are muscarinic receptors.

Question 33

Erectile dysfunction

Answer 33

Always physical
Stress leads to increased sympathetic activity, which causes vasoconstriction
Learned aversions can have central effects
Many of these are difficult to tease apart

Question 34

Orgasm

Answer 34

Controlled by the sympathetic nervous system.
Triggered by combination of local stimulation and central input
Sympathetic stimulation and pulsatile release of oxytocin results in series of smooth muscle contractions

Question 35

Resolution: Satiety

Answer 35

Active inhibition of sexual motivation

During orgasm: blood oxytocin levels peak
Oxytocin is also involved in pair-bond formation

During orgasm: prolactin is released
High prolactin levels suppress sexual motivation