Synaptic Integration and Plasticity: L11-12

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Questions and Answers

What effect do AMPA receptors have on the postsynaptic membrane potential when activated?

They depolarize the cell towards a more positive value (correct)

They hyperpolarize the cell towards -50mV

They have no significant effect on the membrane potential

They maintain the membrane potential at -70mV

Which type of ion channels are selectively activated by glutamate?

Chloride channels

Cation channels (correct)

Anion channels

Potassium channels

What is the role of the driving force in determining the current carried by an ion?

It has no impact on the overall current

It only affects anions, not cations

It is inversely related to the ion's conductance

It is calculated by the difference between membrane potential and equilibrium potential (correct)

During synaptic integration, what do neurons primarily do with multiple synaptic inputs?

Summate the inputs to generate a unified response Signup and view all the answers

What happens to the membrane potential during the opening of GABAA receptors?

It hyperpolarizes, moving it towards a more negative value Signup and view all the answers

What does the capacitance of a biological membrane represent?

The ability to store electric charge Signup and view all the answers

Which ion has a physiological charge of +2?

Ca2+ Signup and view all the answers

How does conductance (G) relate to voltage (V) and current (I)?

I = V / G Signup and view all the answers

In terms of resistance, how would you characterize new neurons compared to old neurons?

New neurons have high resistance and low capacitance. Signup and view all the answers

Which of the following statements about synaptic receptors is correct?

The conductance of AMPA receptors is around 10 pS. Signup and view all the answers

What is referred to as passive propagation of signals in neurons?

Cable properties Signup and view all the answers

Which method is distinct for measuring voltage in a neuron?

Current clamp Signup and view all the answers

What plays a crucial role in determining the active properties of neurons?

Ion channels expressed Signup and view all the answers

What is the primary purpose of the voltage clamp technique?

To dissect currents contributing to activity Signup and view all the answers

Which type of seal is created in the patch clamp method?

Gigaohm seal Signup and view all the answers

What does the Y-axis represent when measuring current using a voltage clamp?

Current in pA Signup and view all the answers

Which of the following statements is NOT true regarding postsynaptic receptors?

They are always ion channels. Signup and view all the answers

Which mode in an amplifier is used to record voltage in the context of patch clamp?

Bridge mode Signup and view all the answers

Which ion channel blocker specifically isolates K+ currents?

TEA Signup and view all the answers

What is the primary function of TTX in neuronal studies?

To isolate Na+ currents Signup and view all the answers

What discovery awarded the Nobel Prize in Physiology or Medicine in 1963?

The ionic mechanisms in nerve cell membranes Signup and view all the answers

Which technique is used to determine the ionic basis of the action potential?

Voltage clamp Signup and view all the answers

Which type of potassium channel is associated with delayed rectifier currents?

Kv1 Signup and view all the answers

What characteristics are used to differentiate neuronal subtypes?

Specific gene expression patterns Signup and view all the answers

Which of the following correctly describes the passive properties of neurons?

Capacitor and resistor in parallel Signup and view all the answers

The seminal paper on membrane current was published in which journal?

Journal of Physiology Signup and view all the answers

What role does calcium flux through NMDARs play in synaptic plasticity?

It initiates a series of events resulting in more AMPA receptors at the synaptic membrane. Signup and view all the answers

Which protein is mentioned as an important component of signal transduction pathways downstream of calcium signaling?

Ras Signup and view all the answers

What is the effect of back-propagating action potential activated calcium (BAC) spike firing in cortical neurons?

It enhances the integrative properties and allows for coincidence integration and plasticity. Signup and view all the answers

What primarily differentiates GABAA receptors in neurons?

They selectively allow chloride (Cl-) ions. Signup and view all the answers

During early neuronal development, why are chloride concentrations higher inside neurons?

KCC2 symporter expression has not yet increased. Signup and view all the answers

What is one consequence of synaptic plasticity in neurons?

Increased spine growth and structural remodeling. Signup and view all the answers

Which of the following best describes sequential activation of AMPA and NMDA receptors?

It leads to synaptic plasticity. Signup and view all the answers

The integration of most sensory signals and mediation of cognitive processes primarily occurs in which part of the brain?

Cerebral cortex Signup and view all the answers

What is the relationship defined by the equation R = V/I?

Resistance is equal to voltage divided by current Signup and view all the answers

What does the time constant (τ) describe in the context of membrane properties?

The rate at which voltage across a membrane changes Signup and view all the answers

How does the length constant (λ) affect electrical signals within a neuron?

It determines how far a voltage change can effectively travel Signup and view all the answers

Which of the following accurately describes the characteristics of new neurons in the dentate gyrus?

They have high input resistance and low capacitance Signup and view all the answers

What role does a voltage clamp play in neuronal studies?

It injects a specific current to maintain a desired membrane potential Signup and view all the answers

Which statement about passive properties in neurons is true?

Passive properties include resistance and capacitance in neurons Signup and view all the answers

What is the primary effect of membrane capacitance on current injection?

It leads to a temporal delay in the voltage response to current Signup and view all the answers

Why is the input resistance important in studying neural properties?

It affects the voltage change that results from current injection Signup and view all the answers

Study Notes

Synaptic Integration and Synaptic Plasticity Lectures

Synaptic integration and synaptic plasticity are the focus of the lectures.
Methods for recording neuronal activity include extracellular and intracellular recordings.
Methods for recording neuronal activity:
- Voltage recording or Current clamp
- Current recording or Voltage clamp
- Action potential: a rapid change in voltage measured in mV and ms.
- Local field potential: Measures the sum activity of the neurons in the region around the electrode measured in µV
- Electroencephalography (EEG): Non-invasive recording of electrical activity in the brain measured in V.
Electrophysiological equipment was shown in images.
Neurons transmit electrical impulses facilitating sensory perception, motor control, and information processing.
Neurons in different species were shown: mouse, frog, squid axon, and rat.
Learning outcomes:
- Lecture 1: Describe passive and active electrical properties of neurons, compare and evaluate methods for measuring voltage and current changes in neurons, and describe postsynaptic responses mechanisms.
- Lecture 2: Explain how neurons integrate excitatory and inhibitory inputs, and explain synaptic plasticity and its mechanisms.

Passive and Active Electrical Properties of Neurons

Neurons have both passive and active electrical properties.
Passive responses are gradual changes in voltage that are dependent on the circuit components (capacitance and resistance).
Active responses are rapid changes in voltage that are dependent on ion channels.
Passive Electrical properties of cells: Can be mimicked by resistors and capacitors.
Ohm's law: V = IR, R = V/I.
Time constants (τ): The time it takes a membrane potential change to reach ~63%
Length constants (λ): The distance a signal travels before decreasing to ~37% of its original strength.

Neurons have both passive and active electrical properties

Time constant (τ): The time it takes for a membrane potential change to reach 63% of its final value.
Length constant (λ): The distance a signal travels before decreasing to 37% of its original strength.

Passive Membrane Properties

The voltage-effect of a membrane current takes time due to membrane capacitance.
The voltage-effect of a membrane current decreases with distance from the injection site (length constant).
The voltage change as a response to current injection depends on the cell's resistance (input resistance).

How do these properties impact actual neuronal function?

Example 1: Dentate gyrus: old vs new neurons: The properties of the neurons affect how well new neurons function compared to older neurons, and how quickly they can communicate with one another.
New neurons are smaller and have a higher input resistance and lower capacitance, while older neurons are larger, have a low input resistance, and high capacitance.

Active Membrane Properties

Multiple types of potassium channels exist with various properties.
The presence of certain ion channels determines a neuron's characteristics.

Approach to Studying Single Neurons

Electrical profile: Whole-cell patch-clamp for studying electrical properties.
Morphological profile: 3D reconstruction for visualizing shapes and connections.
Molecular profile: Multiplex PCR for analyzing gene expression provides information about the neuron's identity and function.

Propagation of Signals

Passive propagation: Also known as cable properties or electrotonic propagation of signals, the signal weakens with distance (as in a cable).
Cable properties: The way signals propagate passively down a cylindrical structure like an axon.
Electrotonic propagation: The way a signal propagates down an axon, which is determined by the cell's capacitance and resistance.

Neuron Anatomy

Neurons are comprised of Dendrites, Soma, and Axon.

Temporal and Spatial Summation

Action potentials can propagate back into dendritic arbors, boosting integrative abilities and enabling coincidence detection.

Many Neurotransmitter Receptors are Ion Channels

AMPA and NMDA receptors are ion channels activated by neurotransmitters.
AMPA receptors: Primarily permeable to sodium ions, leading to depolarization.
NMDA receptors: Permeable to calcium ions in addition to sodium ions, critical for coincidence detection.

Ion current plotting convention

Entry of positive current into the cell depolarizes the cell.
Exit of negative current from the cell depolarizes the cell.

Recall the concept of equilibrium potential to discuss how ligand-gated ion channels encode postsynaptic electric signals.

Equilibrium potential: The potential at which the flow of ions across a membrane is 0.
Permeability: Dictated by the ion channel molecules determining how easily specific ions pass through.
Concentration:Similar concentration of cations inside/outside the cell.
Reversal Potential: The potential at which the current flow through the cation channel is 0.

Reversal potential

The reversal potential determines whether an ion channel depolarizes or hyperpolarizes a cell.

Patch clamp methods

Methods to isolate a small portion of a neuron's membrane for studying ion channels.
Clean glass, air pressure, membrane.

Voltage clamp

A technique for controlling the membrane potential of a cell and measuring the resulting currents.

Ion channel plotting convention & Ion current convention.

Understanding how the entry and exit of ions affect the membrane potential and the cell's overall response to stimuli.

NMDAR act as coincidence detectors

NMDA receptors only open when both glutamate is released and the postsynaptic neuron is depolarized.

Mg²⁺ block makes NMDA receptors voltage-dependent.

The magnesium block in NMDA receptors modulates their activity, making it voltage-dependent.
Determining voltage dependency for different Mg²⁺ concentrations.

Repetitive activation of AMPA and NMDA receptors results in synaptic plasticity

Repetitive activation leads to changes in the number of AMPA receptors influencing synaptic strength.

Synaptic plasticity

Repetitive activation may lead to growth of dendritic spines affecting synaptic strength.

Cortical integration

The cerebral cortex integrates sensory information and mediates cognitive functions including conscious experience.

Signal integration in cortical neurons

Back-propagating action potentials activate Ca²+ spikes, enabling coincidence detection across different cortical layers.

GABA Receptors are Selective for CI-

GABA receptors are selective for chloride and their actions depend on the distribution of chloride ions.

Additional slides provided for your own study

The study of synaptic integration and plasticity includes data analysis of membrane potentials, neuron characteristics, structural changes, and functional effects.
The Nernst equation and other equations were included in the study notes.
More details on specific ionic channels were included in later slides.
Several methods were shown for studying neurons and their interactions.
Methods like whole-cell or outside/inside-out patch clamping were shown.
Data from recordings of different types of cells was also supplied for review.

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Description

This quiz explores key concepts related to synaptic mechanisms, including the effects of AMPA and GABAA receptors, ion channels activated by glutamate, and the role of various ionic currents in neuronal function. Test your understanding of synaptic integration and the physiological properties of neurons.