Biology & Behavior – Comprehensive Study Notes

Nervous System: Foundations & Significance

• Psychology is inseparable from biology; every thought, emotion, memory, or action is ultimately the product of neural and hormonal activity.

• Nervous system = the body's high-speed information network; analogous to the circulatory system for blood.

• Key questions framed by the transcript:

  • How heritable is intelligence?

  • What physiological events accompany strong emotion?

  • Are mental illnesses due to brain chemistry?

  • What do the right vs. left hemispheres actually “do”?

Basic Neural Anatomy

• Neuron = basic unit of the nervous system (≈ “vast assembly of nerve cells” — Francis Crick).

• Major parts

  • Dendrites: branch-like receivers; can accept input from thousands of cells.

  • Soma / cell body: contains nucleus & chromosomes; integrates incoming signals.

  • Axon: single long fiber that conducts impulses away from soma; length can reach several feet.

  • Myelin sheath

  • Lipid insulation formed by glial cells.

  • Speeds conduction via saltatory (“node-to-node”) transmission at the Nodes of Ranvier.

  • Clinical link: Multiple sclerosis = myelin degeneration → slowed/blocked impulses → muscle control loss.

  • Terminal buttons: bulblike endings; release chemical signals.

  • Synapse = junction between neurons; contains synaptic cleft (cells do not physically touch).

Types of Neurons

• Sensory (afferent): carry info from receptors → CNS (e.g., sore ear).

• Motor (efferent): CNS → muscles/glands (voluntary grasping & involuntary digestion).

• Interneurons: neuron↔︎neuron relays; numerically dominant.

Electrical Properties & Action Potential

• Resting potential = -70\ \text{mV} (inside negative relative to outside).

• Important ions: \text{Na}^+,\ \text{K}^+,\ \text{Cl}^-.

• Two graded responses at dendrites/soma:

  • Depolarization: inside becomes less negative (Na⁺ influx) → excitation.

  • Hyperpolarization: inside becomes more negative (K⁺ efflux or Cl⁻ influx) → inhibition.

• Threshold: if membrane potential hits ≈ -50\ \text{mV} at axon hillock, an action potential fires.

• AP = all-or-none spike; amplitude constant, frequency encodes intensity.

• Ionic events during AP

  1. Na⁺ channels open → Na⁺ rushes in.

  2. K⁺ channels open slightly later → K⁺ exits.

  3. Membrane repolarizes; brief overshoot (after-hyperpolarization).

• Absolute refractory period: 1–2\ \text{ms} when no new AP possible.

• Relative refractory period: follows; AP possible only with stronger stimulus.

Chemical Transmission

• AP reaching terminal → synaptic vesicles fuse with membrane → release neurotransmitters (NTs) into cleft.

• NTs bind postsynaptic receptors via lock-and-key fit:

  • Agonists: mimic NT, activate receptor (e.g., nicotine on ACh receptors).

  • Antagonists: occupy receptor without activating, blocking NT.

• Postsynaptic effect = graded potential that may excite or inhibit next cell.

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Major Neurotransmitters & Behavioral Links

• Acetylcholine (ACh)

  • Skeletal muscle activation; attention, arousal, memory.

  • Nicotine = agonist.

  • ACh deficit implicated in Alzheimer’s; drugs that boost ACh slow decline.

• Dopamine (DA)

  • Voluntary movement, reward, addiction.

  • Parkinson’s: DA neurons in substantia nigra die; treated with L-DOPA.

  • Excess/ dysregulation → schizophrenia‐like symptoms.

• Serotonin (5-HT)

  • Sleep/wake, eating, aggression, mood.

  • Low 5-HT linked to depression; SSRIs increase synaptic serotonin.

• Norepinephrine (NE)

  • Mood & arousal; low levels also associated with depression.

• GABA (gamma-aminobutyric acid)

  • Major inhibitory NT; anxiety regulation, sleep.

  • Benzodiazepines (e.g., Valium) = GABA agonists.

• Endorphins

  • Endogenous opioids; pain relief, eating, “runner’s high.”

Endocrine System (Hormonal Broadcast Network)

• Glands secrete hormones into bloodstream → wide-ranging broadcast (vs. synapse‐specific NT).

• Key glands & hormones

  • Pituitary: “master”; controls other glands.

  • Thyroid: growth, metabolism; hypothyroidism → fatigue, depression.

  • Adrenal: adrenaline/epinephrine; emergency “fight-or-flight.”

  • Pancreas: insulin; glucose metabolism.

  • Gonads: testes (testosterone) & ovaries (estrogen); sex development & drive.

Nervous System Organization

• Central Nervous System (CNS): brain + spinal cord.

• Peripheral Nervous System (PNS): all neural tissue outside CNS.

  • Somatic: voluntary skeletal muscles + sensory receptors.

  • Afferent (→ CNS) & efferent (← CNS) fibers.

  • Autonomic (ANS): visceral functions (heart, vessels, glands).

  • Sympathetic: emergency, arousal (↑HR, dilated pupils).

  • Parasympathetic: routine maintenance (digestion, ↓HR).

  • Cooperation example: sexual response — parasympathetic initiates erection/lubrication, sympathetic triggers orgasm.

Spinal Cord

• Conduit for sensory input (dorsal roots) & motor output (ventral roots).

• Houses reflex circuits; segmental organization.

Brain: Gross Divisions

• Hindbrain (medulla, pons, cerebellum, reticular formation)

  • Medulla: vital reflexes (breathing, HR).

  • Pons: respiration, sleep, bridge to cerebellum.

  • Cerebellum: fine motor coordination, balance, procedural learning.

  • Reticular formation (extends into midbrain): arousal filter; anesthetics & comas involve this network.

• Midbrain

  • Tectum: orienting reflexes; superior colliculi (vision), inferior colliculi (audition).

  • Tegmentum: substantia nigra (DA → movement), reward & aversion centers.

• Forebrain

  • Thalamus: relay for all sensory info (except smell) to cortex.

  • Hypothalamus: homeostasis; hunger, thirst, temp, sexual behavior; links nervous to endocrine (pituitary).

  • Basal ganglia (caudate, putamen, globus pallidus): movement initiation, habit learning; damaged in Parkinson’s.

  • Limbic system

  • Hippocampus: declares new memories; damage → anterograde amnesia yet intact procedural learning.

  • Amygdala: fear conditioning, emotional salience; damage → lack of fear, hypersexuality, agnosia.

  • Septal area: reward & motivation (not elaborated in transcript).

Cerebral Cortex

• 3-mm folded gray matter; seat of higher cognition.

• Enables:

  1. Flexible motor control.

  2. Fine sensory discrimination.

  3. Symbolic/abstract thinking (foundation of language & culture).

• Divided into primary areas (sensory & motor) and association areas (integration, planning).

• Hemispheric structure

  • Two halves separated by longitudinal fissure; connected via corpus callosum.

  • Four lobes per hemisphere:

  • Occipital: primary visual cortex; lesions → visual deficits.

  • Parietal: primary somatosensory cortex; spatial attention & body schema.

  • Temporal: auditory cortex, olfaction, complex vision.

    • Wernicke’s area: language comprehension; damage → fluent but nonsensical “word salad” (Wernicke’s aphasia).

    • Prosopagnosia after temporal (especially right) damage.

  • Frontal: primary motor cortex; executive functions (planning, inhibition).

    • Broca’s area (left frontal): speech production & grammar; damage → non-fluent Broca’s aphasia.

    • Personality change example: Phineas Gage (orbitofrontal damage → impulsivity).

• Sensory/motor homunculi: cortical real estate proportional to precision, not size (e.g., fingers vs. torso).

Hemispheric Lateralization & Split-Brain Findings

• Left (in right-handers): language, logic, complex motor sequencing, analytic consciousness.

• Right: spatial maps, face/music recognition, holistic patterns.

• Split-brain surgery (corpus callosum severed) isolates hemispheres:

  • Experiment: word “key” flashed to left visual field → right hemisphere sees it; patient cannot verbalize but left hand can select key by touch.

  • Reveals independent parallel processing without inter-hemispheric awareness.

Genetics, Environment, & Behavior

• Genotype: complete genetic blueprint; phenotype: observable traits.

• Chromosomes: 23 pairs; gametes carry 23 singles.

• Dominant vs. recessive genes; many traits polygenic.

• Degree of relatedness

  • Parent/child or dizygotic twins: 0.50.

  • Monozygotic twins: 1.00.

• Twin & adoption studies → heritability coefficient (h²) (range 0 – 1): proportion of trait variance due to genes.

  • Traits like intelligence, neuroticism, aggressiveness show h^2 \approx 0.15 – 0.50.

  • Interpretation cautions: h² ≠ genetic determinism; environment still critical.

  • Gene expression often environment-dependent (epigenetic activation).

Integrative & Real-World Points

• Psychological disorders (e.g., depression, Parkinson’s, schizophrenia) illustrate bio-behavior links: NT imbalances, degenerative cell loss, genetic vulnerability + environment.

• Ethics & pharmacology: agonist/antagonist drugs can treat illness but also present risks (addiction, side-effects).

• Exercise’s mood benefits plausibly mediated by endorphin release (and other factors: dopamine, serotonin, endocannabinoids).

• Bio-psych knowledge informs clinical interventions (SSRIs, benzodiazepines, L-DOPA, thyroid replacement, deep-brain stimulation).

Key Numerical / Formulaic References

• Resting potential: V_{rest} = -70\ \text{mV}.

• Threshold potential: V_{th} \approx -50\ \text{mV}.

• Absolute refractory period: 1–2\ \text{ms}.

• Chromosome count: 46 = 23 \text{ pairs}.

• Degree of relatedness: r{parent\text{-}child} = 0.5, r{MZ} = 1.0.

• Heritability coefficient: h^{2} \in [0,1] (e.g., h^{2}_{IQ} \approx 0.5 in cited studies).

Revision-Style Takeaways

• Neuron: electrical (graded & action potentials) + chemical (NT) signaling.

• Endocrine hormones = broadcast; pituitary the “master.”

• PNS → somatic (voluntary) & autonomic (sympathetic vs. parasympathetic).

• CNS hierarchical evolution: hindbrain → midbrain → forebrain; cortex at apex for symbolic reasoning.

• Left/right hemispheres specialize but integrate via corpus callosum; split-brain cases reveal dual minds.

• Behavioral genetics: both heredity & environment shape personality, cognition, psychopathology; genes set potentials, environments pull triggers.