BIOL 2401 Dissection of the Sheep and Human Brain Laboratory Objectives After completing this lab, you should be able to: Identify the main structures in the sheep brain and to compare them with those of the human brain. Identify and locate the main structures in the human brain by viewing an actual human brain from a cadaver using Anatomy & Physiology Revealed, Version 0 CD. Describe the functions of the main structures of the sheep brain and human brain discussed in lab. Identify the cranial nerves and describe their functions. INTRODUCTION The human brain is the largest and most complex organ of the nervous system. It weights about 3 pounds in an average adult and is mainly composed of nervous tissue. It is made up of about 100 billion neurons and approximately 900 billion neuroglia cells. The brain is responsible for body sensations and perception, initiates and coordinates muscle contractions and body functions, and carries on higher mental abilities, such as thinking, memory, etc. The brain is divided in four parts: (1) cerebrum; (2) brainstem, which consist of midbrain, pons, and medulla oblongata; (3) diencephalon, which consists of the thalamus and hypothalamus; and (4) cerebellum. Twelve pairs of cranial nerves arise from the underside of the brain: 2 pairs arise from the cerebrum and 10 pairs of cranial nerves arise from the brainstem. These cranial nerves are designated by numbers and names. The number indicates the order in which the nerve arises from the brain, form anterior to posterior. The name comes from the primary functions or general distribution of the cranial nerve. In this laboratory, you will dissect the main parts of the sheep brain. Most of these parts are similar in structure to the human brain while some are not. However, the sheep brain is an excellent organ used to understand the mammalian brain structures and functions. Therefore, the parts of the sheep brain that you will dissect will be compared with those of the human brain in structure and function. You will also identify parts of the human brain by viewing an actual brain from a cadaver by using your Anatomy & Physiology Revealed, Version 0 CD. 1
Procedure NOTE: use TABLE 1 to describe functions and appearance or characteristics for each part of the sheep brain that you dissect. PART A Meninges, Cerebrum, Cerebellum & Spinal Cord Obtain a preserved sheep brain. Examine the surface of the sheep brain for the presence of meninges. Most likely you will only see the pia mater as the outermost layers (dura mater and arachnoid mater) were lost in the removal process of the sheep brain from the cranial cavity. Dura Mater Pia Mater Use the pointed prove to pick a piece of pia mater at several parts of the brain and also at the spinal cord. Sheep Brain Position the sheep brain with its anterior surface on the dissecting tray. Locate the following structures: Cerebrum Cerebellum Spinal Cord Posterior View 2
PART B Cerebrum With the sheep s brain anterior surface on the dissecting tray, identify and locate the longitudinal fissure, the 2 cerebral hemispheres (right and left cerebral hemispheres), and the transverse fissure. Longitudinal Fissure Use the blunt prove to pierce through the pia mater at the surface of the longitudinal fissure. Notice that the 2 fissures you are observing are deep grooves. Left Cerebral Hemisphere Right Cerebral Hemisphere Transverse Fissure Spinal Cord Posterior View Identify gyri and sulci at the cerebrum of the sheep brain. Gyrus = singular Gyri = plural Sulcus = singular Sulci = plural Sulci Gyri How are gyri of the human brain different from the ones on the sheep s brain? Posterior View 3 Use the blunt prove to pierce through the pia mater on the surface of sulci. Notice that sulci are shallow grooves.
The cerebrum is divided in 5 lobes: Frontal, Parietal, Temporal, Occipital, and Insula. In the lab you will only locate and identify the following 4 lobes of the cerebrum: Frontal Lobe-lateral view Parietal Lobe-lateral view Temporal Lobe-lateral view Occipital Lobe-lateral view NOTE: Do other views of the sheep brain to identify lobes: superior, inferior views Grab the cerebrum and the cerebellum and GENTLY bend downward the two of them. This will expose the corpora quadrigemina (four rounded structures that make up the midbrain of the brainstem). Notice that on the superior portion of the corpora quadrigemina you will see the pineal gland. Cerebrum Pineal Gland Midbrain Cerebellum 4
With the anterior portion of the sheep s brain on the dissecting tray, CAREFULLY remove a slice from the parietal lobe using the scapel. Notice the white matter (cerebral medulla) and the gray matter (cerebral cortex) of the cerebrum. cerebral cortex (gray matter)? What structure or structures of the neuron are found in the gray mater of the cerebrum? cerebral medulla (white matter) What structure or structures of the neuron are found in the white matter of the cerebrum? Which matter makes up the MAIN bulk of the cerebrum? Posterior View Using the figure below: A. LABEL: cerebral cortex, cerebral medulla, gyri, cerebrum and cerebellum. B. DRAW: 1) the structures or parts of the neuron found in the cerebral cortex. 2) the structure or part of the neuron found in the cerebral medulla. NOTE: review the three (3) main structures of the neuron in Figure 10.1, pg. 355, of your A&P textbook.? Circle One: a) The cerebral medulla is made of white/gray matter. b) The cerebral cortex is made of white/gray matter. c) Does the cerebellum have.. white matter? Yes No gray matter? Yes No Posterior Anterior Midsagittal Section of the Human Brain 5
Position the sheep s brain on the dissecting tray with its anterior surface upward. Identify the following structures: Olfactory nerve (bulb) Longitudinal fissure Olfactory tract Optic chiasma Optic nerve Optic tract Midbrain Pons Medulla oblongata Spinal cord Anterior View PART C Brainstem: composed of the midbrain, pons, and medulla oblongata Position the sheep s brain on the dissecting tray with its anterior surface upward. Identify the three structures that make up the brainstem. Midbrain Pons Brainstem Anterior View Medulla oblongata 6
Position the sheep brain with its anterior surface on the dissecting tray. Using the scalpel CAREFULLY cut the sheep brain along the longitudinal fissure and continue then through the midline of the cerebellum and spinal cord to produce a midsagittal section of the brain and spinal cord. Longitudinal Fissure Locate the following parts in the midsagittal section of the sheep brain. Cerebrum Pineal Gland Corpora quadrigemina of midbrain Cerebellum Spinal cord Optic nerve Midbrain Pons Medulla oblongata Brainstem Midsagittal Section 7
PART D Diencephalon: composed of Thalamus and Hypothalamus Locate the 2 structures that make up the diencephalon in the longitudinal section of the sheep brain. Thalamus Hypothalamus Diencephalon Midsagittal Section PART E Cerebrum: Revisited! Identify the following structures found in the cerebrum. Corpus callosum Use your blunt prove and insert it inside the corpus callosum to find the lateral ventricle. Lateral ventricle (cavity) Midsagittal Section 8
PART F Cerebellum Identify the gray matter (cerebellar cortex) and white matter (cerebellar medulla) of the cerebellum. Cerebellar cortex (gray matter) Cerebellum Midsagittal Section Cerebellar medulla (white matter)? Note: the white matter pattern in the cerebellum is called arbor vitae. What structure or structures of the neuron are found in the gray matter of the cerebellum? What structure or structures of the neuron are found in the white matter of the cerebellum? LABEL: cerebellum, cerebellar cortex, and cerebellar medulla in this midsagittal section of the human brain. Posterior Anterior Midsagittal Section of the Human Brain 9
TABLE 1 Functions of Brain Structures Brain Structures Function/s Meninges: *Pia Mater *Arachnoid Mater *Dura Mater Cerebrum: *Cerebral Cortex *Cerebral Medulla *Corpus Callosum *Lateral Ventricle Cerebellum: *Cerebellar Cortex *Cerebellar Medulla Longitudinal Fissure Transverse Fissure Gyrus (pl. Gyri) Sulcus (pl. Sulci) Cerebral Lobes: *Frontal Lobe *Parietal Lobe *Temporal Lobe *Occipital Lobe 10
Brain Structures Brainstem: *Pons Function/s *Medulla Oblongata *Midbrain -Corpora Quadrigemina Cranial Nerves: *Olfactory Bulb or Nerve *Optic Nerve -Optic Chiasma *Trigeminal Nerve Diencephalon: *Hypothalamus *Thalamus Spinal Cord: *Central Canal Exercises LABEL: the structures in this midsgittal section of the right half of the human brain. E F A. B. C. A D. D J B C G H K L E. F. (cavity) G. H. I Anterior M Posterior I. J. K. L. (fissure) 11 M.
LABEL: the lobes of the human cerebrum. IDENTIFY: write the name of the brain structures or parts described below. a) A mass of white fibers connecting the left and right cerebral hemispheres. b) A fold of cortical gray matter on the surface of the cerebrum c) The middle of three divisons of the brainstem. d) The gray matter on the surface of the cerebrum. e) The gray matter on the surface of the cerebellum. f) The white matter on the cerebrum. g) The white matter on the cerebellum. h) Fissure dividing the cerebrum and the cerebellum. i) Area where the optic nerves cross. LABEL: the structures of the brain by placing the correct name next to the spaces provided. Skull Meninges 12
Dissection of The Human Brain: Anatomy and Physiology NOTE: You will need to use Anatomy & Physiology / Revealed, Version 0 CD-ROM. BEFORE you start this section of the laboratory, read pages 3-7 Becoming familiar with your Anatomy & Physiology / Revealed, Version 0 CD-ROM. From the Home Screen of Anatomy & Physiology / Revealed CD, click the down arrow on the SYSTEM button and choose the Nervous System. You will then see the opening screen for the Nervous System. PART 1 View an animation about the Divisions of the Brain A) To access the animation Divisions of the Brain, click at the ANIMATIONS icon located at the top center of the Nervous System screen. B) From the ANIMATION LIST, click at the down arrow and select Divisions of the Brain Click at this button to star the animation Click at this button to pause the animation To rewind or forward the animation, click and draw the round, red button. 13
Answer the following questions after viewing the animation: List the four regions of the brain. Use these human brain images to label the 4 regions of the brain How many cerebral hemispheres are there? Name the five lobes of the cerebral hemispheres. Which of the five lobes of the cerebral hemisphere can not be seen? The cerebrum is considered responsible for List the three structures that make up the diencephalon. 8. List the three divisions of the brainstem. PART 2 Coronal View of the Human Brain **NOTE: you need to be able to identify the parts of the human brain studied in this section of the lab AND know functions for each part studied. A) After viewing the Divisions of the Brain animation, click at the DISSECTION icon B) From the Select Topic, select Brain and then from the Select view select Coronal. Click then at the blinking green GO button. 14
C) Click LAYER 1 in the LAYER CONTROLS window, and the following image appears: D) Mouse-over the pins on the screen and name only the labeled parts of the brain that you see in this figure. Label: 8. Know the functions of: cerebrum, longitudinal fissure, parietal lobe, frontal lobe, temporal lobe, brainsterm, cerebellum. 8. E) Click LAYER 2 in the LAYER CONTROLS window, and the following image appears: F) Mouse-over the pins on the screen and name only the labeled parts of the brain that you see in this figure. G) What part or parts of the neuron are found in the gray matter of the human brain? Review Ch 10, pg. 356 and Ch 11, pg. 400 to get the answers. H) What part or parts of the neuron are found in the White Matter of the brain? Review Ch 10, pg. 356 and Ch 11, pg. 400 to get the answers. 15
NOTE: at any time during this laboratory exercise, you can take the SELF TEST. Click at the SELF TEST icon and choose a test topic to take a test on the selected topic. PART 3 Superior View of the Human Brain A) Click at the DISSECTION icon and then click at CHANGE TOPIC button on the left side of the screen. From the Select Topic, select Brain and then from the Select view select Superior. Click then at the blinking green GO button. DISSECTION button B) Click LAYER 1 in the LAYER CONTROLS window, and the following image appears: C) On the LAYER 1 column, click and draw downward the red arrow to remove the skin covering the skull. D) Now you will see the following image: Anterior Anterior E) Click LAYER 2 in the LAYER CONTROLS window and mouse-over the pins on the screen to find the name of the sutures. Only label the parts of the skull that you see labeled in the skull to the left. Posterior F) Click LAYER 3 in the LAYER CONTROLS window to remove the skull. Mouseover the pins on the screen and name only the labeled part on this figure. Name the meninge. Posterior 16
PART 4 Lateral View of the Human Brain A) Click at the CHANGE TOPIC button on the left side of the screen. From the Select Topic, select Brain and then from the Select view select Lateral. Click then at the blinking green GO button. B) Click LAYER 2 in the LAYER CONTROLS window to remove the skin or click and draw down slowly the red arrow in the LAYER 1 column. Now click at LAYER 3 to remove the lateral part of the skull and mouse-over the pins on the screen to identify the structures. C) Remove the dura mater by clicking at LAYER 4 in the LAYER CONTROLS window or slowly draw down the red arrow in LAYER 3 column. D) Mouse-over the pins on the screen and name only the labeled parts of the brain that you see in this figure. Label: E) Click LAYER 6 in the LAYER CONTROLS and mouse-over the pins on the screen to identify the structures. Label only the marked regions on this figure: 8. Label: 8. 17
PART 5 Inferior View of the Human Brain A) Click at the CHANGE TOPIC button on the left side of the screen. From the Select Topic, select Brain and then from the Select view select Inferior. Click then at the blinking green GO button. B) Click LAYER 2 in the LAYER CONTROLS window. Mouse-over the pins on the screen and name only the labeled parts of the human brain that you see in this figure: Label: 8. 9. 8. 9. PART 6 Imaging of the Human Brain (An MRI View) A) Click at the IMAGING icon and then at Select View select Sagittal IMAGING button You will then see the following MRI image: See next page. 18
8. B) Click at TURN TAGS ON button and mouse-over the pins on the screen to identify the structures that are marked in this figure. Label them. Label: 8. NOTE: at any time during this laboratory exercise, you can take the SELF TEST. Click at the SELF TEST icon and choose a test topic to taken a test of the selected topic. **REMEMBER: you need to be able to identify the parts of the brain studied in this lab using: The sheep brain The human brain: using figures similar to the ones in this laboratory handout and photographs of the human brain from a cadaver similar to the ones in your Anatomy & Physiology Revealed CD AND know functions for each structure or part of the human brain studied in this lab. 19