Dissection Tips

Introduction

Dissection is such an important part of experimental neurobiology that it should be made comfortable and efficient. You will have a better and more enjoyable learning experience in these labs if your dissection technique is good. This appendix offers suggestions to improve your dissections. These tips concentrate on (1) creating the stability and comfort required to learn and execute fine motor control and (2) applying techniques and learning to use expensive and delicate tools with care.

Posture

You have the best fine motor control when seated comfortably in a relaxed position in which your arms and hands are stable. Adjust the height of your lab stool so that your back is straight and your feet are flat on the floor when your eyes are at the level of the microscope’s eyepieces (Figure B.1). If possible, rest your forearms on a support with your hands just above the dissecting dish in the position in which you would be performing a dissection. Avoid having the stool too high; this forces you to hunch over the microscope and leaves your feet dangling. Not only is this uncomfortable, leading to neck aches, backaches, headaches, and grumpiness, it decreases your stability and reduces your fine motor control.

Vision

If you can’t see it clearly, you can’t dissect it accurately. Except for the initial steps (removing and pinning a crayfish tail, removing the snail shell), all of the dissections required for these labs are best done under the microscope. Even if you can see a structure without the microscope, you will see it better with the microscope. Use different magnifications at different stages of the dissection. Start with a low magnification when opening the preparation and increase magnification as you progress, always keeping the area of interest filling the view. As you increase magnification, you may notice that the depth of field decreases; focus up and down periodically to see deeper or shallower structures. Use the dissection videos as a guide. If your field of view roughly matches that on the video of the dissection you are doing, you are using the microscope properly.

Good lighting is important to see structures clearly, especially since many are nearly colorless. If you have a light source with a branched light guide, experiment with lighting from the side as well as from above. This is especially useful with the crayfish labs. When recording from the snail brain, a light from the side will help you see the electrode while another light from below will highlight cell bodies. If you have only a single light source, experiment with different angles and change its placement as needed during dissection and recording.

A dissecting microscope has two eyepieces so that you can use binocular vision to judge depth. Most dissecting microscopes allow you to adjust the distance between the eyepieces to match your eyes. Most microscopes also allow the two eyepieces to be focused independently. To do this, determine which eyepiece is adjustable. Look through the nonadjustable eyepiece with the other eye closed and focus on a fine structure using the focusing knob. Now close that eye and focus on the same structure by adjusting only the eyepiece for the other eye. These adjustments are critical because it is difficult to perform a good dissection without clear binocular vision and because a poorly adjusted microscope can give you a headache.

Tools

A standard set of dissecting tools contains cutting tools like those shown in Figure B.2. It is important to use the correct tool for the task, both to accomplish the task efficiently and to avoid damage to the tools. Use the largest scissors to cut off the crayfish tail. Use the smaller scissors to cut through hard parts of the crayfish cuticle, remove swimmerets, or cut through snail shell. The fine Vannas scissors are expensive and delicate and should be used only to cut through soft crayfish and snail tissue. Vannas scissors are preferred but not required for any of the crayfish dissections; if they are not available, a scalpel with fresh #11 blade can be used instead, as shown in the videos.

The standard kit of tools should also include both coarse and fine forceps (Figure B.3). They will not necessarily be the same style as the ones shown in this figure. The coarse forceps are used primarily for tasks like placing pins (snail brain) and removing swimmerets (crayfish). Fine forceps are used to lift or tear delicate tissues.

All of these tools are expensive and fragile. Handle them with care and be sure to rinse off saline solutions, snail slime, and pieces of tissue as soon as you are done with a dissection.

Dissection

Become familiar with the video examples and plan each step of a dissection before starting it. When planning a cut, rotate the preparation to keep your hands in a natural position. Make the preparation and your dissection setup accommodate you, not the other way around.

When cutting a structure, pull it up toward you with forceps while keeping the blade of your scalpel or scissors parallel to structures below the one being cut. This will keep cuts shallow and avoid damage to underlying tissue. Video 4.2, Exposing Superficial Flexor, illustrates this technique and shows rotation of the preparation to make cutting easier.

Use both hands. For example, if right-handed, hold the dissecting tool in the right hand and use the left hand to steady the preparation dish or to steady the right hand. When two tools are needed (e.g., scissors and forceps), hold the cutting tool in the right hand and the grasping tool in the left, if possible resting your wrists or forearms on a surface to steady both hands. Often one pair of forceps will be sufficient to manipulate pins or tissue. However, you can use two, one in each hand, to get greater stability and control than is possible with one alone.

Also in the interests of stability, avoid drinking caffeinated beverages before doing a fine dissection, unless you are desensitized to their effect.