| In this activity, students will
construct a neuron and learn about dendrites and axons as
unique structures associated with this cell. Each organelle
and its function are explained as the individual or pair of
students constructs the neuron, the basic structural unit
of the nervous system. Neurons are found in the brain, the
spinal cord, in ganglia (pl., ganglion, singular, meaning
"little brain"), and in the walls of the gut.
Nervous tissue is considered one of the four basic types of
tissue. These four basic types combine to form organs; organs
performing a like function comprise organ systems. Within
cells of the four basic types, including neurons, small functioning
units known as organelles perform various functions critical
to development, growth, maintenance, and activity of cells.
The neuron is unique among cells because of its structure,
through which the ability to receive and conduct electrical
is conferred. While certain organelles present within the
neuron are common to many types of cells (such as the nucleus
and mitochondria), the cellular extensions (dendrites and
axons) are not.
Within the central and peripheral nervous system, there are
supporting and nutritive cells. In the central nervous system
these are known as glia, from the Greek word for "glue".
There are three types of glial cells: astrocytes, oligodendrocytes,
and microglia. Astrocytes are important in "mopping up"
potassium that leaks out into the extracellular space after
the neurons fire electrical currents, and are also a critical
element in the formation of the "blood-brain barrier".
They play a role in guiding the axons of developing neurons
to their proper targets, and after brain injury, become active
in "scar formation". Oligodendrocytes wrap axonal
processes in myelin, a fatty substance. This acts much like
insulation around an electrical cord and prevents leakage
of current. Through this insulation, the speed of conduction
of the electrical current down the axon is increased dramatically.
Microglial cells are the phagocytes of the nervous system
and have been implicated in the spread of HIV within the brain. |
