Neuronal excitability

An overview of neuronal excitability, its mechanisms, and significance in neuroscience.

Neuronal excitability refers to the ability of a neuron to respond to stimuli and convert them into nerve impulses. This fundamental property of neurons is crucial for the functioning of the nervous system, enabling communication between neurons and the execution of complex behaviors.

Overview

Neuronal excitability is determined by the electrical properties of the neuron's membrane, which is primarily governed by the distribution and movement of ions across the membrane. The key ions involved are sodium (Na⁺), potassium (K⁺), calcium (Ca²⁺), and chloride (Cl⁻). The movement of these ions is controlled by various ion channels, pumps, and exchangers embedded in the neuronal membrane.

Mechanisms of Neuronal Excitability

Resting Membrane Potential

The resting membrane potential is the electrical potential difference across the neuronal membrane when the neuron is not actively sending a signal. It is typically around -70 mV in neurons, with the inside of the cell being more negative than the outside. This potential is maintained by the sodium-potassium pump and the differential permeability of the membrane to various ions.

Action Potential

An action potential is a rapid, transient change in the membrane potential that travels along the axon of a neuron. It is initiated when the membrane potential reaches a certain threshold, leading to the opening of voltage-gated sodium channels and a subsequent influx of Na⁺ ions. This depolarization is followed by the opening of voltage-gated potassium channels, allowing K⁺ ions to exit the cell and repolarize the membrane.

Ion Channels

Ion channels are crucial for neuronal excitability. They can be classified into several types based on their gating mechanisms:

• Voltage-gated ion channels: These channels open or close in response to changes in membrane potential. Examples include voltage-gated sodium, potassium, and calcium channels.
• Ligand-gated ion channels: These channels open in response to the binding of a chemical messenger, such as a neurotransmitter. Examples include the NMDA receptor and the GABA receptor.
• Mechanically-gated ion channels: These channels open in response to mechanical deformation of the cell membrane.

Synaptic Transmission

Neuronal excitability is also influenced by synaptic inputs from other neurons. Synaptic transmission involves the release of neurotransmitters from the presynaptic neuron, which bind to receptors on the postsynaptic neuron, leading to excitatory or inhibitory postsynaptic potentials.

Significance in Neuroscience

Neuronal excitability is fundamental to all neural processes, including sensory perception, motor control, and cognitive functions. Abnormalities in excitability can lead to neurological disorders such as epilepsy, chronic pain, and neurodegenerative diseases.

Also see

• Neurotransmitter
• Synapse
• Neuroplasticity
• Electrophysiology
• Neural coding