Reproductive Behavior and Sex Organs

Reproductive Behavior

• The Y chromosome contains the SRY gene (Sex-determining region)
• SRY encodes a protein responsible for testes formation via autosome gene activation
• SRY's primary function is initiating testes development
• Three general categories of sex organs exist: gonads, internal sex organs, and external genitalia

Gonads

• Testes or ovaries are the first to develop
• They perform dual functions by producing ova/sperm and secreting hormones
• Male and female fetuses are identical through the sixth week (4-7 week frame) of prenatal development
• Both sexes have identical undifferentiated gonads with the potential to develop into either testes or ovaries
• The SRY gene on the Y chromosome controls gonadal development
• Hormones determine secondary sex characteristics
• Gonad development sets off a series of events determining an individual's gender
• Organizational effects occur during prenatal development and are permanent
• Activation effects occur later in life, activating sperm production, erection, ejaculation, and ovulation

Internal Sex Organs

• Early in embryonic development, internal sex organs are bisexual, containing precursors for both sexes
• During the third month of gestation, one precursor develops while the other withers away
• The Mullerian system is the precursor for internal female sex organs
• The Wolffian system is the precursor for internal male sex organs
• The presence or absence of hormones secreted by the testes determines the gender of internal sex organs in a fetus
• Testes secrete anti-Mullerian hormone (defeminizing effect) and androgens (masculinization effect) like testosterone and dihydrotestosterone

External Genitalia

• External genitalia include visible sex organs
• In males, this includes the penis and scrotum
• In females, this includes the labia, clitoris, and outer vagina
• Female external genitalia develop naturally without the need for stimulation by female sex hormones
• Masculine development requires the presence of androgens

Hormonal and Neural Control of Sexual Behavior

• Sexual maturation is regulated by hormones and neural activity
• Organizational effects occur before puberty, while activational effects occur during puberty
• Primary sex characteristics like gonads, internal sex organs, and external genitalia are present at birth
• Secondary sex characteristics, such as enlarged breasts or a beard, appear during puberty
• At puberty, the gonads produce hormones leading to sexual maturation
• The hypothalamus secretes gonadotropin-releasing hormones (GnRH)
• GnRH stimulates the production and release of follicle-stimulating hormone (FSH) and luteinizing hormone (LH)
• FSH and LH are produced in both males and females but have different effects
• Gonads secrete steroid sex hormones in response to gonadotropic hormones
• Testes produce sperm and secrete testosterone
• Ovaries produce estradiol, an estrogen
• Both types of glands produce small amounts of the other sex's hormones
• Estradiol and testosterone initiate closure of growing bone portions, halting skeletal growth
• Estradiol leads to breast development, uterine lining growth, changes in body fat deposition, and female genitalia maturation
• Testosterone stimulates growth of facial, auxiliary, and pubic hair, lowers the voice, stimulates muscular development, and causes genital growth

Developmental Abnormalities

• Males (XY) may experience Androgen Insensitivity Disorder
• Androgen Insensitivity Disorder prevents shutting down the Mullerian system and developing the Wolffian system
• Males may experience Persistent Mullerian Duct Syndrome
• Failure of the anti-Mullerian system results in the development of both sex characteristics (less than 200 cases in known history)
• Turner's Syndrome affects females (XX)
• Females with Turner's Syndrome do not develop ovaries
• Congenital Adrenal Hyperplasia affects both males and females
• Congenital Adrenal Hyperplasia is only detrimental to females
• Adrenal glands secrete excessive amounts of androgens
• Girls born with Congenital Adrenal Hyperplasia develop an enlarged clitoris and partially fused labia

Female Reproductive Cycles and Androgens

• The pituitary gland produces growth hormones
• Female reproductive cycles are controlled by pituitary and ovary secretions
• The follicular phase lasts 14 days
• The luteal phase lasts 14 days
• Ovulation occurs between the follicular and luteal phases
• Androgens cause masculinization and defeminization

Neural Control of Sexual Behavior

• Spinal mechanisms cause stimulation, erection, and ejaculation
• Brain mechanisms are responsible for pleasurable sensations, tactile/visual/cognitive arousal, and pair bonding (vasopressin and Oxytocin)
• Parental behaviors are not activated by hormones, but are facilitated by them
• Nesting and nursing facilitate hormones returning to pre-conception levels
• Nursing reduces risk of post-partum depression
• Dads who spend more time nurturing encourage the release of hormones that encourage them to nurture

Neural Control of Emotional Responses

• Neurons in various amygdala nuclei become active when emotionally relevant stimuli are presented
• The amygdala is located within the temporal lobes
• The amygdala includes the medial nucleus, lateral/basolateral nucleus, central nucleus, and basal nucleus
• Nuclei affect brain regions that control behavioral/physiological responses

Feelings of Emotions - James-Lange Theory

• Emotion-producing situations elicit physiological responses like trembling/sweating/increased heart rate
• Behaviors, such as clenching fists or fighting, are also elicited
• Subjective experiences are our feelings in response to our brain receiving feedback from these physiological processes

Role of the Orbitofrontal Cortex

• Perceiving social situations is more complex than perceiving individual stimuli
• Analysis of social situations involves experiences, memories, inferences, and judgments
• The orbitofrontal cortex plays a role in this
• Translates judgments into appropriate feelings and behaviors
• Damage reduces people's inhibitions and self-concern, making them indifferent to the consequences of their actions
• The cingulate gyrus serves as an interface between frontal cortex decision-making, amygdala's emotional functions, and brain mechanisms controlling movement

Thirst

• The body is mostly water
• Physiological regulatory systems maintain homeostasis
• Negative feedback loops keep things in homeostasis, much like a thermostat
• System variables include body temperature, fluid levels, and energy metabolism
• Set point: optimal value
• Detector: monitors the value of the system
• Correctional mechanism: restores the variable to the set point
• Satiety mechanism: monitors correctional mechanism activity and results in the cessation of hunger/thirst through adequate supplies

Fluid Compartments

• Intracellular fluid: 2/3 of body fluid; within cells
• Intravascular fluid: blood plasma
• Cerebrospinal fluid: protects and nourishes the brain
• Interstitial fluid: bathes the cells and is located between cells
• Compartments are separated by semi-permeable membranes
• Solute concentration is balanced (isotonic)
• Hypertonic: draws water out of a cell through osmosis
• Hypovolemia: reduction in intravascular fluid volume
• Balance is critical in blood plasma
• Too little fluid: water diffuses out of cells
• Too much fluid: can cause rupture (cells explode)
• Blood pressure is closely regulated and can cause blood vessels to rupture and lead to stroke
• Minimal correction is possible through blood vessel constriction

Kidney Function and Types of Thirst

• The kidneys get rid of excess water and salt
• Nephrons are functional units in the kidney that pulls water and sodium from the bloodstream
• The amount of water and sodium secreted by the kidneys is controlled by aldosterone and vasopressin
• There are two types of thirst: osmotic and volumetric
• Aldosterone is released by the adrenal gland and leads to sodium retention
• Vasopressin is released by the posterior pituitary gland and leads to water retention
• Osmotic thirst is controlled by osmoreceptors
• Osmotic thirst is produced by an increase in osmotic pressure of interstitial fluid relative to intracellular fluid and by dehydration
• Osmoreceptors detect solute concentration changes in interstitial fluid
• OVLT (organum vasculosum of the lamina terminalis) is a circumventricular organ located anterior to the anteroventral portion of the third ventricle, and lacks a blood-brain barrier

Volumetric Thirst and Problem of Caffeine

• Volumetric thirst is produced by hypovolemia, or not enough liquid in the bloodstream
• Renin, secreted by the kidneys, causes conversion of angiotensinogen in the blood into angiotensin
• Angiotensinogen, a protein, can be converted into angiotensin by renin
• Angiotensin causes water/sodium retention, constriction of capillaries, salt appetite, and drinking
• Caffeine blocks adenosine receptors
• Adenosine is part of ATP, used as energy
• Caffeine increases renin activity, which elevates blood pressure, and enhances expression of angiotensin II, which also elevates blood pressure
• Caffeine irritates the bladder, increases urination, and is a diuretic

Eating

• Short-term food reservoir is with glycogen and glucose
• Liver and muscle cells convert glucose (soluble) to glycogen (insoluble), stimulated by insulin
• A fall in glucose levels in the blood stream is detected in the brain
• The sympathetic system initiates activity, enervates the pancreas, inhibits insulin secretion, and begins glucagon secretion
• Glucagon stimulates the liver to convert glycogen to glucose
• This short-term reservoir is for the central nervous system
• Long-term food reservoir involves adipose tissue (triglycerides) and consists of adipose tissue (fat)
• Triglycerides contain glycerol and three fatty acids (steric, oleic, palmitic)
• Glycerol comes from breakdown of triglycerides
• These cells can expand
• The sympathetic nervous system participates in the breakdown and utilization of stored nutrients

What Starts and Stops a Meal?

• Signals from the environment incite meal
• Signals from the stomach include the peptide hormone Ghrelin in the intestines
• Metabolic signals include detectors sensitive to glucose and triglycerides
• Head factors, appearance, odor, taste, texture, and temperature stop meals
• Gastric and intestinal factors, receptors detect presence of nutrients
• Liver factors register food and its presence in the intestines
• Insulin's presence facilitates glucose and the brain's insulin receptor

The Nature of Learning

• Learning takes four forms: perceptual, stimulus-response, motor & relational
• Perceptual learning: ability to recognize previously perceived stimuli
• This is a function that identifies stimuli and categorizes objects and situations
• The sensory association cortex accomplishes perceptual learning
• Learning to recognize complex visual stimuli involves changes in the visual association cortex
• Stimulus-response learning: ability to perform a behavior when a stimulus is present
• Connection between circuits that perceive movements
• Two categories: classical and instrumental conditioning
• The Hebb rule states that if a synapse becomes active and when a neuron fires it strengthens its function
• Motor learning: mostly novel circuits of the brain's motor systems need to be modified for the most novel behaviors
• Affects brain systems
• Relational learning: learns relation between individual stimulus
• Spatial learning involves relations between objects
• Episodic learning involves the order of events
• Synaptic plasticity: evidence learning causes changes and functions in structure
• Includes a thicker cortex and a better blood supply
• Long-term pontentiation involves synaptic strengthening during synapses and after cell membrane is depolarized
• Includes more post-synaptic receptors, neurotransmitters, new buttons, and other various factors for synaptic strength

Anterograde Amnesia

• An inability to learn new information
• Perceptual learning, stimulus-response learning, and motor learning are intact
• The hippocampus is involved in relational learning
• The hippocampus is not involved in storig memories, is in involved in converting short term memories into long term memories