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Chapter 3B: Biology and Behavior

Peripheral Nervous System (PNS)

  • The PNS has two primary components:
    • Somatic nervous system (SNS): transmits sensory signals and motor signals between the central nervous system and the skin, muscles, and joints.
    • Autonomic nervous system (ANS): transmits sensory signals and motor signals between the central nervous system and the body’s glands and internal organs.
  • The PNS connects the CNS to the rest of the body and coordinates voluntary and involuntary functions.

Subdivisions and Roles of the PNS

  • Central nervous system (CNS) comprises the brain and spinal cord.
  • Peripheral nervous system (PNS) comprises nerves outside the CNS.
  • PNS transmits signals to and from the CNS:
    • Skin, muscles, and joints send signals to the spinal cord and brain.
    • Brain and spinal cord send signals to the muscles, joints, and skin.
    • Glands and internal organs send signals to the spinal cord and brain.
  • Autonomic nervous system (ANS) subdivisions:
    • Sympathetic nervous system
    • Parasympathetic nervous system
  • Diagrammatic relationships (conceptual): CNS

Autonomic Nervous System: Sympathetic vs. Parasympathetic

  • The ANS maintains homeostasis and regulates essential body functions (temperature, thirst) and the fight-or-flight response.
  • The sympathetic division:
    • Prepares the body for situations requiring energy expenditure (fight-or-flight).
  • The parasympathetic division:
    • Directs the storage of energy and promotes rest-and-digest functions.

Autonomic Effects on Organs (Sympathetic vs. Parasympathetic)

  • Eyes:
    • Sympathetic: dilates pupils
    • Parasympathetic: constricts pupils
  • Lungs:
    • Sympathetic: relaxes bronchi
    • Parasympathetic: constricts bronchi
  • Heart:
    • Sympathetic: accelerates and strengthens heartbeat
    • Parasympathetic: slows heartbeat
  • Stomach and intestines:
    • Sympathetic: inhibits activity
    • Parasympathetic: stimulates activity
  • Blood vessels of internal organs:
    • Sympathetic: constricts vessels
    • Parasympathetic: dilates vessels

The Endocrine System

  • The endocrine system comprises glands that release chemical messengers (hormones) into the bloodstream to communicate with other body parts.
  • Hormone signaling is slower but longer-lasting than neural signaling.
  • The endocrine system responds to input from the nervous system, especially the hypothalamus.
  • Roles: arousal, metabolism, growth, and sex.

The Pituitary Gland – the ‘master gland’

  • The pituitary releases many hormones that activate other glands in the body.
  • It is regulated by the hypothalamus, which lies directly above it.

Endocrine Glands and Their Roles

  • Pineal gland: helps regulate body rhythms and sleep cycles.
  • Pituitary gland: influences growth and lactation; also regulates the activity of other glands.
  • Thyroid gland: regulates the rate of metabolism in the body.
  • Adrenal glands: secrete hormones that arouse the body, help with adjustment to stress, regulate salt balance, and affect sexual functioning.
  • Pancreas: releases insulin to regulate blood sugar and hunger.

Male-Female Endocrine Differences

  • Males: testes are major reproductive glands; secrete testosterone, influencing sexual function and playing a critical role in puberty.
  • Females: ovaries are major reproductive glands; secrete estrogen, influencing sexual function, puberty, and menstruation.

Chapter 3: Nature vs. Nurture

  • This chapter covers:
    • Nature vs. Nurture
    • Genetic basis of psychological science

Nature and Nurture: Core Concepts

  • Nature: contributions of genetic inheritance.
  • Nurture: contributions of learning and environment.
  • The quote (conceptual): Nature provides the genetic options; environment determines which option is taken.
  • Foundational idea: genetics shapes potential; environment shapes expression.

Genetics: Key Concepts

  • Genetics describes how characteristics are passed to offspring and how genes can be turned on or off.
  • Genes: units of heredity that help determine organism characteristics.
  • Gene expression: whether a gene is turned on or off and where in the body it is active.
  • The genome: the master blueprint for making an entire organism; environment can determine which genetic options are taken.
  • Chromosomes: cellular structures made of DNA; segments of chromosomes are genes.
  • Human development is rooted in genetics.

The Genome and DNA

  • The genome provides the option, and the environment determines which option is taken.
  • DNA is a double-stranded helix made of four nucleotide bases: A, T, G, C.
  • DNA structure and the role of sequence determine genetic information.
  • DNA was discovered by Crick and Watson in 1953.
  • All cells carry the full set of DNA needed to provide the blueprint for a person.

Genes, Genotype, and Phenotype

  • Genotype: the entire genetic makeup of an organism.
  • Phenotype: outward expression of genes.
  • Gene expression: whether a gene is on or off, and where in the body it is active.

Sex Chromosomes and Offspring Sex

  • Chromosome 23 determines offspring sex in humans.
  • Mother contributes an X chromosome (XX).
  • Father contributes either X or Y (XX or XY).
  • Offspring:
    • XX → Girl
    • XY → Boy

Allele Variation and Genetic Drift

  • Alleles are alternate forms of a gene that can lead to individual differences.
  • Example: a hemoglobin allele variation can cause sickle-cell shape in red blood cells.
  • Allele: alternative form of the same gene for a trait.
  • Dominant gene: expressed in offspring whenever present.
  • Recessive gene: expressed only when paired with a similar gene from the other parent.

Gene Pairs: Homozygous vs. Heterozygous

  • Homozygous: both alleles are the same (e.g., CC or cc).
  • Heterozygous: two different alleles (e.g., Cc).
  • Illustrative example with curliness vs straight hair: CC (homozygous curly), Cc (heterozygous curly), cc (homozygous straight).

Patterns of Inheritance for Eye Color (Illustrative Examples)

  • Example (a): Parents with brown and blue eyes; genotypes BB x bb produce Brown offspring (Bb).
  • Example (b): Brown eye parent (Bb) x blue-eyed parent (bb) yields Brown and Blue offspring in heterozygous/homozygous combinations.
  • Example (c): Crosses can produce homozygous brown (BB) or homozygous blue (bb) or heterozygous (Bb) offspring depending on parental alleles.
  • Note: These diagrams illustrate Mendelian inference with genotypes BB, Bb, and bb corresponding to brown and blue phenotypes in different combinations.

Allele Frequencies (Illustrative data)

  • Allele frequencies in a population example: 53.7\%, 32.8\%, 32.1\%, 55.1\%, 23\%, 12.2\%.
  • These values illustrate how different alleles can be present at different frequencies in populations.
  • Observational note: higher frequency of particular alleles can influence trait prevalence.

Genetic Drift

  • Genetic drift: any change in allele frequencies in a population due to chance.
  • Example (beetles): in a small sample, random events (e.g., stepping on individuals) can change allele frequencies purely by chance.

Founder Effect (Extreme Genetic Drift)

  • Founder effect occurs when a small subset of a population becomes isolated and interbreeds.
  • This can cause rare alleles to become common in the isolated group, reshaping phenotypes.
  • Classic examples discussed: the Amish (increased frequency of certain mutations like six-fingered condition) and another famous group in Kentucky.

Consequences of Limited Genetic Variation

  • Inbreeding in small populations can lead to genetic errors and inherited disorders.
  • Example: Blue People of Troublesome Creek (the Blue Fugates of Kentucky).

Sexual Reproduction and Genetic Variation

  • Sexual reproduction creates genetic variation similar to a lottery-like process for each child’s genotype.
  • Importance:
    • Increases genetic diversity, aiding survival in changing environments.
    • Provides variability essential for evolution.
    • Founder effect can reduce variation, increasing drift risk.

Genes and Behavior: Behavioral Genetics

  • Genes influence behavior through interactions with the environment.
  • Behavioral genetics studies how genes and environment interact to shape psychological traits and activities.

Behavioral Genetics Methods

  • Twin studies:
    • Monozygotic (MZ, identical) twins share the same genes.
    • Dizygotic (DZ, fraternal) twins share ~50% of their segregating genes, like non-twin siblings.
    • Greater similarity in MZ twins (raised together or apart) suggests a genetic influence.
  • Adoption studies (e.g., the Minnesota Twin Project):
    • Compare biological relatives with adoptive relatives.
    • Nonbiological adopted siblings share home environments but different genes; twins raised apart have the same DNA but different experiences.

Zygote Formation and Fertilization (Illustrative)

  • One sperm fertilizes one egg to form a zygote, which then divides.
  • Two sperm fertilize two eggs to form two zygotes (illustrative diagram).

Understanding Heritability

  • Heredity: transmission of characteristics from parents to offspring through genes.
  • Heritability: a statistical estimate of the extent to which variation in a trait within a population is due to genetics.
  • Important caveats:
    • Heritability refers to populations, not to individuals.
    • Estimates describe the extent that people differ genetically within the group being studied.