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Nervous System Histology
Week 9
Expanded Studies
OBJECTIVES
• Identify the portions of a multipolar
neuron using models & slides
• Differentiate between
pseudounipolar, bipolar & multipolar
neurons from slides
• Identify the components of the nerve
cross section using diagrams &
slides
What is a neuron?
Neuron = Nerve cell
Reflex Arc
Objective 1:
Neuron Structure
Parts of a Neuron animation – click here
Main parts of a neuron
Dendrites (receive)  Cell Body (process)  Axon (send)  Axon Terminals (transfer)
Cell
Body
Axon
Terminals
Multipolar Neuron model
Breakdown 1
Dendrites
(receptive
regions)
Cell body
(biosynthetic center
and receptive region)
Neuron
cell
body
Nissl bodies
(rough ER)
Dendrite
Neurofibrils
Nucleus
Nucleolus
Axon
(impulse generating
and conducting region)
Impulse
direction
Breakdown 2
Axon hillock
Impulse
direction
Axon
Neurilemma
(sheath of Schwann)
Schwann cell
(one internode)
Node of Ranvier
Schwann cells - supporting cells of the PNS that myelinate axons.
• Myelin sheath – whitish lipoprotein that surrounds and insulates
the axon (nerve fiber)
• Neurilamma - external layer containing bulk of cytoplasm with
nucleus and organelles
Schwann cell
myelin sheath
nucleus
axon
neurilemma
Node of
Ranvier
Breakdown 3 – End of axon
Impulse
direction
Terminal branches
(Telodendria)
Axon terminals
(secretory component)
Remember this?
Axon
(branches)
Muscle
fibers
Axon
terminals
Breakdown 4
Axon Collateral
Neuron Pathology
Multiple Sclerosis
MS is thought to be an
autoimmune disease in which the
myelin is lost in multiple areas,
leaving scar tissue called sclerosis.
These damaged areas are also
known as plaques or lesions.
Sometimes the nerve fiber itself is
damaged or broken.
Myelin not only protects nerve
fibers, but makes their job possible.
When myelin or the nerve fiber is
destroyed or damaged, the ability
of the nerves to conduct electrical
impulses to and from the brain is
disrupted, and this produces the
various symptoms of MS.
What you need to draw and label
Cell Body
Spinal Cord Smear – Motor Neuron
Nodes of Ranvier Gaps between successive Schwann cells along the length
of the axon
Microscopic Views
What you need to draw and label
Axon
Node of
Ranvier
Neurilemma
Identify these structures:
Nissle
Bodies
Telodendria
Dendrite
Node
of
Ranvier
Axon
Hillock
Identify these structures:
Dendrites
Nucleus
Cell Body
(Soma)
(w/ nucleolus)
Objective 2:
Neuron Classification
Multipolar
(Interneuron)
Pseudounipolar
(Sensory)
Multipolar
(Motor)
Bipolar
Pseudounipolar:
-
a short process (axon) emerges from the cell body and divides into
proximal and distal branches
-
includes most sensory neurons
In spinal nerves, the distal process is
longer than the proximal process;
The cell body (soma) is very close to
the CNS in a structure called the
dorsal root ganglion
soma
Receptive
Endings
Distal process
(toward periphery)
Proximal process
(toward CNS)
Comparisons between Receptive Endings
Pacinian
Corpuscle
Pseudounipolar Cell Bodies
in the Dorsal Root Ganglion of a
Spinal Nerve
High power
Dorsal Root
Ganglion
Spinal
Cord
Pseudounipolar
Cell Bodies
Low power
“This is a low power slide of the Dorsal Root
Ganglion. The key to knowing that you are
looking at Neurons in the DRG is by looking for
the CENTRALLY LOCATED NUCLEI,
indicated by the Red arrows. These Large nuerons
are Psuedouniplor, Sensory (Afferent)
Neurons. They are responsible for conveying
information to the Central Nervous System. You
can tell that these Neurons have huge cell bodies.
These are some of the largest cells in the body.
The larger the cell body, the further away the
information is coming from.”
Red arrows - Central Nuclei of Sensory Neurons
UMDNJ histsweb
Bipolar neuron
- has a single axon and a single dendrite attached to
opposite sides of the cell body
- found in special sense organs (eye, ear, etc.)
dendrite
axon (branched)
Human retina
Bipolar
neurons
(nuclei visible)
Multipolar:
- has multiple dendrites and a single axon
- includes:
- most neurons
- most CNS neurons (Interneurons)
- all motor neurons
Note: Multipolar neurons have diverse morphologies
You do not need to memorize all these
Some Examples of Multipolar Neurons
Neurons from the spinal cord
(smear)
Neuron from the
cerebral cortex
Silver Stained Neuron
in Gray Matter of
spinal cord
Spinal Cord - Anterior Horn
Multipolar neuron
Glial cell nuclei
(supporting cells)
Multipolar neurons you will be drawing
Pyramidal cell
Hippocampus & Cerebral cortex
Purkinje cell
Cerebellum
Pyramidal cell
(Low Power – Cerebrum)
Purkinje cell
(Low Power - Cerebellum)
Identify the structural class of these neurons
Bipolar
Identify the structural class of these neurons
Multipolar
Identify the structural class of these neurons
Pseudounipolar
Identify the structural class of these neurons
Multipolar
Objective 3:
Nerves are
structures of the
PNS that
consist of axons and
dendrites bundled
together by
connective tissues
Nerves
NERVE
Fascicle: a bundle of axons or dendrites
Epineurium: tough, fibrous connective
tissue sheath surrounding
a nerve
Perineurium: loose, areolar connective
tissue sheath surrounding
fascicles
Endoneurium: delicate connective tissue
wrapping around each nerve
fiber; the endoneurium
electrically insulates each
nerve fiber
Perineurium
Endoneurium
Fascicle
Epineurium
Electron micrograph image
Nerve fiber
(axon)
Epineurium
Epineurium
Perineurium
Epineurium
Perineurium
Endoneurium
Axon
(Nerve fiber)
Endoneurium
Axon
(Nerve fiber)
Myelin Sheath
Identify the components of the nerve cross section
?
?
?
?
?
?
?
Try again:
Label the structures
Epineurium
Perineurium
Fascicle
Endoneurium
(nerve fibers)
Recap:
• Identify the portions of a multipolar neuron
using models & slides
• Differentiate between pseudounipolar,
bipolar & multipolar neurons from slides
• Identify the components of the nerve cross
section using diagrams & slides