Neurochemistry

2025-09-30

Rick Gilmore

Department of Psychology

Prelude

– LadyGagaVEVO (2021)

Today’s topics

Announcements
- No class Thursday, October 2, 2025
Comment on Quiz 1
Behavior requires communication
Synaptic communication
Neurotransmitters

Comment on Quiz 1

9. Electroencephalography (EEG) has _ temporal resolution than functional MRI, but _ spatial resolution.

A. better; similar
B. better; worse
C. worse; better
D. worse; similar

9. Electroencephalography (EEG) has _ temporal resolution than functional MRI, but _ spatial resolution.

A. better; similar
B. better; worse
C. worse; better
D. worse; similar

Back story

Electroencephalograpy (EEG) & magnetoencephalography (MEG) rely on electromagnetic (EM) signals
Large numbers of overlapping action potentials generate EM signals
EM signals propagate quickly through brain, skull, & scalp
High temporal resolution (>> fMRI)
But, EM sources distributed widely, so low spatial resolution (<< fMRI)

Behavior requires communication

Types of communication for behavior

Between organisms
Within organisms
- Sensors (eyes, ears, skin, …)
- Effectors (muscles, glands)
- Linked via CNS

What do animals need to know to behave?

What’s out there
Where is it
What should I do about it
Do it

Nervous systems are communication systems

Chemical communication : short distances
- Force of diffusion
- Cheap, energy-efficient, “compute with chemistry”
Electrical communication : long distances
- Ion flows across membrane \(\rightarrow\) propagating voltages
- More “expensive” (metabolically-speaking)/less energy-efficient
- Much faster

– Sterling & Laughlin (2021)

Nervous systems are communication systems

Synaptic communication
- Chemical (via neurotransmitters)
- Electrical (via ion flow)
Endocrine communication (chemical via hormones released into bloodstream)

Synaptic communication

Steps in synaptic transmission

Step
Action potential arrives at terminal button.
Voltage-gated \(Ca^{++}\) channels open
\(Ca^{++}\) ions enter the cell
\(Ca^{++}\) ions activate synaptic vesicles & trigger exocytosis

Steps in synaptic transmission

Step
Neurotransmitter diffuses across synaptic cleft
Neurotransmitter binds to post-synaptic receptor(s)
Postsynaptic receptor(s) cause EPSP or IPSP
Neurotransmitter unbinds and is inactivated

Action potential propagates from soma

Soma receives input from dendrites
Axon hillock sums/integrates
If sum > threshold, AP “fires”

Action potential propagates from soma

AP propagates
Quickly: myelinated + thick axon
Slowly: unmyelinated or thin

– Neuron (2021)

Action potential arrives at synaptic terminal

How does AP cause chemical release?
Voltage-gated calcium (Ca++) channels open
Ca++ enters

Action potential arrives at synaptic terminal

Ca++ causes synaptic vesicles to bind with presynaptic membrane & merge with it
Neurotransmitters (NTs) released via exocytosis (‘out’ of the cell)

NTs cross the synaptic clef

NTs bind with receptors on postsynaptic membrane
Receptors respond
NTs unbind, are inactivated

Synaptic vesicles get “recycled”

Vesicles reform
Get refilled with neurotransmitter

Why do NTs move from presynaptic terminal toward postsynaptic cell?

~~Electrostatic force pulls them~~
Force of diffusion
Synaptic cleft small relative to vesicles, so diffusion time short (< 0.5 ms)

Postsynaptic receptor types

Ionotropic (receptor + ion channel)
- Chemical (ligand)-gated
- Open/close ion channel
- Ions flow in/out depending on membrane voltage and ion type
- Fast-responding (< 2 ms), but short-duration effect (< 100 ms)

Postsynaptic receptor types

Metabotropic (receptor only, no attached ion channels)
- Trigger G-proteins attached to receptor
- G-proteins activate 2nd messengers

Postsynaptic receptor types

Metabotropic (receptor only, no attached ion channels
- 2nd messengers bind to, open/close adjacent channels or change metabolism
- Slower, but longer-lasting effects

Receptors cause response

Generate postsynaptic potentials (PSPs)
- Small voltage changes
- Amplitude scales with # of receptors activated
- Number of receptors activated ~ # of vesicles released

Two types of postsynaptic potentials (PSPs)

Excitatory PSPs (EPSPs)
- Depolarize neuron (make more +)
- Move membrane potential closer to threshold

Two types of postsynaptic potentials (PSPs)

Inhibitory (IPSPs)
- Hyperpolarize neuron (make more -)
- Move membrane potential away from threshold

Message from dendrites & soma

a mixture of IPSPs and EPSP

What sort of PSP would opening a Na+ channel produce?

Na+ flows in, so Excitatory PSP (EPSP)
Na+ flows out, so Excitatory PSP (EPSP)
Na+ flows in, so Inhibitory PSP (IPSP)
Na+ flows out, so Inhibitory PSP (IPSP)

What sort of PSP would opening a Na+ channel produce?

Na+ flows in, so Excitatory PSP (EPSP)
Na+ flows out, so Excitatory PSP (EPSP)
Na+ flows in, so Inhibitory PSP (IPSP)
Na+ flows out, so Inhibitory PSP (IPSP)

What sort of PSP would opening a Cl- channel produce?

Remember \([Cl^-]_{out}>>[Cl^-]_{in}\); Assume resting potential ~-60 mV. Cl- is negatively charged, so will have opposite effect of positively charged ions.

Cl- flows in, so Excitatory PSP (EPSP)
Cl- flows out, so Excitatory PSP (EPSP)
Cl- flows in, so Inhibitory PSP (IPSP)
Cl- flows out, so Inhibitory PSP (IPSP)

What sort of PSP would opening a Cl- channel produce?

Remember \([Cl^-]_{out}>>[Cl^-]_{in}\); Assume resting potential ~-60 mV. Cl- is negatively charged, so will have opposite effect of positively charged ions.

Cl- flows in, so Excitatory PSP (EPSP)
Cl- flows out, so Excitatory PSP (EPSP)
Cl- flows in, so Inhibitory PSP (IPSP)
Cl- flows out, so Inhibitory PSP (IPSP)

NT inactivated by multiple mechanisms

Buffering
- e.g., glutamate into astrocytes (Anderson & Swanson, 2000)
Reuptake via transporters
- molecules in membrane that move NTs inside
- e.g., serotonin via serotonin transporter (SERT)

NT inactivated by multiple mechanisms

Enzymatic degradation
- e.g., Acetylcholinesterase (AChE) degrades acetylcholine (ACh)

Why must NTs be inactivated?

Or what would happen if they weren’t?
Or weren’t quickly?

Types of synapses

Axodendritic (axon to dendrite)
Axosomatic (axon to soma)
Axoaxonic (axon to axon)
Axosecretory (axon to bloodstream)

General synapse properties

on dendrites
- usually excitatory
on cell bodies
- usually inhibitory
on axons
- usually modulatory (change p(fire))

Main points

Neurons use electrical communication (action potentials) to communicate quickly over long distances
Chemical communication (diffusion) to communicate over short distances
Neurotransmitters are special chemicals that neurons release onto other neurons
Ionotropic and metabotropic receptors generate EPSPs and IPSPs
Amino acid neurotransmitters: glutamate, GABA

Resources

About

This talk was produced using Quarto, using the RStudio Integrated Development Environment (IDE), version 2025.5.1.513.

The source files are in R and R Markdown, then rendered to HTML using the revealJS framework. The HTML slides are hosted in a GitHub repo and served by GitHub pages: https://psu-psychology.github.io/psych-260-2025-fall/

References

Anderson, C. M., & Swanson, R. A. (2000). Astrocyte glutamate transport: Review of properties, regulation, and physiological functions. Glia, 32(1), 1–14. https://doi.org/10.1002/1098-1136(200010)32:1<1::AID-GLIA10>3.0.CO;2-W

Hastoy, B., Clark, A., Rorsman, P., & Lang, J. (2017). Fusion pore in exocytosis: More than an exit gate? A \(\beta\)-cell perspective. Cell Calcium, 68, 45–61. https://doi.org/10.1016/j.ceca.2017.10.005

Haucke, V., Neher, E., & Sigrist, S. J. (2011). Protein scaffolds in the coupling of synaptic exocytosis and endocytosis. Nature Reviews. Neuroscience, 12(3), 127–138. https://doi.org/10.1038/nrn2948

LadyGagaVEVO. (2021). Tony bennett, lady gaga - I get a kick out of you (official music video). Youtube. Retrieved from https://www.youtube.com/watch?v=iTdHQ065A_o&list=RDiTdHQ065A_o&start_radio=1

Neuron, N. (2021). Propagation of action potential. Youtube. Retrieved from https://www.youtube.com/watch?v=tOTYO5WrXFU

Sterling, P., & Laughlin, S. (2021). Principles of neural design. The MIT Press, Massachusetts Institute of Technology. Retrieved from https://mitpress.mit.edu/books/principles-neural-design

Neurochemistry

Prelude

Today’s topics

Comment on Quiz 1

9. Electroencephalography (EEG) has ___ temporal resolution than functional MRI, but ___ spatial resolution.

9. Electroencephalography (EEG) has ___ temporal resolution than functional MRI, but ___ spatial resolution.

Back story

Behavior requires communication

Types of communication for behavior

What do animals need to know to behave?

Nervous systems are communication systems

Nervous systems are communication systems

Synaptic communication

Steps in synaptic transmission

Steps in synaptic transmission

Action potential propagates from soma

Action potential propagates from soma

Action potential arrives at synaptic terminal

Action potential arrives at synaptic terminal

NTs cross the synaptic clef

Synaptic vesicles get “recycled”

Postsynaptic receptor types

Postsynaptic receptor types

Postsynaptic receptor types

Receptors cause response

Two types of postsynaptic potentials (PSPs)

Two types of postsynaptic potentials (PSPs)

Message from dendrites & soma

What sort of PSP would opening a Na+ channel produce?

What sort of PSP would opening a Na+ channel produce?

What sort of PSP would opening a Cl- channel produce?

What sort of PSP would opening a Cl- channel produce?

NT inactivated by multiple mechanisms

NT inactivated by multiple mechanisms

Why must NTs be inactivated?

Types of synapses

General synapse properties

Main points

Resources

About

References

9. Electroencephalography (EEG) has _ temporal resolution than functional MRI, but _ spatial resolution.

9. Electroencephalography (EEG) has _ temporal resolution than functional MRI, but _ spatial resolution.