Neuron


Neuron types and their functionality : The nerve cell is the hub for all of the activity that occurs in the brain, and the connections between neurons create a living, dynamic framework for everything that we see, hear, taste, smell, touch and experience.

How do neurons work?

Nerve cells talk to each other via a complex system of electrical impulses and chemical signals. They are supported by another type of cell, called glia, which help these signals to transfer smoothly from one nerve to the next. Their work is so important that glia outnumber neurons in the brain and spinal cord.

Types of Neurons

Neurons fall into one of three types.Sensory neurons are responsible for relaying information from the senses-eyes, ears, nose, tongue and skin-to the brain to register sight, sound, smell, taste and touch.Motor neurons link the brain and spinal cord to the various muscles throughout the body, including those in our fingers and toes.Interneurons are intermediaries that bridge sensory or motor neurons to their neighbors.

A neuron (/ˈnjʊərɒn/ NYEWR-on or /ˈnʊərɒn/ NEWR-on; also known as a neurone or nerve cell) is an electrically excitable cell that processes and transmits information through electrical and chemical signals. These signals between neurons occur via synapses, specialized connections with other cells. Neurons can connect to each other to form neural networks. Neurons are the core components of the nervous system, which includes the brain, spinal cord and the ganglia of the peripheral nervous system (PNS) which comprises the central nervous system (CNS). Specialized types of neurons include: sensory neurons which respond to touch, sound, light and all other stimuli affecting the cells of the sensory organs, that then send signals to the spinal cord and brain; motor neurons that receive signals from the brain and spinal cord, to cause muscle contractions, and affect glandular outputs, and interneurons which connect neurons to other neurons within the same region of the brain or spinal cord, in neural networks.

A typical neuron possesses a cell body (soma), dendrites, and an axon. The term neurite is used to describe either a dendrite or an axon, particularly in its undifferentiated stage. Dendrites are thin structures that arise from the cell body, often extending for hundreds of micrometres and branching multiple times, giving rise to a complex "dendritic tree". An axon is a special cellular extension that arises from the cell body at a site called the axon hillock and travels for a distance, as far as 1 meter in humans or even more in other species. The cell body of a neuron frequently gives rise to multiple dendrites, but never to more than one axon, although the axon may branch hundreds of times before it terminates. At the majority of synapses, signals are sent from the axon of one neuron to a dendrite of another. There are, however, many exceptions to these rules: neurons that lack dendrites, neurons that have no axon, synapses that connect an axon to another axon or a dendrite to another dendrite, etc.

All neurons are electrically excitable, maintaining voltage gradients across their membranes by means of metabolically driven ion pumps, which combine with ion channels embedded in the membrane to generate intracellular-versus-extracellular concentration differences of ions such as sodium, potassium, chloride, and calcium. Changes in the cross-membrane voltage can alter the function of voltage-dependent ion channels. If the voltage changes by a large enough amount, an all-or-none electrochemical pulse called an action potential is generated, which travels rapidly along the cell's axon, and activates synaptic connections with other cells when it arrives.

Neurons do not undergo cell division. In most cases, neurons are generated by special types of stem cells. A type of glial cell, called astrocytes (named for being somewhat star-shaped), have also been observed to turn into neurons by virtue of the stem cell characteristic pluripotency. In humans, neurogenesis largely ceases during adulthood—but in two brain areas, the hippocampus and olfactory bulb, there is strong evidence for generation of substantial numbers of new neurons.


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