Notes for Experiment #6 -- Bioelectric Measurements
Notes & Hazards
Random helpful notes for your experiment:
- This lab is pretty easy but it might still take about 2 hours or
so. Most of it is pretty self-explanatory; there are a bunch
of new things but since they're almost all software-related,
I'll be doing a demo once we get to lab (I'll essentially take
you guys through a sample recording).
- Still, here are some (hopefully) helpful hints/pointers:
remember that the electrode cream helps lower resistance and
provides good contact between your skin and the electrodes.
But, the stuff tends to dry quickly and you'll be using tape to
hold the electrodes on. So make sure that the less hirsute
partner takes on the role of guinea pig (trust me, it is
not fun pulling off the tape along with a major portion
of your body hair. Along these lines, though, make sure you
wear shorts, sweats, or other easily-accessible clothing.
You'll be taking measurements along your arm and along your leg
so you'll need easy access to em.
- One of the trickiest things in this lab (maybe the only tricky
thing) is to figure out what the signals mean. A good rule of
thumb is what the lab manual suggests: the reflex time is
the time between the (peak of the) trigger signal and the
beginning of the
electrical activity. In other words, what you're really
measuring is the time of travel for the neural signals
associated with the stretch reflexes in the knee and ankle.
This time should be essentially constant as the response is
mediated via the spinal column and doesn't depend on any
secondary processing in the brain whatsoever.
In (gruesome) detail, the
stimulus causes an afferent neuron to fire; this synapses onto
an interneuron in the spinal column; which synapses onto an
efferent neuron in the muscle; the impulse at the
neuro-muscular junction is what we pick up, amplify, and see on
the oscilloscope as the signal.
Since the reflex is completely independent of any other
processes, this time should be constant. Whether a small
stimulus triggers a small number of afferent neurons or whether
a large stimulus triggers a whole mess of sensory neurons, the
amount of time required to initiate the reflex should stay
constant. The intensity of the response itself (e.g., how high
the leg goes), however, might be affected by the strength of
the stimulus or may be controlled to a certain extent
voluntarily. But the only way to have a variable reflex
time is if the subject somehow anticipates the stimulus and
starts to react before ever getting hit. Of course, a whole
bunch of technical issues also arise (distinguishing artifacts
from actual signals, noise in the system from the environment,
noise from overlapping, but unbraided, signal wires, etc.).
- Laboratory Manual (SGM 407)
- Laboratory Answer Book
- Calculator with statistical functions
Some Helpful Links & Miscellaneous Notes
- This lab should allow you a bit of a breather and provide some
biological applications of all the electrical stuff we've been
studying so far. It should be interesting stuff but getting a
handle on the computer stuff might end up taking you a couple
hours. So if you're comfortable with that and you (or your
partner) aren't squeamish about popping on the cream and the
electrodes, you might end up getting outta here pretty
- Remember, the 1st midterm is coming up on 2/29/00
from 5-6:30pm in THH 201. I'll be posting more info and
hints/tips as we finalize the details.
- Feedback on if you're finding these pages helpful (or not) is
definitely good. So if you have any strong opinions, or, dare
I say it, ideas on how to make this better, drop me a line!
Ricky J. Sethi <email@example.com>
Last modified: Tue Apr 18 22:51:02 2000