Download Internal Capsule Dissection Visual Pathway Dissection Limbic

Five Dissections for Human Neuroanatomy Laboratory
L.A. Welke, J. Jakway and J.L Kubie
Department of Anatomy and Cell Biology
S.U.N.Y. Downstate Medical Center, Brooklyn NY
Abstract
For our medical school neuroanatomy labs, we rely on five specific dissections for
demonstration and teaching purposes. Two dissections are “global” and aimed at
showing the fundamental morphology of the forebrain and brainstem. Three dissections are aimed at demonstrating the gross morphological features of specific pathways.
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The Internal Capsule Dissection
The internal capsule dissection is made
on a half brain. Blunt dissection is used to
remove the temporal lobe, and the gray
matter of the parietal and occipital lobes.
This is followed by removal of the insular
cortex. The lenticular nucleus (putamen +
globus pallidus) may be removed, as in figures 2 and 3, but we usually leave it intact
(4).
The forebrain dissection, described by Heimer, (The Human Brain and Spinal Cord,
Springer-Verlag, 1983), focuses on revealing the contours of the lateral ventricle and
structures that line its walls, such as the hippocampus, thalamus, caudate, stria
terminalis and fornix.
The brainstem dissection is a continuation of the forebrain dissection. First, both
lateral ventricles are fully revealed. Second, the corpus callosum, septum pellucidum
and fornix are cut. Finally, bilateral cuts are made across the anterior perforated substance separating the hippocampus and posterior telencephalon from the anterior telencephalon. The posterior telencephalon can then be removed followed by removal of
the cerebellum, revealing the fourth ventricle and cut cerebellar peduncles.
The three “pathway” dissections target the cortico-spinal pathway, the visual pathways and the limbic pathways. The cortico-spinal pathway dissection is done on a midsagitally cut brain where blunt technique is used to remove the temporal lobe and continues deeper to reveal the lateral aspect of the corona radiata/internal
capsule/cerebral peduncle continuity. The final product reveals continuous fiber tracts
from cortex to pyramids. The “visual pathway” dissection starts with one cerebral
hemisphere transected at the midbrain. Blunt dissection is used to reveal the optic
radiation. When completed students can see gross structures of the two-neuron pathway from retina to visual cortex and the one-neuron pathway from retina to
pretectum/midbrain. The limbic dissection also starts with a cerebral hemisphere
transected at the midbrain. Sharp dissection is used to remove the diencephalon.
When completed a student can view difficult temporal lobe structures such as the stria
terminalis, fornix and dentate gyrus. Since the dissection does not damage the telencephalon, it can be used for identification of all cerebral gyri and sulci.
In the presentation we will present detailed written procedures for the dissections
in addition to photographs and videos of the dissection technique.
Internal Capsule Dissection
Forebrain / Lateral Ventricle Dissection
The first part of the lateral ventricle dissection is taken
from Heimer’s dissection guide. In brief:
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Coronal or horizontal knife cuts reveal
the relationship between the intact white
matter and the appearance of white matter
in the sectioned brain.
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1. A horizontal cut is made immediately above the corpus callosum and ventricles (1).
2. The exposure is enlarged to reveal the contour of the lateral
ventricle (2).
3. The superior and middle temporal gyri are removed revealing
the inferior horn of the lateral ventricles. (3-5).
5. Then a coronal cut is made through the corpus callosum,
septum pellucidum and fornix down to the interventricular
foramen (6 and 7).
The Posterior Forebrain
The posterior forebrain is removed rather easily. First, the base of the fornix is lifted from the transverse cerebral fissure (6).
Second lateral-to-medial cuts are made
immediately anterior to the base of the
hippocampus across the anterior perforated substance. The position of the cut is
indicated in red (5,7,8, 9 & 11). The posterior forebrain is removed (7 & 8).
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Visual Pathway Dissection
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Brainstem Dissection
Use of the Dissections
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http://ect.downstate.edu/courseware/neuroscience/
(thanks to Brett Laurance at Downstate’s Educational Computer and
Technology group for help with setting up the website)
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Final Visual Pathway
Left is a final dissection, made “bilateral” in Photoshop. Right is a closeup
showing the optic tract, the geniculates, the pulvinar and the optic radiation.
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We find that each of the other dissections serves similar purposes.
They teach basic anatomical relationships while buttressing functional systems.
The photos on this poster can be viewed and downloaded from:
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Although each of these dissections show useful anatomical relationships, we have found that several do double service at particular
times during the course. In our first wet brain lab students examine
the ventral surface of the brain and see many components of the
cortico-spinal pathway. Introducing the internal capsule dissection
makes it easier to show the continuity of this path, and permits a
clear introduction of a functional system. In a similar fashion, the
visual pathway dissection isi introduced in the second lab, and puts a
number of external brain structures into a functional context.
On the Web
Limbic Dissection
The brainstem remains
behind after the posterior forebrain is
removed in the lateral
ventricle dissection
(above). The posterior
cerebellum is removed
with a single knife cut
revealing the floor of
the fourth ventricle.
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The Visual Pathway Dissection
The visual pathway dissection is a blunt dissection done on a half brain cut at the midcollicular level. It begins by separating the
uncus from the thalamus (2). The medial temporal lobe is removed (3), tearing into the
posterior horn of the lateral ventricle. The dissection concludes by opening the calcarine
fissure and removing most of the occipital
lobe (4 & 5). The goal is to reveal the optic
radiation and the posterior-inferior thalamus –
e.g. the geniculates plus the pulvinar.
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