Week 5-Sexual Behaviour

Question 1

Define sexual dimorphism

Answer 1

2 sexes in many species including humans

Question 2

Define external sex

Answer 2

In humans, sex is usually defined
both medical and in lay terms
by the outward appearance of the
individual from birth (external genitalia).

Question 3

Define internal sex

Answer 3

The internal reproductive organs

Question 4

Define chromosomal sex

Answer 4

Genetic male (XY) or genetic female (XX)

Question 5

How do males and females differ via primary sexual characteristics?

Answer 5

Externally visible at birth i.e. different genitals
- Vagina, labia
- Penis, scrotum

Question 6

How do males and females differ via secondary sexual characteristics?

Answer 6

Becomes apparent during
puberty e.g.
- Body hair, development of
breasts and change in figure.
- Body hair (facial hair), deepening of voice

Question 7

How else may males and females differ internally?

Answer 7

• Ovaries
• Fallopian tubes
• Uterus
• Seminal vesicles
• Prostate

Question 8

Define sexual behaviour

Answer 8

Behaviour associated with mate selection, courtship and intercourse

Question 9

Define sexual identity

Answer 9

■ Does not always coincide with a person’s anatomical sex.
■ Transexualism – a person’s belief that he or she is trapped in the body of the other sex

Question 10

Define sexually differentiated behaviour

Answer 10

Other behaviours that are regarded as ‘female-typical’ and ‘male-typical’ (e.g. parental
behaviour, aggressiveness, emotional intelligence, visuospatial skills and so on …)

Question 11

How many pairs of chromosomes do humans have?

Answer 11

23 (46 in total) in almost all cells (22 pairs of autosomes, 1 pair of sex chromosomes)

Question 12

What are the stages of human embryonic development?

Answer 12

-Intricate co-ordination of molecular, cellular and tissue level processes
-Cells divide, migrate and specialise

Question 13

What occurs in sexual differentiation 1?

Answer 13

-At 6 weeks of conception, all embryos are physically identical (even if they’re XX or XY)
They all possess:
– Internal embryonic glands termed primordial gonads. Cortex could become medulla could become testes.
– Müllerian ducts which have the potential to develop into female internal organs.
– Wolffian ducts which have the potential to develop into male sexual organs
– No external primary sexual characteristics.

Question 14

What occurs during sexual differentiation 2?

Answer 14

-Wolffian ducts (have the potential to develop into male sexual organs)
-Müllerian ducts (have the potential to develop into female
internal organs)

Question 15

What occurs during the male early development pathway?

Answer 15

1.In the 7th week in males (XY) embryos, the Sry gene on the Y
chromosome triggers the synthesis of Sry protein
2.Sry protein stimulates the medulla of the primordial gonad to
develop into a testis.
3.In 3rd month of development, the embryonic testes produce two
hormones:
-androgen Testosterone
-AMH (anti-Mullerian hormone/Mullerian
inhibiting substance)

Question 16

State the function of the androgen testosterone

Answer 16

causes the male embryo to develop male internal and external genitalia (seminal vesicles, scrotum, penis etc.) from Wolffian system, other internal tissue, and germinal ridge. (Masculinising Effect)

Question 17

State the function of the AMH (anti-Mullerian hormone/Mullerian inhibiting substance)

Answer 17

prevents the development of female internal genitalia from Müllerian system (these wither) & causes testes to descend
into scrotum. (Defeminising Effect)

Question 18

What occurs during the female early development pathway?

Answer 18

1.Females are XX and without the Y chromosome they have no SRY gene=no Sry protein is produced.
2.Differentiation of internal ducts of female reproductive system is not under hormonal control. Just ABSENCE of testosterone.
3.The normal development of internal female genitalia from the
Müllerian ducts and other tissue (uterus, fallopian tubes, etc.)

“We are all genetically programmed to develop female bodies; genetic males develop male bodies only because their fundamentally female program of development is overruled” (Pinel & Barnes)

Question 19

What occurs during the development of external reproductive organs?

Answer 19

End of 2nd month of pregnancy, external differences start to appear as 4 structures of bipotential precursor begin to develop.
1. Glans:
* Head of penis (M)
* Clitoris (F)
2. Urethral fold
* Fuse (M)
* Become labia minora (F)
3. Lateral body
* Shaft of penis (M)
* Hood of clitoris (F)
4. Labioscrotal swelling
* Scrotum (M)
* Labia majora (F)

Question 20

What is puberty and its key components?

Answer 20

*The transitional period between childhood (low levels of circulating
gonadal hormones, immature reproductive organs, males and females physically similar) and adulthood.
Key components:
* Growth spurt.
* Development of secondary sexual characteristics.
* Fertility is achieved.

Question 21

What are the five stages of puberty (Tanner stages) defined by?

Answer 21

■ These are defined by pubic hair growth in both boys and girls
■ Stage 1 is prepubescent and stage 5 is adult

Question 22

What are the female stages of puberty?

Answer 22

• Girls defined by breast and nipple area (areola and papilla) development
• In girls breast development
  usually starts in stage 2 (8-14yr)
• In girls first menstruation occurs around stage 3 (9-15yr).
• Ovulation generally occurs in stage 4 (10-16 yr).

Question 23

What are the male stages of puberty?

Answer 23

• Boys defined by development penis and testes.
• Stage 2 - Scrotum and testes enlarge (9-15 yr).
• Stage 3 – growth of penis in
  length (11-16 yr).
• Stage 4 - penis is further enlarged in length and breadth, development of glans, testes and the scrotum are further enlarged (11-17yr).

Question 24

What starts puberty?

Answer 24

■ Poorly understood but likely to be numerous internal and external cues (aka “biological clock”)
■ Explanation supported by lowering age of onset in developed nations in line with improved diets, medical care, socioeconomic conditions (Eckert-Lind et al., 2020

Question 25

What occurs during male-specific sexual maturation?

Answer 25

Gonadotropic hormones (FSH & LH)
Testes:
*start to produce sperm (spermatogenesis)
* rapid increase in testosterone
release
-Some testosterone converted into
dihydrotestosterone, which triggers growth and development of penis

Question 26

What occurs during female-specific sexual maturation?

Answer 26

1.Gonadotropic hormones (FSH & LH)
2.Ovaries: stimulated to release the hormone estradiol (an estrogen)
3.Over time * Maturation of female genitalia THEN release of first ova and first menstrual cycle begins
4.Estrogen and progesterone (controlled by FSH & LH) co-ordinate the menstrual cycle

Question 27

What’s masculinisation?

Answer 27

In pubertal males androgen levels >estrogen levels

Question 28

What’s feminisation?

Answer 28

In pubertal females estrogen levels >androgen levels

Question 29

What occurs during the development of secondary sexual characteristics in females?

Answer 29

■These include the development of breasts, change in figure due to adipose tissue increasing around the bottom and thighs.
■The development of underarm and pubic hair in females (controlled by androstenedione, an
androgen).

Question 30

What occurs during the development of secondary sexual characteristics in males?

Answer 30

These include the broadening out of figure, the deepening of the voice, and the development of
facial, underarm and pubic hair.

Question 31

What are the negatives of puberty?

Answer 31

-Rising levels of androgens change fatty acid composition of perspiration, resulting in a more “adult” body odour.
-Another androgen effect is increased secretion of oil (sebum) from the skin increasing susceptibility to acne vulgaris.

Question 32

What behavioural changes occur during puberty due to hormonal peaks?

Answer 32

Most adolescents develop an interest in sex.
In males in particular, peaks in testosterone levels appear to correlate with a marked surge in sex drive.
Testosterone peaks may also be responsible for a variety of other
behavioural changes and experiences such as:
rapid mood swings,
reduced attention span,
aggression

Question 33

What behavioural changes occur during puberty due to hormonal peaks?

Answer 33

Most adolescents develop an interest in sex.
In males in particular, peaks in testosterone levels appear to correlate with a marked surge in sex drive.
Testosterone peaks may also be responsible for a variety of other
behavioural changes and experiences such as:
rapid mood swings,
reduced attention span,
aggression

Question 34

What’s required for adolescent maturation of reproductive
behaviours?

Answer 34

Requires remodelling and activation of neural circuits
involved in salience of sexual
stimuli and sensory associations,
sexual motivation and sexual performance.

Question 35

How are their sex differences in the brain?

Answer 35

■Physical differences:
–Size
–Typical number of nuclei and fibre tracts
–Numbers and types of neural and glial cells
–Numbers and types of synapses
■Functional differences

Question 36

What’s the aromatization hypothesis?

Answer 36

■Gonadal and adrenal sex hormones are steroids (derived from cholesterol).
■They have similar structures and so can be readily converted from
one to the other.
■It is thought that the brain (specifically the hypothalamus) is
masculinized by perinatal (around the time of birth) estradiol that
has been aromatized from testosterone, rather than testosterone itself

Question 37

What is evidence is there to support the aromatization hypothesis? (animal studies)

Answer 37

1.Early injections of estradiol masculinizes rodent brains.
2.If testosterone is administered along with agents to block aromatization, masculinization of the rodent brain does not occur.
3.If androgens that cannot be aromatized are administered (e.g.
dihydrotestosterone), masculinization of the rodent brain does not occur.

Question 38

All females have estradiol in their blood supply, so how do female
offspring’s brains NOT get masculinized by it?

Answer 38

Alpha-fetoprotein binds to and deactivates circulating estradiol.

Question 39

All females have estradiol in their blood supply, so how do male brains get masculinized if there is alpha-fetoprotein about?

Answer 39

-Testosterone is immune to it!
-Testosterone travels to the brain and is converted to estradiol.
-Alpha-fetoprotein can’t get past the blood-brain barrier.

Question 40

What are 3 important things to remember about sex differences in the brain?

Answer 40

1.Differences are in “average” or “typical” male and female brain and are not that definitive.
2.We would expect differences to affect behaviour but we lack evidence of this.
3.Differentiation of the various areas of the brain occurs over time
(perinatal, puberty), not all at once

Question 41

What functional differentiation is their of the brain?

Answer 41

■Experiments of neural control of sexual behaviour not ethical in
humans
■Information obtained from:
–Laboratory animals.
–Humans with developmental disorders.
■Sex hormones are critical
■Again, default program is to develop a female

Question 42

State the organisational effects (the development era)

Answer 42

Prenatal
Development of nervous system
Specific areas of brain driving male and female specific sexual behaviours

Question 43

State the activational effects (following from organisational effects)

Answer 43

Puberty/adulthood
Activation of nervous system
Hormones interact with specific areas to drive sexual behaviours

Question 44

What’s behavioural masculinisation?

Answer 44

Androgen-stimulated development of the brain areas that will respond to testosterone in adulthood and produce male sexual behaviour

Question 45

What’s behavioural defeminisation?

Answer 45

The inhibitory effects of androgens on the development female brain areas that would respond to estradiol and progesterone in adulthood to stop the production of female sexual behaviour