Neurons

Neurons are specialized cells of the nervous system responsible for receiving, processing, and transmitting information through electrical and chemical signals. They communicate with other neurons, muscles, and glands at synapses, forming complex networks that underlie perception, movement, and cognition.

A neuron typically consists of a soma (cell body) containing the nucleus, dendrites that receive inputs, and a long axon that conducts impulses to distant targets. The axon ends in synaptic terminals, which release neurotransmitters into the synapse. Most neurons are insulated by myelin sheaths, produced by glial cells, which speed signal transmission.

Neuronal signaling starts with the resting membrane potential, usually around -70 millivolts. Upon sufficient stimulation, voltage-gated ion channels open, generating an action potential that propagates along the axon. Sodium inflow depolarizes, followed by potassium efflux repolarization. In myelinated fibers, impulses jump between nodes of Ranvier.

At synapses, electrical signals are converted to chemical signals. The presynaptic terminal releases neurotransmitters into the synaptic cleft, which bind to receptors on the postsynaptic neuron, producing excitatory or inhibitory postsynaptic potentials. These inputs integrate to influence whether the neuron fires.

Neurons vary in structure and function. Common functional classes include sensory (afferent) neurons that convey information from sensors, motor (efferent) neurons that control muscles, and interneurons that connect within the central nervous system. Morphologically, neurons are often multipolar, with several dendrites and one axon.

Neuron development and plasticity include neurogenesis in some regions, synaptic pruning, and activity-dependent changes that underlie learning and memory, such as long-term potentiation and long-term depression.

Neurons form distributed networks that underpin sensation, perception, and behavior. Disruptions to neuronal signaling contribute to conditions such as neurodegenerative diseases, demyelinating disorders, and epilepsy, highlighting the importance of neuronal health and function.