Biology and Behavior Lecture Notes

Influences on Behavior

Key Influences on Human Behavior

• Chemical controls (neurotransmitters)
• Hereditary factors
• Environmental factors

Chemical Controls (Neurotransmitters)

• Acetylcholine
  • Found in central and peripheral nervous systems
  • Peripheral: Transmits nerve impulses to muscles
  • Central: Linked to attention and arousal
• Epinephrine and Norepinephrine
  • Catecholamines (monoamines/biogenic amines)
  • Control alertness and wakefulness
  • Primary neurotransmitters of sympathetic nervous system (fight-or-flight response)
  • Epinephrine (adrenaline): Acts as a hormone
  • Norepinephrine (noradrenaline): Acts at local level
  • Low norepinephrine: Linked to depression
  • High norepinephrine: Linked to anxiety and mania
• Dopamine
  • Catecholamine
  • Role in movement and posture
  • High concentrations in basal ganglia
  • Imbalances linked to schizophrenia (Dopamine Hypothesis of Schizophrenia)
• Serotonin
  • Monoamine/biogenic amine
  • Regulates mood, eating, sleeping, dreaming
  • Imbalances: Oversupply linked to mania; Undersupply linked to depression
• GABA (Gamma-Aminobutyric Acid)
  • Produces inhibitory postsynaptic potentials
  • Stabilizes neural activity by causing hyperpolarization of the postsynaptic membrane
• Glycine
  • Inhibitory neurotransmitter in CNS
  • Increases chloride influx into neurons, hyperpolarizing the postsynaptic membrane
• Glutamate
  • Excitatory neurotransmitter in CNS

Peptide Neurotransmitters

• Endorphins
  • Natural painkillers with effects similar to opioids
  • Act relatively slowly with longer-lasting effects

Endocrine System

• Hypothalamus
  • Links endocrine and nervous systems
  • Regulates hormonal function of pituitary gland via hypophyseal portal system
• Pituitary Gland
  • Referred to as "master gland"
  • Divided into anterior and posterior sections
  • Anterior pituitary: Releases hormones regulating other endocrine glands (controlled by hypothalamus)
• Adrenal Glands
  • Located on top of kidneys; divided into adrenal medulla and adrenal cortex
  • Adrenal medulla: Releases epinephrine and norepinephrine
  • Adrenal cortex: Produces corticosteroids (e.g., cortisol) and sex hormones (testosterone, estrogen)
• Gonads (Sex Glands)
  • Ovaries in females, testes in males
  • Produce sex hormones (testosterone, estrogen)
  • Influence libido, mating behavior, and sexual function

Genetics and Behavior

• Physical traits and behavior can be inherited
• Innate Behavior: Genetically programmed, observed across species
• Learned Behavior: Developed through environmental interactions
• Adaptive Value
  • Contribution of behavior/trait to species' evolutionary fitness

Nature vs. Nurture

• Nature: Genetics influence behavior
• Nurture: Environment influences behavior
• Consensus: Behavior results from interplay of both genetic and environmental factors

Research Approaches

• Family Studies
  • Genetic relatedness influences similarity
  • Cannot clearly distinguish between genetic and environmental factors
• Twin Studies
  • Compare identical (monozygotic) and fraternal (dizygotic) twins
  • Insights into genetics vs. environment influences
  • Identical twins raised apart show more similarity than fraternal twins raised together
• Adoption Studies
  • Compare adopted children to biological and adoptive parents
  • Traits like IQ and criminal behavior show heritable trends

Conclusion

• Both genetics and environment shape behavior
• Relative contribution of each depends on the specific trait
• Next video will cover the final objective on development