UA PSIO 201 - Sheep Brain Dissection Guide 1

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Human Anatomy & Physiology I PSIO 201Sheep Brain Dissection Guide(Includes Important Sheep Brain Structures, Regions, and Features to Know)Before lab please make sure to review the PlayPosIt Bulb on the Sheep Brain.Additionally, this resource is provided for you to see certain steps of the dissection labeled: the Dissection:1. Put on gloves and goggles2. Your sheep brains may have fat around the optic nerves and pieces of the ethmoid boneattached to the olfactory bulbs. If this is the case, remove the fat and ethmoid bone using ascalpel and/or scissors.● The sheep brain is covered with a glossy, tough outer connective tissue layer called thedura mater. You can see two structures before removing the dura mater: the pituitarygland and the optic chiasm. The pituitary gland produces and secretes manyhormones. The optic chiasm is where the optic nerves (cranial nerve II) cross. Whenyou remove the dura mater, these two structures will likely be pulled off.3. Carefully remove the dura mater. Be careful and do not remove the cerebellum.● Once the dura mater is removed, you can clearly see 3 of the 4 principle regions of thebrain: the brainstem, cerebellum, and cerebrum.● The surface anatomy features you can see are the lobes of the cerebrum (frontal lobe,temporal lobes, parietal lobes, and occipital lobe), the longitudinal fissure,which separates the two hemispheres of the cerebrum, the transverse fissure, whichseparates the cerebrum from the cerebellum, as well as the gyri (bumps), and sulci(grooves) of the brain. You should know two specific gyri of the cerebrum: thepre-central gyrus, which is just anterior to the central sulcus, and the post-centralgyrus, which is immediately posterior to the central sulcus. One other sulcus you shouldknow is the lateral sulcus, which separates the frontal and temporal lobes.● When you removed the pituitary gland while cutting the dura mater, you may have alsoremoved the infundibulum, the structure attaching the pituitary gland to thehypothalamus. You can also see the 12 cranial nerves. You should be able to identifycranial nerves I-VI on a sheep brain for the practical. We will go over the cranialnerves during lab 9.4. Look at the posterior view of the brain.● Bend the cerebellum down to view the superior and inferior colliculi. Together,these four structures of the diencephalon make up the corpora quadrigemina. Thesestructures are visible at the gap between the cerebrum and the cerebellum at thetransverse fissure. Above the superior and inferior colliculi, you can see the pinealgland, an endocrine structure that produces melatonin.Human Anatomy & Physiology I PSIO 2015. Use a scalpel and the longitudinal fissure as a guide to separate the left and right hemispheresof the cerebrum and cerebellum.● You are now able to view another principle region: the diencephalon. In thediencephalon, you should be able to locate these specific regions: the thalamus,epithalamus, and hypothalamus. The thalamus, which is the round region in themiddle of the diencephalon, contains the intermediate mass, a structure which may ormay not be visible depending on how you dissected your brain. You can find theepithalamus by first finding the pineal gland, which you found earlier. If you trace thepineal gland anteriorly, the structure you are tracing is the epithalamus. Thehypothalamus is the region below, or inferior to, the thalamus.● In the midsagittal view, you should be able to find these structures: the corpuscallosum, the lateral ventricles, the third ventricle, the fornix, the choroidplexus, the optic chiasm, and the mammillary body. The corpus callosum connectsthe two cerebral hemispheres. The lateral ventricles are spaces that fill with CSF; they arelocated below/inferior to the corpus callosum. The third ventricle is a space surroundingthe thalamus. Like the lateral ventricles, the third ventricle fills with CSF. The fornix ispart of the limbic system and looks as though it helps enclose the lateral ventricles. Thechoroid plexus is a bundle of capillaries that filters blood plasma into CSF and is locatedabove/superior to the epithalamus. The mamillary body is posterior to the optic chiasmaand the hypothalamus.● Looking at the cerebellum, you should see a distinct tree-like white area of white mattercalled the arbor vitae. The gray matter that surrounds this is called folia. Near thebrainstem, you will see a triangular space called the fourth ventricle. The cerebralaqueduct is a structure that joins the third and fourth ventricles. The vermis connectsthe two hemispheres of the cerebellum. This is the structure you cut through whencutting through the longitudinal fissure.● In the brainstem, you should be able to find these specific regions: the medullaoblongata, the pons, and the midbrain. In the midbrain, you should be able to findthese structures that you previously found: superior and inferior colliculi.6. If you cut a cross-section of the cerebrum, you will be able to note the difference between thewhite and gray matter of the cerebrum.Human Anatomy & Physiology I PSIO 201The following structures/regions on the sheep brain are testable for the exam:• Dura mater*• Pituitary gland*, infundibulum• The PRINCIPLE regions of the brain● Cerebrum● Cerebellum● Diencephalon● Brainstem• The SPECIFIC regions of the brain● Medulla oblongata*● Midbrain*● Pons*● Thalamus*● Hypothalamus*● Epithalamus*• The surface anatomy: the specific gyri, sulci, fissures, lobes (4).● Pre-central gyrus● Post-central gyrus● Longitudinal fissure● Transverse fissure● Occipital lobe● Parietal lobe● Frontal lobe● Temporal lobe• Pineal gland*• Optic chiasm• Mamillary body• superior colliculi* & inferior colliculi*= corpora quadrigemina• Arbor vitae, folia, and vermis• Corpus callosum*, lateral ventricles, fourth ventricle, cerebral aqueduct• Gray matter, white matter, choroid plexus*• Cranial nerves*: I-VI*You should be able to name functions for any starred (*)

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