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{{short description|Electrically excitable cell that communicates via synapses}}

{{short description|Electrically excitable cell that communicates via synapses}}

A '''neuron''' or '''nerve cell''' is an [[membrane potential#Cell excitability|electrically excitable]] [[cell (biology)|cell]] that communicates with other cells via specialized connections called [[synapse]]s. The neuron is the main component of [[nervous tissue]] in all [[Animalia|animals]] except [[sponge]]s and [[placozoa]]. [[Plant]]s and [[fungi]] do not have nerve cells.

A '''neuron''' or '''nerve cell''' is an [[membrane potential#Cell excitability|electrically excitable]] [[cell (biology)|cell]] that communicates with other cells via specialized connections called [[synapse]]s. The neuron is the main component of [[nervous tissue]] in all [[Animalia|animals]] except [[sponge]]s and [[placozoa]]. [[Plant]]s and [[fungi]] do not have nerve cells.

 

 

 

 

 

Neurons are typically classified into three types based on their function. [[Sensory neuron]]s respond to [[Stimulus (physiology)|stimuli]] such as touch, sound, or light that affect the cells of the [[Sense|sensory organs]], and they send signals to the spinal cord or brain. [[Motor neuron]]s receive signals from the brain and spinal cord to control everything from [[muscle contraction]]s to [[gland|glandular output]]. [[Interneuron]]s connect neurons to other neurons within the same region of the brain or spinal cord. When multiple neurons are connected together they form what is called a [[neural circuit]].

Neurons are typically classified into three types based on their function. [[Sensory neuron]]s respond to [[Stimulus (physiology)|stimuli]] such as touch, sound, or light that affect the cells of the [[Sense|sensory organs]], and they send signals to the spinal cord or brain. [[Motor neuron]]s receive signals from the brain and spinal cord to control everything from [[muscle contraction]]s to [[gland|glandular output]]. [[Interneuron]]s connect neurons to other neurons within the same region of the brain or spinal cord. When multiple neurons are connected together they form what is called a [[neural circuit]].

 

A typical neuron consists of a cell body ([[Soma (biology)|soma]]), [[dendrite]]s, and a single [[axon]]. The soma is a compact structure and the axon and dendrites are filaments extruding from the soma. Dendrites typically branch profusely and extend a few hundred micrometers from the soma. The axon leaves the soma at a swelling called the [[axon hillock]] and travels for as far as 1 meter in humans or more in other species. It branches but usually maintains a constant diameter. At the farthest tip of the axon's branches are [[axon terminals]], where the neuron can transmit a signal across the [[synapse]] to another cell. Neurons may lack dendrites or have no axon. The term [[neurite]] is used to describe either a dendrite or an axon, particularly when the cell is [[Cellular differentiation|undifferentiated]].

A typical neuron consists of a cell body ([[Soma (biology)|soma]]), [[dendrite]]s, and a single [[axon]]. The soma is a compact structure and the axon and dendrites are filaments extruding from the soma. Dendrites typically branch profusely and extend a few hundred micrometers from the soma. The axon leaves the soma at a swelling called the [[axon hillock]] and travels for as far as 1 meter in humans or more in other species. It branches but usually maintains a constant diameter. At the farthest tip of the axon's branches are [[axon terminals]], where the neuron can transmit a signal across the [[synapse]] to another cell. Neurons may lack dendrites or have no axon. The term [[neurite]] is used to describe either a dendrite or an axon, particularly when the cell is [[Cellular differentiation|undifferentiated]].

 

Most neurons receive signals via the dendrites and soma and send out signals down the axon. At the majority of synapses, signals cross from the axon of one neuron to a dendrite of another. However, synapses can connect an axon to another axon or a dendrite to another dendrite.

Most neurons receive signals via the dendrites and soma and send out signals down the axon. At the majority of synapses, signals cross from the axon of one neuron to a dendrite of another. However, synapses can connect an axon to another axon or a dendrite to another dendrite.

 

The signaling process is partly electrical and partly chemical. Neurons are electrically excitable, due to maintenance of [[voltage]] gradients across their [[Cell membrane|membranes]]. If the voltage changes by a large enough amount over a short interval, the neuron generates an [[All-or-none law|all-or-nothing]] [[electrochemical]] pulse called an [[action potential]]. This potential travels rapidly along the axon and activates synaptic connections as it reaches them. Synaptic signals may be [[Excitatory postsynaptic potential|excitatory]] or [[Inhibitory postsynaptic potential|inhibitory]], increasing or reducing the net voltage that reaches the soma.

The signaling process is partly electrical and partly chemical. Neurons are electrically excitable, due to maintenance of [[voltage]] gradients across their [[Cell membrane|membranes]]. If the voltage changes by a large enough amount over a short interval, the neuron generates an [[All-or-none law|all-or-nothing]] [[electrochemical]] pulse called an [[action potential]]. This potential travels rapidly along the axon and activates synaptic connections as it reaches them. Synaptic signals may be [[Excitatory postsynaptic potential|excitatory]] or [[Inhibitory postsynaptic potential|inhibitory]], increasing or reducing the net voltage that reaches the soma.

 

In most cases, neurons are generated by [[neural stem cell]]s during brain development and childhood. [[Neurogenesis]] largely ceases during adulthood in most areas of the brain.

In most cases, neurons are generated by [[neural stem cell]]s during brain development and childhood. [[Neurogenesis]] largely ceases during adulthood in most areas of the brain.

 

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