What you have here is a Macintosh computer.  Some of you may not be familiar with this type of computer.  For those of you who are not sure how to operate this system, please click on the desktop, then choose "Mac Help" under the Help menu, then click on "Switching from Windows".

Next read about how to acquire data with your computer and you PowerLab unit (below the computer).  Read pages 8-15 in the Scope User's Guide.  A bound copy of this manual is on top of your PowerLab unit.  Next read part of the Scope program's "Quick Start" book, pages 1-18.  You also have a bound copy of this manual on top of your PowerLab unit.  You may wish to skim it now and read it in more detail later as you develop questions.

After reading the "Lab 1. Passive Membrane Properties and Electrophysiology" from your Crawdad CD-ROM, get started on the exercises.

NOTE: You can switch between various programs by moving your cursor to the bottom of the screen (the "dock").

The icon at the upper right of the desktop is your computer's hard drive.  It is named after one of the species that are used in neurobiology research.  Double-click that icon and then choose "Favorites" from the sidebar.  Click on "Exercises", then on "Experimental Neurobiology", then on "Week 1".

Attach three black BNC cables to the front of your PowerLab (the tan box under your computer)—one to "Output 1", one to "Output 2", and the other to "CH1" (which is an input to the PowerLab).  Now attach one end of the red alligator clip wire to the pin in the center of the opposite end of the "Output 1" BNC cable.  Clip the black clip onto the opposite end of the "Output 2" BNC cable.   [The red and black cables are now capable of shocking with voltage so don't touch both red and black at the same time or your body could complete the electrical circuit!].  Attach the green clip to the golden center pin of the "CH1" BNC cable, and the yellow clip to the outer conductor (metal shield) of the BNC cable.

Turn the unit on by flicking the switch at the back panel on the left side.  Now click on the Template file entitled "Week 1- Template".  That will open a program called "Scope", which is a program that simulate the functions of an oscilloscope.  It is designed to take changing electrical inputs and display those changes on a screen with voltage on the y-axis (a.k.a. ordinate) with time as the x-axis (a.k.a. abscissa).  Your instructor has created this template to set up Scope with the configuration you need to complete these experiments.

Click on "Start" at the lower right.  You will see two lines are created.  The top black line is a record of the voltage from Output 1 that was generated by the PowerLab stimulator.  Note the "Stim" box at the upper right and figure out what each of the parameters mean.  Set the AMPLITUDE to 9 Volts.  Ask if you need help.  Move your mouse cursor left and right over the screen and note how the time changes in the "Cursor" window in the upper right of the screen.  Note also how the voltage alters between positive and negative (if you don't see this, increase the scale by clicking on the up arrow in the lower left corner of the window).  This is because the red "trace" is a record of the voltage difference between the green and yellow wires.  Those wires are recording the electrical field in the room that is created by the lights, power cables, and electrical devices nearby.  Note that the wave cycles 60 times per second because all power in North America is supplied in that frequency.  Have your lab partner hold the green and yellow clips in their hands and Start the sweep again.  [NOTE: this is perfectly safe because you are holding the recording cables, not the simulating cables!].  The amplitude of the red trace oscillation will become larger, BECAUSE you are serving as an antenna for electromagnetic radiation!  Your body is mostly salty water so you conduct electricity very well.  Nice job!  You just recorded your first signal onto a computer!

The Model "Axon" (or dendrite)

Now back to the exercise.  In the exercise, they suggest using a battery to stimulate the "model axon" (see Fig 1.1).  Instead, you can use the red and black alligator clips as a voltage source.  Clip the RED to the metal pins of the resistors on the side of the "membrane" marked "inside cell".  Clip the BLACK to the metal pins of the resistors on side of the "membrane" marked "outside cell".  This way, you will be stimulating the "membrane" with positive voltage and making the "inside" of the "axon" positive in charge.  Place your recording electrodes (green on the inside and yellow on the outside)  in the center of the model axon (see Fig 1.2).  Now press START.

Measure the final voltage of the red trace.  Move your cursor and note the value of "A" in the cursor window (or use the DataPad function under the "Window" menu).  Make a note of this in your lab notebook!  [Also explain in your lab notebook what you are doing and the configuration you are using.  The purpose of a lab notebook is to help a scientist like yourself reconstruct EXACTLY what you did].  Make a comment on this page of data to help you remember how far away (in resistors) your stimulus is from the recording site.  Count the number of intervening resistors between your stimulating electrodes and the recording electrodes.  Click on the small box at the lower left that is to the right of the letter "M".  Type the number of resistors distant into the Page Comment box and close the box.  Move your stimulating electrodes closer to the recording electrodes and press START again.  Continue this until you reach the other side of the model axon.  This way you can number the stimulating positions –6 through +6, with 0 being the position when the stimulating electrodes and recording electrodes are at the same place.

This simulates the situation in which you are recording closer or farther away from an incoming electrical stimulus with an intracellular electrode (it also can simulate the movement of an electrical potential along an axon).  Note that you are recording the difference in voltage between the inside (i.e. INTRAcellular) and outside of the membrane.  Save a copy of this file by clicking File/Save As, then click on Documents.  Make a new folder in the Documents folder and give it your and your partner's name.  Save these pages of data as one file called "intracellular".    Save ALL of your files there and they will be SAFE.  Save them elsewhere and they may end up in the Trash.  [The trash won't be emptied very often so you could retrieve it, but someone may empty the trash and you would lose all of your work permanently].

Do your data resemble the sample data?  Open "current spread sample data" to see.

Next, in the extracellular recording situation (see the Crawdad lab manual and Fig 1.3), you are recording the voltage difference between two places along the length of the axon membrane, with both electrodes OUTSIDE (i.e. EXTRAcellular) the membrane.  Here you will use the 9V battery as the stimulus.  Open the template file again and save a copy.  Save these pages as a new file called "extracellular".  Note that these voltages are much smaller than those recorded during intracellular recording.

To plot your data use Excel or Prism.  Go back to the Desktop (i.e. the program called Finder), and open "sample graph".  This is a locked file so you can't change or save it, so save a copy.  Type in your data into Excel.  Save your data in your folder!  Note that some distances may be negative! 

Print one copy of your intracellular graph and one for extracellular and tape them in your notebook.

Answers questions 1-6.  They will help you understand.  Feel free to work in groups to get the answers, but you must write your own answers in your own words; no copying.  Come talk to me if you need any help.

Time Constant

Place your electrodes in the places as indicated in Fig. 1.4.  Note that the stimulating electrodes span across the resistor (R) and the capacitor (C) such that the black is on the outside, and the red on the far end of the resistor.  Note that the recording electrodes are on the opposite side of the circuit and only span across the capacitor (C), such that the yellow is in the same place as the black, and the green is on the inside end of the capacitor.  Save this file as "RC data" to your own user folder.  Click and drag over one entire pulse to highlight it in black.  Choose Zoom Window from the Window menu.  Drag a Marker from the lower left corner from the box with the little "M", and drop it at the beginning of the pulse.  Use the cursor to find the time at which the pulse reaches 63% (63% is related to logarithmic decay and calculated as 1–1/e) of its peak value.  Type "calculator" into the blue spot in the upper right of the screen to open a calculator (you can do this to open any file or program).

Does your data resemble the sample data?  Open "RC sample data" to see.

Print a copy of one of your zoomed pulses, and tape it into your notebook.  Draw on the curve a horizontal line at 63% of pulse height, and drop a vertical line from where it intercepts the curve.  That is your best estimate of the measured time constant of your artificial membrane.

Answer questions 1-3.

Electric Fish

Observe an electric fish in a container of fish water.  Carefully place the silver wire end of the electrode into the tank so as not to disturb the fish.  Plug the BNC cable into the input of small speaker/amplifier.  Turn on the power and listen for sounds.  These are electric fields made by the fish's electric organ (see handout).  The fields induce a current in the wires, and the amplifier uses those currents to drive the speaker.  Now plug a BNC cable into the output of the speaker/amplifier.  Plug the other end of the BNC into the CH1 input of your PowerLab.  Open the file "Apteronotus settings".  Press START.

In this exercise they ask you to change the sampling rate.  You read about sampling rate in the Scope User guide earlier today.   You can change the sampling rate by changing the "samples" and "time" to the lower right of the window.  Try to make the sampling rate decrease from 200 kHz to 2 kHz by chanding the TIME on the right side.  You can also change the size of your signals on your screen by clicking the arrows next to "Range".  Try to make you signal fill the entire window to facilitate measurements.  Or select a section and choose "zoom" from the Window menu.

Answer question 2.
 

Before leaving show your instructor that all of your data are saved in your named User folder and show the instructor you lab notebook.  Also, turn off your PowerLab and Quit all programs (to do so you need to choose File, Quit for each program.

Finally, you need to complete these exercises before Friday so I can return your notebook by next week's lab, but not necessarily today if you run out of time.  Additionally, you can work the "the membrane" and "resting potential" simulations in the program NeuroLab of Neurons in Action.  Find this file in the "Exercises" folder on the Macs in lab.

modified 8-26-07