Neuron Structure and Function


Neurons and glia (cells that support neurons) are specialized cells for electrical signaling over long distances. Understanding neuronal structure is important for understanding neuronal function...

The number of synaptic inputs recieved by each nerve cell in our (human) nervous system varies from 1-100,000!

This wide range reflects the fundamental purpose of nerve cells, to integrate info from other neurons.

Cellular organization of neurons resembles that of other cells, however, they are unique in their ability for intercellular communication. Neuron membrane components are arranged specifically for electrical signaling which is seen best by the extensive branching of neurons.

 


image: http://www.drugabuse.gov/MOM/TG/figure4.gif

Dendrites are the primary target for synaptic input from other neurons and compose the "extensive branching." The complexity of the dentritic branching is directly related to the number of inputs a neuron can recieve. So neurons with lots of dendrites are able to process information at a greater rate than neurons with fewer dendrites.

Most neurons do not make direct connections with surrounding neurons, signals (molecules) must make the transition from the presynaptic (upstream) neuron to the postsynaptic (downstream) neuron. This transition space is called the synaptic cleft. The exchange of information from the pre- to postsynaptic neuron is called a synapse.

image: http://www.nwfsc.noaa.gov/hab/habs_toxins/marine_biotoxins/detection/images/Neuron_transmission_1.jpg

Information conveyed by the synapses on the dendrites is processed and projected from the axon. The axon is extraordinary, it is specialized for signal conduction to the next neuron. Axons vary in length, the ones in your brain are relatively short in comparison to the axons that run from your spinal cord down to your foot (about a meter long).

The electrical event that projects the signal along these distances is known as an action potential. The action potential runs from the axon hillock to the end of the axon where more synaptic contacts are made. Target cells of neurons include nerve cells in your brain, spinal cord, cells of your muscles and various glands.

Axons are like wires in your body, and to reduce current "leakage" axons are myelinated, or insulated with layers of glial cells. Nodes of Ranvier, are gaps between myelin wrapping, these gaps increase the conduction velocity of electrical signaling.

The cell body contains the machinery for cell operation. For example, the nucleus of the neuron regulates protein and neuronal membrane synthesis, both are required for upkeep of the neuron.


http://fig.cox.miami.edu/~cmallery/150/neuro/c7.48.8.node.ranvier.jpg

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Overview
Electrical Signals
Voltage Dependent Membrane Conductances
Long Distance Signaling by Action Potentials
Terminology