PSY 250 Lecture Notes - Lecture 27: Cyp17A1, Stria Terminalis, Heterosexuality
Chapter 7: The Biology of Sex and Gender Book Notes
- Sex as a Form of Motivation
- Sex is a motivated behavior like hunger
- Theorists have had difficulty categorizing sex with other physiological drives because it doesn’t fit
the pattern of a homeostatic tissue need
- Sex ensures the survival of the species, but not of the individual
- Arousal and Satiation
- Excitement Phase: a period of arousal and preparation for intercourse
- Increased heart rate, respiration rate, blood pressure, and muscle tension
- Male’s penis becomes engorged with blood and becomes erect
- Female’s clitoris becomes erect as well, vaginal lips swell and open, vagina
lubricates, breasts enlarge, and nipples erect
- Plateau Phase: the increase in sexual arousal levels off; arousal is maintained at a high
level for seconds or minutes, though it is possible to prolong this period
- Testes rise in the scrotum in preparation for ejaculation
- Vaginal lubrication increases and vaginal entrance tightens on the penis
- Orgasm: rhythmic contractions in the penis are accompanied by ejaculation of
seminal fluid containing sperm into the vagina and similar contractions happen
in the vagina creating a few seconds of pleasurable sensation
- Resolution: follows orgasm as arousal decreases and the body returns to its previous state
- Refractory Period: males are unable to become aroused or have another orgasm for
minutes, hours, or even days, depending on the individual and the circumstances
- Females do not have a refractory period
- Coolidge Effect: a quicker return to sexual arousal when a new partner is introduced
- The Role of Testosterone
- Rats have sex 20 times a day and are not embarrassed to perform in front of an
experimenter
- Hormones have a clearer role in animal sexual behavior
- Castration: removal of the gonads (testes or ovaries), is one technique used to study the
hormonal effects because it removes the major source of sex hormones; results in loss of
sexual motivation in nonhuman mammals of both sexes
- Drugs that counter the effects of androgens (a class of hormones responsible for a number
of male characteristics and functions) is a more attractive alternative
- Drugs that block the production of the androgen testosterone (the major sex hormone in
males), have been 80% to 100% effective in eliminating deviant sexual behavior such as
exhibitionism and pedophelia, along with sexual fantasies and urges
- Anticipation of sex can increase the testosterone level
- Some species, females only have sex during estrus
- Estrus: a period when the female is ovulating, sex hormone levels are high, and the
animal is said to be in heat
- Human females and females of some other primate species engage in sex throughout the
reproductive cycle
- Estrogen: a class of hormones responsible for a number of female characteristics and
functions
- In women who had their ovaries removed, testosterone treatment increased sexual
arousal, sexual fantasies, and intercourse frequency, but estrogen treatment did not
- Brain Structures and Neurotransmitters
- Motivation researchers began to shift their focus from drive as a tissue need to drive as a
condition in particular parts of the brain
- Sexual activity involves a network of brain structures, reaction to a variety of stimuli,
activation of several physiological system, postural and movement responses, a reward
experience, etc.
- Don’t understand how sexual network operates as a whole
- Medial Preoptic Area (MPOA): of the hypothalamus is one of the more significant brain
structures involved in male and female sexual behavior
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- Stimulation of MPOA increases copulation in rats of both sexes and appears to be more
responsible for performance than for sexual motivation
- Sexually Dimorphic Nucleus (SDN): located in the MPOA; 5x larger in male rats than in
females; a male’s level of sexual activity is related to the size of the SDN
- Ventromedial Hypothalamus is active in females during copulation, and its destruction
reduces the female’s responsiveness to a male’s advances
- Medial Amygdala also contributes to sexual behavior in rats of both sexes and the
amygdala is involved in sexual behavior, aggression, and emotions
- Odors, Pheromones, and Sexual Attraction
- The Nose as a Sex Organ
- Each human gives off a distinctive, genetically determined odor
- Women prefer the odor of dominant men, but only during the fertile phase of
their menstrual cycle
- Major Histocompatibility Complex (MHC): a group of genes that contributes to
the functioning of the immune system
- Example: women reported more sexual satisfaction and fewer outside
sex partners when their romantic partners were dissimilar in MHC
- Example: couples similar in MHC tend to be less fertile and have more
spontaneous abortions
- Example: MHC-based mate choices help avoid genetic inbreeding and
increase disease resistance
- Pheromones: airborne chemicals released by an animal that have physiological
or behavioral effects on other animals of the same species
- Humans can distinguish a trillion odors
- Humans have between 500 and 750 odor receptor genes
- Vomeronasal Organ (VNO): a cluster of receptors also located in the nasal
cavity where most pheromones are detected
- The Biological Determination of Sex
- Sex: the term for the biological characteristics that divide humans and other animals into the
categories of male and female
- Gender: the behavioral characteristics associated with being male or female
- Gender Role: the set of behaviors society considers appropriate for people of a given biological
sex
- Gender Identity: the person’s subjective feeling of being male or female
- Chromosomes and Hormones
- Egg will always have an X chromosome but sperm can have an X or Y chromosome
- Male ejaculates into the vagina and the sperm use their flagella-like tail to swim through
the uterus and up the fallopian tubes
- Once one sperm enters the egg, the egg becomes impenetrable (only one sperm is
allowed to fertilize the egg)
- XX = female and XY = male
- Gonads: testes and ovaries; the primary reproductive organs
- Female
- Ovaries: where the ova (eggs) develop
- Mullerian Ducts: develop into the uterus, the fallopian tubes, and the inner
vagina
- The undifferentiated external genitals become the clitoris, the outer segment of
the vagina, and the labia
- Male
- Testes: the organs that will produce sperm
- Mullerian Inhibiting Hormone: defeminizes the fetus by causing Mullerian ducts
to degenerate
- Wolffian Ducts: develop into the seminal vesicles, which store semen, and the
was deferens, which carry semen from the testes to the penis
- Dihydrotestosterone: a derivative of testosterone that masculinizes the external
genitals
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