Neurons, also known as nerve cells, are the body's "controlling" cells. They perform many of the more complex functions in humans and animals including thought, memory, control of bodily functions (both conscious and unconscious), processing of sensory information, voluntary and involuntary movement and transmission of nerve signals both to and from all parts of body.
The interactions between neurons are not only too complex to describe in a few simple sentences but also in a whole library of medical textbooks. Depending on your philosophical and theological persuasion, neurons are either the location of intelligence or the interface between the physical brain and the soul or spirit. Either way, it is generally understood that neurons are the most important cells in the nervous system and that, despite the complexity of what neurons as a whole produce, individually they are better understood.
All neurons have a cell body or soma with a central neucleus that contains most of the DNA. The Soma performs all the basic cellular processes like protein synthesis and energy production. Additionally, neurons have two types of extensions known as dendrites and axons.
The dendrites are thin, branched extensions that communicate to other neurons via a connection called the synapse. The synapse works by sending special chemical signals, called neurotransmitters, across a gap between the neurons known as the synaptic cleft. Dendrites carry signals towards the soma.
Axons are long, sometimes very long, extensions that carry nerve transmissions along the length of the neuron and away from the soma. The nerve transmission is an electrochemical signal that consists of a depolarising current, called an action potential.
Axons are sheathed in a smooth, fatty protein called myelin which assists in nerve transmission and insulates the axons. Normal myelin does not form a continuous sheath along the entire length of an axon but is broken in regular intervals by junctions that are called the nodes of Ranvier.
Neurons vary a great deal both in size and construction depending on their location. Some neurons are the longest cells in the human body whereas others are very small indeed. As regards multiple sclerosis, it is the neurons of the central nervous system (CNS) that are of interest. Specifically, MS is a disease where the myelin sheaths of the CNS white matter become damaged (demyelination) leading to reduced efficacy of nerve transmission along the axons.
Most of the neurons in the human body are laid down before adulthood although there is now evidence that some neurons do grow in adulthood, specifically in the hippocampus region of the brain.
Neuroscience for Kids - Neurons
Neuroscience for Kids - Action Potential
Basic Neuron Physiology