Chapter 9: Hormones
Chapter 9: Hormones NSC 3361
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This 7 page Class Notes was uploaded by Rachael Couch on Thursday February 11, 2016. The Class Notes belongs to NSC 3361 at University of Texas at Dallas taught by Van S Miller in Summer 2015. Since its upload, it has received 39 views. For similar materials see Behavioral Neuroscience in Neuroscience at University of Texas at Dallas.
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Date Created: 02/11/16
Lecture 9: Hormones Have the same job as NT – to communicate with other cells Act in a gradual fashion Slower and longerlasting than neurotransmitters o Neurotransmitters are rapid and shortlasting o Hormone signals can last for hours, months, years, etc Often have pulsatile secretion (in bursts) o Ex: menstrual cycle or secreting growth hormone from 46am every night Some are controlled by circadian clocks Communicate over longer distances and are slower than neural communications Diffuse (not precise like neural communications) Have a graded effect (not all or none like neural/action potential) o Severity of clinical presentation correlates with severity of hormone deficiency Endocrine feedback loops Structure of involved systems: o Hypothalamus is directly below the thalamus (the geometric center of the brain) o The pituitary hangs down from the hypothalamus o Posterior pituitary is right behind the anterior pituitary Secretion steps: o 1) Hypothalamus makes “releasing hormones” that are sent to the pituitary AKA thyrotropinreleasing hormone (TRH) o 2) Pituitary – releases tropic hormones in response to the hypothalamus’ releasing hormones Tropic hormones pituitary hormones that affect other endocrine glands AKA thyroidstimulating hormones (TSH) o 3) Thyroid – releases thyroid hormones in response to tropic hormones o Clinical thyroid deficiency could be from a defect in any of these 3 steps (hypothalamus, anterior pituitary, or thyroid gland) Negative feedback o The thyroid hormones act on target cells and also bind to the pituitary and hypothalamus and serve as an inhibitor = negative feedback o This allows for regulation Regulation o Taking thyroid medicine causes increased release of thyroid hormones The body then lowers production of thyroid hormone by decreasing TSH from the anterior pituitary o If the body has low thyroid, the body tries to compensate by increasing TSH o CQ: “Your mother has a high serum thyroid level. Expect her TSH to be..” low The brain is trying to control the high thyroid by lowering TSH Pituitary Posterior pituitary o Makes/secretes only 2 hormones: vasopressin (raises blood pressure, inhibits urine formation, and involved in thirst control) and oxytocin (maternal bonding) There is some (weak) evidence that autistic children have an oxytocin deficiency Anterior pituitary o Much larger and more important than the posterior pituitary o Makes several tropic hormones (all except vasopressin and oxytocin) o Controls thyroid gland Thyroid gland Needs iodine to work Goiter swelling of the thyroid gland from iodine deficiency o Relatively common o Gland is swollen because the body is trying to compensate from the hypothyroidism that arises from iodine deficiency o Brain stimulates TSH to compensate but this doesn’t work so it makes the thyroid gland larger and larger Hormones affect behavior in many ways Usually a temporary effect but not always o Endocrine pathology mimics psychiatric disorders Cushing’s disease results from longterm excess glucocorticoids, with fatigue and depression o Glucocorticoids – from steroids Roid rage – anger as a result of steroid use Gender and sexual orientation Dichotomy of gender Not biologically or socially true because there are 7 levels of determination Could be male in 5 levels and female in 2, etc. Continuum from maleness to femaleness No amount of “options” would be enough Levels of sex determination Few people are male in all levels or female in all levels 1) Chromosomal sex (XY or XX) o SRY gene on Y chromosome makes testes (gonadal sex) testosterone No Y chromosome female (default sex) o This determines your internal organs o Could have no Y chromosome and still make testes (rare but can happen) 2) Gonadal sex o Gonadal sex is determined by whether you have testes o Testes secrete testosterone which determines your internal organs 3/4) Internal and external organs 5) Brain sex o Brain structures are different in males and females 6) Gender identity (which box you check) 7) Gender preference/sexual 7 ientation (not related to the other levels) Combinations possible 2 = 128 Sexual orientation/gender preference Social influence hypothesis o Emphasizes home environment or early seduction as causes of homosexuality o Little/almost no support Biological hypothesis o Most homosexuals recall feeling “different” as early as 4 or 5 years Changes in the brain are present before social influence can occur o Show gender nonconformity during childhood o Birth order (epigenetic changes) Higher birth order more likely to be homosexual 4 brother more likely to be gay than older brother Genetic influence o Someone with a homosexual sibling is 27 times higher to be homosexual as well Hormonal influence o Male homosexuals and heterosexuals have the same testosterone levels o Any hormonal influence on male homosexuality occurs prenatally Evidence that low testosterone in the womb may predispose individuals to be homosexual Brain involvement in sexual orientation Involved parts are in the hypothalamus Anterior commissure (AC) o White matter that helps the left and right hemispheres talk to each other o Larger in women and gay men than heterosexual men Gay men’s verbal and spatial performance is more similar to women’s than to heterosexual men’s INH3/INAH3– sexually dimorphic nucleus o AKA third interstitial nucleus of the anterior hypothalamus o Dimorphic meaning 2 forms (male and female only) o Smaller in women and gay men than heterosexual men Size is possibly controlled by testosterone Suprachiasmatic nucleus (SCN) o Suprachiasmatic nucleus (SCN) is larger in women and gay men than in heterosexual men and contains more vasopressinsecreting cells Bed nucleus of the stria terminalis (also involved but did not discuss in class) Biological determination of gender Organizing effects o Mostly occur prenatally or shortly after birth o Affect brain and body structure and are lifelong o Testosterone is main organizing hormone in human brain development Activating effects o Occur at any time in life o Come/go with hormone fluctuations or are long lasting, but are reversible o Ex: Body changes during life – bone density, muscle mass, external characteristics o Can change activating effects by taking hormones (ex: transgender) but can’t change organizing effects – they are permanent Brain development differences Hemisphere differentiation o Women have a larger corpus callosum Correlates with cognitive skills in women o Males have greater asymmetry than females Right hemisphere is thicker/larger in males than females Causes “surge” of testosterone in men Correlates with greater spatial orientation in men Gray matter o Women have greater gray matter percentages in 2 areas Dorsolateral prefrontal cortex Involved in thinking before you act, nonimpulsive behavior Superior temporal gyrus Involved in language (listening/talking) Connectivity o Men are better connected fronttoback Better at concentrating on one task o Women are better connected lefttoright Better at multitasking Anterior commissure is smaller in men than women Behavioral and cognitive differences Most girls have greater verbal ability Most boys have better visualspatial ability and are more physically aggressive There are more boys who are great at math than girls, but overall ability is the same There is mostly overlap between men and women o Depends on whether you focus on the small differences or large similarity Behavioral/cognitive differences change when hormones are changed o Spatial ability increases and verbal skills decrease with masculinization Males low in testosterone have impaired spatial ability High estrogen level is associated with depressed spatial ability and enhanced speech and manual skill tasks Spatial abilities are enhanced in androgenized girls Femaletomale transsexuals taking testosterone show spatial improvement, but loss of verbal fluency Sex Why do we have sex? Reproduction, DNA shuffling Mostly because it’s fun (this is not uniquely human) Comparison to hunger/thirst Sex is like hunger and thirst because it involves arousal and satiation, hormonal control, and is controlled by specific areas of the brain Sex is unlike hunger and thirst because t is not a homeostatic tissue need o Individuals don’t require sex for survival, but species do Estrogen and sex Women have pulsatile secretions in estrogen menstrual cycle In animals o Estrogen rise before ovulation promote sexual behavior o During ovulation, a female will be sexually receptive She is said to be in estrus (“in heat”) o Many female animals only have sex at this time Human females don’t have estrus they have sex when they are and aren’t ovulating (pleasure and bonding) o However, women are more likely to initiate sex during ovulation Androgens and sex Androgens – male hormones, such as testosterone Necessary for human male copulation Chemical castration (removes androgens) decreases copulation Testosterone therapy restores copulation in rats Sexual response curves Men are simple, most sexual response curves are the same o Increase in arousal, orgasm, and then a refractory phase Women are more complicated, sexual response curves vary o Depending on the woman, the curve may be more or less malelike o May be more rapid onset and offset o May be longer plateau or may never reach orgasm In both men and women, the sexual response typically involves an excitement phase (arousal), a plateau where arousal levels off, orgasm, and resolution, as arousal falls and body returns to normal Brain areas PET imaging of male orgasm o Primary activation occurs in the ventral tegmental area VTA – involved in addiction (same part of the brain as cocaine) o Oxytocin release at ejaculation may promote bonding PET imaging of female orgasm o Activation of the deep cerebellar nuclei Involved in rhythmic stimulation of the skin o Inhibition of orbitofrontal cortex Orbitofrontal cortex involved in judging o Entire brain involved at different times and not equally distributed Some parts inhibited, some activated o VTA is not activated – sex addiction is less common in women Both sexes o Medial amygdala (MeA; in the temporal lobe) Involved in sex, smell (perfume, pheromones), aggression, and emotions Dimorphic one small subarea of the MeA is much larger in men Important for males o Sexually dimorphic nucleus Located in MPOA (medial preoptic area)/(INH3) 23x larger in men Male sex activity related to its size Size depends on prenatal exposure to testosterone Important for females o Ventromedial hypothalamus – related to hunger Involved in receptivity to male advances Neurotransmitters and sex behavior Dopamine (DA) o Excitatory role in sex o DA activity in MPOA motivates sex behavior in both sexes, esp. in men o Drugs that increase DA increase sexual activity in humans o Increasing levels of DA produces erection in males, then ejaculation Serotonin (5HT) o Inhibitory role in sex o Serotonin is involved in general wellbeing, not needing sex, content o Injecting SSRI into LH increases time before male rats copulate again o Both men and women complain SSRIs impair their sexual interest o Possible that when you have depression you’re more motivated to seek out a bonding experience Gender Case studies Case: C.V. 3 month old boy Symptoms: Severe constipation, cannot hold his head up, microcephaly, low temp (96.1), tongue sticking out and too large Diagnosis – congenital hypothyroidism from iodine deficiency o Common issue at birth but less common now because they do prenatal screening for thyroid deficiency Microcephaly occurred because thyroid is necessary for correct neurogenesis Can fix all symptoms except microcephaly
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