ANAT 322 Lecture 2: ANAT 322 - Lecture 2
7 Jun 2018
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ANAT 322 Winter 2017
Lectures
Lecture 2:
→ Neuroanatomy: Terms and Definitions
2. Organisms that have a well-defined symmetry and orientation are described in anatomy. These axis
are used to describe where structures are located. In humans, ventral and anterior are synonymous but
also the dorsal and posterior also are synonymous. Almost all animals are bilaterally symmetric so there
is a median body axis and the CNS falls in the medial axis in humans and other animals.
3. PET scans and MRI can make optical sections through anatomical specimens and with histology we
can do physical sections.
Parasagittal means the sagittal plain goes laterally.
Horizontal sections are used in medical functional imaging for diagnostic purposes more commonly
because we look at both sides of the body from rostral to caudal.
When doing histological sections of the brain and animal neuroanatomy is coronal sections going
rostral to caudal.
4. In the first picture we can clearly see a neuron that is cortical or pyramidal because there are three
major dendrites. There is a cell body, dendrites that are thick at the cell body and become thinner as
they go further which is called tapering.
In the first picture, the axons is really thin and comes from the bottom of the neuron and is indicated
by an arrow that could also branch. It starts very thin and does not change its caliber along its curse
which is a structural difference compared to dendrites that change diameter.
5. Axons start with a certain thickness and keeps it throughout its length to the terminal whereas
dendrites taper towards the branches.
There is an internal structure to axons and dendrites made of different types of proteinatious fibers
such as microtubules, neurofilaments, actin cytoskeleton which are important for fast transport. In an
axon, this allows things synthetized in the cell body to be transported to the distant terminal in a time
delay.
Myelinated axons travel from one part of the brain to another one or to target organs in the periphery
(long, projection neurons). They have a myelin sheath and these usually go longer distances and it is
made by glial cells, in the CNS by oligodendrocytes and in the PNS by Schwan cells. It is an insulation or
multiple layers of membranes of the glial cell that surround the segment of the axon and the axonal
membrane is only open to the environment at the boundaries of the territories of the myelin, at the
Nodes of Ranvier. These accelerate the propagation of excitation along an axon because the AP needs to
be generated actively using energy and takes time. If the axon would not have myelin then this would
need to happen along each micrometer of that axonal membrane which would not be efficient. In a
myelinated axon it only happens at the nodes and the depolarization of the cytoplasm inside the axon
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ANAT 322 Winter 2017
Lectures
propagates passively where myelin is which is much faster and has to be renewed actively only at the
nodes. This is called saltatory propagation of exaltation and is much faster as compared with the
continuous excitation.
6. It was in the Renaissance times when researchers in Europe started to look at bodies and organs and
try to understand the workings and saw that brain was subdivided into different regions. They looked at
post-mortem brains and saw areas that appear dark or white and this lead them to differentiate matter
in the brain.
White matter: high concentration of myelinated axons due to myelin which is a fatty substance,
plasma membrane made of lipids. Lipids are highly reflective and repel all lights.
Gray matter: no myelinated axons or little, cell bodies, dendrites intertwined with axons, where
computations happened, etc. and these will appear pink, brown or gray depending on the fixation state
of tissue.
. I the 9’s, the siee of histolog started eplodig i parallel ith the deelopig of the
chemical industry and stains that people tried on tissues. With different stains they found that in the
brain there are different types of organization.
Cortical structures is where the cells are organized in layers that can be identified in a histological
sections.
Nuclei is when cell bodies are grouped in a non-discrete way giving it a rounded appearance.
8. Histological stain of a mouse brain in which we can see the cerebral cortex and the hippocampus
where we can see the three layers. Main layer of the hippocampus has cell bodies whereas the
peripheral and central layers are whiter and it is where the mayor dendrites project and establish
contact with axons coming through the central area. There is different densities of cell bodies in the
cortex as well and this is a coronal section.
We can also see nuclear structures in the second picture which is a horizontal section of a brainstem
of a mouse embryo which is a immunohistological stain for serotonin that define the group of nuclei
called the raphe nucleus.
9. Projection neurons are neurons with long connections with other areas of the brain or target organs.
The axons coming from them group together into bundles and eventually tracts that constitute the
white matter of the brain and have a common or similar region of origin or target.
There is for example the corticospinal tract connects the cerebral cortex (motor) to motor neurons in
the spinal cord. There is also the hypothalamus-hypophyseal tract from the hypothalamus to the
hypophysis. For example if we are looking at neuroendocrine neurons that make corticotropin releasing
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Lectures
hormone and project to the median eminence which means that these neurons have axons that form a
tract that end in the median eminence so projection and tract are synonymous.
10. Cortex is Latin for coat or mantle.
There is a system of hollow spaces that are liquid filled with the liquor or the CSF and are important
for the metabolism of the brain.
11. Early in embryogenesis, the CNS develops from a tube of cells called a neural tube. After
gastrulation, the infolding of the primordial gut, has finished, there is development of a structure
between the gut and the superficial ectoderm referred to as the corda dorsalis.
The corda dorsalis is an inducing center or a morphogenic center that induces, in the overlaying
ectoderm, the formation of an elevated plate of cells that becomes thicker, the neural plate. The center
of this plate (green) will fold in towards the corda making grooves. These peak of the neural grooves
have folds on its sides called the neural folds. Eventually, the bottom of that groove will pinch off the
neighbouring ectoderm and form a tube that will become the neural tube and the tissue in the folds will
attach to this tube on top (purple) and later will move away slightly which is referred to as the neural
crest. This neural tube will give rise to all the cells of the CNS so brain and spinal cord whereas the
neural crest will give rise to the cells of the PNS such as neuronal cells bodies not located in CNS
(ganglion), sympathetic nervous system and melanocytes of the skin.
12. The tube has a hollow space which is where the ventricular system comes form. Early on in
development, the anterior end of the tube differentiated into the brain by forming the two hemispheres
that will become the telencephalon as well as the diencephalon.
13. Hemispheres form the cerebral cortex, we have the corpus callosum, the diencephalon
(hypothalamus), midbrain, hindbrain (cerebellum, medulla oblongata).
Medulla oblongata: primary sensory nuclei are located as well as many sensory vital functions that
connect to the spinal cord.
→ Anatomical Organization of the Neuroendocrine Hypothalamus
16. From the ventral side, we can see the olfactory nerves on top and the optic chiasm in the red square
in which optic nerves cross so that information of the eye is processed in the contralateral side of the
hemisphere. In lower vertebrates, there is no 100% crossing in humans only the nasal RGC cross but
most other vertebrates do have complete crossover because of the location of the eyes.
The crossing of the optic nerve and the pons demarcate the anterior and posterior end of the
hypothalamus at the base of the brain. In the frontal section, it is located down.
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Document Summary
Neuroanatomy: terms and definitions: organisms that have a well-defined symmetry and orientation are described in anatomy. These axis are used to describe where structures are located. In humans, ventral and anterior are synonymous but also the dorsal and posterior also are synonymous. Horizontal sections are used in medical functional imaging for diagnostic purposes more commonly because we look at both sides of the body from rostral to caudal. When doing histological sections of the brain and animal neuroanatomy is coronal sections going rostral to caudal: in the first picture we can clearly see a neuron that is cortical or pyramidal because there are three major dendrites. There is a cell body, dendrites that are thick at the cell body and become thinner as they go further which is called tapering. In the first picture, the axons is really thin and comes from the bottom of the neuron and is indicated by an arrow that could also branch.
