AP Psychology

Biological Bases of Behavior | AP® Psychology

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AP® Psychology Students — Essential notes, facts, and formulas

🧠 AP Psychology Unit 1

Biological Bases of Behavior

📊 Exam Details

Class Periods

17-23

AP Exam Weight

15-25%

🧬 1.1 Interaction of Heredity and Environment

🎯 Learning Objectives

  • Explain how genetics and environment interact to influence behavior
  • Identify research methods used to study heredity vs environment
  • Analyze the concept of heritability and its limitations
  • Understand epigenetics and gene-environment interactions

🧬 Nature vs. Nurture

  • Nature: Genetic influences on behavior and traits
  • Nurture: Environmental influences on development
  • Interaction: Genes and environment work together
  • Example: Intelligence influenced by both genetics and education
  • Modern View: Not either/or, but how much of each

👥 Twin Studies

  • Identical Twins: 100% genetic similarity
  • Fraternal Twins: ~50% genetic similarity
  • Separated Twins: Same genes, different environments
  • Together Twins: Same genes, same environment
  • Findings: Many traits show both genetic and environmental influence

🏠 Adoption Studies

  • Purpose: Separate genetic from environmental influences
  • Method: Compare adopted children to biological vs adoptive parents
  • More like biological parents: Suggests genetic influence
  • More like adoptive parents: Suggests environmental influence
  • Limitation: Selective placement, prenatal environment

📊 Heritability

  • Definition: Proportion of trait variation due to genetic differences
  • Range: 0.0 (no genetic influence) to 1.0 (entirely genetic)
  • Population-specific: Applies to groups, not individuals
  • Environment-dependent: Changes with environmental variation
  • Example: IQ heritability ~0.5-0.8 in developed countries

🧬 Epigenetics

  • Definition: Environmental factors affecting gene expression
  • Mechanism: Chemical markers turn genes on/off
  • Transgenerational: Can be passed to offspring
  • Examples: Stress, nutrition, toxins affect gene expression
  • Implication: Environment can have lasting genetic effects

🔄 Gene-Environment Interaction

  • Concept: Genes influence how we respond to environment
  • Evocative: Our genes elicit environmental responses
  • Active: We seek environments matching our genetic tendencies
  • Passive: Parents provide both genes and environment
  • Example: Genetic predisposition to anxiety + stressful environment

🔑 Key Takeaways

  • Both genetics and environment contribute to virtually all human traits
  • Heritability estimates are population and environment-specific
  • Gene-environment interactions are complex and bidirectional
  • Epigenetics shows environment can affect gene expression across generations

🕸️ 1.2 Overview of the Nervous System

🎯 Learning Objectives

  • Identify the major divisions of the nervous system
  • Explain the functions of the central and peripheral nervous systems
  • Compare the sympathetic and parasympathetic nervous systems
  • Understand the role of the somatic nervous system

🗂️ Nervous System Organization

🧠 NERVOUS SYSTEM
├── Central Nervous System (CNS)
│ ├── Brain
│ └── Spinal Cord
│
└── Peripheral Nervous System (PNS)
    ├── Somatic Nervous System
    │ └── Voluntary muscle control
    │
    └── Autonomic Nervous System
        ├── Sympathetic (Fight or Flight)
        └── Parasympathetic (Rest and Digest)

🧠 Central Nervous System (CNS)

  • Components: Brain and spinal cord
  • Function: Processing center for all information
  • Brain: Control center for thoughts, emotions, behavior
  • Spinal Cord: Information highway between brain and body
  • Protection: Skull, vertebrae, cerebrospinal fluid

🕸️ Peripheral Nervous System (PNS)

  • Definition: All nerves outside brain and spinal cord
  • Function: Connects CNS to rest of body
  • Sensory nerves: Carry information TO the CNS
  • Motor nerves: Carry commands FROM the CNS
  • Divisions: Somatic and Autonomic systems

💪 Somatic Nervous System

  • Function: Controls voluntary muscle movements
  • Motor neurons: From CNS to skeletal muscles
  • Sensory neurons: From sense organs to CNS
  • Conscious control: Walking, talking, writing
  • Reflexes: Some automatic responses bypass brain

🤖 Autonomic Nervous System

  • Function: Controls involuntary bodily functions
  • Target organs: Heart, lungs, digestive system, glands
  • Automatic: Works without conscious thought
  • Dual control: Sympathetic and parasympathetic divisions
  • Balance: Two systems usually oppose each other

⚔️ Sympathetic vs Parasympathetic

🚨 Sympathetic (Fight or Flight)

  • Increases heart rate
  • Dilates pupils
  • Increases breathing rate
  • Decreases digestion
  • Releases stress hormones
  • Increases alertness
  • Activates during stress/danger

😴 Parasympathetic (Rest & Digest)

  • Decreases heart rate
  • Constricts pupils
  • Decreases breathing rate
  • Increases digestion
  • Promotes conservation
  • Increases relaxation
  • Activates during rest/recovery

🔑 Key Takeaways

  • CNS (brain + spinal cord) processes information; PNS connects CNS to body
  • Somatic system controls voluntary movement; Autonomic controls involuntary functions
  • Sympathetic system prepares body for action; Parasympathetic promotes rest
  • These systems work together to maintain homeostasis and respond to environment

⚡ 1.3 The Neuron and Neural Firing

🎯 Learning Objectives

  • Identify the parts of a neuron and their functions
  • Explain the process of neural transmission
  • Understand action potentials and resting potentials
  • Describe synaptic transmission and neurotransmitters

🔬 Neuron Structure

🌳 Dendrites

Branch-like extensions that receive signals from other neurons

🎯 Cell Body (Soma)

Contains nucleus and most organelles; integrates incoming signals

📡 Axon Hillock

Junction where action potential is initiated if threshold is reached

🔌 Axon

Long projection that carries electrical signals away from cell body

🧬 Myelin Sheath

Fatty covering that insulates axon and speeds up signal transmission

🎪 Terminal Buttons

End structures that release neurotransmitters into synapses

⚡ Action Potential

  • Definition: Electrical signal traveling down axon
  • All-or-Nothing: Either fires completely or not at all
  • Threshold: ~-55mV (millivolts) needed to trigger
  • Speed: 1-120 meters per second depending on myelination
  • Duration: About 1 millisecond

🔋 Resting Potential

  • Value: -70mV (inside negative relative to outside)
  • Maintained by: Sodium-potassium pump
  • Na⁺: Higher concentration outside cell
  • K⁺: Higher concentration inside cell
  • Ready state: Neuron prepared to fire

🌊 Phases of Action Potential

  • Depolarization: Na⁺ channels open, voltage rises to +30mV
  • Repolarization: K⁺ channels open, voltage drops
  • Hyperpolarization: Brief overshoot below resting potential
  • Refractory Period: Cannot fire again immediately
  • Return: Back to -70mV resting potential

🔗 Synaptic Transmission

  • Synapse: Gap between neurons (~20-40 nanometers)
  • Process: Chemical signal bridges the gap
  • Vesicles: Store neurotransmitters in terminal buttons
  • Release: Action potential triggers neurotransmitter release
  • Binding: Neurotransmitters bind to receptor sites

🧪 Major Neurotransmitters

💪 Acetylcholine (ACh)

Function: Muscle contraction, memory, learning
Location: Neuromuscular junctions, brain
Disorders: Alzheimer's disease

😊 Dopamine

Function: Reward, motivation, movement
Location: Basal ganglia, limbic system
Disorders: Parkinson's, schizophrenia

🧘 Serotonin

Function: Mood, sleep, appetite
Location: Brainstem, throughout brain
Disorders: Depression, anxiety

⚡ Norepinephrine

Function: Alertness, arousal, stress response
Location: Brainstem, sympathetic system
Disorders: Depression, ADHD

🧠 GABA

Function: Inhibitory, reduces neural activity
Location: Throughout brain
Disorders: Anxiety, epilepsy

⚡ Glutamate

Function: Excitatory, learning, memory
Location: Throughout brain
Disorders: Stroke, neurodegenerative diseases

🔑 Key Takeaways

  • Neurons communicate through electrical signals (action potentials) and chemical signals (neurotransmitters)
  • Action potentials are all-or-nothing events that travel down axons at high speed
  • Synaptic transmission converts electrical signals to chemical signals at synapses
  • Different neurotransmitters have specific functions and are associated with different behaviors and disorders

🧠 1.4 The Brain

🎭 Cerebral Cortex

  • Frontal Lobe: Executive functions, personality, motor control
  • Parietal Lobe: Sensory processing, spatial awareness
  • Temporal Lobe: Auditory processing, memory, language
  • Occipital Lobe: Visual processing

❤️ Limbic System

  • Hippocampus: Memory formation
  • Amygdala: Fear and emotion processing
  • Hypothalamus: Homeostasis, hormones
  • Thalamus: Sensory relay station

😴 1.5 Sleep

🌙 Sleep Stages

  • Stage 1: Light sleep, hypnagogic hallucinations
  • Stage 2: Sleep spindles, K-complexes
  • Stage 3: Deep sleep, delta waves
  • REM Sleep: Dreams, memory consolidation

👁️ 1.6 Sensation

🎯 Thresholds

  • Absolute Threshold: Minimum stimulus detected 50% of time
  • Difference Threshold: Just noticeable difference (JND)
  • Weber's Law: JND proportional to stimulus intensity
  • Signal Detection Theory: Response influenced by sensitivity and bias

📚 Study Tips for Unit 1

💡 Memory Techniques

  • Use mnemonics for brain parts and neurotransmitters
  • Draw and label neuron diagrams repeatedly
  • Create concept maps linking nervous system divisions
  • Practice with flashcards for vocabulary terms

🎯 AP Exam Focus

  • Know functions of major brain regions
  • Understand neurotransmitter functions and disorders
  • Memorize sympathetic vs parasympathetic effects
  • Practice FRQ questions on research methods

📝 Essential Vocabulary

Action Potential

Electrical signal traveling down neuron's axon

Neurotransmitter

Chemical messenger released at synapses

Heritability

Proportion of trait variation due to genetic factors

👨‍🎓 About the Author

Adam Kumar

Co-Founder @ RevisionTown

Adam is an education expert specializing in AP Psychology and various international curricula including IB, AP, GCSE, IGCSE, and more. With extensive experience in psychology education, he has helped thousands of students master complex psychological concepts and excel on standardized exams.

Through RevisionTown, Adam creates comprehensive study materials that break down complex topics into manageable, understandable segments. His expertise in both psychology content and educational methodology ensures students receive accurate, exam-focused preparation materials.

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