Dissection of the Sheep Brain

Transcription

1 Physiological Psychology Laboratory Manual 1 Dissection of the Sheep Brain Purpose In this exercise students will further reinforce their knowledge of the anatomy of the sheep brain. This laboratory exercise will involve dissecting/sectioning the sheep brain and subsequently identifying and indicating a number of subcortical structure/function relationships. Upon completion of these exercises students should be able to identify structure/function relationships of pinned areas on a laboratory exam. Prior to completing this activity students should visit the sheep brain dissection guide at: Sheep Brain Dissection Guide: and work through the guide to further familiarize themselves with the anatomy. Additional online and text sources students may wish to consult before, during, and after the laboratory exercise include: Atlas of the Sheep Brain: Sheep Brain-Anatomy of Memory: Cooley, R.K. & Vanderwolf, C.H. (1979). The sheep brain: A basic guide. Canada: Dobbyn Creative Printing Limited. Rosenzweig, M.R., Breedlove, S., & Leiman, A.L. (2002). Biological psychology: An introduction to behavioral, cognitive, and clinical neuroscience (3 rd ed.). Sunderland, MA: Sinauer Associates, Inc. Materials 1 Sheep Brain (dura mater intact) 1 Sheep Brain (dura mater removed) Latex Gloves Lab Coat Dissecting Tray Dissecting Frame Paper Towels Brain Dissecting Knife Dissecting Kit: Scalpel Fine Straight Forceps Fine Curved Forceps 8 Dissecting Pins Curved Probe

2 Physiological Psychology Laboratory Manual 2 Sharp Probe Ruler Atlas of the Sheep Brain: ( Safety Precautions Each sheep brain was originally fixed with a formaldehyde solution and is maintained in a preservative called Carosafe tm. This preservative is much less toxic than formaldehyde and serves to prevent mold growth and tissue deterioration. Due to the presence of these chemicals, students are required to wear laboratory coats and gloves at all times. Students should notify the instructor immediately if any of these chemicals come into direct contact with their skin or eyes. Since formaldehyde is a possible human carcinogen, students who are or may be pregnant may opt out of participating directly in this laboratory exercise. If you experience any irritation in your respiratory system or if you become dizzy at any point during the laboratory exercise, tell one of your group partners immediately and get assistance leaving the room (do not stand-up by yourself!). All food and beverages should be left outside of the classroom and students should wash their hands thoroughly following the completion of the laboratory exercise. Method Dissection and Identification of Mid- and Hindbrain Structures Carefully remove the scalpel from the dissecting kit. Place the sheep brain with dura mater removed in the dissecting tray. Pull down on the hindbrain so that you can see the midbrain. Separate the midbrain from the rest of the sheep brain by cutting just above the superior colliculi. Set the remaining portions (forebrain) to the side. Balance the midbrain/hindbrain section on its ventral surface in the dissecting tray. Beginning on the dorsal surface, cut the cerebellum in half, being careful NOT to cut into the medulla or pons with the scalpel. As you near the medulla/pons toward the ventral surface of the cerebellum you should find a large cavity, the fourth ventricle. Pull back the two hemispheres of the cerebellum, exposing the fourth ventricle. Remove two pins from the dissecting kit and pin back each cerebellar hemisphere in the dissecting tray. Identify the following structures of the midbrain and hindbrain and place a check mark in the appropriate bullet point. o Cerebellar Hemispheres o Cerebellar Vermi o Folia o Arbor Vitae o Cerebellar Peduncles o Fourth Ventricle o Central Canal

3 Physiological Psychology Laboratory Manual 3 o Superior Colliculi o Inferior Colliculi o Pons o Medulla Separating the Two Cerebral Hemispheres and Identifying Midsagittal Structures Place your forefinger and middle finger (of your non-dominant hand) on the left and right hemispheres respectively. Pick up the scalpel with the other hand and position it at the longitudinal fissure toward the posterior end of the brain. Put slight pressure on each hemisphere by pressing down with your two fingers and very gently draw the scalpel down the longitudinal fissure toward the anterior end of the brain using short strokes, cutting through the remaining meninges connecting the two hemispheres. Do not cut into the brain tissue or plunge the scalpel into the longitudinal fissure. Continue cutting through the meninges toward the anterior end of the sheep brain. Once completed, gently bend the hemispheres down, opening the longitudinal fissure (do not tear the hemispheres apart). You should be able to see the corpus callosum, a thick white band of tissue deep within the longitudinal fissure. Return you fingers to their original positions on the left and right hemispheres. Place pressure on each hemisphere, insert the scalpel into the longitudinal fissure toward the posterior end of the sheep brain and carefully separate the two hemispheres by drawing the scalpel toward the anterior end of the brain. Arrange each hemisphere in the dissecting tray so that the midsagittal surface is facing up. Identify each of the following midsagittal structures and place a check mark in the appropriate bullet point. You may also wish to label the midsagittal picture below. o Cerebral Aqueduct o Cingulate Gyrus o Corpus Callosum o Splenium o Body o Genu o Hypothalamus o Lateral Ventricle o Pineal Body o Septum Pellucidum o Thalamus o Third Ventricle

4 Physiological Psychology Laboratory Manual 4 Coronal/Frontal Dissection of the Right Hemisphere of the Sheep Brain Place a paper towel on the laboratory table surface and arrange the dissecting frame in the center of it. Obtain a brain-dissecting knife from your professor. Please be extremely careful, these knives are razor sharp and may cause serious injury if not handled with care. Set the right hemisphere of the sheep brain, anterior tip down (midsagittal edge flush with the brain-dissecting frame) into the dissecting frame and place the dissecting knife so that the blade rests on both edges of the dissecting frame (parallel with the table). With a firm grip on the posterior end of the brain, trying to keep the brain as straight as possible, draw the knife through the brain using long smooth strokes. Do not use short choppy or jerking strokes with the knife, as this will produce ridges in the tissue slices and may make it more difficult to identify sub-cortical structures. Please be careful not to strike the blade against the aluminum brain-dissecting tray. Flip the coronal/frontal slice over so the anterior tip of the brain is facing up and place it in the dissecting tray. Repeat this procedure until you have completely sliced the right hemisphere and arranged the tissue sections in sequential order on the dissecting tray. Please hold the right hemisphere very carefully as you approach the posterior end with each successive slice. Do not risk cutting your fingers just to get another slice of tissue. Each slice will be approximately 1/8 inch in thickness. Listed below is a table in which you should label your slices and indicate the cell stain section number and fiber stain section number (from the online Sheep Brain Atlas) which best match each of your sections. In addition, list

5 Physiological Psychology Laboratory Manual 5 the major subcortical anatomical structures and their general functions that you can identify in your slices without having to stain the sections. Slice # Cell Stain Section # Page # Fiber Stain Section # Page # Slice 1 Slice 2 Slice 3 Slice 4 Slice 5 Slice 6

6 Physiological Psychology Laboratory Manual 6 Slice 7 Slice 8 Slice 9 Slice 10 Slice 11 Slice 12

7 Physiological Psychology Laboratory Manual 7 Slice 13 Slice 14 Slice 15 Slice 16 Slice 17 Sagittal Dissection of the Left Hemisphere of the Sheep Brain Place a paper towel on the laboratory table surface and arrange the dissecting frame in the center of it. Obtain a brain-dissecting knife from your professor. Please be extremely careful, these knives are razor sharp and may cause serious injury if not handled with care. Set the left hemisphere of the sheep brain, medial surface down, in the center of the dissecting frame. Place the brain-dissecting knife so that the blade rests on both edges of the dissecting frame (parallel with the table). With a firm grip of the lateral surface of the brain, draw the knife through the brain using long smooth strokes. Do not use short choppy or jerking strokes with the knife, as this will produce ridges in the tissues slices and make it

8 Physiological Psychology Laboratory Manual 8 more difficult to identify sub-cortical structures. Please be careful not to strike the blade against the aluminum brain-dissecting frame, as this will quickly dull the knife. Flip the sagittal slice of tissue over so the midsagittal surface is facing up and place it in the dissecting tray. Repeat this procedure until you have completely sliced the left hemisphere and arranged the tissue sections in sequential order on the dissecting tray. Please hold the left hemisphere very carefully as you approach the lateral surface with each successive slice. Do not risk cutting your fingers just to get another slice of tissue. Each slice will be approximately 1/8 inch in thickness and the left hemisphere and the entire hemisphere should provide 8-10 slices of tissue. Below are sagittal sections of the left hemisphere of a sheep brain. Compare these with your sections and identify/label as many structures/regions as you can. Section 1:

9 Physiological Psychology Laboratory Manual 9 Section 2: Section 3:

10 Physiological Psychology Laboratory Manual 10 Section 4: Section 5:

11 Physiological Psychology Laboratory Manual 11 Section 6: Section 7:

12 Physiological Psychology Laboratory Manual 12 Section 8: Section 9: