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Boxster
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VIII.
MUSCLE There
are three basic types of muscles in vertebrates, smooth, skeletal, and
cardiac. It is essential that you learn to recognize each of these three types
of muscle in any plane of section. Pay attention to the shapes of cells
and their relative sizes. Compare the size, shape, and location of nuclei.
Note the banding pattern in the two types of striated muscle. A.
Skeletal Muscle Slides
12, 57, 30 (skeletal muscle, tongue) Skeletal
muscle fibers (cells) range in size from 10-100 um in diameter.
They may be as long as a whole muscle. They arise from the fusion of many
multinucleate cells in the embryo. Each fiber is a syncytium
(a multinucleate mass of protoplasm derived from the fusion of uninucleate
cells). Each fiber consists of many contractile units called myofibrils which
are in turn composed of thick (myosin) and thin (actin) filaments. Each
fiber appears banded or striated because of the ordered arrangement of the
myofibrils (side by side) within the fiber. The fundamental repeating units
within the myofibril are the sarcomeres which are
visible with the light microscope. Examine the slides of skeletal muscle and
tongue. Locate the sarcomeres and with the aid of
the diagrams in your text locate the Z- lines, I-bands, and A-bands. Also
note the evidence of connective tissue associated with striated muscle. Locate
the epimysium which surrounds the whole muscle,
the perimysium which ensheathes
groups of muscle fibers and the endomysium made up
of reticular and collagen fibers that surrounds the
individual muscle fibers. Also note the different classes of muscle fibers,
slow or red, fast or white and intermediate. Using light and electron
micrographs identify the following:
1. Nuclei (peripheral location in mammals)
2. Sarcolemma (plasmalemma)
3. External lamina (on the outer surface of the sarcolemma)
4.
Myofilaments (thick and thin filaments)
5. Sarcomeres (between two successive
Z-lines)
6. Z-line
7. I-band
8. A-band
9. Motor end plate (neuromuscular junction)
10. Sarcoplasmic reticulum (smooth ER)
11. Transverse tubules (T-tubules)
12. Glycogen B.
Smooth Muscle Slides
12, 20, 21 (muscle composite, smooth muscle in artery and vein) Smooth
muscle fibers are much smaller than skeletal muscle fibers (5 um in diameter
and 20-200 um in length is typical). They are spindle-shaped and have a single
central nucleus. Their myofilaments are not
organized into sarcomeres.
The cytoplasm of smooth muscle fibers is acidophilic as in the other
two types of muscle. In H & E stained sections it is sometimes difficult
to distinguish between smooth muscle fibers and collagen fibers. Examine slide
21 and find an isolated cell. Use care in location this cells because they are
difficult to See
and it is possible to break the coverslip when searching for it. C.
Cardiac Muscle Slide
13, 22, 23 (heart muscle) Cardiac
muscle fibers usually have a single nucleus. They are found in the myocardium
of the heart and in the vessels joining the heart. The fibers appear to form a
syncytium, but in EM one can see junctions between
the cells. Regions of close contact between the ends of fibers resemble large desmosomes.
These
are called intercalated discs. Myofibrils within cardiac muscle fibers
terminate or anchor within
the area of the intercalated disc. Parts
of the intercalated disc are the macula adherents (desmosomes)
and other regions that resemble intermediate junctions in epithelia but are
spread out. These parts called fascia adherens to
distinguish them from zonulae adherents. Examine
the slide of heart muscle and note the branching nature of the fibers. Find an
area where striations are obvious to study.
Identify the connective tissue between the fibers, the centrally
located nuclei, and the intercalated discs. IX. NERVOUS SYSTEM Nervous
tissue is involved in the reception, conduction, and coordination the nervous
impulses. The structures formed by this tissue constitute the nervous system.
The nervous system is divided into the brain and spinal cord or the CNS and
the outlying nerves and fibers of called the PNS. We will first examine some
examples of different individual neurons and then nerve as a tissue. The sense
organs are specialized regions of nervous tissue and will be examined at a
later lab. Neurons A
neuron in mammals consists of a nerve cell body and its processes. The cell
body or perikaryon contains the nucleus and often
the characteristic patches of basophilic material called Nissl
bodies or tigroid bodies. What
other organelles would you expect to find in the cell body? Most
of the neurons in the CNS are multipolar neurons.
They usually have many branching processes called dendrites and a single long
process called an axon. Axons may give off collateral branches some distance
from the cell body. The term fiber
or axis cylinder can be used when it is impossible to know whether a process
is an axon or dendrite. A.
Multipolar Nerve Cells
Slides 15, 17? (neurons,
spinal ganglia?) Multipolar motor
neurons can be found in the ventral horn or the gray matter, also consult your
text. Axons from these cells pass out of the spinal cord by way of the white
matter through the ventral root of the spinal nerve. They become peripheral
nerve fibers and
eventually make contact with muscle cells at the motor end plate. Dendrites
or cell bodies of motor neurons make synaptic connections with axons of
functionally related neurons (sensory or association neurons) within the CNS.
Examine the slides of the spinal cord and observe the cells in the ventral
horn of the gray matter of the spinal cord. Locate a cell to study that has
several processes. Note the large nucleus and prominent nucleolus. B.
Unipolar Nerve Cells Slides
17 (spinal ganglia) Cell
bodies of unipolar or pseudounipolar
neurons can be found in the dorsal root spinal ganglia. These neurons are
described as T-shaped. Their processes extend from a sensory ending (for
example in the skin) within a nerve toward the spinal cord. The fiber enters
the dorsal surface of the spinal cord (dorsal root) and makes a few or many
synaptic contacts with association or motor
neurons. These cells are often stained with silver stain which
stains the The
cell body is located at the end of a side branch of the fiber (leg of the T)
along with many other cell bodies within the spinal ganglia. Try to identify
the nuclei of supporting cells called satellite cells around the cell bodies.
These are probably identical in origin with Schwann
cells. C.
Nerves and Nerve Fibers Slides
59, 19, 21 (nerve fibers) A
nerve is a bundle of neuronal processes plus their enveloping sheaths of schwann
cells and connective tissue elements. Try to locate the individual nerve
fibers (axons) within the nerves. Several hundred of these fibers are bundled
together and surrounded by a connective tissue sheath called the perineurium.
Individual nerve fibers are ensheathed by an endoneurium.
Fibroblasts, collagen fibers, capillaries and small blood vessels may be
observed within nerves. Both the myelinated
and unmyelinated fibers are surrounded by a sheath
of Schwann cells. Find the nuclei of these cells.
The myelin sheaths of myelinated fibers are a
light eosin in color. Most
of the lipid content of the myelin has been dissolved out during preparation.
Some myelin sheaths appear to have radially
arranged cracks in them (like spokes in a wheel). These are artifacts and do
not appear in high quality EM's. Try to identify
the gaps or the spaces between the schwann cells
that make up the nodes of Ranvier.
Examine
the white matter of the spinal cord (slide 15). Nerve fibers in the white
matter are myelinated and oriented parallel to the
spinal cord. In the CNS as you know there are no Schwann
cells, the myelin is formed by oligodendroglial
cells. One of these cells may form myelin around several axons at the same
time. Schwann cells do not do this. Identify the
following structures:
1. myelin
5. node of Ranvier
2. myelinated fiber
6. axon
3. unmyelinated fiber
7. Schmidt-Lanterman
clefts
4. Schwann cell Slide
16 (motor end plates) Motor
end plates are junctions between the ends of neurons and muscle fibers. A
single motor neuron may innervate one or several hundred muscle fibers. A
motor neuron plus its muscle fibers is called a motor unit. Find the
following:
1. junctional folds or clefts
2. synaptic troughs
3. synaptic vesicles
4. sarcolemma 5. plasmalemma of nerve fiber |