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”

Wikipedia

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)

Hastoy, Clark, Rorsman, & Lang (2017)

Wikipedia

NTs cross the synaptic clef

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

Wikipedia

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

http://pittmedneuro.com/synaptic.html

Two types of postsynaptic potentials (PSPs)

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

http://pittmedneuro.com/synaptic.html

Two types of postsynaptic potentials (PSPs)

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

http://pittmedneuro.com/synaptic.html

Message from dendrites & soma

  • a mixture of IPSPs and EPSP

Wikipedia

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
  • 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)

Wikipedia

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