Neuron
A neuron[1] (or neurone) is a nerve cell that carries electrical impulses.[2] Neurons are the basic units of our nervous system.
Neurons have a cell body (soma or cyton), dendrites and an axon.[2] Dendrites and axons are nerve fibers. There are about 86 billion neurons in the human brain. Almost all brain cells are neurons. The human brain has about 16 billion neurons in the cerebral cortex. The neurons are supported by glial cells and astrocytes.[1]
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 neurons
By connection
There are three classes of neurons: motor neurons, sensory neurons and inter neurons.
- Sensory neurons carry information from tissues and organs into the central nervous system.
- Motor neurons transport signals from the central nervous system to the effector cells.
- Interneurons connect neurons within the central nervous system.
By function
- 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 division
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.[3][4][4][5][6]
Neuron Media
- Gyrus Dentatus 40x.jpg
Golgi-stained neurons in human hippocampal tissue
- SUM 110913 Cort Neurons 2.5d in vitro 488 Phalloidin no perm 4 cmle-2.png
Actin filaments in a mouse cortical neuron in culture
- GFPneuron.png
Image of pyramidal neurons in mouse cerebral cortex expressing green fluorescent protein. The red staining indicates GABAergic interneurons.
- Structural classification of neurons by polarity hariadhi.svg
Different kinds of neurons
- Neurotransmitters.jpg
Synaptic vesicles containing neurotransmitters
- Chemical synapse schema cropped.jpg
A signal propagating down an axon to the cell body and dendrites of the next cell
A neuromuscular junction (or myoneural junction) is a chemical synapse formed by the contact between a motor neuron and a muscle fiber. It is at the neuromuscular junction that a motor neuron is able to transmit a signal to the muscle fiber, causing muscle contraction.*Labels from top right: myelin sheath, mitochondria,
As long as the stimulus reaches the threshold, the full response will be given. A larger stimulus does not result in a larger response, and vice versa.: Script error: The function "hyphen2dash" does not exist. 
Drawing by Camillo Golgi of a hippocampus stained using the silver nitrate method
Drawing of a Purkinje cell in the cerebellar cortex done by Santiago Ramón y Cajal, demonstrating the ability of Golgi's staining method to reveal fine detail
Related pages
References
- ↑ 1.0 1.1 Lua error in Module:Citation/CS1/Utilities at line 38: bad argument #1 to 'ipairs' (table expected, got nil).
- ↑ 2.0 2.1 Lua error in Module:Citation/CS1/Utilities at line 38: bad argument #1 to 'ipairs' (table expected, got nil).
- ↑ Wade, Nicholas (1999-10-15). "Brain may grown new cells daily". The New York Times. https://www.nytimes.com/1999/10/15/us/brain-may-grow-new-cells-daily.html.
- ↑ 4.0 4.1 Lua error in Module:Citation/CS1/Utilities at line 38: bad argument #1 to 'ipairs' (table expected, got nil).
- ↑ Blinkov S.M. & Glezer I.I. 1968. The human brain in figures and tables: a quantitative handbook. New York, Plenum.
- ↑ Roth, Gerhard 2013. The long evolution of brains and minds. Springer, Dordrecht.
Other websites
- Fibrinogen found to inhibit EGFR in neuronal cells Archived 2021-04-13 at the Wayback Machine Blood clotting protein may inhibit spinal cord regeneration
- Cell Centered Database Archived 2007-08-13 at the Wayback Machine UC San Diego images of neurons.
- High resolution neuroanatomical images of primate and non-primate brains Archived 2019-06-21 at the Wayback Machine.