A&P 1 Brain & Cranial Nerves Guide - Lab Exercises

Transcription

1 1 A&P 1 Brain & Cranial Nerves Guide - Lab Exercises Have someone in your group read the following out loud, while the others read along: In this "Lab Guide", we will be looking at the brain & cranial nerves. This guide should only be attempted after reading the correct sections in either the lab or lecture book, or watching any videos that have been assigned. The First 2 Parts must be done in lab, with the dissections and other lab materials. Parts 3 & 4 can be done outside of lab.

2 2 Part 1. Review Key Concepts from the book and videos Read Me #1 Have someone in your group read this, while the others follow along: Look over the list of regions and sub regions is below. Make sure you understand this outline, and write down any individual structures you can think of. For example, you could write corpus callosum under inner white matter and pituitary under hypothalamus. You might want to come back and complete this after the next section! A. Cerebrum (telencephalon) 1. cerebral cortex (outer gray matter) 2. inner white matter (inner tracts, nuclei, etc.) B. Diencephalon 1. epithalamus 2. thalamus 3. hypothalamus C. Brain Stem 1. midbrain 2. pons 3. medulla oblongata D. Cerebellum

3 3 Part 2. Find the Regions and Structures of the Brain you need, on both the models and the sheep brain. #1 Have someone in your group read this, while the others follow along: Get a dissecting pan, 1 scalpel, 1 pair scissors, and some latex-free surgical gloves. Your group should have the following in front of you: 1. Human Brain Model 2. Sheep Brain - Whole, with Dura Mater (you willl be dissecting this!) 3. Sheep Brain Whole - without dura mater (you will not be dissecting this) 4. Sheep Brain Frontal Section Human brain model Sheep brain with meninges Sheep brain without meninges Sheep brain - Frontal section We will be comparing these four at the same time.

4 4 #2 Meninges Obtain one of the preserved sheep brains that is still encased within the protective membranes known as the meninges. The meninges consistt of three layers; an outer dura mater, a middle arachnoid, and an internal pia mater. Do This! While looking at the "sheep brain with meninges": Do This! Examine the dura mater, a protective outer membrane composed of a tough densee connective tissue. Describe the appearance andd feel of this membrane. Continued on nextt page

5 5 Do This! Examine the surface of the "sheep brain whole - withoutt dura mater". Note the thin filmy membrane covering over the actual brain tissue. This is more delicate tissue of the arachnoid and pia mater. The arachnoid willl only look like a film with dark patches here and there...you may not really see it. The pia mater will look like a shiny coat directly attached to the neural tissue. #3 Study the external features of the brain. On this guide, we will use images from either the model or sheep brain. However, find all of the following on the surface of the "sheep brain without dura mater", the dissected Sheep Brain - Whole,, with Dura Mater and the "human brain model". Use the imagess in your lab book as needed. A fissure is a deep groove that goes deep and separates big regions. Examine the sheep brain from a superior view (see figure below). Note the two large cerebral hemispheres that constitute the cerebrum and envelop most of the brain. The cerebral hemispheres are almost completely separated by a deep longitudinal fissure. The cerebrum and cerebellum is separated by the transverse fissure.

6 6 Do This! If you gently spread the hemispheres apart, you can see a band off tissue that connects the two hemispheres medially. This is the corpus callosum. We will be cutting through this when we dissect the brain. The surface of each hemisphere consistss of upward folds of nervous tissue called gyri and shallow grooves called sulci. Thesee increase the surface area of the cerebral cortex to allow more complex interaction between neurons. Next locate the cerebellum just caudal to the cerebrum. It is separated from the cerebral hemispheres by the deep transverse fissure. Like the cerebrum, the cerebellum has a highly convoluted surface (gyri and sulci) and lobes (see image below). Caudal and inferior to the cerebellum note the medulla oblongata which tapers out to form the more slender r spinal cord. Find these structures on the model and sheep brain. Keep in mind that you have to locate any motor and sensory cortices on your wordlist:

7 7 The dorsal portion (or "roof") of the midbrain can be examined by carefully spreading apart the transverse fissure on the whole sheep brain without meninges (see figure). This exposes four rounded bulges calledd the corpora quadrigemina. The two superior colliculi are larger than the two inferior colliculi. If you look onn the midline between and just above the superior colliculi you will see a small fingerlike extension of tissue called the pineal body or gland. Examine the brain from an inferior view (see Figure below). At the cranial end of the brain note the two olfactory bulbs that lay against the undersurface of the cerebrum. The band of tissue extending caudally y from these bulbs are the olfactory tracts. Caudal to the olfactory bulbs and tracts is the X-shaped optic chiasma. This is the point where the two optic nerves from the eyes meet and partially cross over before forming the optic tracts that extend back to the visual area of the cerebrum. Caudal and inferior to the optic chiasma is a small bean shaped pituitary gland. This is a major endocrine gland and is attached to the brain by a slender stalk called the infundibulum. The pituitary gland may be missing from some of the preserved brains, leaving only the infundibulum. The infundibulum is rooted in a bulge of nervous tissue called the mammillary body. This mammillary body and the nervous tissue superior to itt comprise the brain region known as the hypothalamus. A portion of the pituitary gland is actually an extension of this hypothalamus. Note: The mamillary body is NOT very defined or clear on the sheep brain!!

8 8 The ventral portion (or "floor") of the midbrain consistss of the cerebral peduncles. These bands of nervous tissue connect the cerebrum with other regions of the brain and are located just caudal to the hypothalamus. Caudal to the midbrain is the hindbrain which consistss of the pons and the medulla oblongata. The nervous tissue then tapers to form the spinal cord. Do This! Dissecting the Sheep Brain Now it is time to dissect the Sheep Brain - Whole, with Dura Mater, as we want to see internal structures. You will be comparing this with the brain model, which you should now separate thee 2 halves, and any pre-sectioned preserved sheep brains you want for variability (available in a bucket at the front of the room). Determine if your specimen still has a part of the ethmoid bone attached on the anterior frontal lobe. If the bone is present, slip a blunt probe between the bone and the dura to carefully separatee the bone away from the specimen. Then, using yourr scissors, snip away any attached dura. Examine the removed ethmoid bone and identify the cribriform plates, where the olfactory bulbs were sitting, and the crista galli: crest of bonee where that serves as the surface of attachment of the meninges. Also, the optic nerve may still be attached to 2 largee fat bodies these are 2 pads that sit behind your eyeball. Using the scissors, cut the optic nerves to remove the pads, trying to get the brain to look like the one in the image below. Lay the brain, upside down, on the dissecting tray. Always use a scalpel like a butter knife; never saw through the tissue. It will take you several passes to get through the brain. Each time you slide the scalpel through the brain, try to stay in the previous slice. Stay as close to center of the pituitary as possible. WATCH YOUR FINGERS! Use the following images to guide you through the parts you need to know, finding the structures on the brain model and dissected sheep brain, using the images in your text or lab book as youu need. Make sure you find everything indicated on your wordlist indicatedd with an Asterisk (*) on the sheep brain.

9 9 1. Specific Parts of the Cerebrum Locate the corpus callosum, the band of tissue that connects the two cerebral hemispheres. Also locate the band of tissue below the corpus callosum known as the fornix. Depending on the exact position of the sectioning cut you should either see a membrane linking the fornix and corpus callosum or a cavity between them. The membrane is the choroid plexus, where cerebrospinal fluid is produced and circulated. Make sure you see the corpus callosum and the lateral ventricles on the Sheepp Brain Frontal Section. 2. Specific Parts of the Diencephalon: Before we go on: A word about the diencephalon and its individual sub-regions : So a good way to look at it is like a thick The diencephalon is the region that surrounds the 3 rd ventricle. box: 4. Find the diencephalon, and its sub regions, on the Sheep Brain Frontal Section. Depending on where your frontal section was taken, youu may not seee exactly what is shown below! These structures, on a Sheep Brain Frontal Section, will not be on the Practical!

10 10 Inferior to the fornix is a round structure called the intermediate mass. This is the medial portion of the two portions of the thalamus that lie within each cerebral hemisphere. If there appears to be a depressed area around the intermediate mass of the thalamus, this will be the third ventricle. 3. Specific Parts of the Brain Stem, including the midbrain: Examine again the midbrain structures; the dorsal corpora quadrigemin a and pineal body, and the ventral cerebral peduncles. Also reexamine the parts of the hindbrain; the pons, the medulla, and the cerebellum. 4. Specific Parts of the Cerebellum The white matter structure in the center is the arbor vitae. Note that there is a slender canal that passes through the midbrain to the cavity between the cerebellum and the medulla. The cavity is the fourth ventricle of the brain and the canal is the cerebral aqueduct. The cerebral aqueduct carries cerebrospinal fluid from the third ventricle to the fourth ventricle. Blockage of this passage causes the condition known as hydrocephalus.

11 11 On the dissected Sheep Brain - Whole, with Dura Mater, note the following structures, and how different they look on the dissected brain, versus the whole brain: Dura mater Pituitary gland (hypophysis) Optic chiasma Mamillary body (human brain model only) Central sulcus Midbrain and corpora quadrigemina Pons Pineal gland There are others, but these really stand out! Also notice how different these structures look on the shhep brain versus the human model, do to the fact that a sheep has a neck that goes straight out, whereas our has a 90 degree bend: Hypothalamus Midbrain Do This! Clean Up Procedures 1. Replace the following back into the buckets from which they came: Sheep Brain Whole - without dura mater (you will not be dissecting this) Sheep Brain Frontal Section 2. Place the brain you dissected, and any parts, in the designated container. When you are ready, place your gloves in a regular trash can and NOT in the container with the dissected brains. 3. Take the dissection tray and all instruments to the sink to be washed. 4. Remove the pad from the dissection tray and wash them separately using the provided disinfectant and sponge. 5. Also spray the instruments with disinfectant and clean them using the provided toothbrushes. 6. Rinse the pad, dissecting tray, and all tools and place them in the drying tray. 7. Place the instruments SHARP END DOWN in the appropriate portion of the drying tray. 8. Spray down the area of the lab bench where the dissection was completed with disinfectant and dry using a paper towel.

12 12 Part 3. Identify and study the Cranial Nerves Can be done out of lab! #1 Have someone in your group read this, while the others follow along: Read Me No two instructors are the same when it come to the cranial nerves. Some want you to know the names only, some want names and function, some want you to be able to ID them on images and models. You should confirm with your instructor what you need to know regarding the cranial nerves. Here, we will have you: 1. name all 12 in order, starting with the most anterior. 2. know something about their basic function. 3. ID the first 6, and number 10, on an image. If you need to know more, your instructor can guide you. Continued on next page

13 #2 Fill out this table: Cranial Nerve: Major Functions: 13 I II III IV Sensory only: Sensory only: Mainly Motor: Mainly Motor: V Motor & Sensory: VI VII VIII Mainly Motor: Motor & Sensory: Mainly Sensory: IX Motor & Sensory (only sense listed here): X Motor & Sensory: XI Mainly Motor: XII Mainly Motor:

14 #3 Label the Cranial Nerves Label the cranial nerves listed below, and number X, on this diagram. Label them on both the right and left sides. If you cannot directly label the nerve, label the structure that accommodates the nerve (for example, the optic and olfactory nervess cannot be directly seen on the image, but the structures that attach to them can be). Vagus Olfactory Trochlear Oculomotor Abducens Optic Trigeminal 2 If your instructor wants you to be able to ID the other 5, label them on the image now!

15 15 Part 4. Assess yourself using a series of thinking questions Can be done out of lab! #1 Have someone in your group read this, while the others follow along: Read Me This will help in both lecture and lab. Answer these questions while identifying the structures on a model or image. You may do this exercise outside of lab if time is short. Answer them out loud, if you want to save time. Use a separate piece of paper if you need more space. 1. Beginning with the outside layer, the names of the three meninges that enclose the CNS. 2. Name the three major regions of the Diencephalon. 3. Name the three major regions of the midbrain.

16 16 4. Name the two major regions of the cerebrum 5. Name the band of tissue at the base of the longitudinal or sagittal fissure that is the primary nerve pathway connecting right and left cerebral hemispheres. 5. Name of the brain region to which the pituitary gland is attached. Part of the pituitary (posterior lobe) is actually formed from tissue of this part of the brain. Also name the stalk that attached the gland. 6. Name of the small cavity around the thalamus which contains CSF. 7. Name of the point where the two optic nerves meet and partially cross over, before passing to the cerebrum.

17 17 8. Name of the outer layer of each cerebral hemisphere. (HINT: it is composed of grey matter) 9. The region of the brain consisting of two major hemispheres. 10. Name of the deep fissure that separates the cerebellum from the cerebral hemispheres. 11. Name of the grooves and folds of tissue characteristic of each cerebral hemisphere. Groove - Fold -

18 What do we call the large, obvious sulcus running across the cerebral cortex? 13. Finish this sentence: All functions of the brain are posterior to the Central Sulcus. 14. Finish this sentence: All functions of the brain are anterior to the Central Sulcus. 15. Name the ridges of tissue anterior and posterior to the central sulcus of the cerebrum. What are their functions? Anterior ridge - Posterior ridge Name the gland that is found in the epithalamus. What does it secrete?

19 Brain region that includes "vital centers" for involuntary control of heart function, respiratory function and vasomotor activity. 18. Brain center that functions as the "master gland" of the endocrine system. (HINT: fill in the blanks below): "The of the brain acts to control homeostasis of the visceral organs, mainly by controlling the output of the gland, also known as the. " 19. Primary visual area of cerebrum are found where?

20 Brain center that acts as a primary organizational control center for all information entering the cerebrum. 21. Brain center that includes involuntary centers critical to maintenance of muscle tone, equilibrium and posture. 22. What is the white matter of the cerebellum called?

21 How do the relative sizes of the cerebral hemispheres compare in the sheep brain and the human brain? What conclusions can you draw from this? 24. How do the relative sizes of the olfactory bulbs compare in the sheep brain and the human brain? What conclusions can you draw from this? 25. What is the importance of the fact that the surface of the cerebral hemispheres is highly convoluted?

22 What is the importance of the corpus callosum? 27. What is the function or importance of the ventricles of the brain? How are they related to the central canal of the spinal cord, and the subarachnoid space?