Transcript lab 8: Nervous Tissue

Nervous Tissue
is found in the brain, spinal cord, and
peripheral nerves.
Nervous tissue is
composed of two main cell
types: neurons (nerve cells)
and glial cells.
Neurons transmit nerve
messages.
Glial cells are in direct
contact with neurons and
often surround them.
Humans have about 100
billion neurons in their brain
alone! While variable in
size and shape.
Pyramidal Neurons from the Central Nervous System (SEM
x3,960). This image is copyright Dennis Kunkel at
www.DennisKunkel.com, used with permission.
Neuron Smear
Identification: Note distinctive shape of neuron, with long
processes (dendrites, 5) extending out from main cell body.
There are also numerous supporting glial cells, though only
their small dark nuclei (4) are easily seen. Also see the
nerve cross section below.
Features to Know: The
large, irregularly shaped
cell body (3) contains a
darker nucleus (2), which
contains an even darkerstaining nucleolus (1)
Diagram of multipolar neuron
Neurons are the basic and functional cells of the nervous tissue.
they are sensitive to certain types of changes in their surroundings and
respond by transmitting nerve impulses along cellular extensions
(nerve fibers) to other neurons or to muscles or glands.
.
Because neurons communicate with
each other and with various body
parts, they coordinate, regulate, and
integrate many body functions.
All neurons have three parts.
• Dendrites receive information from
another cell and transmit the
message to the cell body.
• The cell body (perikaryon) contains
the nucleus, mitochondria and other
organelles typical of eukaryotic cells.
• The axon conducts messages away
from the cell body.
Neurons are individaul nerve cells. neuron (black arrows).
Type of neurons
• Unipolar: when they contain a single fiber, the
axon, and no dendrites as seen in sensory
ganglia.
• Bipolar: when there is one axon and one
dendrite, as in the retina of the eye;
• Multipolar: when there are several dendrites
and only one axon, as in the motor neuron
MOTOR NEURON:
Note distinctive shape of neuron (multipolar).
The cell body or perikaryon (A) is filled with Nissl bodies which are
chromatophilic substances ; pick up the stain in this micrograph. The
cell's axon can not be distinguished from its dendrites in the micrograph.
B marks the axon and dendrite threads. The "C's" marks the neuroglia
cells (dark spots) and the neurofibrils .
Thoracic spinal Cord - silver stain
Neurofilaments: are aggregated into neurofibrils;
which are part of the cytoskeleton of neurones is (like the
reticular connective tissue fibers) argyrophilic, i.e. they
"love" silver and can be stained by silver stains.
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Aside from the neurones and their
processes, fine fibrils are visible in
the neuropil. Many of the fibrils
represent axons travelling in the
grey and white matter of the spinal
cord.
Note the large cell, prominent
nucleus and nucleolus.
the spinal cord/vertebrae model
Hint: to distinguish the posterior from anterior side of the spinal cord,
note that only the posterior horns of the gray matter extend to the edge
of the spinal cord.
•
9. Dura Mater 10.
Epidural Space 11.
Subdural Space
12. Arachnoid
Mater 13.
Subarachnoid
Space 24. Pia
Mater 25. Anterior
Median Fissure
28. Posterior
Median Sulcus 30.
Anterior Funiculus
31. Lateral
Funiculus 32.
Posterior
Funiculus 35.
Central Canal
Spinal Cord Model
• 1. Posterior Funiculus † 2. Lateral Funiculus † 3. Anterior Funiculus †
5. Posterior Horn * 6. Lateral Horn * 7. Anterior Horn * 8. Gray
commissure * 9. Central Canal 10. Posterior Median Sulcus 14.
Anterior Median Fissure 23. Dorsal Root 24. Dorsal Root Ganglion
25. Ventral Root 26. Spinal Nerve
•
* Gray Matter
† White Matter
The Spinal Cord
The Spinal Cord
The Spinal Cord
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Key:
Structures:
1. Posterior Median Sulcus
2. Gray Commissure
3. Central Canal
4. Anterior Median Fissure
Gray Matter:
5. Posterior Horn
6. Lateral Horn
7. Anterior Horn
White Matter:
8. Posterior Funiculus
9. Lateral Funiculus
10. Anterior Funiculus
•
Optional Features (you
will not need to find these
on the slide):
11. Pia Mater
12. Subarachnoid Space
13. Dura & Arachnoid
Maters
SPINAL CORD A" marks the central canal" .B" is the
anterior medial fissure .The posterior medial sulcus is not seen in this
preparation. C is the posterior horn composed of axons of the sensory
neuron. D is the anterior horn composed of the cell bodies of motor neurons.
C and D are gray matter .Outside the horns and the commissure that
connects them is the white matter .
Thoracic spinal Cord - H&E, silver stain
Try to identify neurones (primary dendrites, Nissl-bodies) and glial cell nuclei in the H&E
stained section. Part of the cytoskeleton of neurones is (like the reticular connective tissue
fibers) argyrophilic, i.e. they "love" silver and can be stained by silver stains. Aside from the
neurones and their processes, fine fibrils are visible in the neuropil. Many of the fibrils
represent axons travelling in the grey and white matter of the spinal cord.
The ventricles of the brain and the central canal of the spinal cord are lined with
ependymal cells. The cells are often cilated and form a simple cuboidal or low
columnar epithelium. The lack of tight junctions between ependymal cells allows a free
exchange between cerebrospinal fluid and nervous tissue.
Ependymal cells can specialise into tanycytes, which are rarely ciliated and have long
basal processes. Tanycytes form the ventricular lining over the few CNS regions in
which the blood-brain barrier is incomplete. They do form tight junctions and control the
exchange of substances between these regions and surrounding nervous tissue or
cerebrospinal fluid.
Spinal cord - center (4x objective lens)
This low magnification view shows the central region of the spinal cord .The gray matter ,which
contains the cell bodies of neurons, is more darkly stained than the surrounding white matter ,
which contains axons and dendrites. Locate the central canal of the spinal cord, located in the
center of the image. It is surrounded by a thin band of gray matter, called the gray comissure ,
which connects the larger masses of gray matter located in the left and right halves of the
spinal cord. Lighter stained regions of white matter can be seen both above and below the gay
commisure. In the lower center of the image is the ventral fissure of the spinal cord, which
divides the ventral region of the cord into two halves .
Stain = silver .
Multipolar (motor) neuron:
from the anterior horn of the spinal cord.
Peripheral Nerves
Myelination of a peripheral axon
Schwann cells form a sheath around one axon and surround this axon with several double
layers (up to hundreds) of cell membrane. The myelin sheath formed by the Schwann cell
insulates the axon, improves its ability to conduct and, thus, provides the basis for the fast
of impulses. Each Schwann cell forms a myelin segment, in which saltatory transmission
node of Ranvier the cell nucleus is located approximately in the middle of the segment. The
.is the place along the course of the axon where two myelin segments abut
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Myelination of a peripheral axon
Animation from Blue Histology, Copyright
Lutz Slomianka 1998-2004
(The image should be animated, if you watch
patiently.)
A Schwann cell is illustrated with brown
cytoplasm.
The blue oval is the Schwann cell's nucleus.
Observe that as the growing Schwann cell
spirals inward around the axon, it wraps its
membrane into layers of myelin.
In peripheral nerves, myelin consists of Schwann cell membrane
wrapped around and around an axon, while most of the
Schwann cell cytoplasm lies alongside the axon.
To visualize myelin formation:
Imagine that a Schwann cell is a pillow
with the pillowcase representing
Schwann cell membrane and the
stuffing representing Schwann cell
nucleus and cytoplasm.
Next imagine a broomstick
(representing the axon) lying across
one end of the pillow.
Now roll the broomstick up in the
pillow, wrapping the pillowcase tightly
around and around the broomstick
while squeezing the pillow-stuffing into
one end.
The tight wrappings of pillowcase now
represent the myelin, while the
remaining pillow with stuffing
represents the Schwann cell body with
nucleus and cytoplasm.
Teased nerve fibres
Osmic acid- stained teased nerve fibres to demonstrate
nodes of Ranvier.
Peripheral Nerve, rat - H&E
In longitudinal H&E stained sections it is possible to identify the axon running in its myelin sheath,
nodes of Ranvier and Schwann cell nuclei. Components of the connective tissue elements, which
accompany the nerve, should be visible and identifiable in both longitudinal and transverse sections.
H&E stained and transversely cut preparations give a good picture of the axon in the middle of a ringwhich represents the remains of the myelin sheath. Due to their small ,)sometimes fussy( like structure
size and the lack of a myelin sheath, type C fibres are very difficult to detect in either osmium or H&E
.stains
.
Nerves or nerve trunks of
peripheralnervous system
are arranged in groups or bundles
of fibers containing axons,
dendrites, and their
collaterals,bound together by
connective tissue and invested with
blood capillaries.
Peripheral Nerve cross section
Identification: A similar basic arrangement as in muscles, with fibers (4)
bundled into fascicles (1). Note that nerve fibers are much smaller than
muscle fibers and instead of being uniformly red in color have a dark
central axon (3), surrounded by white myelin (2). Individual nerve fibers,
fascicles, and the entire nerve are each surrounded by connective tissue
sheaths (5-7).
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Features to Know: connective
tissue sheaths: endoneurium (5),
perineurium (6), & epineurium (7);
nerve fiber (4) composed of an axon
(3) surrounded by myelin (2);
fascicle (1).
A nerve fascicle at higher power
Each myelinated axon appears as a dot surrounded by a
clear space where the myelin has been removed during
preparation of the histological section.
Part of a peripheral nerve treated with osmic acid
which stains myelin black. Note the variable diameters
of the myelinated axons.