Neuron

electrically excitable cell
(Redirected from Nerve cells)
Diagram of neuron

A neuron (or neurone) is a nerve cell that carries electrical impulses.[1] Neurons are the basic units of our nervous system.

Neurons have a cell body (soma or cyton), dendrites and an axon.[1] Dendrites and axons are nerve fibers. There are about 86 billion neurons in the human brain, which is about 10% of all brain cells. The human brain has about 16 billion neurons in the cerebral cortex. The neurons are supported by glial cells and astrocytes.

Neurons are connected to one another, but they do not actually touch each other. Instead they have tiny gaps called synapses. These gaps are chemical synapses or electrical synapses which pass the signal from one neuron to the next.

Types of neuronsEdit

By connectionEdit

There are three classes of neurons: motor neurons, sensory neurons and interneurons.

By functionEdit

  • Sensory neurons carry signals from sense organs to the spinal cord and brain.
  • Relay neurons carry messages between sensory or motor neurons and the central nervous system
  • Motor neurons carry signals from the CNS to muscles, motor neurons are connected to the relay neurons. The signal passes between the neurons via synapses. Synapses are microscopic voids between cells where chemicals are released from the axon terminal of one cell to specialized chemical receptors on the dendrite of the receiving cell.

Cell divisionEdit

Mature neurons never divide: that is the general rule. They do not undergo cell division. In most cases, neurons are generated by special types of stem cells. A type of glial cell, called astrocytes, have also been seen to turn into neurons. In humans, neurogenesis (the origin of new nerve cells) largely ceases during adulthood – but in two brain areas, the hippocampus and the olfactory bulb, there is strong evidence for substantial numbers of new neurons.[2][3]

The largest part of the human brain by far is the neocortex. It has at least~1010 neurons[4] which stay with us from cradle to grave.[3]

ReferencesEdit

  1. 1.0 1.1 Fullick, Ann. Edexcel ICSE Biology Revisions Guide1. p. 40. ISBN 9780435046767.
  2. Wade, Nicholas (1999-10-15). "Brain may grown new cells daily". The New York Times.
  3. 3.0 3.1 Nowakowski, R.S. (2006). "Stable neuron numbers from cradle to grave". Proceedings of the National Academy of Science. 103 (33): 12219. doi:10.1073/pnas.0605605103.
  4. Blinkov S.M. & Glezer I.I. 1968. The human brain in figures and tables: a quantitative handbook. New York, Plenum.

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