Biomedical Engineering Reference
In-Depth Information
close-packing of the lipid molecules. The membranes contain protein
assemblies which constitute ion channels and ion pumping configurations. The
channels can be gated by voltage effects or by chemical stimulation via
molecules
termed neurotransmitters. The electrochemical nature of
the
signaling process is described below.
With respect to type, neurons, which are highly variable in nature (see
Figure 2.6 for examples) can be categorized via number of different classifi-
cations. However, the most important parameters are location in the nervous
system, morphology and function. At the first level, neurons exhibit unipolar,
bipolar or multipolar character. This is not an electrical term, but is employed
to describe the positioning of dendrites with respect to the soma and axon.
Additionally, in general terms of behavior, cells that relay information about
their environment, such as olfactory cells, for transmission to the CNS are
called afferent neurons. Those that orchestrate signals originating from CNS
are termed efferent neurons. There are also interconnecting neurons between
these two types of structure. At the molecular level neurotransmitters,
through interaction with particular receptors, can excite, modulate or inhibit
activity in target cells. This leads to a neural classification based on the
chemistry of generation of neurotransmitters—the terms end in '-ergic' as a
descriptor. Examples are cholinergic (acetylcholine production), dopaminergic
(dopamine) and serotonergic (serotonin) neurons. The biochemical activity of
these
d
n
4
t
3
n
g
|
0
n
3
.
types of neuron and other neurotransmitter-producing cells
is
summarized in Table 2.3.
Figure 2.6
Neurons with different polarity.
