Introduction to neuron electrophysiology

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Neurons are the body's electrical powerhouses, capable of generating and transmitting signals through the movement of ions across their cell membranes. Most cells, including neurons, use charged particles, known as ions, to create electrical charges across their cell membranes, which influence ion movement between the extracellular and intracellular environments. The neuron's cell membrane, made up of a phospholipid bilayer, is selectively permeable to these ions, allowing them to move via specific ion channels that open or close in response to various stimuli.

Although the ion concentrations in these fluids are generally balanced, resulting in a net neutral charge, there is a slight difference in charge right at the cell membrane surface—negative inside and positive outside—due to the uneven distribution of ions. This difference in charge creates an electrical gradient, or electrical potential, across the membrane, known as the membrane potential.

When a neuron is at rest, this membrane potential is called the resting membrane potential, typically around -70 mV, which is crucial for the neuron's ability to transmit electrical signals. This potential arises from the concentration differences and electrochemical gradients of ions like sodium (Na⁺), potassium (K⁺), and chloride (Cl⁻) across the membrane.

Neurons maintain these gradients through active transport mechanisms, such as the sodium-potassium pump, which moves Na⁺ out and K⁺ into the cell, as well as different types of ion channels, including leakage, ligand-gated, voltage-gated, and mechanically-gated channels, that regulate ion flow.

Watch the following video to learn how the resting membrane potential is established, maintained, and altered by various ion channels and active transport mechanisms.

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Cell membrane structure and properties

The cell membrane, or plasma membrane, is a dynamic structure essential for neurophysiology. Composed primarily of a phospholipid bilayer, it serves as a selective barrier, maintaining the internal environment of neurons while allowing communication with the extracellular space. Its fluidity enables flexibility and the rapid rearrangement of molecules, while its selective permeability ensures precise control over cellular signaling and homeostasis in the nervous system.

Ion channels

Ion channels are specialized proteins embedded in the cell membrane that play a crucial role in neurophysiology. By controlling the flow of ions such as sodium (Na⁺), potassium (K⁺), calcium (Ca²⁺), and chloride (Cl^-), ion channels help establish and modulate the electrical activity of neurons. They are essential for generating action potentials, transmitting signals across synapses, and maintaining the resting membrane potential.

Membrane potential

Membrane potential is the electrical difference across the neuron's cell membrane. It arises due to the uneven distribution of ions, primarily sodium (Na⁺), potassium (K⁺), and chloride (Cl^-), between the intracellular and extracellular spaces. The resting membrane potential, typically around -70 mV, is maintained by ion pumps and channels, with the sodium-potassium pump being particularly important. 

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Take the following quiz to test what you already know about membrane potentials in neurons, the ion movements and the different types of ion channels. 

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