Lab 8. Sheep Brain Dissection online Lab Handout-1

Summer 2020 Bio160 Name(s): ____Evelyn Alvarado___________________________ Date: __________________________ Lab 8: Sheep Brain Dissection online lab This lab is similar to the lab done in class; you use a video to watch the dissection. The link to the video is on canvas Materials: Dissection tools and trays, safety goggles, lab gloves, preserved specimen Introduction : The sheep brain is quite similar to the human brain except for size. The sheep has a smaller cerebrum and the sheep brain is oriented anterior to posterior whereas the human brain is superior to inferior. Instructions: Read through the following instructions to dissect the sheep brain and identify the structures in bold associated with the brain. Boxes are provided after each step so you can keep track of where you are in the procedure by placing a check mark in the box. 1. The tough outer covering of the sheep brain is the dura mater , one of three meninges (membranes) that cover the brain. As you remove the dura mater you can see fine strands of tissue that look like a spider-web – that is the arachnoid mater . The clear membrane that covers the surface of the brain and gives it a shiny appearance is the pia mater . 2. The brain has 4 main divisions: Cerebrum, Cerebellum, Brainstem and Diencephalon . The Brain stem is further divided into midbrain , pons and medulla . The diencephalon is further divided into thalamus , hypothalamus and epithalamus . 3. The most prominent feature of the brain is the cerebrum - which is divided into nearly symmetrical left and right hemispheres by a deep fissure, called the longitudinal fissure. Gently pull the two cerebral hemispheres away from each other (do not tear the brain tissue) and look down in the longitudinal fissure. The structure that connects the cerebral hemispheres physically and functionally is the corpus callosum. 4. The superficial wrinkled area of the cerebrum is called the cerebral cortex. In general, the cerebral cortex is involved in forming memories, higher reasoning, learning, and the conscious perception of sensation. The cerebral cortex is divided into lobes. The names of the lobes correspond to the skull bones that cover the lobe. Identify the general areas of the following lobes: temporal lobes, parietal lobes, frontal lobe, and occipital lobe . 5. The surface of the cerebrum is covered with large folds of tissue called gyri . The grooves between the gyri are sulci . 6. The smaller, rounded structure at the back of the brain is the cerebellum . The transverse fissure is the deep sulcus that separates the cerebrum from the cerebellum. The cerebellum has smaller gyri than the cerebral gyri. 1

Summer 2020 Bio160 7. Turn the brain over so you are looking at the inferior side of it. The most prominent structure visible on the ventral side of the brain is the optic chiasma , where the two optic nerves cross over each other and form an “X” shape. This structure is involved in vision. 8. The pituitary gland is a pea-sized, round structure that hangs inferior to the chiasma. Many times, the pituitary might be missing as it may be accidentally removed with the dura mater. 9. Toward the anterior part of the brain are two prominent round structures, the olfactory bulbs . These are involved in transmitting signals to the brain that give us a sense of smell. 10. Find the optic chiasma (the “X”) again – moving posteriorly/inferiorly along the brain stem , identify the bulges of the midbrain , the pons , and the medulla oblongata . 11. Carefully bend the cerebellum away from the cerebrum to look down into the transverse fissure to get an inside glimpse of the midbrain. The bumps you see (that kind of resemble a “butt”) are the superior colliculi . The smaller ones underneath are the inferior colliculi . 12. Use a large knife to cut the specimen in half along the longitudinal fissure . This will allow you to separate the brain into the left and the right hemisphere . You should also cut through the cerebellum . Lay one side of the brain on your tray to locate the structures visible on the inside. 13. The corpus callosum had been connecting the two cerebral hemispheres and can now be clearly seen in the brain section as a lighter-colored band of tissue that looks like a flattened “C”. 14. Inferior to the corpus callosum is a round structure known as the thalamus . Just posterior to the thalamus is the pea-sized, round pineal body (gland), which is also known as the epithalamus. The hypothalamus is inferior to the thalamus. The pituitary gland hangs inferior to the hypothalamus and it can be seen externally just posterior to the optic chiasma. The thalamus, hypothalamus, and epithalamus are all part of the diencephalon . 15. The pons , medulla oblongata , cerebellum, and spinal cord are also visible in the side view of the brain. The spinal cord is the structure connected to the brainstem inferior/posterior to the medulla oblongata. 16. Within the cerebellum, you can see white matter called the arbor vitae , named because the white lines resemble a tree. 2

Summer 2020 Bio160 Pic 3. Midsagittal view of the sheep brain (Kwantien Polytechnic University.edu) Questions: 1. Put the meninges (“maters”) in order from superficial to deep. Dura mater, arachnoid mater, and pia mater. 2. What are the two halves of the cerebrum called? The two halves of the cerebrum are called the right and left hemispheres. 3. What is the superficial, wrinkled region of the cerebrum called? It's called the cerebral cortex but also gray matter. 4. What is the name of the deep sulcus that divides the two halves of the cerebrum? The longitudinal fissure divides the two halves. 5. What structure connects the two halves of the cerebrum structurally and functionally? The corpus callosum connects both halves. 4 Cerebral cortex Epithalamus Colliculi Corpus callosum Cerebellum White matter is Arbor vitae Medulla oblongata Thalamus Optic Chiasm

Summer 2020 Bio160 6. What is the name of the deep sulcus that separates the cerebrum from the cerebellum? The longitudinal fissure also separates the cerebrum from the cerebellum. 7. What three structures make up the diencephalon? The thalamus, hypothalamus, and epithalamus make up the diencephalon 8. What three structures make up the brainstem? The midbrain, pons, and medulla oblongata make up the brainstem. 9. The optic chiasma is associated with which special sense? The optic chiasma is associated with vision. 10. The olfactory bulbs are associated with which special sense? The olfactory bulbs are associated with sense of smell. 5