Electrophysiology and EEG Basics

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Questions and Answers

How do inhibitory post-synaptic potentials (IPSPs) affect the neuron?

They prevent sodium influx

They result in hyperpolarization (correct)

They allow potassium to enter the cell

They result in depolarization

What is the net result of excitatory post-synaptic potentials (EPSPs)?

No change in membrane potential

Increase in negative extracellular charge

Hyperpolarization of the neuron

Depolarization of the neuron (correct)

What is a dipole in the context of pyramidal neurons?

A structure with a positive end and a negative end (correct)

A neuron with an equal positive and negative charge

A construct with charges remaining neutral

A neuron lacking any charge separation

What occurs during the binding of excitatory neurotransmitters to their receptors?

Sodium and calcium ions enter the cell Signup and view all the answers

Which ions are involved in the mechanism responsible for hyperpolarization in neurons?

Chloride ions and potassium ions Signup and view all the answers

What does EEG stand for?

Electroencephalography Signup and view all the answers

Which part of the neuron primarily generates EEG signals?

Dendritic membrane of pyramidal neurons Signup and view all the answers

What type of signals are reflected in an EEG reading?

Extracellular currents from dendrites Signup and view all the answers

What is the physiological basis for EEG generation at the cellular level?

Transmembrane ion currents in pyramidal neurons Signup and view all the answers

Which cortical layers primarily contribute to EEG signal generation?

Layers IV-V Signup and view all the answers

What do the black ellipsoids in EEG schematics represent?

Volume conduction of return currents Signup and view all the answers

Which component is primarily involved in the recording of EEG signals from the scalp?

Conductive paste in cup electrodes Signup and view all the answers

What does the schematic representation in EEG analysis illustrate?

Local field potentials in the cortical generator Signup and view all the answers

What is the orientation of the dipoles generating interictal epileptiform discharges?

Negative pole closer to the superficial cortical layers and positive pole closer to the deeper layers Signup and view all the answers

What primarily affects the specific orientation of dipoles in epileptiform discharges?

The types of synapses along the apical dendrites at cortical connections Signup and view all the answers

How does the position and orientation of the cortical area generating the EEG signal affect the scalp topography?

It dictates the distribution of negative and positive potentials on the scalp Signup and view all the answers

What do voltage maps or amplitude-based maps visualize in relation to scalp topography?

The potential distribution resulting from cortical electrical activity Signup and view all the answers

Which orientation is illustrated in the schematic drawing regarding current flow generated by cortical sources?

Radial orientation indicates current flow directed outward from the cortical surface Signup and view all the answers

What is the process called when current flows between the electrical generator and the recording electrode through tissues?

Volume conduction Signup and view all the answers

How does the orientation of a dipole affect the measured voltage in volume conduction?

It affects the measured voltage based on resistance. Signup and view all the answers

What is essential for creating a reliably recorded scalp potential in EEG analysis?

At least 6 cm2 of cortex with synchronous activity Signup and view all the answers

Which neurotransmitter is primarily released by excitatory neurons to generate an EPSP?

Glutamate Signup and view all the answers

What receptor type is activated by glutamate in the EPSP process?

Non-NMDA (Q or quisqualate) receptor Signup and view all the answers

What is the role of GABAergic interneurons in the EPSP-IPSP sequence?

They synapse back to the excitatory neuron with IPSP. Signup and view all the answers

What occurs immediately after the generation of an EPSP in the excitatory neuron?

Action potential is triggered in the postsynaptic neuron. Signup and view all the answers

Which of the following describes the electric fields surrounding a neuron?

They decrease in potential the farther they are from the neuron. Signup and view all the answers

What neurotransmitter is released by the excitatory neuron to produce an EPSP?

Glutamate Signup and view all the answers

What is the primary function of the GABAergic interneuron in the EPSP-IPSP sequence?

To inhibit the excitatory neuron with IPSPs Signup and view all the answers

What occurs when EPSPs summate sufficiently in neurons?

Action potentials are generated Signup and view all the answers

What characterizes the Paroxysmal Depolarizing Shift (PDS)?

A large amplitude and long duration depolarization Signup and view all the answers

What role do calcium-dependent K+ channels play during the PDS?

They assist in hyperpolarization after the paroxysm Signup and view all the answers

What happens during tonic-clonic seizures regarding neuronal activity?

Persistent depolarization occurs without resulting hyperpolarization Signup and view all the answers

Which receptor is associated with the generation of EPSPs?

AMPA receptor Signup and view all the answers

What limits the duration and extent of the paroxysm during a PDS?

GABAergic interneuron feedback and calcium-dependent K+ channels Signup and view all the answers

Study Notes

Electrophysiology of Neurons and EEG

Electroencephalography (EEG) represents voltage differences between cerebral locations over time.
EEG signals mainly originate from excitatory and inhibitory post-synaptic currents in pyramidal neurons found in cortical layers IV-V.
Pyramidal neurons act as dipoles, having a positive and negative pole, with extracellular currents contributing to the EEG generation.

Action Potentials

Action potentials are initiated by excitatory neurotransmitter binding leading to excitatory post-synaptic potentials (EPSPs) or inhibitory post-synaptic potentials (IPSPs).
EPSPs allow sodium and calcium influx, leading to neuron depolarization.
IPSPs permit chloride entry or potassium exit, causing hyperpolarization of the neuron.

Summation and Dipole Concept

EPSPs and IPSPs summate to determine the membrane potential and can convert neurons into dipoles.
The apical dendrite represents one end of the dipole, while the soma and basal dendrites represent the other end.

Volume Conduction

Volume conduction entails the transfer of currents from the neuronal source to the recording electrodes on the scalp.
The measured voltage is influenced by the orientation of the dipoles and the tissue's resistance.

Electric Fields

Electric fields around neurons create concentric ellipses, with potential decreasing further from the neuron.
The currents' flow direction influences the shape and orientation of the electric fields.

Basis for EEG Recording

Electrodes on the scalp capture the electrical activity from at least a 6 cm² area of synchronized cortical activity for reliable recording.
Sparse areas can be recorded if they exhibit high intensity and synchronization (e.g., epileptiform spikes).

EPSP-IPSP Circuits

An excitatory neuron releases glutamate, activating EPSP in a post-synaptic neuron, which can lead to an action potential.
This excitatory neuron also stimulates GABAergic interneurons that provide inhibitory feedback through IPSPs.

Paroxysmal Depolarizing Shift (PDS)

EPSPs can summate to cause a PDS, which results in prolonged depolarization and stimulation of action potentials.
Calcium influx opens voltage-dependent sodium channels, resulting in repetitive action potentials followed by hyperpolarization via GABAergic interneurons.

Interictal Discharges and PDS

Interictal discharges are linked to the PDS and characterized by high amplitude and duration, generating subsequent action potentials and followed by after-hyperpolarization.

Scalp Topography and Orientation of Epileptic Discharge

The orientation of dipoles generating interictal epileptiform discharges influences the distribution of negative and positive potentials on the scalp.
Excitatory synapses are located farther from the cell body, while inhibitory synapses are closer, affecting the scalp's voltage mapping.

Effect of Cortical Current Orientation

Current flow orientation (radial vs. tangential) from cortical sources determines the scalp topography.
Voltage maps can visualize how these orientations affect the distribution of electrical potentials across the scalp.

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Description

Explore the fundamentals of the electrophysiology of neurons and the principles of electroencephalography (EEG). This quiz covers action potentials, excitatory and inhibitory post-synaptic potentials, and the dipole concept. Test your knowledge on how neurons generate EEG signals and their physiological mechanisms.