Neurone

A neurone is the basic functional unit of the nervous system that transmits information through electrical and chemical signals and forms networks that underlie sensation, movement, and cognition.

A typical neurone consists of a soma, or cell body, containing the nucleus; dendrites that receive signals; an axon that conducts impulses away from the soma; and synaptic terminals that form connections with other neurones. The axon hillock initiates action potentials, and long axons may be insulated by a myelin sheath formed by oligodendrocytes in the central nervous system and Schwann cells in the peripheral nervous system. Gaps between myelin sheaths, called nodes of Ranvier, facilitate rapid conduction.

Electrical signalling begins with a resting membrane potential, usually around -70 millivolts. A sufficient depolarizing stimulus raises the membrane potential to threshold, triggering an action potential that travels along the axon. In myelinated neurones, conduction occurs in a saltatory fashion, with impulses leaping between nodes of Ranvier.

At synapses, the arrival of an action potential at the presynaptic terminal stimulates release of neurotransmitters into the synaptic cleft. These chemicals bind to receptors on the postsynaptic neurone, producing excitatory or inhibitory responses that influence whether the postsynaptic neurone fires an action potential. Most synapses are chemical, though electrical synapses also occur in some circuits.

Neurones come in several functional classes, including sensory (afferent) neurones that convey information from receptors to the central nervous system, motor (efferent) neurones that control muscles and glands, and interneurones that connect neurones within the brain and spinal cord.

Neurones develop from neural progenitors, exhibit plasticity in learning and memory, and can degenerate in disease. Common topics include neurodegenerative disorders, stroke, demyelinating diseases such as multiple sclerosis, and aging-related changes in connectivity and function.