AP Psychology Unit 1 – Biological Basis of Behavior & Sensation

Nature AND Nurture – Setting the Stage

  • “Nature vs Nurture” is outdated ➜ modern view = Nature AND Nurture.

    • Nature = heredity, genetics, DNA.

    • Nurture = environment (family, peers, culture, education, society, etc.).

  • Each psychological perspective leans differently:

    • Evolutionary ➜ heavier on heredity (Darwin’s natural selection).

    • Social-cultural, behaviorist, human-factor ➜ highlight environment.

Genetics, Evolution & Epigenetics

  • Charles Darwin: traits aiding survival are “selected” & passed on.

  • Eugenics (ethical misuse): selective breeding to “improve” humans.

  • Epigenetics

    • Studies how the environment/behaviour switch genes on/off without altering the DNA sequence.

    • Slow, accumulative; explains why identical twins diverge over time.

    • Famous studies:

    • Minnesota Twin Study (twins reared apart).

    • COL Adoption Project (initiated 1975; longitudinal)\text{(initiated 1975; longitudinal)} .

  • Epigenetics ≠ Neuroplasticity: epigenetics = gene expression; plasticity = brain rewiring (synaptic strength).

Dividing the Nervous System

  • Central Nervous System (CNS): brain + spinal cord (issuing “orders”).

  • Peripheral Nervous System (PNS): nerves linking CNS to organs & muscles.

    • Afferent (sensory) neurons: Approach brain.

    • Efferent (motor) neurons: Exit brain.

PNS ➜ Somatic vs Autonomic

  • Somatic (Skeletal) NS

    • Voluntary control; 5 senses + skeletal muscles.

  • Autonomic NS (involuntary life-support)

    • Sympathetic: arouses (fight/flight) – ↑heart rate, dilated pupils, ↑respiration.

    • Parasympathetic: calms (rest/digest) – slows heart, ↑digestion, energy storage.

    • Mnemonic: “Para = parachute ➜ slows you down.”

Neuron Types & Supporting Cells

  • Glial Cells (majority)

    • Structure, insulation (myelin), nourishment, waste removal; do not transmit info.

  • Neurons (functional units)

    • Communicate via electro-chemical signals.

    • Three working together in spinal cord ➜ Reflex Arc:

    • Sensory (afferent) → Interneuron → Motor (efferent).

    • Allows instant withdrawal from pain without cortical involvement.

Neural Transmission – Step by Step

  1. Resting Potential: inside ≈ −70 mV-70\,\text{mV}, more K+\text{K}^+ in, Na+\text{Na}^+ out.

  2. Threshold reached ➜ Depolarization (voltage-gated Na+\text{Na}^+ channels open).

  3. Action Potential travels along axon (all-or-none).

  4. Repolarization/hyperpolarization then Refractory Period.

  5. Arrival at axon terminal ➜ Ca2+\text{Ca}^{2+} channels open ➜ vesicles release neurotransmitters into synaptic gap.

  6. NTs bind to postsynaptic receptors (excitatory = depolarize; inhibitory = hyperpolarize).

  7. NTs unbind ➜ destroyed or reuptake by presynaptic neuron.

  • Damage illustrations:

    • Multiple Sclerosis: myelin sheath deterioration.

    • Myasthenia Gravis: antibodies block acetylcholine receptors.

Major Neurotransmitters & Functions

  • Acetylcholine (ACh): muscle action, learning, memory (ACh down ⇨ Alzheimer’s).

  • Dopamine: movement, reward, attention, emotion (excess ⇨ schizophrenia; lack ⇨ Parkinson’s).

  • Serotonin: mood, hunger, sleep, arousal (low ⇨ depression).

  • Norepinephrine (NE): alertness, blood pressure (fight/flight).

  • Epinephrine: emotional memories, adrenaline surge.

  • Glutamate: major excitatory; learning, LTP; excess ⇨ migraines, seizures.

  • GABA: major inhibitory; sleep, movement (low ⇨ seizures, anxiety).

  • Endorphins: natural painkillers, euphoria.

  • Substance P: transmits pain signals.

Hormones & the Endocrine System

  • Slower, bloodstream, widespread.

  • Key examples:

    • Adrenaline (Epinephrine): fight/flight; ↑heart rate, bronchodilation.

    • Leptin: inhibits hunger.

    • Ghrelin: triggers hunger & growth hormone release.

    • Melatonin (pineal): regulates circadian rhythm.

    • Oxytocin (hypothalamus → pituitary): bonding, affection (“love hormone”).

  • Pituitary Gland = “master gland” – directs endocrine orchestra under hypothalamus.

Psychoactive Drugs: Agonists vs Antagonists

  • Agonist = enhance NT effect (mimic, ↑release, block reuptake).

    • e.g.

    • Xanax ➜ ↑GABA (anti-anxiety).

    • Prozac (SSRI) ➜ blocks serotonin reuptake.

    • Opioids mimic endorphins.

  • Antagonist = inhibit NT (block release or receptors).

    • Schizophrenia meds ➜ block dopamine receptors.

    • Alcohol ➜ blocks glutamate release.

Drug Categories & Effects

  • Stimulants (caffeine, nicotine, cocaine): excite neural activity, energy, ↓appetite.

  • Depressants (alcohol, barbiturates): ↓neural activity, drowsiness, respiratory risk.

  • Hallucinogens (LSD, marijuana, peyote): distort perception, possible panic.

  • Opioids (heroin, morphine, oxycodone): pain relief, highly addictive.

  • Chronic use ➜ tolerance, dependence, withdrawal.

Brain Structure & Regions

Hindbrain

  • Spinal Cord: info highway.

  • Medulla Oblongata: heart rate, breathing.

  • Pons: bridge; coordinates movement, sleep, dreaming.

  • Reticular Activating System (RAS): arousal, alertness.

  • Cerebellum ("little brain"): balance, coordination, implicit memory.

Midbrain (brief)

  • Integrates auditory/visual with motor; orientation.

Forebrain / Cerebrum

  • Corpus Callosum: connects hemispheres.

  • Cerebral Cortex (gray matter) – 4 lobes per hemisphere:

    • Frontal

    • Prefrontal Cortex: planning, judgment.

    • Motor Cortex (posterior frontal): voluntary movement; contralateral; mapped by motor homunculus.

    • Broca’s Area (left only): speech production ➜ damage = Broca’s aphasia (non-fluent).

    • Parietal

    • Somatosensory Cortex: touch; contralateral; sensory homunculus.

    • Temporal

    • Auditory Cortex.

    • Hippocampus: memory formation (not storage).

    • Amygdala: fear, aggression, anxiety.

    • Wernicke’s Area (left): language comprehension ➜ damage = fluent but meaningless speech.

    • Occipital

    • Primary Visual Cortex: vision (receives from thalamus).

Subcortical Forebrain

  • Thalamus: sensory relay (except smell).

  • Limbic System (emotion, drives, memory) = amygdala + hippocampus + hypothalamus + thalamus.

  • Hypothalamus: homeostasis, drives (hunger, thirst, sex, temp), controls pituitary.

Hemispheric Lateralization

  • Left: language, logical analysis.

  • Right: spatial, facial recognition, creative insight.

  • Contralateral control: each hemisphere manages opposite body side.

Classic Cases & Research Tools

  • Phineas Gage: rod damaged frontal/limbic ➜ personality change; evidence for localization.

  • Split-Brain Studies (cut corpus callosum for epilepsy): show independent operation & specialization.

  • Lesion Studies: purposeful destruction (animals or clinical) to identify functions.

  • Autopsies: post-mortem functional mapping.

  • Imaging

    • EEG: scalp electrodes; measures electrical firing; great temporal, poor spatial (sleep/seizure studies).

    • fMRI: tracks blood-oxygen; reveals metabolic activity; high spatial detail.

Neuroplasticity

  • The brain can rewire by LTP\text{LTP}synaptogenesis; the basis for learning, recovery after injury (extent depends on severity, age, environment).

Consciousness & Sleep

Circadian Rhythm

  • ~2424-hour biological clock; regulates body temp, hormones, sleep-wake.

  • Disruption ➜ jet lag, shift-work fatigue.

Brain Waves

  • Beta: awake/alert (low amp, high freq).

  • Alpha: relaxed wakefulness (slower, larger).

  • Theta: light sleep.

  • Delta: deep sleep (slowest, largest).

Sleep Stages (≈90 min cycles)

  1. NREM 1: 5-10 min, alpha, hypnagogic jerks.

  2. NREM 2: 10-20 min, theta, sleep spindles & K-complexes.

  3. NREM 3: 30 min, delta, growth hormone, sleep-walking/talking.

  4. REM: 10+ min; paradoxical (beta-like); vivid dreams, muscle paralysis; periods lengthen across night.

  • REM Deprivation ➜ REM Rebound (enter REM faster, stay longer).

Dream Theories

  • Activation-Synthesis: brain weaves story from random neural activity.

  • Consolidation: REM strengthens memories, learning.

  • Restoration: sleep restores energy, body tissues.

Sleep Disorders

  • Insomnia: difficulty falling/staying asleep.

  • Sleep Apnea: breathing interruptions, no deep/REM.

  • REM Behaviour Disorder: act out dreams (paralysis absent).

  • Somnambulism: sleepwalking (stage 3, kids>adults).

  • Sleep Terrors: intense panic during deep sleep.

  • Narcolepsy: sudden daytime REM attacks.

  • Hypnagogic Sensations: hallucinations during NREM 1 (falling, floating).

Sensation – Fundamental Concepts

  • Sensation: detection & transduction of environmental energy.

  • Perception: interpretation (Unit 2 topic).

  • Transduction: convert stimulus energy → neural impulses.

  • Absolute Threshold: minimum stimulation detected 50%50\% of time.

  • Difference Threshold (\Delta I): smallest detectable change; Weber’s Law: ΔII=k\frac{\Delta I}{I}=k (constant proportion, not amount).

  • Sensory Adaptation: decreased responsiveness to constant stimulus (candle smell fades).

  • Habituation: learned reduced response to repeated stimulus (drug tolerance).

  • Sensory Interaction: senses blend (taste + smell = flavour).

  • Synesthesia: cross-modal perceptions (seeing sounds as colours).

Vision System Essentials

  • Light ➜ Cornea ➜ Pupil (iris regulates) ➜ Lens (accommodation changes curvature) ➜ Retina.

  • Photoreceptors:

    • Rods (periphery): dim light, no colour.

    • Cones (fovea): fine detail, colour.

  • Blind Spot: optic nerve exit, no receptors; brain fills gap.

  • Colour Theories:

    • Trichromatic (Young-Helmholtz): 3 cone types (R, G, B).

    • Opponent-Process: ganglion/optic pathway pairs (R–G, B–Y, Bk–Wh); explains after-images.

  • Wavelength ➜ hue (short = cool/blue; long = warm/red).

  • Amplitude ➜ brightness.

  • Vision Disorders:

    • Myopia: focus before retina (near-sighted).

    • Hyperopia: focus behind retina (far-sighted).

    • Colour Blindness: dichromatism (red-green), monochromatism (one hue), achromatopsia (B/W).

    • Prosopagnosia: face blindness (occipito-temporal damage).

    • Blindsight: cortical blindness with uncanny residual ability.

Auditory System Essentials

  • Sound Wave Properties

    • Frequency (Hz) ➜ pitch (short λ = high).

    • Amplitude (dB) ➜ loudness.

  • Pitch Theories

    • Place: spot on basilar membrane.

    • Frequency: firing rate matches frequency (works <1,0001{,}000 Hz).

    • Volley: neuron groups alternate to surpass individual limit.

  • Sound Localization: brain compares timing & intensity between ears.

  • Hearing Loss

    • Sensorineural: cochlea/auditory nerve damage ➜ cochlear implant.

    • Conductive: mechanical blockage ➜ hearing aid.

Chemical Senses

Olfaction (Smell)

  • Odorants bind to olfactory receptors in nasal epithelium ➜ electrical signals ➜ olfactory bulb ➜ limbic & cortex (no thalamus relay).

  • Links smell with memory/emotion.

  • Pheromones: species-specific chemical messengers influencing behaviour.

Gustation (Taste)

  • Papillae house taste buds (receptor cells).

  • Six basic tastes: sweet, sour, salty, bitter, umami (protein), fatty (gustus).

  • Transduction ➜ cranial nerves ➜ thalamus ➜ gustatory cortex & limbic.

  • Taster Categories: supertasters, medium, non-tasters.

  • Taste + smell → flavour; blocked smell = muted taste.

Touch, Pain & Body Senses

  • Skin layers: Epidermis, Dermis (receptors, blood), Hypodermis (fat).

  • Mechanoreceptors: pressure; Thermoreceptors: temp.

  • Nociceptors: pain.

  • Gate Control Theory: spinal “gate” modulates pain; psychological factors can close gate (distraction, rubbing injury).

  • Phantom Limb: pain from removed limb; due to nerve & cortical re-organisation.

Balance & Kinesthesis

  • Vestibular Sense: semicircular canals’ fluid & hair cells detect head movement for equilibrium.

  • Kinesthesis: proprioceptors in muscles/tendons inform position & movement; cerebellum integrates.

Final Connections & Applications

  • Study actively (take notes, quizzes) ➜ forms new synaptic pathways (plasticity).

  • Ethical reflections: misuse of evolutionary ideas (eugenics) vs modern, inclusive applications (gene-environment research).

  • Real-world relevance: Shift workers manage circadian misalignment; psychoactive prescriptions target specific neurotransmitters; rehabilitation leverages plasticity; sensory adaptations are exploited in marketing (ambient scents).

Key Formulae / Numbers

  • All-or-None law (qualitative) – amplitude independent of stimulus once threshold met.

  • Weber’s Law: ΔII=k\frac{\Delta I}{I}=k.

  • Resting potential ≈ −70 mV-70\,\text{mV}, threshold ≈ −55 mV-55\,\text{mV}.

  • Circadian ≈ 2424 h; typical sleep cycle ≈ 9090 min.

• End of Unit 1 comprehensive notes •