Sex and the brain Flashcards

Question

describe the oestrous cycle

Answer 1

-Non-primate mammals, such as rats and mice, the luteal phase is much shorter. -In other oestrous animals, such as dogs, cats, and farm animals, the phases are more nearly equal in duration. -Many oestrous animals have only one cycle per year, usually in the spring. Presumably, this timing is for the production of offspring when the weather and food supply are optimal. -At the other extreme are animals such as rats, which are said to be polyoestrous because they have short periods of oestrus, or “heat,” throughout the year.

Answer 2

Arousal followed by plateau, orgasm, and resolution phases

Answer 3

From the cerebral cortex—where erotic thoughts occur—but the spinal cord coordinates this brain activity with sensory information from the genitals and generates the critical outputs that mediate the sexual responses of the genital structures

Answer 4

-certain parts of the external genitals in men and women to be engorged with blood, and thus to swell -In women, these structures include the labia and the clitoris; in men, it is primarily the penis

Answer 5

The external genitals are densely innervated by mechanoreceptors, particularly within the clitoris and the glans of the penis. Stimulation of these sensory endings can, by itself, be enough to cause engorgement and erection

Answer 6

Most men who have suffered a complete transection of the spinal cord at the thoracic or lumbar level can nevertheless experience an erection when their penis is mechanically stimulated

Answer 7

The mechanosensory pathways from the genitals are components of the somatosensory system, and their anatomy follows the usual pattern: Axons from mechanoreceptors in the penis and clitoris collect in the dorsal roots of the sacral spinal cord. They then send branches into the dorsal horns of the cord, and into the dorsal columns, through which they project toward the brain

Answer 8

the parasympathetic division of the ANS

Answer 9

Within the sacral spinal cord, the parasympathetic neurons can be excited by either mechanosensory activity from the genitals (which can directly trigger reflexive erection) or by axons descending from the brain (which account for responses mediated by more cerebral stimuli)

Answer 10

-release a potent combination of acetylcholine, vasoactive intestinal polypeptide (VIP), and nitric oxide (NO) directly into the erectile tissues

Answer 11

-relaxation of smooth muscle cells in the arteries and the spongy substance of the clitoris and penis --> the usually flaccid arteries then become filled with blood, thereby distending the organs

Answer 12

by enhancing the effect of NO

Answer 13

the spongy internal tissues swell against two thick, elastic outer coverings of connective tissue that give the erect penis its stiffness. In order to keep the organs sliding easily during copulation throughout the plateau phase, parasympathetic activity also stimulates the secretion of lubricating fluids from the woman’s vaginal wall and from the man’s bulbourethral gland.

Answer 14

The sympathetic efferent axons then trigger the process of emission: Muscular contractions move sperm from storage sites near the testes through two tubes called the vas deferens, combine the sperm with fluids produced by various glands, and propel the resulting mixture (called semen) into the urethra. During ejaculation, a series of coordinated muscular contractions expel the semen from the urethra, usually accompanied by the intense sensations of orgasm

Answer 15

Stimulation adequate to trigger orgasm probably also activates the sympathetic system. Sympathetic outflow causes the outer vaginal wall to thicken and, during orgasm itself, triggers a series of strong muscular contractions.

Answer 16

Following an orgasm, some time must pass before another orgasm can be triggered in men. The orgasmic experience of women tends to be considerably more variable in frequency and intensity. The resolution phase, which ends the sexual response cycle, includes a draining of blood from the external genitals through veins, and a loss of erection and other signs and sensations of sexual excitement

Answer 17

To maximise the survival of offspring and parental genes. Species variations in preferred mating systems seem to depend on the investment that males and females make in raising their offspring, although there are exceptions

Answer 18

The male mates with many females but the female mates with only one male for one or multiple mating seasons

Answer 19

One female mates with many males but the males mate with only that female, is rare among mammals and vertebrates in general. One exception is the phalarope, a shorebird that breeds in the cold tundra

Answer 20

Polygyny and polyandry both examples of this --- i.e., having more than one mate

Answer 21

a male and a female form a tightly bound relationship that includes exclusive (or nearly exclusive) mating with each other

Answer 22

Prairie voles (Microtus ochrogaster): social and monogamous --> After mating, a female prairie vole spends more time with its partner than by itself or with a strange Montane voles (Microtus montanus): asocial and promiscuous --> Female montane voles, spend most of their time in a neutral area alone rather than with their recent mating partner or a stranger.

Answer 23

Prairie voles: more oxytocin (female) and vasopressin (male) --> Vasopressin antagonists given to a male prairie vole before mating prevent him from forming a pair-bond relationship. This disruption of pair bonding can be produced with the antagonist selectively infused into the ventral pallidum (the anterior portion of the globus pallidus). Oxytocin antagonists have no such effect. When a male is given vasopressin while he is exposed to a new female, he quickly forms a strong preference for her even without the intense mating that usually precedes pair-bonding. In females, oxytocin appears to be necessary to establish a preference for her mate, while vasopressin has little effect Montane voles: fewer receptors for oxytocin and vasopressin --> A virus was used to deliver genes to the ventral pallidum of male montane voles, causing an overexpression of vasopressin receptors. Consequently, the male montane voles had numbers of vasopressin receptors in the ventral pallidum comparable to prairie voles. The manipulated montane voles also pair-bonded like prairie voles. If this cause-and-effect link is supported by further studies, it will dramatically show that a complex social behaviour can be altered by the overexpression of a single protein at one location in the brain

Answer 24

-Vasopressin increases the male prairie vole’s paternal proclivities, causing him to spend more time with his pups, and oxytocin similarly stimulates maternal behaviours in the female -administering vasopressin or oxytocin to the naturally promiscuous montane voles does not evoke the effects on pair-bonding and parenting seen in prairie voles, perhaps because they don’t have receptors in the necessary places

Answer 25

There is evidence that human plasma oxytocin levels increase during activities like breastfeeding in mothers and sexual intercourse in men and women, suggesting its role in bonding and attachment.

Answer 26

the experiments showed that several brain areas, including the anterior cingulate cortex, caudate nucleus, and striatum, are more activated when people view pictures of their children and partners compared to unrelated individuals.

Answer 27

Many of the brain areas activated in response to loved ones are rich in oxytocin and vasopressin receptors, similar to the vole story, suggesting a connection between these chemicals and bonding in humans.

Answer 28

fMRI studies suggest that oxytocin and vasopressin play roles in human bonding, potentially similar to what is observed in voles

Answer 29

-In men, there was a correlation between a particular vasopressin gene variant (V1aR) and lower scores on measures of the quality of their marriage. These men were also twice as likely to report experiencing a marital crisis in the year before the survey. -In women, there was no connection between the vasopressin gene variants and the quality of their marriage as assessed by a variety of questionnaires

Answer 30

Wives of men with the vasopressin gene variant also reported lower marital quality compared to the wives of men without the variant.

Answer 31

The function of this gene variant is not known, but the study's results suggest that, even in humans, vasopressin receptors might play a role in pair-bonding.

Answer 32

Male and female brains are expected to have differences, known as sexual dimorphisms, due to the different neural systems required to control unique body parts and behaviours associated with each sex.

Answer 33

The BC muscles, located at the base of the penis in men and around the opening of the vagina in women, have a role in penile erection, assisting in ejecting urine, and slightly constricting the vagina in women.

Answer 34

Onuf's nucleus, located in the sacral spinal cord, controls the BC muscles. It is moderately dimorphic, with more motor neurons in men due to the larger BC muscles in males.

Answer 35

The preoptic area of the anterior hypothalamus, clustered around the third ventricle, exhibits the most distinct sexual dimorphisms in the mammalian brain and appears to play a role in reproductive behaviours.

Answer 36

-In rats, histological sections of male and female preoptic areas show an obvious difference: the sexually dimorphic nucleus (SDN) is five to eight times larger in males than in females. -lesions of the preoptic area disrupt the oestrous cycle in females and reduce the frequency of copulation in males

Answer 37

There are small and controversial sexual dimorphisms in the preoptic area of the human brain. Four clusters of neurons called the interstitial nuclei of the anterior hypothalamus (INAH) have been studied, with INAH-1, INAH-2, and INAH-3 reported to be larger in men than women. INAH-3 is the clearest dimorphism, reported to be twice as large in men.

Answer 38

There may be subtle differences in the size of certain hypothalamic nuclei that correlate with sexual orientation in people.

Answer 39

Various neurons of the medial preoptic area in male rhesus monkeys fire vigorously during specific phases of sexual behaviour, including arousal and copulation.

Answer 40

the most reliable conclusion about sexual dimorphisms in human brain structure is that there are very few of them, likely because the vast majority of men's and women's behaviours are very similar.

Answer 41

An evolutionary explanation suggests that men evolved as hunters and relied more on their navigation abilities, while women evolved behaviours like staying closer to home to care for children, making them more social and verbal

Answer 42

Studies have reported that women excel at verbal tasks, including naming objects of the same colour, listing words beginning with the same letter, and verbal memory. Starting at around age 11 years, girls tend to perform slightly better on tests of comprehension and writing, and this effect is sometimes said to extend through high school and beyond.

Answer 43

Tasks that reportedly favour men in performance include map reading, maze learning, and mathematical reasoning. Researchers speculate that these advantages evolved from the days when men roamed large areas to hunt wild animals. One of the largest reported differences is in the mental rotation of objects, a task that appears to favour men. Considerations include that not all studies yield the same results, there are huge performance differences across large groups, and the differences may result from individual variations or differences in experience.

Answer 44

Evidence includes correlations between spatial reasoning and the menstrual cycle in women, as well as improved spatial performance in older men with low testosterone levels after receiving testosterone.

Answer 45

A variety of factors, including genetics, culture, and life experiences, may make a behavior more common in one sex than the other, but ultimately, all behaviors are controlled by the brain

Answer 46

Steroids can influence neurons by acting quickly to alter membrane excitability, sensitivity to neurotransmitters, or neurotransmitter release through direct binding to various enzymes, channels, and transmitter receptors. For example, certain metabolites (breakdown products) of progesterone bind to the inhibitory GABA receptor and potentiate the amount of chloride current activated by GABA. The effects of these progesterone metabolites are quite similar to the sedative and anticonvulsant effects of the benzodiazepine class of drugs. They can also diffuse across the outer membrane and bind to specific steroid receptors in the cytoplasm and nucleus, promoting or inhibiting the transcription of specific genes.

Answer 47

Specific types of steroid receptors in the cytoplasm and nucleus can promote or inhibit the transcription of specific genes in the nucleus, a process that can take minutes to hours, depending on the type of sex hormone and receptor involved.

Answer 48

The organizational effects of hormones during development refer to the ability of hormones like testosterone to alter young genitals and brain circuitry in ways that lead to distinctly male genitals and masculine behaviours later in life. These effects are irreversible and allow for the generation of male functions after sexual maturity.

Answer 49

Activational effects refer to the temporary effects of steroid hormones on the nervous system in mature animals, often required for the full expression of sexual behaviors. These effects can activate changes in certain brain regions necessary for specific behaviors

Answer 50

The hormone responsible for masculinization of the male brain during prenatal development is estradiol, which results from the conversion of testosterone into estradiol within neuronal cytoplasm, catalyzed by the enzyme aromatase.

Answer 51

α-fetoprotein, found in high concentrations in fetal blood, binds estrogens and protects the female fetus from masculinization by preventing the effects of maternal estrogens on the developing brain.

Answer 52

(Role of elevated testosterone and oestradiol level) Prostaglandins are compounds derived from arachidonic acid and have various roles, including inducing pain and fever after tissue damage. Prostaglandins are involved in brain masculinization, with COX inhibitors reducing copulatory behavior in male rats and inducing male-like copulatory behaviors in female rats.

Answer 53

Unusually high levels of α-fetoprotein are a possible indicator of neural tube defects, while unusually low levels are found in Down syndrome when measuring α-fetoprotein levels in maternal blood or amniotic fluid.

Answer 54

-Yes, in situations where hormonal function is altered, it is possible for genetic males to have female brains and genetic females to have male brains. -Treatment with testosterone early in development in mammals leads to decreases in at least some features of adult female sexual behaviour

Answer 55

If genetically female (XX) rats are exposed to testosterone during the few days around birth, they will fail to elicit the typical female mating posture, called lordosis, when they reach maturity

Answer 56

-androgen receptor gene located on X chromosome males thus only have one copy and males with the defective gene cannot produce function androgen receptors -Genetic males with a defective androgen receptor gene may experience profound androgen insensitivity. They develop normal testes, but these remain undescended in the abdomen. While they produce ample testosterone, their tissues cannot respond to androgen, resulting in outwardly female appearance

Answer 57

Individuals with androgen insensitivity may have a vagina, a clitoris, and labia, and they may develop breasts and a female body shape during puberty.

Answer 58

Normal levels of Müllerian-inhibiting factor prevent the development of the female reproductive system, leading to the absence of menstruation and infertility in androgen-insensitive genetic males.

Answer 59

Androgen-insensitive genetic males typically identify themselves as women, dress like women, and choose men as their sex partners, even when they understand the circumstances of their biology.

Answer 60

Congenital adrenal hyperplasia (CAH) is a condition in genetic females where the adrenal glands secrete unusually large amounts of androgens, leading to abnormally high levels of circulating androgens early in development.

Answer 61

-At birth, CAH females have normal ovaries and no testes, but their external genitals are intermediate in size between a normal clitoris and a penis. -Surgery and medications are the usual treatments for CAH females after birth to address the condition.

Answer 62

CAH girls (and their parents) are more likely to describe their behaviour as aggressive and tomboyish. As adults, most CAH women are heterosexual, but a higher percentage of them are homosexual compared to other women.

Answer 63

Prenatal exposure to high levels of androgens is presumed to cause a somewhat male-like organization of certain brain circuits in CAH women, analogous to animal studies

Answer 64

It is challenging to determine whether masculine behavior in CAH females is solely due to early androgen exposure and male-like brain dimorphisms or if it is influenced by subtle differences in the way they are treated by others, particularly parents dealing with a child with ambiguous genitals.

Answer 65

-Genes can play a role in complex sex behaviors in organisms like the fruit fly Drosophila melanogaster. -Male fruit flies exhibit courtship behaviors, including orienting toward and following the female, singing a courtship song, and tapping her with his forelegs before attempting to mate. -Males know how to court even if they have never seen courtship by other flies, suggesting that these behaviors are genetically coded.

Answer 66

The fru gene (fruitless) may be essential for male courtship behaviors in fruit flies. In males, the fru gene is expressed in various cell types, leading to the development of a male central nervous system that automatically triggers male courtship behaviors.

Answer 67

Females without fru expression develop a complete central nervous system, but its wiring is somewhat different, and female courtship behaviors are "built-in."

Answer 68

In the absence of the fru gene, male courtship behaviors are significantly reduced or nonexistent. Conversely, females that express fru exhibit male courtship behaviors and resist courtship by males.

Answer 69

The dsx gene plays an important role in the sexual differentiation of the body, including the development of male or female genitals. It also interacts with fru in controlling sexual differentiation of the central nervous system (CNS) and sex-specific behaviours

Answer 70

In the case of the fru gene, it is either expressed in males or not expressed in females. The dsx gene is expressed in both males and females, but alternative splicing leads to the production of male-specific and female-specific proteins.

Answer 71

In men, testosterone has a two-way interaction with sexual behavior. It can rise in anticipation of a sexual act or while fantasizing about it, and reduced testosterone levels are associated with decreased sexual interest.

Answer 72

It has been reported that women are more likely to initiate sex when estradiol levels are highest during their menstrual cycle.

Answer 73

In rats, during pregnancy, even though leptin levels rise, appetite and food intake increase instead of decreasing due to hormonal changes associated with pregnancy leading to leptin resistance in the hypothalamus.

Answer 74

During lactation and nursing, maternal rats experience a unique behavior related to somatosensory cortex changes. The somatosensory cortex in female rats has a sensory representation of the ventral skin surrounding the nipples.

Answer 75

Tactile stimulation during nursing leads to a dramatic increase in the representation of the ventral skin and a shrinkage of receptive fields to half their normal size.

Answer 76

No, this somatosensory map plasticity appears to be temporary and reversible. Several months after weaning, the receptive fields return to their normal size.

Answer 77

Both addictive drugs and maternal behaviors appear to enhance the influence of dopamine released by neurons projecting from the ventral tegmental area (VTA) into the nucleus accumbens (NA). This activation of the dopamine system is associated with reward and addiction. In the case of maternal behavior, the tactile stimulation of suckling pups activates this system, reinforcing mother-infant bonding and promoting pup survival.

Answer 78

Surprisingly, brain activation was quite similar in both groups, particularly in the nucleus accumbens (NA). This similarity suggests that both nursing and cocaine injection stimulate the dopamine system associated with reward and addiction. This finding highlights the reinforcing nature of maternal behavior during lactation.

Answer 79

The hypothesis is that the tactile stimulation of suckling pups during nursing activates the dopamine system, making nursing a reinforcing behavior. This reinforcement promotes mother-infant bonding and, ultimately, the survival of the pups. These brain changes are significant for ensuring the care and well-being of the offspring.

Answer 80

Fatherhood in species like marmosets might alter brain structure of the prefrontal cortex by increasing the density of dendritic spines on pyramidal cells and potentially increasing the number of vasopressin receptors on these spines.

Answer 81

-By modulating the flow of potassium ions, oestradiol depolarizes some neurons and increases their firing of action potentials. -estradiol can exert its effects on neurons within minutes of experimental application. -Estradiol treatment of tissue taken from the hypothalamus of newborn mice can lead to neurite outgrowth, increased cell viability, and higher spine density in neurons.

Answer 82

They found that the number of dendritic spines on hippocampal neurons fluctuated during the 5-day estrous cycle, with spine density and estradiol levels peaking together. Additionally, injected estradiol increased spine numbers even in animals with low natural estradiol levels.

Answer 83

The variation in spine density, which tracks estradiol levels, is thought to influence hippocampal excitability. When estradiol levels increase, the hippocampus in experimental animals is more prone to generate seizures.

Answer 84

Estradiol and progesterone levels peak during the proestrus phase of the estrous cycle. During this time, seizure thresholds are lowest, meaning that the likelihood of seizures occurring is increased

Answer 85

Woolley and McEwen confirmed that estradiol itself triggers the increase in spine numbers on hippocampal neurons. As spine density increases, so does the growth of excitatory synapses in these neurons.

Answer 86

-Estradiol enhances synaptic plasticity in the hippocampus by increasing the postsynaptic responses to glutamate in the presence of estradiol, resulting in stronger excitatory synapses. -Estradiol may also alter hippocampal function by decreasing synaptic inhibition. Estradiol causes some inhibitory cells to produce less GABA, their neurotransmitter, and therefore synaptic inhibition becomes less effective. Less inhibition increases neural activity, complementing the estradiol effect at excitatory synapses. When the pieces are put together, it seems that estradiol produces a hippocampus with less effective inhibitory synapses and stronger excitatory synapses, thereby triggering an increase in the number of spines on the pyramidal cells

Answer 87

Reduced inhibition, as induced by estradiol, leads to increased neural activity, which complements the strengthening of excitatory synapses caused by estradiol.

Answer 88

The hippocampus in rats is particularly important for spatial memory and navigational skills.

Answer 89

Estradiol enhances memory formation in rats when administered shortly before or after training on memory tasks.

Answer 90

If estradiol is given 2 hours after training, the memory benefit associated with estradiol disappears. Evidently, estrogens must be present near in time to the learning experience to facilitate memory.

Answer 91

The peak in hippocampal spine number coincides with the rat's peak in fertility.

Answer 92

Behaviors such as heightened spatial ability, which could be beneficial for seeking out mates.

Answer 93

The female rat's brain fine-tunes itself on a 5-day cycle to meet changing reproductive needs.

Answer 94

Estradiol helps neurons survive hypoxia, oxidative stress, and exposure to neurotoxic agents.

Answer 95

Estrogen replacement therapy may delay the onset of Alzheimer's disease, reduce tremors in Parkinson's disease, and alleviate the severity of multiple sclerosis when pregnant.

Answer 96

Tamoxifen, an estrogen receptor antagonist used in breast cancer treatment, is associated with an increased risk of stroke in women.

Answer 97

Both neurons and astrocytes express estrogen receptors, and the benefits of estrogen in neurological diseases may arise from its effects on both cell types.

Answer 98

-While there is no evidence that sexual orientation is related to the activational effects of hormones in adults, some believe it may be influenced by structural differences in the brain due to organizational effects. -No, administering androgens or estrogens to adults, or removing the gonads, has no effect on sexual orientation

Answer 99

The SDN (sexually dimorphic nucleus) is a brain region located in the preoptic area of the anterior hypothalamus in rats.

Answer 100

After a surgical lesion to the SDN, male rats spend more time with sexually active males than with sexually receptive females, reversing their preference before surgery.

Answer 101

The causal relationship between the size of hypothalamic nuclei, such as the SDN, and sexual orientation is unclear.

Answer 102

The INAH-3 nucleus is one of the interstitial nuclei of the anterior hypothalamus. It is about twice as large in men as in women.

Answer 103

Studies have suggested that gay men tend to have an INAH-3 nucleus size similar to that of women, which is about half the size of the nucleus in straight men.

Answer 104

While the differences in INAH-3 size have been observed in relation to sexual orientation, it is challenging to interpret these findings in terms of complex human behavior. Moreover, subsequent studies have not always confirmed a consistent correlation between INAH-3 size and sexual orientation.

Answer 105

The anterior commissure and suprachiasmatic nucleus.

Answer 106

The bed nucleus of the stria terminalis is larger in men than women, and male-to-female transsexuals have a nucleus comparable in size to females.