Computational Visualization Center

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Brain-Molecules/cells/Tissue

• Chandrajit Bajaj

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Neurons

• The basic units of the nervous system is a
  special cell called a neuron, or nerve cell. This
  has a cell body with a central nucleus and
  various other structures that are important for
  maintaining cell life. Neurons have long
  projections, or processes, known as axons (nerve
  fibers) and dendrites. Axons carry nerve impulses
  away from the cell dendrites receive impulses
  from other neurons.

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Neurons
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Neuron types

• According to their function and location in the
  body, the shape and size of neuron cell bodies
  vary greatly, as do the type, number, and length
  of their processes. Illustrated are three main
  types of neurons unipolar, bipolar, and
  multipolar.

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Anatomic and functional categories of neurons
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Glial cells and their functions
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Glial Cells supporting neuronal cells

• Several types of support cells,or glial cells,
  act to protect and give structural support to the
  neurons. The smallest (microglia) destroy
  microorganisms others help to insulate axons or
  regulate the flow of cerebrospinal fluid.

Astrocytes Delicate processes of cytoplasm extend
from these starlike cells. Some cell processes
connect with capillaries and help to regulate the
flow of substances between neurons and the blood.
Oligodendrocytes These cells wrap their plasma
membranes around neurons of the brain and spinal
cord to form myelin sheaths.
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The blood-brain barrier
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Axonal transport of membranous organelles
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Neuron Behavior
Synapse The communication point between neurons
(the synapse, enlarged at right) comprises the
synaptic knob, the synaptic cleft, and the target
site.

• Neurons must be triggered by a stimulus to
  produce nerve impulses, which are waves of
  electrical charge moving along the nerve fibers.
  When the neuron receives a stimulus, the
  electrical charge on the inside of the cell
  membrane changes from negative to positive. A
  nerve impulse travels down the fiber to a
  synaptic knob at its end, triggering the release
  of chemicals (neurotransmitters) that cross the
  gap between the neuron and the target cell,
  stimulating a response in the target.

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neuron-synapses
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Neuro-muscular junctions
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Nmj_coupling
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membrane_wide
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The Neuronal Cell Body
This low magnification electron micrograph of an
anterior horn cell shows the basic features of a
neuronal cell body. In the center of the cell
body is the pale nucleus (Nuc) that contains a
nucleolus (ncl). In the surrounding perikaryal
cytoplasm the most prominent organelles are the
Nissl bodies (NB), composed of cisternae of rough
endoplasmic reticulum. Profiles of the Golgi
apparatus (G), mitochondria (mit), and a few
lipofuscin granules (Lf) are also apparent. The
processes extending from the perikaryon are
dendrites (Den). Anterior horn of spinal cord,
Rhesus monkey. X4000.
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Motor End Plate
The upper picture is a light micrograph of a
neuromuscular junction. Coming into the field
from the right is a myelinated axon (Ax). The
myelin sheath is lost as the axon branches into
its terminals (At), which contain the dark
profiles of mitochondria. These terminals are the
nuclei (Nuc) of Schwann cells associated with the
nerve ending. The blank granules surrounding the
nerve terminals are mitochondria (mit) of the
muscle cells. Superior oblique muscle of a
rat. The Lower picture is an electron micrograph
of a motor end plate similar to that shown above.
The terminals (At) of the motor nerve fiber
contain mitochondria (mit) and a synaptic
vesicles (sv), and are seperated from the surface
of the muscle cell by a wide interval that
contains the basal lamina (B). In this region the
sarcolemma shows junctional folds (arrows) and
the sarcoplasm is rich in mitochondria (mit1).
Covering the axon terminals are two Schwann
cells (SC), Superior oblique muscle of a
2-week-old rat
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Motor End Plate
Passing down the middle of the fields is the
basal lamina (B), which occupies the synaptic
cleft separating the plasma membranes of the axon
terminal (At) and the muscle cell. The axon
terminal is crowded with synaptic vesicles (sv),
which become concentrated at the active zones ()
of the axolemma. Although no coated vesicles are
apparent in the axon terminal, the empty shells
or baskets that form the coats of such vesicles
can be seen (arrowheads). Although the
presynaptic membrane is relatively smooth, the
sarcolemma is thrown into junctional folds
(arrow) lines by the basal lemina (B) of the
synaptic cleft. At the crests of the folds the
cytoplasmic face of the sarcolemma is coated by a
ense material. Rat diaphragm.
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Gap-Junctions
a
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Gap-Junctions
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Gap-Junctions
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Gap-Junctions
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Gap-Junctions
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Neurononal Tissue
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Schwann Cells/Myelin Sheath
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