INTRODUCTION TO THE MEMBRANE POTENTIAL

Neuron Doctrine

States that the neuron is the fundamental structural and functional unit of the central nervous system (CNS) and that neurons are discrete cells that communicate via electrical and chemical transmission.

Dendrites

Branched projections of a neuron that conduct electrochemical stimulation received from other neural cells to the cell body.

Soma

The large, rounded portion of the neuron containing the nucleus, which is important for gene expression and protein synthesis.

Axon

A long thin projection of a neuron that conducts electrical impulses (action potentials) away from the soma to the axon terminal.

Axon terminal

The distal end of the axon that forms the pre-synaptic component of the synapse, specialized for neurotransmitter release.

Myelin sheath

A covering of the axon provided by glia (oligodendrocytes or Schwann cells) that facilitates electrical conduction down the axon.

Membrane potential

The voltage difference across a neuron's plasma membrane, approximately -65 mV in most neurons, resulting from the unequal distribution of electrical charge.

Resting potential

The value of the membrane potential when a neuron is at rest, typically around -65 mV.

Hyperpolarization

Occurs when the membrane potential is more negative than the resting potential.

Depolarization

Occurs when the membrane potential is less negative or more positive than the resting potential.

Ion channels

Pores that span the neuronal membrane and regulate membrane permeability to particular ions.

Equilibrium potential

The membrane potential at which the net current for a particular ion is zero, where diffusion and electrical forces balance each other.

Na⁺/K⁺ ATPase

An active transport mechanism that pumps 3 sodium ions out of the cell and 2 potassium ions into the cell, essential for maintaining ion concentration gradients.

Selective permeability

The property of a neuron's membrane that allows it to be more permeable to K⁺ than to Na⁺ at rest due to potassium leak channels.

Leak channels

Channels that allow certain ions to move across the membrane passively, significantly contributing to the resting potential.

Ion Concentration Gradients

The differences in concentrations of ions (particularly sodium and potassium) inside and outside the neuron which create potential differences.

Membrane

A hydrophobic barrier (lipid bilayer) that encloses the cytoplasm and cellular organelles, containing proteins that allow transport of ions and small molecules.

K⁺ leak channels

Channels that allow K⁺ to exit the cell more easily, contributing to a negative charge inside the neuron.

Sodium channels

Channels that allow only Na⁺ and its associated water of hydration to pass through, contributing to selective ion permeability.

Potassium channels

Channels that strip K⁺ of its water of hydration and allow only K⁺ to pass, preventing Na⁺ from passing through.