A neuron is a specialized cell that transmits nerve impulses, communicates via signals, and forms neural networks.A neuron is an electrically excitable cell, the basis of the nervous system. The neuron's membrane uses ion channels to create a potential difference (resting potential around -70 mV). Upon excitation, sodium channels open, sodium ions enter, and the potential becomes positive—this is the action potential. It propagates along the axon at speeds up to 120 m/s. At synapses, the electrical signal is converted into chemical: neurotransmitters (e.g., glutamate) are released and bind to receptors of the next neuron, continuing the relay.
In 1873, Camillo Golgi developed a method for staining nervous tissue with silver nitrate (the Golgi stain), which made it possible to see neurons in their entirety. Santiago Ramón y Cajal, using this method in the 1880s, detailed the histology of the nervous system and formulated the neuron doctrine—the idea that the nervous system is composed of discrete cells. Their opposition to the reticular theory ended in the 20th century with the invention of the electron microscope, which confirmed the synaptic cleft. In 1952, Alan Hodgkin and Andrew Huxley created a mathematical model of the action potential in the giant squid axon, laying the foundations of computational neuroscience.
The functioning of a neuron is determined by the laws of electrochemistry. The membrane separates ions: more Na⁺ outside, more K⁺ inside. The sodium-potassium ATPase (Na⁺/K⁺ pump) actively transports 3 Na⁺ out and 2 K⁺ in, creating ion gradients. The resting potential is close to the potassium equilibrium potential, described by the Nernst equation: E_K = (RT/F) ln([K⁺]out/[K⁺]in). Upon stimulation, voltage-gated sodium channels open, Na⁺ enters, depolarizing the membrane; when the potential reaches a threshold (~-55 mV), more sodium channels open—a positive feedback loop generates the spike. Then sodium channels inactivate, potassium channels open, expelling K⁺ and returning the potential to rest. The refractory period ensures unidirectional impulse propagation. At synapses, the action potential activates calcium channels, Ca²⁺ enters, causing vesicle fusion with the membrane and release of the neurotransmitter. The neurotransmitter diffuses to receptors; excitatory neurotransmitters (glutamate) open sodium channels, inhibitory ones (GABA) open chloride or potassium channels, shifting the potential closer to the equilibrium. Synaptic plasticity (long-term potentiation) underlies memory.
Artificial neural networks, inspired by the work of neurons, recognize faces, translate texts, and drive cars. Understanding neurons has allowed treating epilepsy and Parkinson's disease through brain stimulation.
The conduction speed along some axons exceeds 400 km/h. And the total number of synapses in the brain is estimated at a quadrillion (10^15).













