Brain Anatomy

Directions

Print this PDF worksheet for a hardcopy guide as you work through this lesson.
Within the lesson click the red linked headings to bring up the desired starting point within the cadaver for your work.
Use the provided images on the worksheet to annotate and identify specific anatomical structures.

Lateral Brain

Identify each of the following in your dissection. As always, rotate your specimen as directed or as needed to optimize your perspective. Surface anatomy is "faded" in so you have some relative reference points. Feel free to fade it out using the skin control in the toolbar below your specimen for a clearer view.

Cerebrum - Obviously the largest part of our brain, this is the "seat of our intelligence". All facets of our thinking lives occurs here.
- Gyrus (plural Gyri) - These convolutions are the gray outer folds of the brain.
- Fissures - These are the deepest grooves between brain folds. The longitudinal fissure separates the right and left cerebral lobes.
- Sulcus (plural Sulci) - the shallower grooves between the gyri
- Frontal Lobes - If you have not done so already, rotate your specimen to the anterior perspective. Locate the right and left frontal lobes. From this anterior perspective you can easily observe the right and left halves of the cerebrum referred to as the cerebral hemispheres.
- Temporal Lobes - Locate the right temporal lobe from this perspective. The lateral cerebral sulcus separates the frontal lobe from the temporal lobe.
- Parietal Lobes - Rotate your specimen back to a lateral perspective. Locate the right parietal lobe. Of course, it is mirrored on the left side as well. The parieto-occipital sulcus separates the parietal lobe from the occipital lobe.
- Occipital Lobes - Rotate your specimen to the posterior perspective. Locate the right and left occipital lobes.
Corpus Callosum - Rotate your specimen back to the anterior perspective. Reveal and locate the corpus callosum by dissecting away both frontal lobes. This nerve tract (called a commissure) internally connects the right and left cerebral hemispheres. VH Dissector labels the "genu" (Latin for "bend") which is the most anterior portion of the corpus callosum. Dissect it away and locate the trunk of the corpus callosum. As previously mentioned, this nerve tract connects between the two cerebral hemispheres allowing them to "communicate" with each other.

Ventricles

Identify each of the following cerebrospinal fluid (CSF) filled cavities of the brain called ventricles. CSF is produced by networks of capillaries in the ventricle walls called choroid plexuses. Rotate your specimen laterally to get a second perspective.

Lateral Ventricles (Right and Left)
Third Ventricle
Fourth Ventricle

Posterior Brain

Identify each of the following in your dissection. Some structures are labeled in your specimen whereas others will need to be identified with the aid of your textbook. Once again, feel free to improve the brain resolution by fading out the external anatomy. Note the prominent longitudinal fissure separating the two cerebral hemispheres extending all the way through the occipital lobes.

Tentorium - This is a part of the dura mater that creates a horizontal "shelf" between the cerebellum and the cerebrum. It should not be visible before dissecting away either the cerebrum or the cerebellum, however, it is incorrectly shown wrapping the entire cerebellum in your specimen. This is NOT accurate and will be corrected in the next version of the VH Dissector but it does allow you to highlight and dissect the tentorium without removing the cerebrum or cerebellum. Highlight the tentorium using the highlight tool and note its location in the cross section. This is the most superior aspect of the "true" tentorium. Once you have identified the tentorium, dissect it away using the dissection tool.
Cerebellum - Accounting for about 10% of the brain's total mass, the cerebellum is the second largest part.
Transverse Fissure - The deep groove that separates the cerebellum from the cerebral occipital lobes.

Rotate your specimen to the anterior perspective and locate the following:

Pons - As you can see, the pons is immediately anterior to the cerebellum. Pons literally means "bridge" which is what it does as it connects parts of the brain with one another by axon bundles. The pons is also the body's "breathing center".
Medulla Oblongata - This continuation of the spinal cord is immediately inferior to the pons. Identify the following medullary parts highlighted in your specimen:
- Right & Left Pyramids (Corticospinal Tracts & Corticobublar Tracts) - These protrusions are formed by the largest motor tracts that pass from the cerebrum to the spinal cord.
- Decussation of the Pyramids - This is the point just superior to the spinal cord where 90% of the left pyramid axons cross over to the right and 90% of the right pyramid axons cross over to the left which is why one side of the brain controls movements of the opposite side of the body.

The brain stem is the part of the brain between the spinal cord and diencephalon. The medulla oblongata, pons, and midbrain are the three parts of the brain stem.

Midbrain

You've got some dissecting to do to get into these next structures. This isn't called the "midbrain" for nothing! :-) Locate and dissect out each of the following:

Cerebellar Tentorium
Pons
Cerebral, Occipital and Temporal Lobes (Right & Left)

The posterior part of the midbrain is called the tectum which contains two pairs of rounded elevations. Locate each:

Superior Colliculus (Right & Left) - This elevation is a reflex center for certain visual activities such as tracking moving images, scanning stationary images (just as you are doing right now), pupillary reflexes, lens accommodation reflex (for focusing close and far), and various eye and head movements essential for vision.
Inferior Colliculus (Right & Left) - This elevation is part of the auditory pathway relaying nerve impulses from the ear receptors to the thalamus. It is also a "startle reflex" center causing the sudden movement of your head when you are startled.

Remove the four tectum colliculi as well as the gray columns and locate the right and left reticular formations. These monitor, filter, and integrate activities of the thalamic nuclei (which we examine in just a moment).

Diencephalon

The diencephalon extends from the brain stem to the cerebrum and includes the thalamus, hypothalamus, epithalamus, and subthalamus. It surrounds the third ventricle. We'll examine only the thalamus, hypothalamus, and a part of the epithalamus.

80% of the diencephalon is the thalamus which is only about 3 cm in length. We're going to go about this dissection a bit differently. Use the tabs at the top of this window to toggle over to "Systems", expand the "Nervous system" (click the "+" next to it on a PC, the arrow on a Mac), expand the "Central nervous system" and then expand the "Brain" which brings up a brain anatomy list. Then come right back here to "Lessons"...

What took you so long. I was beginning to get worried! You are going to dissect away major parts of the brain using the systems list. Start by selecting "Cerebrum" in the list and clicking the "Remove" button. That took care of quite a bit, eh? Next, do the same with the cerebellum. Finally, remove the midbrain, medulla oblongata, and the pons in the same manner. All that remains is the diencephalon.

Expand the diencephalon. FINALLY, select the thalamus and click the "Add & Highlight" button to fully reveal the thalamus. The thalamus is the major relay station for most sensory impulses that reach the primary sensory areas of the cerebral cortex from the spinal cord, brain stem, and midbrain. Crude perception of pain, thermal, and pressure sensations start at the level of the thalamus, exact localization of these sensations depends on nerve impulses arriving at the cerebral cortex.

Click any black space (or space with transparent skin only) in the dissection area to "de-highlight" the thalamus. Select the hypothalamus from the systems list and click the "Add & Highlight" button. As you can see, the hypothalamus is inferior and anterior to the thalamus (hence its name ... pretty clever, eh?). The hypothalamus controls many body activities and is one of the major regulators of homeostasis. Use your textbook to investigate the following important functions of the hypothalamus:

Control of the Autonomic Nervous System (ANS)
Hormone Production
Regulation of Emotional and Behavioral Patterns
Eating and Drinking Regulation
Body Temperature Regulation
Regulation of Circadian Rhythms and States of Consciousness

Pineal Body (Gland)

The epithalamus is a small area of the diencephalon that includes the pineal body (gland) which is about the size of a small pea. Obviously, the cerebrum has been removed in this posterior perspective. Locate the pineal body, a midline structure immediately superior to the cerebellum. The pineal gland is part of the endocrine system and secretes melatonin. Melatonin is thought to promote sleep since more is secreted during darkness than light. The hormone is also thought to contribute to the setting of the body's biological clock.