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LABORATORY 10 The Central Nervous System: Brain Objectives 1. Identify the following components of the human brain and the cranial nerves using a diagram, model or a human brain specimen. gyrus longitudinal fissure parietal lobe parieto-occipital sulcus cerebellum precentral gyrus cerebral white matter optic chiasma intermediate mass cerebral peduncles fourth ventricle corpora quadrigemina midbrain interventricular foramen dura mater arachnoid mater arachnoid vili trigeminal nerve vestibulocochlear nerve superior cerebrellar peduncles inferior cerebellar peduncles olfactory nerve lateral ventricle choroid plexus epithalamus fissure central sulcus lateral sulcus occipital lobe pons prefrontal cortex olfactory bulbs pituitary gland optic nerve corpus callosum cerebral cortex superior colliculi diencephalon infundibulum superior sagittal sinus subarachnoid space oculomotor nerve abducens nerve vagus nerve middle cerebellar peduncles glossopharyngeal nerve transverse fissure third ventricle meninges transverse fissure 113 sulcus frontal lobe temporal lobe postcentral gyrus medulla oblongata cerebral aqueduct olfactory tracts mammillary bodies septum pellucidum fornix pineal gland inferior colliculi arbor vitae vermis hypothalamus pia mater trochlear nerve facial nerve accessory nerve thalamus hypoglossal nerve cerebral hemispheres fornix basal nuclei 2. Identify the following structures of a sheep brain and the cranial nerves using a specimen: longitudinal fissure corpora quadrigemina gyri superior cerebellar peduncles inferior cerebellar peduncles middle cerebellar peduncles cerebral hemispheres mammillary body oculomotor nerve trigeminal nerve septum pellucidum intermediate mass cerebral aqueduct diencephalon lateral ventricle lateral fissure parietal lobe corpora quadrigemina epithalamus corpus callosum transverse fissure arachnoid mater inferior colliculi superior colliculi olfactory bulbs olfactory tract pituitary gland cerebral peduncles trochlear nerve corpus callosum hypothalamus fourth ventricle pineal gland occipital lobe temporal lobe arbor vitae meninges dura mater sulci pia mater cerebellum optic nerve optic tract optic chiasma infundibulum medulla oblongata pons fornix thalamus third ventricle midbrain frontal lobe central sulcus vermis cerebral cortex Introduction The brain, located in the cranial cavity, is part of the central nervous system. Cranial nerves belong to the peripheral nervous system, but because they are attached to the brain, they are often studied along with the brain. In this exercise you will learn about the anatomy of the human brain and the cranial nerves associated with it. You will then dissect a sheep brain to identify structures, and to compare it to a human brain. Materials Models and diagrams of the human brain Sheep brain with meninges intact Dissecting pan Dissecting tools: scissors, scalpel, blunt probe, teasing needle, forceps Bag/tag for storage or bag for disposal 114 Activity 1: Human Brain Anatomy Resources: Textbook: pages 428-448; 458-461; 492-500 Photographic Atlas: pages 104-108 Identify the following structures on diagrams, charts and models of the human brain. Meninges and Associated Structures: dura mater arachnoid mater subarachnoid space arachnoid vili Ventricular System lateral ventricles cerebral aqueduct septum pellucidum Structures of the cerebrum: gyrus longitudinal fissure parietal lobe parieto-occipital sulcus precentral gyrus olfactory bulbs optic chiasma cerebral cortex pia mater superior sagittal sinus interventricular foramen fourth ventricle third ventricle choroid plexus fissure central sulcus lateral sulcus occipital lobe prefrontal cortex olfactory tracts fornix cerebral hemispheres sulcus frontal lobe temporal lobe postcentral gyrus cerebral white matter corpus callosum basal nuclei Diencephalon and Associated Structures pineal gland epithalamus intermediate mass hypothalamus pituitary gland mammillary bodies thalamus infundibulum Brain Stem cerebral peduncles inferior colliculi medulla oblongata superior colliculi pons corpora quadrigemina midbrain Cerebellum/Associated Structures middle cerebellar peduncles arbor vitae vermis superior cerebellar peduncles inferior cerebellar peduncles transverse fissure Cranial Nerves oculomotor nerve trigeminal nerve vestibulocochlear nerve glossopharyngeal nerve trochlear nerve abducens nerve vagus nerve hypoglossal nerve 115 olfactory nerve facial nerve accessory nerve optic nerve Activity 2: Resources: Sheep Brain Dissection Photographic Atlas: pages 109-112 1. Place the sheep brain in the dissection pan, resting on its ventral surface. 2. Examine the dura mater, the tough connective tissue layer that is the outer meninx. Using a scissors, carefully cut through the dura mater and remove it carefully from your specimen. Be careful when removing the dura from the ventral surface – try to preserve the attachment of the pituitary gland and as many of the cranial nerves as possible. 3. Deep to the dura mater is a filmy, vascular layer called the arachnoid mater. Underneath this layer, adhering to the surface of the brain, is the pia mater. 4. Examine the external features of the sheep brain: Cerebrum: This is the most prominent and largest of the brain areas. It is divided by a longitudinal fissure into nearly symmetrical right and left cerebral hemispheres. Gently pull the two hemispheres away from each other and look down into the longitudinal fissure. There you will observe the corpus callosum, a band of white, myelinated fibers that connects the two cerebral hemispheres.The surface of each cerebral hemisphere has ridges (convolutions) called gyri and depressions which are called either sulci (shallow depressions) or fissures (deeper depressions). A lateral view of a cerebral hemisphere should enable you to differentiate etween the frontal lobe, parietal lobe, temporal lobe, and occipital lobe. Cerebellum: The cerebellum, the second largest brain area, is a rounded structure caudal to the cerebral hemispheres. The cerebellum has smaller gyri that are parallel to each other. Locate the vermis (L, worm),a short, narrow band of tissue that connects the two cerebellar hemispheres. Ventral Surface From this view, you can see the frontal lobes and temporal lobes of the cerebral hemispheres. Observe the olfactory bulbs on the underside of the frontal lobes. Locate the pituitary gland which is attached to the hypothalamus by a stalk called the infundibulum. The optic chiasma, a X shaped junction of fibers at the junction of the optic nerves is located anterior to the pituitary gland. Two small rounded processes called mammillary bodies are posterior to the pituitary gland; they are part of the hypothalamus. Posterior to the mammillary bodies lie the cerebral peduncles, groups of myelinated fibers that are inferior portions of the midbrain. Moving posteriorly, locate the pons, clearly seen as a large bulge. Finally, locate the medulla oblongata which caudal to the pons (it looks like a swollen region of the spinal cord). Together the midbrain, pons and medulla oblongata make up the brainstem. 116 Corpora Quadrigemina Cranial Nerves Internal Structures Hold the specimen in front of you, looking from the posterior to the anterior end, cerebral hemispheres on top. Carefully pull the cerebral hemispheres away from the cerebellum, widening the transverse fissure (do not sever these areas from each other). You may have to tease some connecting tissue away with a probe. A small rounded body called the pineal gland should be visible at the midline, nearest the cerebrum. Beneath the pineal body there are the four bodies of the corpora quadrigemina of the midbrain. The two superior bodies, called superior colliculi are slightly larger than the two inferior bodies, called inferior colliculi. Place the brain in the dissecting pan so that the ventral surface is facing upward. Starting at the anterior end, locate as many of the cranial nerves as you can. Place the brain in the dissecting pan so that the dorsal surface is now facing upward. Using a knife or a long bladed scalpel, carefully cut the specimen along the midsagittal line, through the corpus callosum, using the longitudinal fissure as a cutting guide. Now observe the following internal structures: Locate the corpus callosum that was cut through to produce the two midsagittal sections. The fornix is anterior to the corpus callosum. Look for the lateral ventricles in each brain half, just below the corpus callosum. In the whole brain, they are separated from each other by the septum pellucidum. Depending on your cutting plane, the septum pellucidum may still be visible. Try to locate the choroid plexus which produces the CSF that fills each ventricle. Also, note the rounded intermediate mass which lies in the diencephalon. The intermediate mass is the commissure that connects the nuclei of the thalamus and is the only portion of the thalamus that can be seen in this section. It appears as a circle of grey matter surrounded by a shallow section of the third ventricle. The hypothalamus includes the tissue located inferior to the thalamus. Observe the cerebellum. Identify the internal white matter, called the arbor vitae. Ventral to the cerebellum is the fourth ventricle which is connected to the third ventricle by the cerebral aqueduct which lies in the midbrain. Locate these additional structures on the sectioned sheep brain: medulla oblongata, pons, cerebellar peduncles, cerebral peduncles, superior colliculi, inferior colliculi, mammillary bodies, optic chiasma and pineal gland. 117 5. Observe the coronal section of the brain on display in the lab. You should be able to see the cerebral cortex, cerebral nuclei, lateral ventricles, corpus callosum, third ventricle, thalamus and hypothalamus. 6. When you are finished with your dissection, you may save the brain sections using the bags/tags, or dispose of them as directed by your lab instructor. Checklist: A. Human Brain Structures: Meninges and Associated Structures: ___ dura mater ___ arachnoid mater ___ pia mater ___ subarachnoid space ___ arachnoid vili ___ superior sagittal sinus Ventricular System ___ lateral ventricles ___ interventricular foramen ___ third ventricle ___ cerebral aqueduct ___ fourth ventricle ___ choroid plexus ___ gyrus ____ fissure ____ sulcus ___ longitudinal fissure ____ central sulcus ____ frontal lobe ___ parietal lobe ____ lateral sulcus ____ temporal lobe ___ parieto-occipital sulcus ____ occipital lobe ____ postcentral gyrus ___ precentral gyrus ____ prefrontal cortex ____ cerebral white matter ___ olfactory bulbs ____ olfactory tracts ____ corpus callosum ___ optic chiasma ____ fornix ____ basal nuclei ___ cerebral cortex ____ cerebral hemispheres ___ septum pellucidum Structures of the cerebrum: Diencephalon and Associated Structures ___ pineal gland ____ epithalamus ____ thalamus ___ intermediate mass ____ hypothalamus ____ infundibulum ___ pituitary gland ____ mammillary bodies 118 Brain Stem ____ cerebral peduncles _____ corpora quadrigemina _____ superior colliculi ____ inferior colliculi _____ midbrain _____ pons ____ medulla oblongata Cerebellum/Associated Structures _____ middle cerebellar peduncles _____ arbor vitae _____ vermis _____ superior cerebellar peduncles _____inferior cerebellar peduncles _____ transverse fissure Cranial Nerves _____ oculomotor nerve _____ trochlear nerve _____ olfactory nerve _____ trigeminal nerve _____ abducens nerve _____ facial nerve _____ vestibulocochlear nerve _____ vagus nerve _____ accessory nerve _____ glossopharyngeal nerve _____ hypoglossal nerve _____ optic nerve B. Sheep Brain Dissection Meninges and Associated Structures: ___ dura mater ___ arachnoid mater ___ pia mater Ventricular System ___ lateral ventricles ___ interventricular foramen ___ third ventricle ___ cerebral aqueduct ___ fourth ventricle ___ choroid plexus ___ gyrus ____ fissure ____ sulcus ___ longitudinal fissure ____ central sulcus ____ frontal lobe ___ parietal lobe ____ lateral sulcus ____ temporal lobe ___ septum pellucidum Structures of the cerebrum: 119 ___ occipital lobe ____ cerebral white matter ____ olfactory bulbs ___ olfactory tracts ____ corpus callosum ____ optic chiasma ___ fornix ____ cerebral nuclei ____ cerebral cortex ___ cerebral hemispheres Diencephalon and Associated Structures ___ pineal gland ____ epithalamus ____ thalamus ___ intermediate mass ____ hypothalamus ____ infundibulum ___ pituitary gland ____ mammillary bodies Brain Stem ____ cerebral peduncles _____ corpora quadrigemina _____ superior colliculi ____ inferior colliculi _____ midbrain _____ pons ____ medulla oblongata Cerebellum/Associated Structures _____ middle cerebellar peduncles _____ arbor vitae _____ vermis _____ superior cerebellar peduncles _____inferior cerebellar peduncles _____ transverse fissure Cranial Nerves _____ oculomotor nerve _____ trochlear nerve _____ olfactory nerve _____ trigeminal nerve _____ abducens nerve _____ facial nerve _____ vestibulocochlear nerve _____ vagus nerve _____ accessory nerve _____ glossopharyngeal nerve _____ hypoglossal nerve _____ optic nerve 120 Name: ____________________ Lab 10 worksheet Score: __________________ 1. Match the letters of the diagram of the human brain with the correct label. _____ precentral gyrus _____ parietal lobe _____ central sulcus _____ temporal lobe _____ post central gyrus _____ medulla oblongata _____ lateral sulcus _____ occipital lobe _____ white matter _____ cerebellum _____ pons _____ frontal lobe ‘ _____ gray matter H I J K G L F M E D C B A 121 2. Match the letters of the diagram of the human brain with the correct label. _____ corpus callosum _____ pineal gland _____ pituitary gland _____ hypothalamus _____ cerebral hemisphere _____ thalamus _____ infundibulum _____ corpora quadrigemina _____ intermediate mass _____ arbor vitae _____ pons _____ medulla oblongata _____ choroid plexus _____ fourth ventricle _____ cerebral aqueduct A B O C N D M E L F G K J H I 122 3. Provide the name and number of each cranial nerve listed below: A G B H C I D J E F K L A. __________________________________ G. __________________________________ B. __________________________________ H. __________________________________ C. __________________________________ I. __________________________________ D. __________________________________ J. __________________________________ E. __________________________________ K. __________________________________ F. __________________________________ L. __________________________________ 123 4. Label the structures associated with the circulation of cerebrospinal fluid. 5. In what structure of the skull does the pituitary gland sit? Be specific name the bone and the specific structure of that bone. _________________________________________________________________ 6. In what structure of the skull do the olfactory bulbs sit? Be specific, name the bone and the specific structure of that bone. ___________________________________________________________________ 7. Compare the relative sizes of the cerebral hemispheres in sheep and in human brains. What is the significance of these differences? ________________________________________________________________ ________________________________________________________________ 8. Why are the olfactory bulbs much larger in the sheep than in the human? ________________________________________________________________ 124 Post lab worksheet lab 10 1. In which cerebral lobes would the following functional areas be found? Primary visual area: ________________________________ Broca’s area: ________________________________ Gustatory area: ________________________________ Olfactory area: ________________________________ Primary sensory area ________________________________ Primary motor area ________________________________ Premotor area ________________________________ Auditory area ________________________________ 2. Using the following terms, match the structure with the description: cerebral aqueduct thalamus diencephalon corpus callosum corpora quadrigemina medulla oblongata olfactory tract parietal lobe cerebellum hypothalamus pituitary gland pineal gland (body) choroid plexus ___________ Site of regulation of body temperature and water balance; important ANS center ___________ Sensory perception depends on the function of this area ___________ Encloses the third ventricle ___________ Connects the third ventricle and the fourth ventricle ___________ Located in the midbrain; contains reflex centers for vision and audition ___________ Regulates posture and coordinates complex muscular movements ___________ Fiber tract concerned with olfaction ___________ Large commissure connecting the cerebral hemispheres ___________ Major relay site for afferent (sensory) impulses traveling to the sensory cortex 125 ___________ Reflex centers for blood pressure, heart rate, salivating and coughing are located here ___________ Connected to the hypothalamus by the infundibulum; an endocrine gland ___________ Located in the diencephalons this gland secretes melatonin which induces sleep __________ Produces cerebrospinal fluid (CSF) 3. Identify the meningeal (or associated) structure described below: Outermost meninx covering the brain; composed of tough __________________ fibrous connective tissue A dural fold that separates the cerebrum from the cerebellum __________________ A dural fold that attaches the cerebrum to the crista gall __________________ Middle meninx __________________ Structure that produces cerebrospinal fluid (CSF) __________________ Innermost meninx covering the brain; delicate and highly vascular __________________ Structures instrumental in returning fluid to the venous blood located in the dural sinuses __________________ It’s outer later forms the periosteum of the skull __________________ 4. List in order the structures that cerebrospinal fluid passes through from the lateral ventricles to the dural venous sinuses. _________________________________________________________________ _________________________________________________________________ _________________________________________________________________ 126 5. Explain why trauma to the base of the brain is often so much more dangerous than trauma to the frontal lobe (hint: which are contains centers that are more vital to life)? _________________________________________________________________ _________________________________________________________________ _________________________________________________________________ 6. List the basal nuclei. What is their function? ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ 7. Provide the name and the number of the cranial nerve(s) involved below: a. Three nerves that are involved in eye movement __________________ __________________ __________________ b. Slows the heart and increases the motility of the digestive tract __________________ c. Activated while chewing food __________________ d. Activated while smelling a flower __________________ e. Activated while shrugging the shoulders __________________ f. Activated while listening to music, seasickness __________________ g. Activated while feeling a toothache __________________ h. Activated while salivating, tasting spicy food __________________ i. Involved in facial paralysis (Bell’s palsy) __________________ j. Activated while raising the eyelids, focusing the lens of the eye for accommodation; used for pupil constriction __________________ Activated while looking at a picture __________________ k. 127 l. List three nerves that are sensory only __________________ __________________ __________________ m. List the three nerves involved in taste. __________________ __________________ __________________ 128
