Development of Sexual Behavior and Correlated

Characteristics

Lecture 36

PS Timiras

Inheritance of X and Y chromosomes

NeuroendocrinologyNeuropsychoendocrinology

• CNS modulates endocrine functions and hormones modulate CNS functions– CNS modulates endocrine functions

• Hypothalamic hormones– ADH, Oxytocin

• Hypophysiotropic hormones– GHRH, PLRH, CRH, TRH, GnRH, and respective

inhibitors

• Steroid Hormones– Androgens, Estrogens, Glucocorticoids, Mineral

Corticoids

• Insulin, PTH, Calcitonin, Thyroid Hormones, IGF-1, IGF-2

Hormones Modulate CNS Functions

• Embryo– GH control of CNS growth centers (hypothalamus,

feedback)– IGF-2 ??– T3, T4 CNS development– Androgens differentiation of sex organs and related

CNS areas

• Childhood– GH, GHRH, IGF-1, T3, T4

• Puberty– Androgens, Estrogens, GH, IGF-1, T3, T4, PTH, Calcitonin,

Insulin

• Responses to Stress– CRH, ACTH, Adrenal Cortical hormones

Sexualized BehaviorsBiological Factors

Prenatal Sexualization

Genes

Gonads Brain

Hormones steroids

Testosterone (Male)No Testosterone (Female)

Reproductive Structures

(Internal and External)

Cerebral Cortex: cognitive skills (parenting; survival)Hypothalamus: cyclic (female) or acyclic (male) reproductive

Cycles, mating, gender identity, sexual orientationSpinal cord

Environmental Factors

that cause biological responsesstressdrugspesticides(endocrine disrupters)

Sexualized Behaviors

Childhood

preparation for adulthood

Gonads Brain

Quiescent until pubertyExcept for transient surge of testosterone in male in 1st 3 months.

GenitalsInternal and external genitalsAre infantile

Practices parenting andSurvival skills. AcknowledgesGender identity and sexual Orientation

Interest in genitals and Reproductive behavior

The actions of hormones can be categorized into:

Examples:-thyroid hormones T3 on growth and maturation on neural cells

-masculinizing actions of androgens on CNS structures

(e.g. hypothalamus sexually dimorphic nucleus of preoptic area SDN-POA)

Organizational Regulatory

Masculinization of Some CNS Structures

1. Depends on presence of androgens

at “critical” time

The “window” of androgens’ organizing actions is:

First 4 postnatal days in rats

Probably 3rd trimester of gestation in humans

Actions of Neonatal Androgens

Males:• Larger (than in females) sexually

dimorphic nucleus of the preoptic area (SDN-POA) in hypothalamus

• Larger spinal nucleus of the bulbocavernosus (SNB) muscle

• Development of male sexual behavior

Actions of Neonatal Androgens

Females

• Smaller SDN-POA and SNB enlarge

• Female sexual behavior is suppressed

(e.g. absence of lordosis)

Sexualized BehaviorsPuberty

Doorway to adulthood

Brain turns on adult cycles of gonadal function.Gonads begin production of adult levels of sex

hormones.Sex hormones stimulate adult male or female body

types.Sex hormones stimulate reproductive behaviorStatus becomes a primary goal especially among boysDesire for independencePractice skills for attracting sexual partnersPeer Pressure

Sexualized BehaviorsSocial expectationsBased on external genitals

Gender ConformityBehavior is reinforced or

Rejected by family or society

Gender ExpectationsAre reinforced and social

responses escalate

Sexual AttractionIn humans, ever vigilent brain circuits survey the environment for

prospective mates with biological and psychological traits that signify fertility and evidence of good parenting skills.

Males and females evaluate each other by chemical attractants and by evidence of an anatomical, physiological and behavioral fitness Females are attracted to:

Small ButtocksNarrow PelvisWell developed musclesTaller than she isUnblemished skin, white teethSymmetrical featuresGood postureSigns of dominance when competing with other menTreating her with affection and sensitivitySigns of parenting skillsSigns of potential economic successNot necessarily interested in his formal sexual experiencesAge is not an issue

Sexual AttractionMen are Attracted to:Large BreastsNarrow WaistBroad PelvisFat deposition that rounds the shoulders and

buttocksShorter stature than hisFemale voiceGood posture and Graceful GaitFull Lips and White TeethVery interested in her fertility, prior sexual activityHer age

For both sexes the most valued characteristics:Kindness and understandingIntelligenceTendency for co-operation and teamwork

The Ultimate Goal is to Reproduce and Be A Good Parent

Right Hemisphere:Controls the leftside of the body

Left Hemisphere:Controls the rightside of the body

Gender Related Anatomical and Behavioral Characteristics

• Differences in Digit Length– 2D =4D in females– 2D < 4D in Males

• Cognitive Function– Conscious process of knowing

of events (objects in the environment)

– Using that knowledge for understanding and problem solving

Depend on PrenatalConcentrations of Testosterone

Cognitive Function

• Female Generally More Skilled in:– Caring for the Children– Foraging Close to Home– Managing Home Area– Better in

• Verbal Fluency• Verbal Recall• Understanding Facial Expression• Memory of Object Location• Fine Motor Skills

Gender Related Differences in Cognitive Function

• Males Are Better Equipped:– to Protect Territory– Go long distances to hunt for food– Better in visual and spatial tasks

• Inferior portion of parietal lobe

– Mathematical thinking– Navigating and Targeting