THE NEURON
PREPARED BY HUGH POTTER,Ph.D
BIOLOGY DEPARTMENT
UNION COUNTY COLLEGE
ALL IMAGES USED WITH THE PERMISSION OF THE
PUBLISHERS OF THE SLICE OF LIFE VIDEO DISK
THE NEURON
d
cb
a
d
d
The cell body (perikaryon) is the portion of the nerve cell that
surrounds the nucleus. The size of a typical neuron cell body varies
from 4 to 135um. Multipolar neurons have several branches arising
form the cell body (cb). There is usually one axon (a) and many
dendrites (d). Dendrites carry nerve impulses to the cell body. The
axon is designed to carry nerve messages away from the cell body.
NISSLE BODIES
Nissle bodies(arrows) are widely distributed in the cytoplasm of most
neurons. They are more numerous in motor neurons. Nissle bodies
are formed by clumps of ribosomes attached to portions of
endoplasmic reticulum. They signify a high level of protein synthesis
UNIPOLAR NEURONS
In A DORSAL ROOT GANGLION
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Unipolar cells have a globular cell body (asterisks) with a single
branch that divides. One of these divisions carries nerve impulses
into the cell body from receptor tissue. The other division passes
these impulses onto the spinal cord. Cell bodies of this type of
neuron can be found in the dorsal root ganglia near the spinal cord.
MYELINATED AXON
All nerve cell processes in the
central nervous system (CNS)
peripheral nervous system
(PNS) have one or more
sheaths or coverings.
Myelinated processes in the
PNS have a sheath of Schwann
cells around a myelin
wrapping. The myelin is
produced by the Schwann
cells.
NODES OF RANVIER
The myelin sheath is seen to be interrupted
every 0.1 micron to 1.5 mm by a gap called the Node
of Ranvier (arrows). The jumping of the nerve
message from node to node speeds up the passage of
the nerve impulse along myelinated axons.
NEUROFILAMENTS
Neurofilaments (arrows) are delicate
fibers present throughout the
cytoplasm of the cell body and
extending in bundles into dendrites
and axons. These bundles can extend
from the cell body to the ends of cell
processes. Neurofibrils are composed
of microtubules formed from the
protein tubulin and microfilaments of
actin and myosin. They are
responsible for supporting the internal
framework of the cell, as well as,
transport of substances within the cell.
END BRANCHES AND MOTOR END PLATES
The axon (a) is seen
to divide into many
telodendria (t) (end
branches). At the
terminus of each end
branch is a synaptic
knob (arrow).
The motor end plates
are under the knob
on the surface of
the skeletal muscle
fiber.
a
t
SYNAPTIC KNOB
sn
s
s
The synapse is located at the end
of each axonal end branch. Here
the end branch forms a small
synaptic knob (sk). This knob is
adjacent to a tiny cleft or synapse
(s). When a nerve impulse reaches
this knob, a drug called a
neurotransmitter is released from
vesicles into the synapse The
neurotransmitter diffuses across
the gap and binds to receptors on
the membrane of the adjacent
neuron or muscle cell. This will
initiate an electrical change in the
membrane of the adlacent neuron
leading to a nerve impulse in that
cell.