The Nervous System: Multipolar Neurons::
The nervous system serves as a great metaphor for the construction of cyberspace. We will use the anatomy of a neuron as a tool to describe our conceptual metaphor. Furthermore, we would like to discuss the process of how nerves are stimulated and transmitted, as the active and reactive nature of the world wide web. Sensory receptors reside in virtually every part of the body. They are responsive to different stimuli and provide the brain and spinal cord with information about our internal environment and about the world around us. The sensory system gives us an accurate “sensory” map of the external world. Nerve endings throughout the body respond to particular stimuli and send critical messages to the spinal cord and brain. Using these signals, the brain develops “a map” of the external world which is used for every movement that we make.

The Nerve Cell: Multipolar Neuron::

AXON is the neuronal process that carries the action potential from the nerve cell body to a target.
ACTION POTENTIAL is the electrical signal conducted along axons (or muscle fibers) by which information is conveyed from one place to another in the nervous system.
DENDRITE is a neuronal process that receives synaptic input.  It usually branches near the cell body and is typically unable to support an action potential.
SYNAPSE is a specialized apposition between a neuron and its target cell for transmission of information by release and reception of a chemical transmitter agent (neurotransmitters).
NEUROTRANSMITTER is a substance released by synaptic terminals for the purpose of transmitting information from one nerve cell to another.
TERMINAL BUTTON (presynaptic button) is where the axon ends.  When an action potential (message) reaches the terminal button, a neurotransmitter substance is secreted.
MYELIN is the lipid substance (fat) that surrounds some axons. It serves to speed axonal transmission.

The Anatomy of a Neuron: Principal Internal Structures of a Multipolar Neuron::

NUCLEUS (pl, Nuclei) is a collection of nerve cells in the brain that are anatomically discrete and which typically serve a particular function.
ENDOPLASMIC RETICULUM is the system of rough plate-shaped membranous sacs in the cytoplasm of cells.  It's rough appearance stems from the fact that it is covered with ribosomes.  In the neuron it is located in the cell body.
LYSOSOME is an organelle surrounded by a membrane.  It contains enzymes that break down waste materials.
ORGANELLE is a minute structure serving a specific function in the life of cells.
MEMBRANE is a structure consisting principally of lipid molecules that defines the outer boundaries of cells.  It also constitutes many of the cell organelles, such as the golgi apparatus.
CYTOPLASM
MICROTUBULE is a long strand of bundles of protein filaments arranged around a hollow core.  It is part of the cytoskeleton and is involved in transporting substances from place to place within the cell.
DENDRITE is a neuronal process that receives synaptic input.  It usually branches near the cell body and is typically unable to support an action potential.
DENDRITIC SPINE is the small bud on the surface of the dendrite with which a terminal button (presynaptic button) from another neuron forms a synapse.
MYELIN is the lipid substance (fat) that surrounds some axons. It serves to speed axonal transmission.
MITOCHONDRIA are organelles which make use of molecular oxygen.  They generate ATP, the major molecule by which cellular energy is transferred or spent.

The Anatomy of a Synapse::

SYNAPSE is a specialized apposition between a neuron and its target cell for transmission of information by release and reception of a chemical transmitter agent (neurotransmitters).
NEUROTRANSMITTER is a substance released by synaptic terminals for the purpose of transmitting information from one nerve cell to another.
SYNAPTIC VESICLES are spherical, membrane-bound organelles in presynaptic terminals that store neurotransmitters.
SYNAPTIC CLEFT is the space that separates pre- and postsynaptic neurons at chemical synapses.
GOLGI COMPLEX  are the organelles that represent the main protein biosynthetic machinery of the neuron.
MITOCHONDRIA are organelles which make use of molecular oxygen.  They generate ATP, the major molecule by which cellular energy is transferred or spent.
DENDRITIC SPINE is the small bud on the surface of the dendrite with which a terminal button (presynaptic button) from another neuron forms a synapse.
TERMINAL BUTTON (presynaptic button) is where the axon ends.  When an action potential (message) reaches the terminal button, a neurotransmitter substance is secreted. 
PRESYNAPTIC MEMBRANE is the membrane of a terminal button (or presynaptic button) in a synapse that lies adjacent to the postsynaptic synaptic membrane. 
POSTSYNAPTIC MEMBRANE is the cell membrane opposite the terminal button (presynaptic button) in a synapse.  This is the membrane of the cell that receives the message carried by the neurotransmitter substances. 
MICROTUBULE is a long strand of bundles of protein filaments arranged around a hollow core.  It is part of the cytoskeleton and is involved in transporting substances from place to place within the cell.

The Neurotransmitter process: A Closer Look::