Lecture 13: Sexual Behaviour Flashcards
sexual dimorphism
Two sexes of the same species exhibit different characteristics beyond the differences in their sexual organs
what causes sexual dimorphism
genetic and hormone differences before and after birth
Triplewart Seadevil and sexual dimorphism
female is a fish, but the male is a tiny rudimentary creature that lives on the female parasitically
main type of sexually dimorphic behaviours in mammals
reproductive behaviours
why does the brain give rise to sexually dimorphic behaviours
because it’s a sexually dimorphic organ
t or f: In humans, the size and interconnectivity of different brain regions vary according to sex
t
sex
Defined at birth by the presence of particular sex chromosomes, sex hormones, and sex organs
gender
The range of characteristics that pertain to, and differentiate between, masculinity and femininity, which are the characteristics associated with men and women, respectively. These characteristics reflect biology and culture
sexual reproduction
involves the fusion of specialized cells known as gametes (one from each parent) to form offspring that inherit traits from each parent
sex chromosomes
The X and Y chromosomes that typically determine an organism’s sex. (23rd pair)
gonads
ovaries or testes
gametes
reproductive cells which are either ova (egg cells) or sperm.
how many chromosomes do gametes have
23
5 factors that determine sex
- sex chromosomes
- gonads
- sex hormones
- internal reproductive anatomy
- external anatomyt
result of unexpected combinations of the 5 factors of sex determination
intersex people
what types of sexual precursors do embryos contains
precursors for both female and male sex organs
undifferentiated gonads
embryonic precursor of ovaries/testes
mullerian system
embryonic precursors of female internal sex organs
wolffian system
embryonic precursors of male internal sex development
second month of gestation for sex determination
the undifferentiated gonads typically develop into ovaries or testes
third month of gestation for sex determination
typically either the Müllerian or Wolffian system develops while the other withers away
sry gene
normally located on the Y chromosome. encodes a protein that causes undifferentiated fetal gonads to develop into testes.
male sex organ development sequence
SRY Gene -> Development of tests -> embryonic testicular release of 1) antimullerian hormone 2) androgens (testosterone) -> stops the development of Mullerian system trigger & Triggers development of male sex organs (both internal and external)
defeminizing effect
Effect of anti-Müllerian hormone early in development, which prevents the development of the female-typical internal anatomy
masculinizing effect
Effect of androgen hormones early in development, which triggers the development of male-typical anatomy
androgens
Male sex hormones
what is the most common mammalian androgen
testosterone
what triggers the development of male external sexual anatomy
dihydrotesetorone (made from testosterone)
female sexual organ development sequence
XX chromosome -> development of ovaries (which are largely silent until puberty) -> puberty is triggered by hormones released from gonads
absence of anti-mullerian signalling in females
the Mullerian system develops into internal female reproductive anatomy, which includes the inner vagina, uterus, and fallopian tubes.
absence of testosterone signalling in females
external female sex organs (vulva) develop while the Wolffian (male internal) system withers away.
what is needed for the development of gonads
the SRY gene or two X chromosomes
turner syndrome
you only have one sex chromosome (X0), so don’t have ovaries or testes
swyer syndrome
you are XY but have a bad SRY so the gonads don’t develop
do gonads develop in people with turner syndrome and swyer syndrome?
In both cases, gonads don’t develop, but female-typical sex organs develop normally
are people without gonads fertile?
People without gonads are infertile and can go through puberty through artificial hormone injections
people with more than two x chromosomes and the sry gene
typically develop as males and are often infertile with small testes and have trouble growing a beard.
what 2 hormones do the testes of healthy males release
anti-Mullerian and androgen
what types of molecules are anti-Mullerian and androgen
peptides that work via g-protein-gated metabotropic receptors
what happens if there is insufficient anti-mullerian signalling
they will have insufficient anti-Müllerian hormone signalling. Causes insufficient anatomical defeminization: both male and female internal sex organs will develop and get tangled together. there is often functional external male genitalia
what happens if there is insuffiscient androgen signalling?
they have androgen insensitivity syndrome
androgen insensitivity syndrome
Results in anatomical defeminization with partial or no masculinization
severe cases of androgen insensitivity syndrome
no internal sex organs develop. In these cases, people typically develop normal external female genitalia and identify as heterosexual women, but they will be infertile and have a short vagina
mild cases of androgen insensitivity syndrome
external genetalia is fully masculinized
intermediate cases of androgen insensitivity syndrome
ambiguous external genitalia
organizational effects
Effect of sex hormones during the development of the body
behavioural defemnization
Refers to the organizational effect of androgens on the brain that prevents animals from displaying female-typical behaviours in adulthood
behavioural masculinzation
Refers to the organizational effect of androgens on the brain that enables animals to engage in male-typical behaviours in adulthood
activational effects
Effects of sex hormones after puberty
examples of activational effects
The production of sperm, ovulation and general horniness
how do the mind and body respond to activational hormone signalling in adulthood?
depends on how the body and brain were organized by hormone signalling in utero.
hormone control puberty steps
- Starts with the release of the peptide kisspeptin in the hypothalamus
- It goes over to another group of hypothalamus neurons, which causes it to release gonadotropic hormones
3, It diffuses into the pituitary, which releases follicle-stimulating hormone (FSH) and luteinizing hormone (LH)
kisspeptin
Neuropeptide produced by neurons in the hypothalamus that initiates puberty and maintains reproductive ability by triggering the release of gonadotropin-releasing hormone
Gonadotropin-releasing hormone
Hypothalamic hormone that stimulates the anterior pituitary gland to secrete gonadotropic hormones
Gonadotropic hormones
Hormones of the pituitary gland (follicle-stimulating hormone, FSH, and luteinizing hormone, LH) that have a stimulating effect on cells of gonads.
t or f: men resemble other mammals in their behavioural responsiveness to testosterone
true
effect of testosterone on male sexual behaviour
With normal levels of testosterone, men can be fertile; without testosterone sperm production ceases, and sooner or later, so does the ability to have sex.
what happens to men taking a gonadotropin-releasing hormone antagonist
they will not show testicular release of androgens and have a decrease in sexual interest and intercourse
estrogen
Class of sex hormones released by the ovaries that cause maturation of the physical features and characteristics of females, such as the growth of breast tissue and female genitalia
estradiol
Principal estrogen of many mammals, including humans
how are the menstrual and estrous cycles controlled?
controlled by the two ovarian hormones estradiol and progesterone
main difference between the menstrual and estrous cycles
Relative to the estrous cycle, menstrual cycles are associated with only very small fluctuations in sexual behaviour and sexual desire.
what animals use the menstrual vs. estrous cycle?
menstrual cycle: primates
estrous cycle: most non-primate mammals
characterization of menstrual vs. estrous cycle
menstrual cycle: characterized by menstruation, concealed ovulation, and the absence of a mating season
estrous cycle: no menstruation; animals reabsorb their endometrium and display clear outward signs of ovulation and fertilityt
organizational effects of hormones on the body in humans
are largely over by birth
organizational effects of hormones on the body in rodents
continue for a few weeks after birth
how can we masculinize or feminize the brain of rodents?
by altering hormone signalling immediately after birth
effect of castration after birth on male mice
they develop female typical behaviours
effect of female hormone injection on castrated male mice
they will try to get other males to have sex with them
effect of female hormone injection on non-castrated male mice
there are minimal behavioural consequences
rodent sexual behaviour in the presence of testosterone
Around the time of birth, testosterone masculinizes and defeminizes rodents’ sexual behaviour
human adrenal glands
are present in men and women. They typically secrete a small number of androgens
excessive androgen signalling from adrenal glands in males
minimal effect since their tests already secrete tons of androgens
excessive androgen signalling from adrenal glands in females
causes cogenital adrena hyperplasia (CAH)
Congenital adrenal hyperplasia (CAH)
Excessive androgen signalling in females that is present at birth
implication of androgen signalling research
homosexuality and transgenderism might be caused by variations in the timing and effectiveness of androgen signalling during the development of particular brain regions
effect of androgen signalling during development
sex organs can become slightly masculinized
oxytocin & vasopressin
Released during sex, birth, and breastfeeding
effect of increasing oxytocin & vasopressin receptor expression
causes non-monogamous prairie voles to form monogamous pair bonds
female sexual behaviour neural circuitry
Ventromedial nucleus (VMH) -> Periaqueductal gray matter (PAG) -> Nucleus Pargigantocellularis (nPGI) -> motor neurons in the spinal cord
male sexual behaviour neural circuitry
Medial preoptic area (mPOA) -> Periaqueductal gray matter (PAG) -> Nucleus Pargigantocellularis (nPGI) -> motor neurons in the spinal cord
what system does the Anti-Mullerian hormone signal to?
Mullerian system
what system do androgen hormones signal to?
the Wolffian system and the Primordial external system
what happens if the ventromedial nucleus and medial preoptic area are lesioned
there is no sexual behaviour
how did researchers identify the neural circuitry of sexual behaviour?
by injecting transneuronal retrograde tracers (ex. rabies virus) in muscles responsible for lordosis response
Periaquaductal gray matter (PAG)
- destruction abolishes sexual behaviour
- Estradiol treatment or stimulation of VMH increases neural activity
- Neurons contain estrogen and progesterone receptors
Nucleus Paragigantocellularis (nPGI)
normally inhibits mating behaviour
medial amygdala
- gets sensory information from all the different sensory systems and produces sexual arousal
- Causes production of Fos protein
- Neurons contain estrogen and progesterone
ventromedial nucleus (VMH)
A large nucleus in the hypothalamus critical for the female sexual response
electrical stimulation of VMH in females
facilitates sexual behaviour
Media preoptic area (mPOA)
Nucleus in the anterior hypothalamus that plays an essential role in male sexual behaviour
electrical stimulation of mPOA in males
facilitates sexual behaviour
electrical stimulation of mPOA in female
doesn’t affect sexual behaviour, but causes them to ignore their offspring
sexually dimorphic nucleus
found in the medial preoptic area. is bigger in males than females
who posesses mPOA?
both males and females
who possesses VMH
just females
how are vasopressin and oxytocin released?
as neuropeptides in the brian and hormones in the blood
do peptides cross the blood-brain barrier?
not very well
what things cross the blood-brain barrier?
lipid-soluble things
