28 Dissection of the Brain

Elise C. Davis, PhD

Anatomy Lab Information

Ebling Library’s Anatomy Resources Guide

Link to Brain chapter in M&M e-book

Link to Brainstem chapter in M&M e-book

The instructions in this chapter give you some different approaches to follow as you examine the brain. However, you are free to dissect the brain as you like to explore the structures and anatomical relationships that you are interested in. Feel free to ask for guidance from an instructor.

There are no videos of this dissection.

Learning Objectives

  • Locate and identify major anatomical features of the cerebrum, cerebellum, and brainstem, including lobes, sulci, gyri, nuclei, and tracts on whole brains and in sections and dissections.
  • Trace the pathways of CSF and blood flow around the brain and brainstem.
  • Dissect to find structures in coronal, axial, sagittal, and other sections through the brain and brainstem.

Quick Links to Each Step

Whole Brain

Sagittal Sections

Coronal Sections

Axial Sections

Dissections

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Instructions

The brain and brainstem are complicated three-dimensional structures. A single dissection does not expose all of their regions and structures or give an adequate picture of the three-dimensional organization. For this lab, there are several different sets of instructions to use:

Use these instructions to first examine the whole brain from the donor. Then choose a way to dissect it–one of the methods listed here, or your own exploration. There are also whole and already-sectioned brains available for study. Look for the buckets in the lab.

Whole Brain

In this approach, you will gently dissect away the arachnoid in order to examine the structural landmarks on the superior, lateral, and inferior surfaces of the brain and brainstem. Then, you will follow the courses and branching of the cerebral and cerebellar arteries from their origins on the inferior surface of the brain.

Step 1: Gently Remove Arachnoid from the Superior and Lateral Brain

Using the blunt end of a probe, gently pick away the arachnoid on the superior and lateral sides of the cerebral hemispheres. Your goal is to see the gyri and sulci of the cerebral cortex more clearly.

  • For now, do not dissect the arachnoid over the inferior brain and brainstem. You will do that in a later step.
  • Brain tissue is very soft and easy to gouge out. Keep your probe very shallow as you remove the arachnoid.

Atlas Images – Click to Enlarge

Donor Images – Click to Enlarge

 

 

SMPH Collection

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Step 2: Identify Brain & Brainstem Regions; Locate Longitudinal and Transverse Fissures

Delineate the main regions of the brain and brainstem that are visible in a whole brain:

  • cerebrum
  • midbrain
  • pons
  • medulla
  • cerebellum

Find the two large fissures which separate the brain into different parts:

  • transverse fissure
    • separates the cerebrum from the cerebellum
  • longitudinal fissure
    • separates the right and left hemispheres of the cerebrum

Gently move the right and left cerebral hemispheres apart and look down into the longitudinal fissure to see the corpus callosum.

  • The corpus callosum (a commissural tract) is the major white matter connection between the left and right cerebral hemispheres.

Atlas Images – Click to Enlarge

Donor Images – Click to Enlarge

Knowledge Check

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Step 3: Delineate Lobes, Sulci, & Gyri of the Cerebral Cortex

Locate and delineate the frontal, parietal, temporal, and occipital lobes of the cerebral cortex.

  • Be sure to find each lobe from the lateral, superior, and inferior surfaces.

Locate the following features of the cerebral cortex:

  • lateral sulcus (aka lateral fissure)
  • central sulcus
    • separates the frontal and parietal lobes
  • parieto-occipital sulcus
    • separates parietal and occipital lobes
    • may be visible at the superior margin of the cerebral cortex, but is mostly visible medially
  • precentral gyrus (primary motor cortex)
    • just anterior to the central sulcus
    • origin of axons of the lateral corticospinal tract (LCST)
  • postcentral gyrus (primary somatosensory cortex)
    • just posterior to the central sulcus
    • destination of dorsal columns & spinothalamic pathways
  • uncus
    • anteromedial projection of temporal lobe (part of the parahippocampal gyrus)
    • adjacent to the midbrain

Spread the lateral fissure apart to see the insular lobe of the cerebral cortex deep to the frontal, parietal, and temporal lobes.

  • During development, the frontal, parietal, and temporal lobes grow over the insula due to the extensive growth and folding.

Remember that the precentral gyrus and postcentral gyrus are organized somatotopically.

  • Specific regions of the cerebral cortex control sensation or movement from particular parts of the body. Understand the general patterns of somatotopic organization in these gyri.
    • Areas of the pre- and postcentral gyri that are near the lateral sulcus control movement and sensation from the face and head, while areas of these gyri near the longitudinal fissure control movement and sensation from the lower limb.

Atlas Images – Click to Enlarge

Donor Images – Click to Enlarge

Knowledge Check

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Step 4: Find Broca’s and Wernicke’s Areas

There are two language association areas in the cerebral cortex which are critical to production and comprehension of meaningful language. These two areas are typically located in the left cerebral hemisphere.

  • Broca’s Area (production of language)
    • located in the left prefrontal cortex, just anterior to the parts of the precentral gyrus that control the muscles involved in speech
  • Wernicke’s Area (comprehension of language)
    • located at the posterior end of the lateral sulcus in the temporal and parietal lobes

Donor Images – Click to Enlarge

Adapted from Marieb et al

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Step 5: Gently Remove Arachnoid from the Inferior Surface of the Brain and Brainstem

As you did in the first step of this dissection, use the blunt end of a probe to gently pick away the arachnoid on the inferior side of the brain and brainstem if it is still intact.

  • Your goal is to see the brainstem and the arteries of the circle of Willis more clearly.
  • Keep all of the branches of the basilar artery and circle of Willis intact.
  • Brain tissue is very soft and easy to gouge out. Keep your probe very shallow as you remove the arachnoid.

Atlas Images – Click to Enlarge

Netter

Donor Images – Click to Enlarge

Adapted from Marieb et al.

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Step 6: Locate Structures of the Diencephalon and Midbrain

At the base of the diencephalon, identify the:

  • optic chiasm
    • where the fibers of CN II (optic nerve) cross
  • pituitary stalk (infundibulum)
    • the pituitary gland is pulled off when the brain is removed from the cranial cavity
  • mammillary bodies
    • nuclei of the hypothalamus

Pay attention to the anatomical relationships of these structures to other areas of the brain and to bones of the skull and the cranial cavity.

Find the midbrain and its features:

  • crus cerebri (the basis / basilar region of the midbrain)
    • on the ventral side
    • white matter tracts connecting the midbrain and the cerebral cortex
    • contains the axons of the lateral corticospinal tract (LCST)
    • The crus cerebri are often referred to as the “cerebral peduncles.” The term cerebral peduncles can also refer to the crus cerebri and parts of the midbrain tegmentum together.
  • Dorsally, gently open the transverse fissure to see:
    • superior colliculi (visual reflexes)
    • inferior colliculi (auditory reflexes)
    • Together the 2 pairs of colliculi comprise the tectum of the midbrain (the region dorsal to the cerebral aqueduct).

Atlas Images – Click to Enlarge

Donor Images – Click to Enlarge

Adapted from Marieb et al

 

Knowledge Checks

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Step 7: Locate Structures of the Cerebellum, Pons, and Medulla

Find the cerebellum.

  • The cerebellum can be divided into right and left hemispheres. The hemispheres are divided into lobes.

Locate these landmarks:

  • superior, middle and inferior cerebellar peduncles
    • white matter tracts connecting the cerebellum to the brain and brainstem
    • on the inferior surface of the brain, the middle cerebellar peduncles (from the pons to the cerebellum) are the most obvious
    • **You can dissect to see the course/extent of the cerebellar peduncles later. Link to instructions:
  • cerebellar tonsils
    • the inferiormost part of the posterior lobe of the cerebellum; located just superior to foramen magnum of the skull.

On the ventral brainstem, locate:

  • pons
  • ventral (basilar) pons
    • the horizontally-oriented band of fibers
  • medulla
    • pyramids
      • more medial set of longitudinal swellings, flanking the midline
      • contain the fibers of the lateral corticospinal tract (LCST)
    • olives
      • swellings just lateral to pyramids

Atlas Images – Click to Enlarge

Donor Images – Click to Enlarge

Knowledge Check

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Step 8: Trace the Courses of the Cerebral and Cerebellar Arteries

In this step, you will trace the course of the cerebral and cerebellar arteries from their origins at the circle of Willis and the basilar artery. Structures in the brain and brainstem receive blood from whichever arteries are nearby.

  • To get oriented, find the internal carotid artery.
  • Trace the anterior cerebral artery anteriorly.
    • It travels between the cerebral hemispheres, within the longitudinal fissure, and runs superior to the corpus callosum.
  • Trace the middle cerebral artery laterally.
    • It travels within the lateral sulcus between the frontal and temporal lobes and runs along the insula.
  • Trace the posterior cerebral artery as it arises from the basilar artery.
    • It travels through the transverse fissure between the cerebrum and cerebellum.
  • Trace the superior cerebellar arteries from their origin at the basilar artery.
    • They travel from the superior part of the basilar artery across the pons to the cerebellum.
    • Note that the oculomotor nerve (CN III) emerges from the midbrain between the posterior cerebral artery and superior cerebellar artery.
  • Trace the anterior inferior cerebellar arteries (AICA) which branch from the inferior part of the basilar artery toward the cerebellum.
  • Trace the posterior inferior cerebellar arteries (PICA) which branch from the left and right vertebral arteries.

Atlas Images – Click to Enlarge

Donor Images – Click to Enlarge

SMPH Collection

Knowledge Checks

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After you have reviewed the whole brain, choose which plane you will section your brain in: sagittal, coronal, or axial. Or, feel free to dissect the brain any way you like to see structures and relationships that you’re interested in. (Instructions for dissecting the internal capsule, hippocampus, and cerebellar peduncles are below.)

Sagittal Sections

In this approach, you will section the brain and brainstem into right and left halves by making one cut in the mid-sagittal plane, through the longitudinal fissure and extending through the brainstem. This will give you a good view of structures located near the midline of the brain and brainstem.

Step 1: Section the Brain in the Mid-Sagittal Plane

Use A Really Big Knife to cut the brain into right and left halves. Position the knife in the center of the longitudinal fissure. Make the cut carefully, in one smooth motion, to keep the midline structures from shredding as you cut. Continue the cut all the way through the brain and brainstem.

Donor Images – Click to Enlarge

Adapted from Marieb et al.

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Step 2: Delineate Lobes, Sulci, and Gyri on the Medial Side

Locate the following features of the medial side of the cerebral cortex:

  • central sulcus
    • separates the frontal and parietal lobes
  • parieto-occipital sulcus
    • separates parietal and occipital lobes
  • calcarine sulcus
    • within the occipital lobe (is flanked by the primary visual cortex)
  • cingulate sulcus
    • superior and parallel to the corpus callosum; is superior to the cingulate gyrus (part of the limbic system)
  • precentral gyrus (primary motor cortex)
    • just anterior to the central sulcus
    • origin of axons of the lateral corticospinal tract (LCST)
  • postcentral gyrus (primary somatosensory cortex)
    • just posterior to the central sulcus
    • destination of dorsal columns and spinothalamic pathways
  • uncus
    • anteromedial projection of temporal lobe (part of the parahippocampal gyrus)
    • adjacent to the midbrain

Atlas Images – Click to Enlarge

Donor Images – Click to Enlarge

Knowledge Checks

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Step 3: Examine Corpus Callosum and Lateral Ventricles

On the medial side of the brain, examine the extent and anatomical relationships of the corpus callosum.

  • The corpus callosum is just superior to the lateral ventricles, which are C-shaped and located within each cerebral hemisphere.
  • Each lateral ventricle drains into the third ventricle through an interventricular foramen (there are two).
    • Look for the interventricular foramina (foramina of Monro) at the base of the lateral ventricle.
    • Look for patches of choroid plexus in the ventricles.
      • Cerebrospinal fluid is made in the patches of specialized ependymal cells.
  • The cingulate gyrus surrounds the external margins of the lateral ventricles (and corpus callosum) superiorly.

Atlas Images – Click to Enlarge

Netter

Donor Images – Click to Enlarge

 

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Step 4: Locate Structures of the Diencephalon and Brainstem

On the medial side of the diencephalon, locate:

  • thalamus
    • the right and left thalami flank the midline third ventricle
  • hypothalamus
    • the (small) triangle-shaped region between the bulge of the thalamus and the optic chiasm and pituitary stalk (infundibulum)
    • the mammillary bodies are nuclei in the postero-inferior hypothalamus
    • the right and left hypothalami flank the inferior part of the third ventricle
  • pineal gland (part of the epithalamus)
  • fornix
    • just superior to the thalamus
    • fiber tract connecting the hippocampus and hypothalamus
      • the tract ends at the mammillary bodies

Delineate the regions and landmarks of the brainstem:

  • midbrain
    • tectum
    • superior & inferior colliculi
    • cerebral aqueduct
  • pons
    • ventral/basilar pons
      • contains the fibers of the lateral corticospinal tract (LCST)
    • tegmentum
      • contains the cranial nerve nuclei
  • medulla
  • cerebellum
  • fourth ventricle
    • between the pons/medulla and cerebellum
    • There are three openings in the posterior wall of the fourth ventricles that connect to the subarachnoid space. CSF flows through these openings, into the subarachnoid space. CSF will return to the venous circulation through arachnoid granulations near the superior sagittal sinus.
      • These openings can be difficult to see (but you never know!):
        • Lateral apertures (foramina of Luschka) are paired openings in the lateral part of the roof of the fourth ventricles.
        • Medial aperture (foramen of Magendie) is a single midline opening.

Atlas Images – Click to Enlarge

Donor Images – Click to Enlarge

Knowledge Check

Using one or both of your sagittal sections, you can continue to a dissection of the Internal Capsule, Hippocampus, and/or Cerebellar Peduncles.

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Coronal Sections

In this approach, you will section the brain and brainstem in the coronal plane. The coronal sections will give you a good view of deeper structures and their relationships to each other and to the ventricular system. You will make 5 cuts and end up with 6 coronal sections. There are already-sectioned brains in buckets in the lab.

Step 1: Cut the Brain in the Coronal Plane

(Don’t you love an instruction that rhymes…?)

Adapted from Marieb et al.

Instructions for Coronally Sectioning the Brain

You will be making 5 coronal cuts in the brain and brainstem with A Really Big Knife. Make the cuts in the sequence listed and approximate the landmarks given. Make each cut carefully, in one smooth motion, to keep the structures from shredding as you cut. Continue the cuts all the way through the brain and brainstem.

  • Cut 1: Bisect the brain through the mid-temporal lobe and midbrain
    • You now have 2 halves: anterior and posterior.
  • Cut 2: Bisect the posterior half through the posterior end of lateral fissure and the superior part of the medulla.
    • Set aside the posterior-most section.
  • Cut 3: Bisect the anterior half through the mid-frontal lobe.
    • Set aside the anterior-most section.
  • Cut 4: Section through the mid-parietal lobe, cerebellum, and medulla.
  • Cut 5: Bisect the remaining piece, cutting through the frontal and temporal lobes.

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Step 2: Delineate Lobes, Sulci, and Gyri on Coronal Sections

Locate and delineate the frontal, parietal, temporal, occipital and insular lobes of the cerebral cortex on the coronal sections.

  • Follow each lobe from the lateral, superior, and inferior surfaces.

Locate the following features of the cerebral cortex in coronal sections:

  • longitudinal and transverse fissures
  • lateral sulcus (aka lateral fissure)
  • uncus
    • anteromedial projection of temporal lobe (part of the parahippocampal gyrus)
    • adjacent to the midbrain
  • cingulate gyrus and sulcus

Remember that the precentral gyrus and postcentral gyrus are organized somatotopically.

  • Specific regions of the cerebral cortex control sensation or movement from particular parts of the body, as illustrated in the diagram. Understand the general patterns of somatotopic organization in these gyri.
    • Areas of the pre- and postcentral gyri that are near the lateral sulcus control movement and sensation from the face and head.
    • Areas of these gyri near the longitudinal fissure control movement and sensation from the lower limb.

Atlas Images — Click to Enlarge

Donor Images – Click to Enlarge

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Step 3: Examine White Matter and Lateral Ventricles

On the coronal sections of the brain, examine the extent and anatomical relationships of the white matter tracts in the brain.

  • The corona radiata is located just deep to the cerebral cortex.
    • It contains axons traveling into and out of the cerebral cortex.
  • The internal capsule is located deeper in the cerebrum and is composed of projections fibers, including the fibers of the lateral corticospinal tract (LCST).
    • These axons will continue caudally into the crus cerebri of the midbrain.
  • The corpus callosum is just superior to the lateral ventricles, which are C-shaped and located within each cerebral hemisphere.
  • The cingulate gyrus surrounds the external margins of the lateral ventricles and corpus callosum superiorly.

Atlas Images – Click to Enlarge

Donor Images – Click to Enlarge

 

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Step 4: Locate the Deep Nuclei and Limbic Structures of the Cerebrum

The basal nuclei (or basal ganglia) are deep nuclei in the cerebrum which regulate motor signals by promoting or inhibiting movements.

  • The corpus striatum consists of three structures:
    • caudate nucleus
      • C-shaped nucleus; wrapped around lateral ventricles
      • medial to the internal capsule
    • putamen
      • just deep to the insula
      • lateral to the internal capsule
    • globus pallidus
      • inferomedial to putamen; lateral to internal capsule
        • In coronal section, the putamen and globus pallidus together look like a candy corn (pointing medially).

Find the structures associated with the limbic system. These structures have curved shapes and oblique orientations. You will need to follow them through several coronal sections to see their full extent.

  • cingulate gyrus
    • functions in selective attention
  • hippocampus
    • functions in long-term memory
    • in three-dimensions, it’s shaped like a seahorse
      • hippocampus = seahorse (in Greek)
    • inferior to the inferior (temporal) horns of the lateral ventricles
  • amygdala
      • important for fear response and memories of fear
      • almond-shaped and –sized nucleus, just anterior to the hippocampus and the inferior horn of the lateral ventricles
  • fornix
      • arch-shaped fiber tract connecting the hippocampus to the mammillary bodies of the hypothalamus
      • arches over the thalamus
      • travels in inferior part of septum between the two lateral ventricles

Atlas Images – Click to Enlarge

Donor Images – Click to Enlarge

 

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Step 5: Locate Structures of the Diencephalon and Brainstem

In the coronal sections, find the following structures in the diencephalon:

  • thalamus
    • inferior to the lateral ventricles
    • the right and left thalami flank the midline third ventricle
  • hypothalamus
    • lateral to the inferior part of the third ventricle
    • you may see the mammillary bodies in coronal section
      • the mammillary bodies are nuclei in the posteroinferior hypothalamus
  • fornix
    • just superior to the thalamus; between the lateral ventricles
    • arching fiber tract connecting the hippocampus and hypothalamus (mammillary bodies)

On the coronal sections, find the following regions and landmarks of the brainstem:

  • midbrain
    • crus cerebri
      • white matter tract continuous with internal capsule
      • contains the fibers of the lateral corticospinal tract (LCST)
    • substantia nigra
      • black-colored region medial/dorsal to crus cerebri
    • red nucleus
      • just dorsal to substantia nigra
    • cerebral aqueduct (maybe)
    • pons
    • medulla
    • cerebellum
      • superior, middle, & inferior cerebellar peduncles
      • dentate nucleus
        • deep nucleus in the cerebellum
    • fourth ventricle
      • anterior to cerebellum

Atlas Images – Click to Enlarge

Donor Images – Click to Enlarge

Knowledge Checks

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Axial Sections

In this approach, you will section the brain and brainstem in the axial (transverse; horizontal) plane. The axial sections will give you a good view of deeper structures and their relationships to each other and to the ventricular system. You will make 5 cuts and end up with 6 axial sections. There are already-sectioned brains in buckets in the lab.

Step 1: Cut the Brain in the Axial Plane

You will be making 5 transverse cuts in the brain and brainstem with A Really Big Knife.

Adapted from Marieb et al.

Instructions for Axially Sectioning the Brain

Make the cuts in the sequence listed and approximate the landmarks given. Make each cut carefully, in one smooth motion, to keep the structures from shredding as you cut. Continue the cuts all the way through the brain and brainstem.

  • Cut 1: Bisect the brain just superior to the lateral fissure.
    • You now have 2 halves: superior/cranial and inferior/caudal.
  • Cut 2: In the inferior half, cut through the transverse fissure and midbrain.
  • Cut 3: Bisect the superior half that you’ve created.
  • Cut 4: In the section containing the temporal and occipital lobes, cut to divide the section in half.
  • Cut 5: Bisect the cerebellum and pons in the remaining inferior section.

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Step 2: Delineate Lobes, Sulci, and Gyri on Axial Sections

Locate and delineate the frontal, parietal, temporal, occipital and insular lobes of the cerebral cortex on the axial sections. Follow each lobe from the lateral, superior, and inferior surfaces.

Locate the following features of the cerebral cortex in axial sections:

  • longitudinal fissure
  • lateral sulcus (aka lateral fissure)
  • uncus
    • anteromedial projection of temporal lobe (part of the parahippocampal gyrus)
    • adjacent to the midbrain
  • cingulate gyrus and sulcus
    • just cranial (superior) to the corpus callosum

Atlas Images – Click to Enlarge

Donor Images – Click to Enlarge

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Step 3: Examine White Matter and Lateral Ventricles

Examine the extent and anatomical relationships of the white matter tracts on the axial sections.

  • The corona radiata is located just deep to the cerebral cortex.
    • It contains axons traveling into and out of the cerebral cortex.
  • The internal capsule is located deeper in the cerebrum and is composed of projections fibers, including the fibers of the lateral corticospinal tract (LCST).
    • These axons will continue caudally into the crus cerebri of the midbrain.
  • The corpus callosum is just superior to the lateral ventricles, which are C-shaped and located within each cerebral hemisphere.
  • The cingulate gyrus surrounds the external margins of the lateral ventricles and corpus callosum superiorly.

Atlas Images – Click to Enlarge

Donor Images – Click to Enlarge

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Step 4: Locate the Deep Nuclei and Limbic Structures of the Cerebrum

The basal nuclei (or basal ganglia) are deep nuclei in the cerebrum which regulate motor signals by promoting or inhibiting movements.

  • The corpus striatum consists of three structures:
    • caudate nucleus
      • C-shaped nucleus; wrapped around lateral ventricles
      • medial to the internal capsule
    • putamen
      • just deep to the insula; lateral to the internal capsule
    • globus pallidus
      • inferomedial to putamen; lateral to internal capsule

Find the structures associated with the limbic system. These structures have curved shapes and oblique orientations. You will need to follow them through several transverse sections to see their full extent.

  • cingulate gyrus
    • functions in selective attention
  • hippocampus
    • functions in long-term memory
    • in three-dimensions, it’s shaped like a seahorse
      • hippocampus = seahorse (in Greek)
    • inferior to the inferior (temporal) horns of the lateral ventricles
  • amygdala
    • important for fear response and memories of fear
    • almond-shaped and –sized nucleus, just anterior to the hippocampus and the inferior horn of the lateral ventricles
  • fornix
    • arch-shaped fiber tract connecting the hippocampus to the mammillary bodies of the hypothalamus
    • arches over the thalamus
    • travels in inferior part of septum between the two lateral ventricles

Atlas Images – Click to Enlarge

Donor Images – Click to Enlarge

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Step 5: Locate Structures of the Diencephalon and Brainstem

Find the following structures in the diencephalon that are visible in axial sections:

  • thalamus
    • inferior to the lateral ventricles
    • the right and left thalami flank the midline third ventricle
  • hypothalamus
    • lateral to the inferior part of the third ventricle
  • fornix
    • just superior to the thalamus; between the lateral ventricles
    • arching fiber tract connecting the hippocampus and hypothalamus (mammillary bodies)

Find the following regions and landmarks of the brainstem:

  • midbrain
    • crus cerebri
      • white matter tract continuous with internal capsule
      • contains the fibers of the lateral corticospinal tract (LCST)
    • substantia nigra
      • black-colored region medial to crus cerebri
    • red nucleus
      • just dorsal to substantia nigra
    • tectum (superior or inferior colliculi)
    • cerebral aqueduct
    • pons
    • medulla
    • cerebellum
      • superior, middle, & inferior cerebellar peduncles
      • dentate nucleus (depends on sections)
        • deep nucleus in the cerebellum
    • fourth ventricle
      • anterior to cerebellum

Atlas Images – Click to Enlarge

Donor Images – Click to Enlarge

Knowledge Checks

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Dissections

Using a whole or sagittally-sectioned brain, you can dissect to find the internal capsule, hippocampus, and/or cerebellar peduncles.

**To bluntly dissect structures of the brain, you can use the handle of a scalpel or a popsicle stick. Sharp poky tools don’t really work.

Internal Capsule

This dissection approaches the internal capsule from the lateral side, by dissecting through the insula and putamen/globus pallidus. Once you reach the internal capsule, you can follow it cranially to the corona radiata and/or caudally to show the continuity with the crus cerebri of the midbrain.

  • Open the lateral fissure with your hands, pulling the temporal and frontal lobes apart.
  • Make an incision through the frontal lobe about an inch (2 cm) from the margin of the lateral fissure. Make the incision parallel to the fissure.
    • Slowly remove the overhang of the frontal lobe until you expose most of the insula.
    • Do not cut into the insula (yet). Just remove part of the frontal lobe.
  • Notice the course and branching of the middle cerebral artery over the surface of the insula.
    • As you dissect, try to preserve the larger of the branches of the middle cerebral artery.
  • Make a narrow, wedge-shaped, vertical incision in the middle of the insula. Slowly but progressively enlarge the wedge-shaped opening both vertically and in depth.
    • From the surface, the layers of tissue are:
      • insula of cerebral cortex
      • thin layer of white matter (capsula extrema)
      • thin layer of gray matter (claustrum)
      • thicker layer of white matter (external capsule)
      • mass of gray matter (putamen)
        • separated by a thin fibrous layer from the deeper globus pallidus
    • Once you are deep to the globus pallidus, you will see fibers running dorsolaterally. That’s the internal capsule.
    • Continue removing the softer putamen and globus pallidus rostrally to expose a larger extent of the internal capsule.
    • You can continue to follow the internal capsule rostrally to the corona radiata and caudally to the crus cerebri of the midbrain.

 

 

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Hippocampus

The easiest way to see the course of the hippocampus is to approach it from above, as shown in the figures below. On one hemisphere, you will remove the cerebum that is cranial to the corpus callosum, then dissect the corpus callosum away to see into the lateral ventricle from above. Then, you will follow the fornix to the posterior part of the hippocampus and follow it as it courses toward the tip of the temporal horn of the lateral ventricle.

  • On one hemisphere, make an axial cut just superior to the corpus callosum. Remove that part of cerebrum.
  • Cut a window in the corpus callosum into the lateral ventricle.
    • Once you can see into the lateral ventricle, keep widening the hole in the corpus callosum and open up the roof of the lateral ventricle.
  • In the posterior end of the lateral horn, look for the fibers of the fornix sweeping posterolaterally.
    • Dissect around the fornix and follow it inferiorly as it runs into (out of) the hippocampus.
    • The hippocampus is immediately inferior to the inferior horn of the lateral ventricle.

 

 

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Cerebellar Peduncles

The cerebellar peduncles can be hard to visualize in a sagittally-sectioned brain. In this dissection, you will dissect the gray matter away from each of the three cerebellar peduncles to understand their courses, extents, and relationships.

  • Using the handle of a scalpel, or a popsicle stick, follow the middle cerebellar peduncle toward the cerebellum.
    • In the direction of the fibers, scrape away the cerebellar folia.
    • Continue peeling the cerebellar cortex away from the middle peduncle until you can see the lateral, cranial, and caudal sides of it.
    • Where the middle cerebellar peduncle meets the brainstem (and CN VIII emerges) is the cerebellopontine angle, an important clinical landmark.
  • Similarly, follow the inferior cerebellar peduncle as it meets the medulla.
    • You may see the lateral aperture (foramen of Luschka) as you dissect near the inferior part of the inferior cerebellar peduncle.
  • Then, follow the superior cerebellar peduncle as it meets the midbrain.
    • The superior cerebellar peduncle is the most medially located of the three tracts.

 

 

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Images Sources

Marieb et al, Human Anatomy, 5th edition, Pearson Education, 2008.

Netter Presenter, through Ebling Library: https://netterreference-com.ezproxy.library.wisc.edu//content/netter_atlas_8e/?task=home

http://www.neuroanatomy.ca

 

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UW-SMPH Anatomy Labs and Workshops Copyright © by University of Wisconsin School of Medicine and Public Health. All Rights Reserved.

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