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