The web browser you are using does not have features required to display Crawdad correctly.
Please use the most recent version of one of the following:
For most students, this is the first course involving dissections in which the preparations must be physiologically viable. The most common problem in dissection is cutting too deeply and destroying the nerve or muscle that is to be recorded from. This error is avoided by making sure that students can see the dissection area clearly, use the correct tools, and cut carefully, following the suggestions in the student version of this appendix.
The most common posture problem is having the stool too high such that the student is hunched over the microscope. This can easily happen when students trade positions and between lab sections. Many students do not know how to adjust lab stools. During the first few lab periods, it helps to note how students are sitting, suggest corrections, and show how to adjust lab stools (Figure B.1).
Many students have only minimal experience with microscopes when entering this course. Although it is probably not necessary to have a session introducing the microscope, be aware of potential problems and watch for them during the lab. Be sure students know how to adjust the microscopes. The most common problem during dissection is not changing magnification; some students attempt an entire dissection with 6 to 12× objectives.
The best light source for dissection has a branched Y-shaped fiber-optic light guide, which allows you to bring half of the light from the side or underneath the preparation, with half of the light coming from above. This configuration makes it easier to see fine structures like nerve 3 of a crayfish, the cells of a snail brain, or the tip of a microelectrode. If only a single-source light is available, experiment with different orientations. You may need to switch from overhead to side lighting when going from dissection to recording.
In addition to the flexibility of lighting placement allowed by a fiber-optic light source, this type of source is preferable because it brings less electrical noise into the recording setup than other light sources. This is because the light source can be kept outside of the Faraday cage, with only the fiber-optic guides extending into the cage.
We use homemade Plexiglas stands to hold preparations under the microscope. They raise the preparation to the correct level for the microscope and micromanipulators while also allowing light to come from the side and from beneath the preparation.
Ideally, each lab group would have one of each of the cutting tools shown in Figure B.2, but some substitutions can be made. The large scissors for cutting off the crayfish tail need not be surgical quality, and one pair could suffice, with lab groups taking turns at this part of the dissection. The small scissors shown here could be replaced with cheap cuticle scissors from a drugstore (note, however, that sharp points are desirable). Although Vannas scissors are desirable for cutting the thin crayfish cuticle in muscle dissections, they are not essential, and a scalpel will suffice if its blade is new and sharp. For snail brain dissections, however, Vannas scissors are necessary. The less expensive student Vannas type are adequate.
Scalpel blades deteriorate rapidly and may become unsuitable for fine work after a single lab period. We suggest starting each lab period with a fresh blade. Blades should probably be replaced by instructors (use pliers for safety), unless you have one of the blade removal tools available from many supply companies. Different brands of #11 blades vary; look for one with a sharply pointed tip.
Each lab group should also have one or two pairs of forceps like those shown in Figure B.3. The coarse forceps do not need to be of this style; any blunt forceps will do (old #5 style forceps are particularly good). They are mainly used for pinning and for removing crayfish swimmerets. For fine forceps, any stainless ones of the #5 style will do. They do not need to be the expensive Biologie type.
Forceps and student Vannas scissors can be sharpened, either to improve the points when new or to renew them after damage. When #5 forceps are past repair, blunt and smooth the tips with a sharpening stone to produce a good pair of pinning forceps (you may want to mark them in some way so that students do not confuse them with sharp ones; colored nail polish is an effective marker).
In addition to the set of tools shown in Figure B.2 and Figure B.3, you should have one or two pairs of fine Biologie forceps and one pair of fine Vannas scissors for use by the instructor alone. These are required for the snail brain desheathing.
Although the video clips in the manual should be sufficient to teach the dissections, you may want to demonstrate some dissections live. The most effective way to do this for a large group is with a video camera connected to a dissecting microscope. Many good small CCD video cameras with C-mounts are available at reasonable prices, and phototube attachments are available for most microscopes. Get the more expensive type of phototube that splits the image with a prism, because this allows you to use both eyepieces while using the camera. (Cheaper models close off one of the eyepieces, making dissection very difficult.) Many computers have video inputs and software that allows video to be watched on the screen. When used with an inexpensive video splitter box (available by order from most video stores), this setup makes it possible to show a dissection simultaneously on all the computers in a teaching lab, so students do not have to crowd around one monitor. Because such software usually allows one to capture and save images, this also opens the possibility for students to save still pictures for use in their lab reports (e.g., a picture of the muscle that is mapped in Lab 5, Synaptic Connectivity or the staining results of Lab 3, Motor Nerve Anatomy).
The main disadvantage of demonstration by video is that binocular vision is lost, making it difficult to convey a sense of depth. You can illustrate depth by grasping and moving structures, so that parallax illustates depth. If you have access to a dual-headed teaching microscope, it is ideal for demonstrating to one student at a time.