Membrane potential

2a2 Membrane potential

Organized Notes on Neuroanatomy and Neuronal Communication

Overview

  • Discussed brain regions' functions related to mood, movement, and processes.

  • Neurons communicate via electrical activity.

Key Concepts

1. Neuronal Communication

  • Nerve Conduction: Electrical process within neurons.

  • Neurotransmission: Chemical communication between neurons via neurotransmitters.

2. Electrical Properties of Neurons

  • Action Potential: Generated by the flow of charged ions across the neuron's membrane.

  • Resting Membrane Potential: Typically -60 to -80 mV when inactive.

3. Ion Concentrations

  • Outside Cell: High sodium (Na⁺) and chloride (Cl⁻).

  • Inside Cell: High potassium (K⁺) and negatively charged proteins.

4. Ion Channels

  • Potassium Channels: Typically open, allowing K⁺ to leak out.

  • Sodium Channels: Usually closed at rest, preventing Na⁺ influx.

5. Sodium-Potassium Pump

  • Pumps 3 Na⁺ out and 2 K⁺ in, contributing to negative interior charge.

6. Forces Acting on Ions

  • Chemical Force: Tendency to diffuse from high to low concentration.

  • Electrostatic Force: Attraction of positive ions to negative charges.

Measurement Techniques

  • Voltmeter: Measures voltage differences between two locations.

  • Intracellular Patch Clamp Recording: Measures voltage inside a neuron.

Energy Consumption

  • Maintaining resting potential requires significant energy, impacting caloric needs.

Conclusion

Understanding these processes is crucial for grasping how neurons communicate and function within the nervous system.

2a3 equilibrium potential

Organized Notes on Ion Driving Forces and Equilibrium Potentials

Key Concepts

  • Driving Force: Sum of electrical and chemical forces acting on an ion.

  • Electrical Force: Determined by membrane potential; opposite charges attract.

  • Chemical Force: Driven by concentration gradients; ions move from high to low concentration.

Ion Behavior

Potassium (K⁺)

  • Inside Cell: Higher concentration; negative membrane potential.

  • Forces:

    • Electrical: Inward (attracted to negative inside).

    • Chemical: Outward (concentration gradient).

  • Result: Forces oppose; potassium remains inside despite leak channels.

Sodium (Na⁺)

  • Outside Cell: Higher concentration; negative membrane potential.

  • Forces:

    • Electrical: Inward (attracted to negative inside).

    • Chemical: Inward (more Na⁺ outside).

  • Result: Both forces direct inward, but low permeability prevents influx.

Electro-Chemical Equilibrium

  • Condition: Driving force = 0 (forces cancel).

  • Equilibrium Potential (E): Membrane voltage where driving force is zero.

    • Potassium (Eₖ): -80 mV

    • Sodium (Eₙₐ): +60 mV

Resting Membrane Potential

  • Closer to Eₖ due to higher permeability of K⁺ compared to Na⁺.

  • Influenced by relative permeabilities and equilibrium potentials.

Nernst Equation

  • Used to calculate equilibrium potentials based on ion concentrations and charge.

  • Not required to memorize for this course.

Summary

  • Equilibrium potentials dictate ion movement across membranes.

  • Driving forces depend on both electrical and chemical gradients, influenced by permeability.

2a4 Spacial and Temporal Summation

Notes on Ion Channels and Neuron Function

Types of Ion Channels

  1. Leak Channels

    • Always open (ungated).

    • Allow continuous ion flow.

  2. Ligand-Gated Channels

    • Open/close in response to specific molecules (e.g., neurotransmitters).

    • Example: Glutamate receptor opens for sodium when glutamate binds.

  3. Voltage-Gated Channels

    • Open at specific membrane voltage ranges.

    • Crucial for action potential generation.

  4. Mechanically-Gated Channels

    • Open due to mechanical pressure or deformation.

    • Important for touch sensation.

  5. Optical-Gated Channels

    • Open/close in response to light.

    • Found in photoreceptor neurons.

Neuron Structure

  • Dendrites: Receive input from other neurons via neurotransmitters.

  • Axon: Conducts action potentials to axon terminals.

Synaptic Transmission

  • Excitatory Synapses: Release glutamate, causing depolarization (EPSP).

  • Inhibitory Synapses: Release GABA, causing hyperpolarization (IPSP).

Summation Mechanisms

  1. Spatial Summation: Multiple nearby excitations combine.

  2. Temporal Summation: Rapid successive excitations combine.

Action Potential Generation

  • Requires sufficient depolarization at the axon hillock.

  • Integrates excitatory and inhibitory signals from dendrites.

Key Terms

  • EPSP: Excitatory postsynaptic potential.

  • IPSP: Inhibitory postsynaptic potential.