Download Neurons Short Version

Neurons Short Version
Dr. Ron Pohala
Nervous System
Central Nervous System consists of
the brain and the spinal cord.
 Peripheral Nervous System consists
of any of the nerve tissue outside of
the central nervous system such as
the thorax, abdomen or the arms and
legs.
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Type of nerve cells
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Neuroglia
The supporting structure of nervous tissue. It
consists of a fine web of tissue made up of
modified ectodermal elements, in which are
enclosed peculiar branched cells known as
neuroglial cells or glial cells. The neuroglial cells
are of three types: astrocytes and
oligodendrocytes which appear to play a role in
myelin formation, transport of material to
neurons, and maintenance of the ionic environment
of neurons; and microcytes (microglia), which
phagocytize waste products of nerve tissue.
Neuroglia (glia)
Function to physically support or
assist with metabolism.
 90 percent of the nerve cells in the
brain are neuroglia
 Four types of neuroglia exist,
astrocytes, oligodendrocytes,
ependyma cells. Sometime microglia
come under this listing.
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Neuroglia
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A special type of connective tissue cell
holding functioning neurons together
Astrocytes, star shaped neuroglia attach
neurons to small blood vessels
Microglia, smaller than astrocytes,
generally are stationary but can move
about as microbe eating scavengers
(phagocytes)
The oligodendroglia ( oligodendrocytes)
hold nerve fibers together and produce
myelin in the CNS
ASTROCYTES
Play a very important role in the
blood- brain barrier. Since neurons
are so vitally important and can’t
carry out mitosis for replacement the
body particularly tries to prevent
dangerous substances from reaching
them.
 Play a role in supplying the neurons
with glucose.
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Neurons
It is important that you know the
anatomy of the neuron and how it
functions and to learn the basics of the
neurons and how they communicate with
one another and other type of cells.
Nerve cells that transmit impulses are
known as neurons.
Neuron
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A neuron consists of three main parts the
cell body or perikaryon or soma, dendrites
and axons.
The cell body is the central region which is
the most important part of the neuron
containing the nucleus of the cell.
Dendrites are extensions that carry
impulses toward the cell body and are
referred to as being afferent fibers.
Neurons
Axons carry impulses away from the
cell body and are known as efferent
fibers.
 The axon is the section of the neuron
that communicates with another
neuron by releasing
neurotransmitters.
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Point of Reference
for nerve fibers
The point of reference for the fibers
carrying the impulse is the cell body,
perikaryon or soma.
 Dendrites carry the impulse toward
the cell body.(afferent fibers)
 Axons carry impulses away from the
cell body. (efferent fibers)
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Neuron (cont.)
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The region between the two neurons
is known as the synaptic gap or
snaptic cleft or neural junction.
Personally I prefer to use the word
synapse as an action verb and refer
to the actual transmission as the
synapse not the space.
Neurons
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May be classified by how many fibers are
extending from the cell body.
Unipolar neurons has one extension from
the cell body.
Bipolar neurons have two extensions from
the cell body.
Multipolar neurons ( which are the most
common) and usually the one referred to
has many dendrites and usually one axon.
Classification of Neurons
More commonly neurons are based on
the location and the direction the
neuron conducts the impulse.
 A sensory neuron carries and impulse
toward the CNS. AKA an afferent
neuron.
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Point of Reference
The point of reference for
differentiating neurons is the Central
Nervous System.
 So the brain and the spinal cord have
neurons carrying impulses toward or
away from them.
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Motor neurons
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Carry impulses away from Central Nervous
System.
Classifying neurons according to
number of fibers .
Unipolar
 Bipolar
 Multipolar
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Interneuron
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Also know as internuncial neuron,
connecting neuron, association neuron.
Addionally known also called relay neuron,
association neuron or local circuit
neuron)
A human brain contains about 100 billion
interneurons.
Sheaths
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The neuron may have either a neurilemma
sheath, myelin sheath or both or none at
all.
Neurilemma sometimes spelled neurolemma
is one that is cytoplasmic in its makeup and
allows for the repair of damaged fibers. It
is found only in the peripheral neurons none
are found in the central nervous system
neurons.
Neurilemma or Neurolemma
Neurolemma (also known as neurilemma or sheath
of Schwann) is the outermost nucleated cytoplasmic
layer of Schwann cells that surrounds the axon of the
neuron. It forms the outermost layer of the nerve fiber
in the peripheral nervous system.[1]
It is important to note that in CNS, axons are myelinated
by oligodendrocytes, thus lack neurolemma.
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White and gray matter in CNS
White matter –myelinated axons.
 Gray matter- unmyelinated axons, cell
bodies, dendrites.
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White verses Gray Matter
Most of the surface and outer few
millimeters is gray matter, while most of
the inner tracts are composed of white
matter (myelinated neurons).
 Remember in the brain the outer layers
are gray matter and the inner is white
matter while in the spinal cord the outer
layer is white matter and the inner layer
is gray matter.
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