Neurobiology of Sex

How far, how fast, how precise, and how graded does neural communication act?

NEURAL communication acts in short millimeter distances, in short milliseconds, in a very precise, all-or-none manner.

How far, how fast, how precise, and how graded does hormonal communication act?

HORMONAL communication acts in long distances (up to meters), in longer time (minutes/hours/days), in a diffusive, GRADED manner.

What type of communication occurs in bursts?

HORMONAL communication has pulsatile secretion

What are the three structural types of hormones?

PEPTIDE HORMONES, MONOAMINES, and STERIOD HORMONES

What are peptide, monoamine, and steroid hormones made/derived from?

Peptide hormones are made of AMINO ACIDS (protein subunits).

Monoamines are a modified version of a single amino acid

Steroids hormones are derived from CHOLESTEROL.

Which type of hormones binds to receptors ON THE SURFACE of the cell and releases a second messenger?

PROTEIN AND AMINE HORMONES bind to the surface of the cell, then a second messenger is released inside the cell (the protein and amine hormone stays outside).

Which type of hormones pass through the cell membrane and bind to receptors INSIDE the cell?

STEROID HORMONES act inside the cell as a TRANSCRIPTION FACTOR, binding to DNA and controlling GENE EXPRESSION

Which brain structure does Neuroendocrine cells effect and what hormones does the site release?

Neuroendocrine cells produce and secrete hormones that effect the POSTERIOR PITUITARY.

The two hormones that the posterior pituitary releases are vasopressin and oxytocin

What biological effect does Oxytocin have?

Oxytocin promotes reproductive and parenting behavior, uterine contractions, and mil letdown reflex.

In the mammary gland example, what encourages the posterior pituitary to secrete oxytocin?

Sensory signal from nipple stimulation —- Somatosensory Cortex —- Hypothalamus —- Neuroendocrine Signals  —Posterior Pituitary

The posterior pituitary then releases oxytocin which contracts the mammary glands.

What is the order of the endocrine feedback loop?

HYPOTHALAMUS  RELEASING HORMONES (TRH) — ANTERIOR PITUITARY TROPIC HORMONES (TSH)  —THYROID GLAND — THYROID HORMONES — TARGET CELLS

What is the purpose of releasing hormones? What structure synthesizes them?

The HYPOTHALAMUS secretes RELEASING HORMONES (such as TRH) into blood vessels, which controls pituitary’s release of tropic hormones.

What is the purpose of tropic hormones? What structure synthesizes them?

The ANTERIOR PITUITARY makes TROPIC HORMONES (such as Prolactin, FSH, LH, ACTH, and TSH) which affect OTHER endocrine glands. THYROID STIMULATING HORMONE (TSH) stimulates the THYROID.

What is a goiter?

a swelling of the thyroid gland in the neck as a result ofiodine deficiency

Due to too much TSH from Anterior Pituitary.The negative feedback loop is not working and there is no inhibition of the releasing hormone, causing a build up.

What is Congenital Hypothyroidism caused by?

Inadequate thyroid hormone production in newborn infants. Could be due to too little releasing hormone (TRH), or tropic hormone (TSH)

What is Cushing Disease and what is it caused by?

Cushing’s Disease is a psychiatric disorder that results in fatigue and depression. It is caused by long term excess glucocorticoids

What releasing hormone does the hypothalamus secrete to begin gonad hormone production?

GONADOTROPIN RELEASING HORMONE (GnRH)

GnRH stimulate the anterior pituitary to release what hormone? What are the effects of these hormones?

In response to GnRH, the anterior pituitary releases FOLLICLE-STIMULATING HORMONE(FSH) and LUTEINIZING HORMONE(LH)

For males:

• testes sense LH and make/release testosterone.

• The testes also sense FSH and produce sperm

For females:

• Ovaries sense FSH, leads to egg maturation and estrogen secretion.

• LH stimulates the follicles in the ovary to rupture. release the egg, forms a corpus luteum to secrete progesterone

How do Oral Contraceptives work?

they use a negative feedback loop.

They inhibit the release of GnRH from the hypothalamus which stop FSH and LH from releasing. This prevents LH stimulating the follicle and prevents the egg releasing from the ovary

What are the 7 Levels of Sex Determination?

Chromosomal Sex

Gonadal Sex (testis, ovaries)

Internal Sex Organs (prostate, uterus) 

External Sex Organs 

Brain Sex 

Gender Identity

Gender Preference

What decides whether the embryo will develop male or female gonads?

The presence of the SRY gene determines whether testis or an ovary develops. The SRY Gene is on the Y chromosome, which females (XX) don’t have.

What kind of effects affect genitalia maturation and growth, and are lifelong? When do these mostly occur?

ORGANIZING EFFECTS, which mostly occur prenatally or shortly after birth.

What kind of effects come and go, but also can be long lasting? When do these mostly occur?

ACTIVATING EFFECTS, which occurs at any time in life. (Breast growth, sex development, and hair growth) —are reversible!

Additionally, in both boys and girls, a common activating effect is dramatic increase in sexual interest.

Without the SRY gene, what type of ducts develop further and what type of ducts shrink?

In females the Mullerian ducts develop into the fallopian tubes, uterus, and vagina. The wolffian ducts shrink.

In males, what hormone guides development of the wolffian ducts? What hormone causes the Mullerian ducts to shrink?

Testosterone promotes the development of the wolffian ducts. The Anti-Mullerian hormone causes the Mullerian ducts to shrink.

What was going on in the Dominican Republic??

• What chromosomes did they have?

• What sex were they raised as?

In the D.R., a population of people had an enzyme deficiency. This caused testosterone to not have its developmental effect.

These people had the chromosomes for a male (XY) but did not have their Wolffian Ducts develop/ Mullerian Ducts shrink. At puberty, there was a surge in testosterone, which led them grow male teste despite being raised female.

What causes Klinefelter Syndrome?

Klinefelter Syndrome is a trisomy of the sex chromosomes. They have the  two female sex chromosomes(XX), but also have the male (Y) chromosomes. This leads to conflicting genetic material resulting in small testes, osteoporosis, and poor hair growth.

During sexual activity, how do hormones influence women?

In non-human females, estrogen produced before OVULATION promotes sexual behavior.

female rat is sexually receptive = ESTRUS.

women dont have estrus, but are likely to initiate sex at ovulation

How do response curves differ between male and females during sex?

Males have a standard response curve: excitement, plateau, orgasm, and resolution—similar to action potential.

Females have many different curves (Can experience orgasms multiple time)

What hormone is released at ejaculation? What drug treatment would block this?

Oxytocin is released at ejaculation. Naloxone drug treatment would block this, and men report less pleasurable orgasm

What are important brain areas for reproductive behavior in both sexes?

the medial amygdala and medial preoptic area.

What brain areas for sex are important for males?

The SEXUALLY DIMORPHIC NUCLEUS. It is in the MPOA (INAH3).

Lesions here cause impairment, while stimulation causes enhancement.

2-3X LARGER in men, with its size related to activity and prenatal exposure to testosterone.

  What structure is especially important for women in sex?

VENTROMEDIAL HYPOTHALAMUS- important for receptivity to male advances

During orgasm, which part of the brain do you see light up in males and females?

During orgasm, the VTA is activated in males, making orgasm very pleasurable and even addicting.

For females, the deep cerebellar nuclei, but there is also decreased orbitofrontal cortex activity.

What neurotransmitter motivates sexual behavior?

DOPAMINE-

men: more dopamine = erection/ejaculation.

dopamine agonists would NOT interfere with sexual activity, unlike other drugs.

What neurotransmitter impairs sexual ability?

SEROTONIN

How are the brains of males and females different?

Males:

• GREATER ASYMMETRY

• LARGER RIGHT HEMISPHERE.

• less gyrification.

Females:

• LARGER CORPUS CALLOSUM, = better cognitive skills.

• more symmetrical.

• greater gray matter in the Dorsolateral Prefrontal Cortex and superior temporal Gyrus.

What percent of Americans identify as lesbian, gay, or bisexual?

3.5%

What are the two hypotheses for sexual orientation? Which has more support?

Two Hypothesis:

SOCIAL INFLUENCE HYPOTHESIS:

• Home environment or early seduction cause homosexuality.

BIOLOGICAL HYPOTHESIS:

• biology helps to determine sexuality.

• alluded by early childhood gender nonconformity.

• Homosexuals prefer to be with the opposite sex early on

• much more support than social influence hypothesis.

When you compare hormonal levels between homosexuals and heterosexuals, what do you find?

testosterone is the SAME between people, suggesting that its influence occurs prenatally

  What brain structures are usually different in straight versus gay men?

HOMOSEXUAL MALES

• a smaller INAH3

• larger ANTERIOR COMISSURE (same in heterosexual female brains)

• a larger SCN with more vasopressin-secreting cells.

Straight male/gay female brains = NOT SIMILAR

Gay male/straight female= SIMILAR

Which group of people has better verbal ability?

Females-

• due to HIGH ESTROGEN LEVELS

• associated w/ decreased spatial ability, but enhanced speech/ manual skill tasks

How are the brain connection differences between males and females?

Males

• better connected front to back

• better at concentrating on one task.

Women

• better connected left to right usually

• better at multitasking.

Which group of people, males or females, has better visual spatial ability?

Males

• due to TESTOSTERONE which increases growth of the right hemisphere.

• low in testosterone = impaired spatial ability.