College Level Design: Tim Cannon http://academic.scranton.edu/department/psych/sheep/newsheep/ welcome2.html Edited by Dr. S.C. Wache
Goal: We will compare sheep brain structures with human brain structures. Compared to human cerebrum a human’s olfactory bulb is much shorter than sheep olfactory bulbs compared to the sheep cerebrum. Human cerebellum is bilobed, sheep cerebellum is not. First, we will learn body positions applied to the whole sheep brain. We will do two sections: one group will do a mid-sagittal cut, the other a coronal cut. Use the mid-sagittal section to find your location through each consecutive coronal section.
Methods and Materials: We will be dissecting a preserved adult sheep brain. Our dissection kit contains a scalpel, a fine tipped pair of scissors, a blunt metal probe, a fine tipped forceps, a blunt-tipped forceps. It is vital to wear vinyl gloves. It is important to be careful when working with preservatives. If necessary protect your eyes. Follow OSHA (office of safety and Health administration) regulations. Dispose of the dissected specimen as indicated on the MSDA (material safety and data administration) sheets. These are some additional web sites where you can obtain more information: http://labs.ansci.uiuc.edu/rwjohnson/class/braintext.html University of Scranton, Dissection of the Sheep Brain University of Scranton, The Sheep Brain Dissection Guide Michigan State University, Atlas of the Sheep Brain Interactive Atlases, Digital Anatomist Project University of Wisconsin, Global Anatomy University of Utah, Anatomy-Histology Tutorials Gray Cancer Institute On-line Medical Dictionary
Results: The result section should consist of drawings with labels on the structures that were identified.
Sheep brains arrive crudely prepared. You can see fatty tissue and three membranes, the meninges . The white film consists of a tough fibrous connective tissue, the dura mater . Note : Underneath the dura mater, there is the arachnoid mater and the pia mater. spinal cord
(Anterior) (Posterior) BODY POSITIONS:
Diencephalon LATERAL VIEW Note the gyri and sulci .
Temporal lobe Insula Note : Insula - the lobe in the center of the cerebral hemisphere that is situated deeply between the lips of the sylvian fissure -- called also central lobe , island of Reil Frontal lobe Parietal lobe Lobes of the Sheep Brain Cerebrum Occipital lobe
Pineal gland CEREBRUM AND CEREBELLUM BENT APART TO EXPOSE THE DORSAL MIDBRAIN.
Note the abducens, hypoglossal, and spinal accessory nerves. Synonym: Vestibulo-cochlear Nerve
Note : You are asked to learn all 12 cranial nerve pairs.
‘ Arbor vitae’ or ‘tree of life’ Thalamus Pineal Gland
Corpus callosum Thalamus Lateral Ventricle Third Ventricle Use this frame to assess your location in the following coronal sections. Pineal Gland
Lateral Ventricle Note the gyri and sulci. FIRST CORONAL SECTION: STARTS WITH THE ANTERIOR PORTION OF THE FRONTAL LOBE
Optic Chiasma Diencephalon:
Pituitary Gland Thalamus Hypothalamus CORONAL SECTION AT THE LEVEL OF THE PITUITARY GLAND Note: septum pellucidum - the thin double partition extending vertically from the lower surface of the corpus callosum to the fornix and neighboring parts, separating the lateral ventricles. Septum pellucidum Diencephalon:
Lateral Ventricle ThirdVentricle Midbrain (ventral surface) with mammillo-thalamic tract of fibers connecting thalamus and mammillary bodies Caudate Nucleus Caudate nucleus : one of the four basal ganglia in each cerebral hemisphere that comprises a mass of gray matter in the corpus striatum , forms part of the roof of the lateral ventricle, and is separated from the lentiform nucleus by the internal capsule
Diencephalon: Pineal gland (releases melatonin which controls circadian rhythm) Midbrain toward the Superior Colliculi
Caudate nucleus : comprises a mass of gray matter in the corpus striatum and forms part of the lateral roof of the lateral ventricle . Hippocampus: : a curved seahorse-shaped ridge extending over the roof of the descending horn of each lateral ventricle , but tissue within the temporal lobe; the hippocampus is part of the limbic system, and consists of gray matter covered on the ventricular surface with white matter. From: www.neuropat.dote.hu/anastru/test2na.htm (near Pons) Connecting tissue between colliculi (cerebral aqueduct)
Cerebellum Corpora quadrigemina (visible externally on the dorsal surface when bending open the brain between the cerebrum and cerebellum at a 45 o angle) Midbrain / near Pons (ventral surface)
Note the H-shaped center of the spinal cord consisting of gray matter.
Summary: We have studied the structures on a preserved sheep brain specimen. We have learned the functions of such structures using the lecture handout and comparing to what is known about the human brain function. We learned body positions applied to the whole sheep brain. The mid-sagittal cut was helpful in identifying the extension of the lateral ventricle to the third ventricle. The coronal cuts made it possible to find the cerebral aqueduct (aqueductus sylvii) that joins the third and fourth ventricles which house the CSF. The coronal cut helped in the location of the hippocampus along the roof of the descending lateral ventricle.