From: PERShadow@aol.com
Date: Sat Mar 08 2003 - 09:34:32 PST
From: PERShadow@aol.com Message-ID: <128.24f2049c.2b9b83a8@aol.com> Date: Sat, 8 Mar 2003 12:34:32 EST Subject: Muscle contraction activity
I'm not sure what level students you're working with, but the following is an
activity I wrote up several years ago for a TI workshop, and I've used very
successfully in teaching Physiology and AP Biology students. Depending on
how deep into muscle contraction's mechanics you want to go, it could also be
done in a regular biology course. The key here is to practice the "trick" on
yourself several times until you get a feeling for how important it is that
the student really exhausts him/herself.
Hand Paralysis Trick
Purpose: This activity demonstrates an interesting aspect of the molecular
mechanism for muscular contraction. It also provides quick practice in
problem-solving and research.
Materials:
Reference text(s) (one must describe the role of ATP in the release of
myosin crossbridges from actin. Look for an explanation of rigor mortis.
It is also useful if the role of calcium and the sarcoplamic reticulum is
described).
Student volunteer
Broom stick/stool leg (some kind of STRONG cylinder about one inch in
diameter)
Procedure:
1. Select a student from the class (typically, this works best with the
eager/willing to do anything type).
2. Have the student squeeze the broomstick as hard and as long as s/he can
with one hand. Make sure that it is a steady squeeze, and that s/he doesn’t
shift her/his grip.
3. Keep up a patter to ensure that the student is trying as hard as s/he
can, i.e. “You need to keep your knuckles white,” “I can feel you slacking
off,” “That’s good, see if you can keep squeezing longer than I can,” etc..
4. Tell the student to let you know when s/he is getting tired, but NOT to
let go until you tell her/him.
5. While the student squeezes, tell her/him that when you tell her/him to
relax, s/he is to open her/his hand just enough to allow you to slide the
broomstick out easily and to NOT try to move the hand AT ALL until you say.
6. When the student says s/he is getting tired, see if you can coax her/him
to go longer. If not, remind her/him of step 5, then say s/he will relax on
a count of 10. Dawdle over the countdown, constantly urging her/him to give
it her/his last reserves of energy. Extend the countdown by several times
reminding them about how they are to only open their hand enough to slide it
off the stick, and then not move it until you tell them to.
7. Once s/he has opened her/his grasp, slide out the stick, then GENTLY
stroke the outside and inside of her/his hand and down her/his wrist,
alternating between the three about three or four times. It is not a bad
idea in today's classroom to actually have the student stroke their own hand
as you show how using your own hands.
8. Emphasizing that they should stop if they feel any pain and not to force
it, tell the student to SLOWLY try to open her/his hand. S/he should have a
difficult time doing so. Have the student explain their sensations to the
class. Depending on the student, their hand will likely remain "paralyzed"
for about a minute, but I've had students remain "stuck" for up to 15 minutes.
9. Have students work in pairs to figure out why this trick works using the
resource books. In my class, I have them write two paragraphs. The first is
to be a DETAILED description of the steps involved in a muscle contraction
(this is to help point out the possible solution). The second is to be their
hypothesis explaining the hand paralysis and more importantly, their
reasoning behind that hypothesis. An extension of this is to have students
experiment to determine if the stroking of step 7 is necessary. I usually
try to provide two different texts, usually one that is simpler than the
other to provide an overview of contraction that helps them understand the
more complex text’s details.
What’s going on?: Muscle cells contain thousands of tiny protein filaments.
There are two types, thick (or myosin) and thin (or actin) filaments. These
contract or shorten the muscle cell when extensions of the thick filaments
called crossbridges grab ahold of the thin filaments and slide them over the
thick filaments (it’s like someone pulling a long pole off the back of a
truck by alternating pulling with each hand). The energy to do this is
provided by ATP. What is interesting is that the crossbridges can’t let go
of the thin filaments and grab further down to continue pulling UNTIL the
crossbridge gets another ATP molecule. This also means the muscle can’t
relax unless it has sufficient ATP to disengage its crossbridges. This is
what causes the phenomenon of rigor mortis or stiffness of a corpse. When
someone dies, obviously the cells start to die, too, and stop making more
ATP. Eventually, they run out and those crossbridges that were attached to
thin filaments are stuck. This is increased because muscle cell death
triggers the release of Calcium within the cell, which is the chemical that
helps/signals the crossbridges to attach. In a living cell, Calcium is
constantly being pumped into storage (again using ATP), so for the muscle to
relax, ATP is needed both to allow the crossbridges to release the thin
filaments, and to remove the Calcium so that the crossbridges don’t
immediately reattach.
In this trick, students are forced to use up as much ATP as possible, and
hopefully go into oxygen debt (the cells switch to anaerobic respiration to
get ATP when they can’t get enough oxygen, but the byproducts require oxygen
to be gotten rid of). This causes those muscle cells’ crossbridges to lock
in place. When they slowly try to open their hand, they feel strong resistan
ce as if their hands were paralyzed. It’s just their locked up muscles are
still in contraction, but because the students aren’t sending nerve signals
to those muscles to contract, they aren’t aware of it. They wind up
unknowingly fighting their own muscles to open their hand. Once the cells’
oxygen supply has been replaced and more ATP is synthesized, the muscles
slowly can relax. I’m not sure, but I think the gentle stroking helps slow
the return of blood, prolonging the sensation.
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