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Nervous System
What is a neuron?
Neuron is a cell

How many neurons are in your nervous
system?
Answer

There are estimated to be as many as 100
billion neurons in our nervous system!
Anatomy of the neuron
Physiology

A typical neuron has all the parts that any
cell would have, and a few specialized
structures that set it apart. The main
portion of the cell is called the soma or
cell body. It contains the nucleus,
which in turn contains the genetic material
in the form of chromosomes.
Physiology

Neurons have a large number of
extensions called dendrites. They often
look likes branches or spikes extending
out from the cell body. It is primarily the
surfaces of the dendrites that receive
chemical messages from other neurons.
Physiology

One extension is different from all the others,
and is called the axon. The purpose of the axon
is to transmit an electro-chemical signal to other
neurons, sometimes over a considerable
distance. In the neurons that make up the
nerves running from the spinal cord to your
toes, the axons can be as long as three feet!
Physiology

Longer axons are usually covered with a
myelin sheath, a series of fatty cells
which have wrapped around an axon
many times. These make the axon look
like a necklace of sausage-shaped
beads. They serve a similar function as
the insulation around electrical wire.
Physiology

At the very end of the axon is the axon
ending, which goes by a variety of names
such as the bouton, the synaptic knob,
the axon foot,
Physiology

Between the axon ending and the dendrite
of the next neuron is a very tiny gap
called the synapse (or synaptic gap, or
synaptic cleft), which we will discuss in a
little bit. For every neuron, there are
between 1000 and 10,000 synapses.