Unit 3: Biological Basis of Behavior

Neurons

• Nerve cells that handle information processing.
  
  

Firing Neuron

• Communication is electrochemical.
  
  

• Neurotransmitters trigger an electric impulse in the nerve cell.
  
  

• The electric charge (action potential) is generated by the movement of charged ions through the axon's semipermeable membrane.
  
  

Resting Potential

• Neuron is not firing, at rest.
  
  

• Inside: Negatively charged.
  
  

• Outside: Positively charged.
  
  

• Channels for ions are closed.
  
  

• Charge: -70 mV.
  
  

Action Potential

• Chemical signals from neighboring neurons reach threshold → neuron fires.
  
  

• First node of Ranvier opens, allowing positive ions in → changes the charge.
  
  

• Depolarizes section of axon → opens next section's gates.
  
  

• Continues down axon → reaches terminal → neurotransmitters released into synapse.
  
  

• After impulse: Refractory period → sodium/potassium pump resets ions.
  
  

How Neurons Communicate

• Synapse: Junction between axon terminal & neighboring neuron's dendrites.
  
  

• Synaptic cleft: The gap.
  
  

• Neurotransmitters cross the gap, binding like keys in locks.
  
  

• Message becomes electrical impulse in next neuron.
  
  

• Neurotransmitters are reabsorbed (reuptake).
  
  

How Neurotransmitters Influence Us

Effects of Drugs

• Mimic neurotransmitters.
  
  

• Inhibitory (antagonists): Stop pain.
  
  

• Excitatory (agonists): Excite activity.
  
  

• More on this in consciousness chapter.
  
  

The Nervous System

Nerves

• Bundles of axons connect CNS to muscles, organs, glands.
  
  

Types of Neurons

• Afferent (Sensory): Carry impulses to CNS.
  
  

• Interneuron: Connect neurons.
  
  

• Efferent (Motor): Carry impulses from CNS to muscles/glands.
  
  

Peripheral Nervous System (PNS)

• Somatic NS: Voluntary control of skeletal muscles.
  
  

• Autonomic NS: Controls glands & internal organs (can be overridden).
  
  

Autonomic NS Breakdown

• Sympathetic NS: Arousal; fight-or-flight response.
  
  

Spinal Cord and Reflexes

• Carries messages between brain & PNS.
  
  

• Sensory info to brain, motor info from brain.
  
  

• Reflex: Simple, automatic response to stimulus.
  
  

Brain and Neural Networks

• Brain = CPU: takes info, interprets, sends orders.
  
  

• Neural Networks: Interconnected neurons; learning strengthens or inhibits connections.
  
  

Endocrine System

• Glands release hormones into bloodstream.
  
  

• Slower than nervous system.
  
  

• Hormones: Chemical messengers from glands affecting other tissues.
  
  

Module 11: Studying the Brain

• Observing disease/injury.
  
  

• Manipulating brain: electric, chemical, magnetic stimulation.
  
  

• EEG: Records electrical activity.
  
  

• Neuroimaging.
  
  

Neuroimaging Techniques

• CT Scan: Uses radiation, shows structure not function.
  
  

• MRI: Magnetic fields, detailed soft tissue image.
  
  

• fMRI: Shows blood flow & activity in addition to structure.
  
  

• PET: Radioactive glucose shows areas of high activity.
  
  

Older Brain Structures

• Brain Stem: Autonomic survival functions.
  
  

• Thalamus: Relay system; senses → processing areas.
  
  

• Reticular Formation: Arousal.
  
  

• Medulla: Controls heart & breathing.
  
  

• Cerebellum: “Little brain”; sensory info, voluntary movement, balance.
  
  

The Limbic System

• Emotional center: fear, aggression, hunger, sex drive.
  
  

Key Structures:

• Hypothalamus: Hunger, thirst, temperature; controls pituitary; reward.
  
  

  • Food & sex, food & sex, that's the hypothalamus
    
    

• Amygdala: Aggression & fear.
  
  

  • AHHHmygdala
    
    

• Hippocampus: Memory.
  
  

Structure of the Cortex

• Web of neurons covering cerebrum.
  
  

• 20-23 million nerves, 2 hemispheres, 4 lobes.
  
  

• Supported by Glial Cells:
  
  

  • Guide connections.
    
    

  • Provide nutrients/myelin.
    
    

  • Help transmit info.
    
    

  • Clean ions/neurotransmitters.
    
    

Functions of the Cortex

• Motor Cortex: Voluntary movements.
  
  

• Somatosensory Cortex: Touch & movement sensations.
  
  

• Visual Cortex: Occipital lobe; visual info.
  
  

• Auditory Cortex: Temporal lobe; auditory info.
  
  

Association Areas

• Higher functions: thinking, learning, memory, speaking.
  
  

• Found in all 4 lobes.
  
  

  • Frontal Lobe: Judgment & reasoning.
    
    

  • Phineas Gage
    
    

Language Areas

• Broca’s Area: Frontal lobe (left hemisphere); controls speech muscles.
  
  

• Wernicke’s Area: Left temporal lobe; language comprehension.
  
  

Aphasia

• Language impairment.
  
  

  • Broca: Speaking.
    
    

  • Wernicke: Understanding.
    
    

Plasticity

• Brain’s ability to change, especially in childhood.
  
  

• Can reorganize or build new pathways.
  
  

• Some functions cannot be rewired.
  
  

• Neurogenesis: Production of new neurons.
  
  

• Diminishes with age.
  
  

Our Divided Brain

Splitting the Brain

• Corpus Callosum: Connects hemispheres.
  
  

• Severed in epilepsy treatment.
  
  

• Few cognitive changes, some visual effects.
  
  

• Rare side effect: Alien Hand Syndrome.
  
  

Hemispheric Functions

• Left Hemisphere:
  
  

  • Right side control.
    
    

  • Speaking, reading, writing.
    
    

  • Math, analytical thinking.
    
    

• Right Hemisphere:
  
  

  • Left side control.
    
    

  • Perception, music, spatial reasoning.
    
    

  • Figurative thinking, emotions, shapes.
    
    

Handedness

• 90% right-handed.
  
  

• Right-handers: Language in left hemisphere.
  
  

• Left-handers: 3/10 use right or both hemispheres.
  
  

• Left-handedness linked to reading disabilities, allergies, migraines.
  
  

• More common in musicians, mathematicians, artists.
  
  

Behavior Genetics

• Study of heredity & genetics' influence on behavior.
  
  

Genes: Our Codes for Life

• Chromosomes: DNA strands with genes.
  
  

  • 46 chromosomes (23 pairs).
    
    

• DNA: Genetic info.
  
  

• Genes: Units of heredity, code for protein.
  
  

• Genome: Complete set of instructions for an organism.
  
  

Twin Studies

• Compare identical & fraternal twins.
  
  

• Measure genetic influence = heritability.
  
  

Minnesota Twin Studies (T.J. Bouchard, 1979)

• Twins raised apart = as similar as those together.
  
  

• Differences = environment.
  
  

Findings:

• Intelligence: .70
  
  

• Substance abuse: .78
  
  

• Traditionalism: .53
  
  

• Other traits: .43 - .55
  
  

Adoption Studies

• Personality: Closer to genetic than adoptive parents.
  
  

• Siblings raised together: Personality differences.
  
  

• Environment affects attitudes/values more than personality.
  
  

Temperament Studies

• Stable over time.
  
  

• Heritable element shown in twin studies.
  
  

Molecular Genetics

• Study of gene structure/function.
  
  

• Identify genes for traits/diseases.
  
  

• Ethical concerns: screening, engineering.
  
  

• Potential for new treatments.
  
  

Heritability

• Extent variation in individuals is due to genes.
  
  

• High heritability ≠ group differences.
  
  

• Gene expression changes in different environments.
  
  

Gene-Environment Interaction

• Genes turn on/off in response to environment.
  
  

• Epigenetics: Environmental influence on genes without DNA change.
  
  

  • Example: Radiation.
    
    

Natural Selection

• Adaptive traits passed on → survival/reproduction.
  
  

• Mutation: Random gene error → can help adaptation → passed on.
  
  

Evolutionary Psychology

• Study of evolution of behavior and mental processes.
  
  

• Behavior shaped by adaptive traits from ancestors.
  
  

• Selfish Gene Theory – Richard Dawkins.
  
  

Evolutionary Perspective: Sexuality

Male:

• Stronger sex drive.
  
  

• Okay with casual sex.
  
  

• Think about sex more.
  
  

• More visual.
  
  

• Misinterpret friendliness as flirtation.
  
  

• Prefer youthful, fertile women.
  
  

Female:

• Value affection in relationships.
  
  

• Less casual sex.
  
  

• Think about sex less.
  
  

• Attracted to strong, healthy, affluent men.