PSYC 312 · Week 4 · Lecture Adventure

Brain City → Synapse Station

Week 3 got the electrical message down the axon. Week 4 answers: how does that message get across to the next neuron?

Week 4 · Synapses

🔗 How Week 3 becomes Week 4

WEEK 3: action potential travels down the axon → reaches the presynaptic terminal → WEEK 4: Ca²⁺ enters → vesicles release neurotransmitter → transmitter crosses the cleft → receptor responds → EPSP/IPSP changes the postsynaptic neuron → inputs sum → threshold may be reached → a NEW action potential can begin.

Brain City connection: Last week you learned the electrical highway inside one neuron. This week you arrive at Synapse Station, the transfer station between neurons. The electrical message cannot simply drive across the gap; the neuron converts the message into a chemical delivery, then the receiving neuron converts that information into a postsynaptic response.

🧠 Remember: Axon = electrical travel. Synapse = chemical handoff. Postsynaptic membrane = decision area.

🏙️ Brain City Story — The Synapse Station Delivery

1
The train arrives.

The Week 3 action potential reaches the presynaptic terminal.

College: Presynaptic = the neuron delivering the synaptic transmission.
2
Calcium opens the loading dock.

Ca²⁺ enters the terminal and triggers vesicles to release their chemical cargo.

Memory: Ca²⁺ = “Cargo, come out!”
3
The delivery bubbles dock.

Synaptic vesicles fuse with the presynaptic membrane and release neurotransmitter.

College: Neurotransmitters are chemicals released by one neuron at a synapse that affect another neuron.
4
The messenger crosses the street.

Neurotransmitter diffuses across the synaptic cleft.

Memory: Cleft = crack/gap.
5
The right key finds the right lock.

The transmitter binds a receptor on the postsynaptic cell.

College: The effect of a neurotransmitter depends on the receptor it activates.
6
The receiver gets a GO or BRAKE signal.

EPSP pushes toward threshold; IPSP pushes away from threshold.

Memory: E = Excite = closer. I = Inhibit = farther.
7
Brain City counts all the votes.

Signals combine across time and across locations.

Temporal summation = repeated inputs over time. Spatial summation = inputs from separate locations.
Memory: Temporal = Time. Spatial = Space.
8
The station cleans up.

Transmitter action must stop so the synapse can reset.

Course examples include enzymatic breakdown and reuptake by transporters.
9
Different control panels change the speed.

Ionotropic receptors act quickly; metabotropic receptors start a slower internal cascade.

Memory: IONotropic → ION channel now. METAbolic → metabolic chain.
10
Drugs can interfere with almost any station step.

They can alter synthesis, vesicles, release, reuptake, breakdown, or receptors.

Agonist mimics/increases an effect; antagonist blocks an effect.
Built only from Week 4 textbook Chapter 2, professor Synapses slides, and Week 4 lecture transcript.

👀 Visual Lab — See the relationships

1. Chemical synapse map

PRESYNAPTICPOSTSYNAPTICvesicles + transmitterSYNAPTIC CLEFTreceptorsAP → Ca²⁺ → releasereceptor → EPSP/IPSP

2. EPSP vs IPSP

EPSP ↑ toward thresholdIPSP ↓ away from threshold

3. Summation = adding votes

TEMPORAL = TIMEsame input repeats quicklySPATIAL = SPACEdifferent locations combine

4. Ionotropic vs metabotropic

⚡
Ionotropic

Transmitter binds → ion channel opens directly → quick, brief effect.

🔁
Metabotropic

Transmitter binds → receptor changes → G-protein → second messenger → slower, longer-lasting effect.

📚 Teach It — simple first, college terms second

Open one section at a time. These 15 lessons cover the important Week 4 material across all supplied sources.

🖥️ Professor Slides → Course Material

This is the important content from the 51-slide Week 4 deck rebuilt as study material rather than dumping the slide deck on you.

Synapses + postsynaptic potentials

Synapse; presynaptic sender; postsynaptic receiver; EPSP = graded depolarization; IPSP = temporary hyperpolarization.
Remember: EPSPs and IPSPs are graded, not action potentials.

Summation + probability of firing

Temporal summation adds repeated inputs over time. Spatial summation adds inputs from separate locations. The balance of EPSPs and IPSPs changes the probability/rate of action potentials.
Time = temporal. Space = spatial.

Sherrington + reflex evidence

Reflexes were slower than axonal conduction; weak stimuli could sum; excitation of one muscle set could accompany inhibition of another. These observations supported synaptic delay, summation, and inhibition.

Chemical transmission

Most synaptic transmission depends on chemical stimulation. Neurotransmitters are released by one neuron and affect another.
Week 3 electrical message reaches terminal → Week 4 chemical handoff begins.

Neurotransmitter families + synthesis

Slides group transmitters as amino acids, modified amino acids/monoamines, neuropeptides, purines, and gases. Precursors include phenylalanine/tyrosine for catecholamines, choline for acetylcholine, and tryptophan for serotonin.

Receptors

Ionotropic: receptor directly opens an ion channel. Metabotropic: receptor acts through a G-protein and second messenger system.
IONotropic = ion channel now.

G-proteins + second messengers

Metabotropic receptor activation changes a G-protein; the G-protein can alter a channel directly or activate a second messenger that communicates within the cell.

Neuromodulators + hormones

Neuropeptides can act as neuromodulators with prolonged effects. Hormones are secreted mainly by glands and travel through blood to distant targets; neural and hormonal systems interact.

Stopping the signal

Acetylcholinesterase breaks acetylcholine into acetate and choline. Many other transmitters are removed by transporter-mediated reuptake; COMT and MAO metabolize catecholamines.

Feedback

Autoreceptors on the presynaptic terminal respond to the released transmitter and inhibit further synthesis/release. Postsynaptic cells can also send retrograde signals back to the presynaptic terminal.

Drugs at synapses

Drugs can alter synthesis, storage, release, reuptake, enzymatic breakdown, or receptor activation. Agonists mimic/increase transmitter effects; antagonists block them.

Course drug examples

Slides discuss amphetamine/methamphetamine and catecholamine release, cocaine and dopamine reuptake, methylphenidate and dopamine transporters, nicotine and nicotinic acetylcholine receptors, opiates and endorphin receptors, and cannabinoids/THC at cannabinoid receptors.

📖 Textbook Practice Questions

The actual Module 2.1 and Module 2.2 end-of-module quiz questions from your uploaded textbook, with the textbook answer key.

🧪 Week 4 Practice Quiz

A longer quiz built only from the verified Week 4 textbook, professor slides, and lecture transcript.

👩🏾‍🏫 Professor Quiz

No Week 4 professor quiz has been uploaded yet. This remains separate. When you provide the real professor quiz, it will go here and will not be mixed with generated practice.

🔗 How it ALL connects

Dendrites receive graded inputs → soma integrates → axon hillock reaches threshold → action potential travels axon (Week 3) → presynaptic terminal → Ca²⁺ → vesicles → neurotransmitter → receptor → EPSP/IPSP → temporal + spatial summation → threshold in the next neuron → another action potential.

Then the course expands the same system: receptor type controls how the signal acts; transmitter cleanup controls how long it lasts; autoreceptors and retrograde signals regulate the sender; hormones/neuromodulators broaden communication; drugs can modify particular steps.