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Week 3 · Lecture outline

Week 3 — Lecture Outline · Biological Bases of Behavior

Introduction to Psychology · PSYC 1 Fall 2026 · Prof. Bennett Fictional sample

Course: Introduction to Psychology (PSYC 1) · Silver Oak University (fictional sample) · Prof. Bennett
Objectives covered: Objective 3 — Describe the biological bases of behavior — neurons, neurotransmitters, and the structures and functions of the nervous system and brain.
SLOs touched: A (apply concepts to real-world behavior) · B (reason scientifically about claims regarding mind and behavior)
Meeting pattern: 2 sessions × 75 min = 150 min. Segment minutes below total ~150; scale to your own pattern.

Week at a Glance
The week's big question "If every thought, feeling, and movement is built from cells passing chemical messages, how does a brain made of biology produce a mind?"
By the end of the week, students can… (1) label the neuron and trace a signal from dendrites to terminal buttons; (2) explain the all-or-none action potential and how neurons talk across the synaptic gap; (3) match the major neurotransmitters to their roles; (4) lay out the nervous system — CNS vs. PNS, somatic vs. autonomic, sympathetic vs. parasympathetic; (5) locate the brain's key structures and the four lobes, and explain neuroplasticity.
Key vocabulary neuron, dendrite, soma/cell body, axon, myelin sheath, terminal buttons, glial cells, resting potential, threshold, action potential, all-or-none, refractory period, synapse, synaptic gap, neurotransmitter, receptor, reuptake, acetylcholine, dopamine, serotonin, GABA, glutamate, endorphins, central nervous system, peripheral nervous system, somatic, autonomic, sympathetic, parasympathetic, reflex, brainstem, medulla, cerebellum, limbic system, amygdala, hippocampus, hypothalamus, cerebral cortex, frontal/parietal/occipital/temporal lobes, corpus callosum, neuroplasticity, EEG, fMRI
Materials slides (Deck 3), the week's readings + video links, one approved chatbot (Gemini / Claude / ChatGPT) for the AI-critique moment and the tutorial
Timing note 8 segments, ~150 min total. Session 1 = Segments 1–4 (~75). Session 2 = Segments 5–8 (~75).

Segment 1 — Hook & the Promise (8 min) · Session 1 opens

Hook. Tell the room to do something tiny — "snap your fingers, right now." Then: "That snap just took a round trip through a system of billions of cells. A decision formed in your frontal lobe, an electrical pulse shot down a nerve fiber wrapped in fatty insulation, a burst of chemicals leapt a microscopic gap to the next cell, and a muscle in your hand fired — all in under a tenth of a second. This week we open the hood."

Then put up the brain myth everyone has heard: "True or false — we only use 10% of our brains?" Hands up. "It's false — and brain imaging shows nearly all of it active even at rest. By Friday you'll know why that myth survives and what the evidence actually shows."

The promise (write it on the board): "By Friday you'll be able to trace a single message from one neuron to the next, name what the major brain chemicals do, lay out the nervous system from spinal cord to cerebral cortex, and explain why 'we only use 10% of our brains' is a myth — using the right words."

Why it matters line (memory hook): "Every feeling you've ever had, and every move you've ever made, is cells passing notes. Today we learn how the notes get passed."

Segment 2 — The Neuron, Part by Part (18 min)

Plain language first.
- A neuron is a single nerve cell — the basic unit of the nervous system. You have roughly 86 billion of them. A neuron's whole job is to receive a signal, decide whether to pass it on, and send it to the next cell.
- Walk the parts in signal order (put a labeled diagram on a slide):
- Dendrites — the bushy, branching antennae that receive incoming signals from other neurons.
- Soma (cell body) — the cell's core; holds the nucleus and keeps the neuron alive. It sums up the incoming signals.
- Axon — the long cable that carries the signal away from the soma toward the next cell.
- Myelin sheath — a fatty layer wrapped around many axons that insulates the cable and speeds the signal up (myelinated signals travel far faster than bare ones).
- Terminal buttons (axon terminals) — the knobs at the axon's end that release neurotransmitters to the next neuron.
- Glial cells (briefly): the neuron's support crew — they nourish, insulate (they build the myelin), and clean up around neurons. There are even more of them than neurons.

Memory hook (put it on a slide):

"Dendrites receive, the soma decides, the axon delivers, the terminals release. Myelin is the bubble wrap that makes the delivery fast."

Quick clarification students need: the myelin sheath isn't the message and it isn't optional fluff — when it breaks down (as in multiple sclerosis), signals slow or scramble. That's the clearest proof of what myelin is for.

Segment 3 — The Neural Impulse + The Synapse (the first worked example) (24 min)

Plain language first — how one neuron fires.
- At rest, a neuron sits at a resting potential — charged up and waiting, like a loaded mousetrap.
- Incoming signals nudge it. If they push it past a tipping point — the threshold — the neuron fires an action potential: an electrical pulse that races down the axon.
- The firing is all-or-none. A neuron either fires fully or not at all — there's no "half-fire." Plain language: it's like a gun — pulling the trigger harder doesn't make a bigger bullet; it either fires or it doesn't. Or a row of dominoes — once the first one tips past the point of no return, the whole row falls.
- Right after firing, the neuron needs a split-second reset — the refractory period — before it can fire again.

One fully worked example (the signature — do it out loud, slowly):

Trace one message end to end. (1) A signal arrives at the dendrites of a neuron. (2) The soma adds it up; the neuron crosses threshold and fires an all-or-none action potential. (3) The pulse races down the axon, sped along by the myelin sheath. (4) It reaches the terminal buttons, which release neurotransmitters. (5) Those chemicals cross the synaptic gap and bind to receptors on the next neuron's dendrites — and the whole process begins again in that cell.
"One message, one neuron, then a chemical handoff to the next. String billions of these together and you get a thought."

The synapse — the part everyone gets wrong.
- Neurons do not touch. Between the terminal button of one and the dendrite of the next is a microscopic gap — the synapse / synaptic gap.
- The electrical signal can't jump the gap, so it converts to a chemical one: neurotransmitters are released, drift across, and bind to receptors like a key into a lock.
- Leftover neurotransmitter doesn't linger — the sending neuron vacuums it back up in a process called reuptake (this is exactly the step many medications target).

Memory hook: "Electrical down the axon, chemical across the gap. Neurons never touch — they text."

Segment 4 — Misconceptions + Quick Interaction (18 min) · Session 1 closes (~75)

Name the misconceptions out loud, then cure each:

  • ❌ "We only use 10% of our brains."
    ✅ Cure: false. Brain imaging (fMRI, PET) shows activity across virtually the whole brain, and even at rest the brain is busy; damage to almost any region causes deficits, which couldn't happen if 90% were idle. "There's no spare 90% waiting to be unlocked."
  • ❌ "Neurons touch each other to pass the message along."
    ✅ Cure: they don't — there's a synaptic gap. The signal is electrical inside a neuron but chemical between neurons; neurotransmitters cross the gap. "Inside, electrical; across, chemical."
  • ❌ "People are either 'left-brained' (logical) or 'right-brained' (creative)."
    ✅ Cure: the hemispheres do specialize (e.g., language leans left for most people), but they're wired together by the corpus callosum and you use both constantly. The personality version — "I'm a right-brained creative" — is a pop-psych myth.
  • ❌ "A bigger or stronger stimulus makes a neuron fire a bigger signal."
    ✅ Cure: no — firing is all-or-none. A stronger stimulus makes a neuron fire more often (and recruits more neurons), but each individual action potential is the same size.

Interaction — Think-Pair-Share (rapid-fire, ~8 min):
Put six items on a slide; for each, students decide which neuron part or which brain structure is responsible, solo (30 sec), compare with a neighbor (1 min), then call it out. Suggested items: "the part that receives signals" (dendrites) · "the insulation that speeds the signal" (myelin) · "keeps your heart beating and lungs breathing" (medulla) · "balance and coordination" (cerebellum) · "forms new memories" (hippocampus) · "the brain's alarm for fear" (amygdala).
Debrief that the nervous system is modular — different jobs live in different places — which is exactly why the 10% myth falls apart.

Segment 5 — The Neurotransmitters & Their Jobs (22 min) · Session 2 opens

Hook back in: "Last session a message crossed the synaptic gap as a chemical. Today: which chemicals — and why a shortage or surplus of one can change your mood, your movements, even your memory."

Plain language first — the major neurotransmitters (one line each; keep the links careful — say associated with, never causes):
- Acetylcholine (ACh) — triggers muscle movement; also vital to memory and attention. (Low ACh is associated with Alzheimer's.)
- Dopamine — reward, motivation, and movement. Too little is associated with Parkinson's disease (movement breaks down); dysregulation is associated with schizophrenia.
- Serotonin — mood, sleep, and appetite. Low serotonin activity is associated with depression (many antidepressants act on it).
- GABA — the brain's main inhibitory ("calming") messenger; it puts the brakes on. Low GABA is associated with anxiety and seizures.
- Glutamate — the main excitatory messenger; the brain's "go" signal, important for learning and memory.
- Endorphins — the body's natural pain relief and the "runner's high"; released during exercise, stress, or injury.

Memory hook (put it on a slide):

"Acetylcholine acts your muscles · Dopamine drives reward & movement · Serotonin soothes mood & sleep · GABA = the brakes · Glutamate = the gas · Endorphins = the body's painkiller."

Careful-language reminder (say it): these are associations, not simple on/off switches. "Low serotonin causes depression" overstates it — the honest claim is that serotonin activity is associated with mood, and the picture is more complicated than one chemical. We model that careful wording in this class.

Segment 6 — The Nervous System, Top to Bottom (20 min)

Set it up: "Zoom out from single cells to the whole communication network. It branches in a tidy, learnable way — and every branch has a job."

Plain language first — the branching map (build it as a tree on the slide):
- Central Nervous System (CNS) = the brain + spinal cord — the command center, where information is processed.
- Peripheral Nervous System (PNS) = all the nerves outside the CNS — the wiring that connects the command center to the body. It splits two ways:
- Somatic — carries voluntary signals: senses in, deliberate muscle movements out (typing, walking).
- Autonomic — runs involuntary, automatic functions (heartbeat, digestion). It has two opposing branches:
- Sympathetic — fight-or-flight: arousing. Speeds the heart, dilates pupils, dumps adrenaline, pauses digestion — the "gas pedal" for emergencies.
- Parasympathetic — rest-and-digest: calming. Slows the heart, restarts digestion, conserves energy — the "brake pedal" that brings you back to baseline.

Spinal reflex (briefly): some reactions are too urgent to wait for the brain. Touch a hot stove and your spinal cord fires the "pull back" command on its own — sensory in, motor out — and you yank your hand away before your brain even registers the pain. The reflex protects you first; the feeling arrives a beat later.

Memory hook: "CNS = headquarters (brain + cord). PNS = the wiring. Somatic = on purpose; Autonomic = on autopilot. Sympathetic = gas; Parasympathetic = brake."

Segment 7 — The Brain: Structures & the Four Lobes (20 min)

Plain language first — a quick tour from bottom to top (point to a brain diagram):
- Brainstem & the medulla — sits where brain meets spinal cord; the medulla runs the things you'd die without and never think about: heartbeat and breathing.
- Cerebellum ("little brain," tucked at the back) — balance, coordination, and smooth movement. (Alcohol hits it hard — hence stumbling.)
- Limbic system — the emotional/memory core:
- Amygdala — the brain's alarm: fear and strong emotion.
- Hippocampus — forms new memories (damage here and you can't lay down new long-term memories).
- Hypothalamus — the thermostat/drives center: hunger, thirst, temperature, and homeostasis.
- Cerebral cortex — the wrinkled outer surface where higher thought happens, in four lobes (one set per hemisphere):
- Frontal — planning, judgment, decision-making, and the motor cortex (voluntary movement). ("The CEO.")
- Parietal — touch and body sensation (the somatosensory cortex).
- Occipital — vision (at the very back).
- Temporal — hearing (and language comprehension), by the temples.
- Hemispheres & the corpus callosum: two halves, specialized but constantly talking through the corpus callosum, the thick cable of axons that links them.
- Neuroplasticity: the brain rewires itself with experience and practice, and can shift functions after injury. Your brain is not fixed hardware — it's remodeled by what you do. (This is the bridge to learning, memory, and habits.)
- Brain imaging (briefly): EEG reads electrical activity through the scalp (great timing); fMRI maps blood flow to show where activity happens (great location). These tools are how we know the 10% myth is false.

Memory hook: "Medulla keeps you alive · Cerebellum keeps you balanced · Amygdala keeps you afraid · Hippocampus keeps your memories · Cortex lobes: Front plans, Parietal feels, Occipital sees, Temporal hears."

Segment 8 — Technology Workflow + AI-Critique, Callback & Hand-off (10 min) · Session 2 closes (~75)

Technology workflow — explore the brain, don't just memorize it:
1. Open a reputable interactive brain explorer or a labeled neuron diagram (linked in the readings) and find each structure you just learned — point, name, say its job out loud.
2. Trace the signature signal one more time on the diagram: dendrites → threshold → all-or-none action potential → down the myelinated axon → synaptic gap → next neuron.
3. Pick one everyday action (snapping, flinching, remembering a name) and name which structure and which neurotransmitter the textbook would credit.

AI-critique moment (students verify, not consume):

Paste this to an approved chatbot: "Which neurotransmitter is most associated with Parkinson's disease, and which with reward and movement?"
Then check its work against today's notes. The answer to both is dopamine. Chatbots sometimes swap dopamine and serotonin (serotonin is the mood/sleep one), or overstate a link as "causes" instead of "associated with." Your job all semester: the tool drafts, you judge. This is exactly how the weekly Lecture Tutorial works — you'll catch the model, not trust it.

Callback + tease:
- Callback: "Two weeks ago we asked what makes psychology a science; last week, how we study it. Today we found where behavior lives — in cells, chemicals, and structures. Every later topic — sensing, learning, emotion — runs on this hardware."
- Tease next week: "We've built the brain. Next week: how it gets information in — sensation and perception, where your eyes and ears hand raw signals to that occipital and temporal cortex, and why your brain sometimes makes things up."

Hand-off (the week's graded work):
- Lecture Tutorial 3 (AI tutor, share-link submission) — the neuron, the action potential, the synapse, the neurotransmitters, the nervous system, and the brain.
- Quiz 3 (end of week) and Discussion 3 ("Nature, Nurture, and Your Brain" — how much of a trait is biology vs. experience).
- Assignment 3 — label the neuron, match chemicals and structures to functions, classify sympathetic vs. parasympathetic, and bust the 10% myth.

Instructor FAQ — Common Stumbles

Student says / does Quick cure
"We only use 10% of our brains, right?" No — imaging shows near-whole-brain activity, and damage almost anywhere causes deficits. The 10% line is a myth, not a finding.
Thinks neurons physically touch. They don't — there's a synaptic gap. Signal is electrical inside a neuron, chemical across the gap (neurotransmitters).
Believes people are "left-brained" or "right-brained." Hemispheres specialize but are joined by the corpus callosum; everyone uses both. The personality version is pop-psych.
Thinks a stronger stimulus = a bigger action potential. Firing is all-or-none. Strength is coded by how often neurons fire and how many, not by spike size.
Swaps dopamine and serotonin. Dopamine = reward/movement (Parkinson's, schizophrenia links); serotonin = mood/sleep/appetite (depression link).
Confuses sympathetic and parasympathetic. Sympathetic = gas (fight-or-flight, arousing). Parasympathetic = brake (rest-and-digest, calming).
Mixes up hippocampus and hypothalamus (similar names). Hippocampus → memory; hypothalamus → homeostasis/drives (hunger, thirst, temperature). Say both twice.
Says a neurotransmitter "causes" a disorder. Careful wording: associated with. One chemical rarely tells the whole story — model the cautious claim.

Scope flag

This outline stays within Objective 3 at intro-survey depth — neuron structure, the action potential conceptually (no membrane biochemistry or ion-channel math), the major neurotransmitters and their associations, nervous-system divisions, and the key brain structures, lobes, and neuroplasticity. Deeper neuroanatomy, the endocrine system in detail, and genetics are beyond this week's scope and are touched only as needed. Brain-imaging is named (EEG, fMRI), not taught as a methods unit. Clinical links (Parkinson's, Alzheimer's, depression, schizophrenia, MS) are stated as associations, accurately and non-sensationally; the instructor and institution remain fictional.

~ Prof. Bennett's edition · Fall 2026 · built with thecoursemaker.com