Title

Example of a chat session from a 2004/2005 Biology AP Session meeting

The names of the participating students have been changed to Peter, Susan, and Lucy from their originals to protect the students' privacy. I chose this log because it demonstrates something of the nature of a discussion that is not a lecture (we do that kind of information presentation with website pages) but instead a discussion that responds to immediate concerns the students need to address. This was an AP option discussion group, so it was small, and discussed both the examination, ways to prepare for it, test-taking and essay writing techniques, and specific material the student might encounter on the test from the course material we were covering at the time in the regular course.

DrCMcM: Got any questions? I know Susan said she had some about the recent material.

Susan: Good morning Dr. Christe!

Susan: Yes, a couple

Susan: ? (About SAT II/AP)

DrCMcM: GA Susan

Susan: If I take the AP and do well, would you recommend taking the SAT II Bio as well? Or is it unnecessary?

DrCMcM: If it is a choice between taking the SAT subject exam in bio and something else, once you've got a solid grade (3,4,5) on the AP, then take the something else.

DrCMcM: If you want to major in life sciences, it doesn't hurt to have them both under your belt, because the SAT score will reinforce your performance on the AP.

DrCMcM: As I tried to point out in the Biology Website pages on the SAT and AP, they really are meant for different purposes. The SAT validates your claim to know bio at a high school level and be ready to pursue it in college if you want; the AP says you know it at an intro college level.

Susan: Aha. That's what my mom told me -- so I wasn't sure if I needed the reinforcement of SAT in addition to AP.

DrCMcM: Normally you'd take the AP course AFTER taking a high school course, so you've kind of skipped that step.

DrCMcM: It also depends on where you apply to college and just how they organize data when considering admission.

DrCMcM: One would hope that they would be able to make an adjustment to an AP score where they asked for a SAT score, but you'd have to check with the colleges you want to apply to.

DrCMcM: Honestly, I haven't had much experience with students who've done ONLY AP in a subject; most of mine who've done the AP exam have also taken the SATs in the subject.

DrCMcM: (And more of my students just take the SATs in their science subjects and don't take the AP.)

DrCMcM: One of the issues is timing: if you take the AP in May, you don't get results in time to decide whether to take the SAT in June, and then you have to crowd it into the fall, when you may have other subjects to take.

Susan: Right... and I know I would rather not take any more tests than I have to.

DrCMcM: When do you apply to college?

Susan: Long time... three years or so. I don't have to rush.

Peter: 2007, i believe.

Lucy: I apply in '07

Susan: I'm a freshman, so '08 for me, I think

DrCMcM: The normal sequence is to take the National Merit/Pre SAT in October of your junior year (you have to take it then for it to count for scholarship consideration; you can take it other years but your scores won't be considered).

DrCMcM: You should have a short list of colleges that you want to apply to in mind by spring of your junior year and take your SAT Is in May or June, and one batch of subject exams.

DrCMcM: Then if you don't do as well as you like on those, you can retake them, or take other subject exams in the fall and still be in time to report your scores for admission consideration.

DrCMcM: If you try for early admission (you know exactly where you want to go and will go there if accepted), you'll have to have all your paperwork in by 1 November of your senior year, otherwise the deadline is usually 1 January.

DrCMcM: Then you bite your nails until April.

DrCMcM: Notice that AP exams don't show up in that timeline -- that's because usually students take AP their senior year, and the AP exam in May -- when they've already been accepted to the college of their choice and they are just trying to establish standing and credit so they can select classes.

DrCMcM: You're doing it all backwards (not that that's a bad thing), but it does mean that you should be aware, taking the AP this year, that your "competition" will be mostly students several years older than you, with theoretically more experience in bio, in exams, even in writing.

DrCMcM: I'm not trying to scare you, but to just give you an idea of what you are facing.

DrCMcM: Have you taken a diagnostic exam yet from one of the AP prep books?

Peter: I'm preparing. I have an AP Prep book.

Susan: I haven't yet. There's two different ones with total of 5 different practice APs. Neither version has a diagnostic exam, though.

Lucy: no, but a have an AP book too

DrCMcM: I encourage you to find time in the next couple of weeks to take at least one under the test conditions described.

DrCMcM: You can check your multiple choice answers and determine whether you have any holes in a given topic area, then we can review that.

DrCMcM: I'm mostly interested in seeing your free response answers: they are often the make-it-or-break-it difference, because you have to show that you understand the question and can put together an organized, well-substantiated clear answer.

Susan: They look like they're going to be the hardest part

DrCMcM: Or the most fun.

DrCMcM: Depends on whether you like writing essays.

DrCMcM: Put yourself in teacher mode and assume that you are explaining the answer to someone bright but who knows less than you, and be sure to fill in necessary background.

DrCMcM: Okay -- do you have questions on any of the stuff we've been covering lately in class?

Lucy: ?

DrCMcM: Susan mentioned that she had some questions yesterday and I want to be sure to cover those.

DrCMcM: Lucy, ga

Susan: ?

Peter: ?

Lucy: do we need to memorize all the names (and actions) of the neurotransmiter molecules discussed in Ch 28.8?

DrCMcM: I'm looking to see what kinds of questions there are for nervous systems in the AP examples I have.

DrCMcM: There actually is one that asks you to identify which chemical is most likely to be made in a particular part of the nerve cell.

Lucy: what are the answer choices?

DrCMcM: acetylcholine, adrenalin, epinephrine, serotonin, insulin

DrCMcM: You can eliminate insulin; it is secreted by the pancreas. Adrenalin = epinephrine, so neither of those can be right because if one is, both must be.

DrCMcM: Serotonin's in the brain -- so in the particular situation of the question (what neurotransmitter is secreted at the junction of a motor neuron with the effector organ), the answer has to be acetylcholine.

DrCMcM: Notice that you use some test-taking techniques as well as factual knowledge in analyzing the question -- you can eliminate impossible answers and then concentrate on choosing between the remaining ones.

DrCMcM: You should probably remember acetylcholine as the example of the neurotransmitter between the nervous systems and muscles; serotonin and dopamine, because they come up in drug treatments for headaches and personality disorders, and epinephrine because it's an example of a chemical made by both the nervous system and the endocrine glands.

DrCMcM: The rest are mostly amino acids or slight variations -- which makes proteins "brain food".

DrCMcM: That gives you a short list of 4 to know and a class for the rest; does that help?

Lucy: yep, thanks

DrCMcM: Susan, ga

Susan: Is it possible at times for a signal to completely bypass the Central Nervous System (CNS), being conveyed straight to muscles (or other tissue) by the Peripheral Nervous system (PNS)?

DrCMcM: I think that's the current theory.

DrCMcM: For example, if you touch a hot stove, the heat/pressure/pain sensing nerves of the PNS take to the motor nerves of the PNS and you jerk away in reflex before the signal gets to your brain and is identified.

DrCMcM: I know at one time the texts insisted that the PNS had to at least communicate with CNS cells in the spine; your text (in ch 28.12) seems to indicate the PNS is talking to itself.

Susan: So this is a feature that can actually 'preserve' us. Would an evolutionist consider it significant enough to have played a part in natural selection? (I.e. those who had PNS that could bypass the CNS had a higher survival and hence reproduction rate?)

DrCMcM: Absolutely.

Susan: Or is it just something nice that keeps us from burning our fingers too badly? *g*

DrCMcM: The ability to respond quickly to a given situation without having to process conscious thought would be especially important in a period when humans were hunters and hunted -- and wouldn't be good just for reducing burn injury.

DrCMcM: There's also the kind of "memory" training that you do when you learn a piano piece or type a given pattern over and over again.

DrCMcM: Again, we are not sure exactly how this works but your PNS seems to be able to store some kinds of information locally -- so your hands remember the piece and the pattern of the keys to use.

Susan: Unfortunately, that memory doesn't always seem to stick under pressure... *sigh*

DrCMcM: All of these features would give their holders a survival advantage over slower-reacting, more clumsy individuals.

DrCMcM: Peter, did you still have a question?

Peter: Can you post the Weblectures, please? It would be nice to have the material handy, because it offers a extra view of the materials we are currently going through.

DrCMcM: I'll tell mycroft that he actually has to write them, then.

DrCMcM: I don't think the set for anatomy is complete; I'll check.

mycroft can't draw, and so much of anatomy is attaching names to things.....

DrCMcM: I'll see what I can do. One of the problems I've had is that I'm never sure if students are actually reading the weblectures in addition to the text, CD, and workbook.

Susan: I always do - there's sometimes quiz questions on them

Lucy: I read them

Susan: *on material from them

DrCMcM bows to her demanding public.

Susan: lol

Lucy: *throws roses*

DrCMcM: I see...you guys just like all the neat little tables.

Peter: I have increasing found that the weblectures contain all the material for the tests, so I find them profitable to learn.

Susan loves neat little tables that look so nice when copied into her notebook

DrCMcM puts writing lectures back on the schedule.

DrCMcM: What else about bio for this morning? Any other questions about the materials in recent chapters?

Susan: ?

DrCMcM: Susan, ga

Lucy: no ma'am

Susan: How does a stimulus trigger Na+ channels to begin opening? Is it a process similar to signal transduction?

DrCMcM: The stimulus -- whatever it is -- changes the local potential.

DrCMcM: A stimulus could be a neurotransmitter that reacts with the neuron's membrane, resulting in the formation of ions that carry a local charge -- and affect the local voltage differences.

DrCMcM: Pressure on the nerve could cause a physical shift in distribution of internal components, and change the local potential.

DrCMcM: Whatever the change is, the resting potential difference between the inside and outside of the cell goes up -- and the gates open and drive it up even more.

DrCMcM: Make sense?

Susan: Yes ma'am

Lucy: mhmm

DrCMcM: Anything with a charge is affected by anything else nearby with a charge (just like in gravity, anything with mass is affected by every other mass -- usually only the nearby ones make an effective difference).

DrCMcM: Since the gates open or shut depending on the difference in electrical charge inside and outside the cell, any shift in the distribution of any ions, or big molecules with locally-charged areas, can cause the gates to respond.

DrCMcM: What else?

Susan: ?

Susan: What specifically does the myelin sheath protect the axon against? Why does the loss of it result in problems like multiple sclerosis?

DrCMcM: The myelin sheath allows the nerve signal to travel the length by jumping from node of Ranvier to the next node of Ranvier to the next.

DrCMcM: That is, the signal travels as raw electrical energy.

DrCMcM: This is faster than having the signal travel down the axon chemically -- the way we described it coming in along the dendrites, with Na+ and K+ moving in and out and local potential changing.

DrCMcM: The signal travels about 20 times faster this way than it would if it traveled as a chemical/electrical signal directly in the axon.

DrCMcM: So think of what happens in the myelin sheath deteriorates and the signal starts to travel as a flow of ions.

Susan: Ah - so simply slowing down these signals is enough to wreak havoc on the body's functions?

DrCMcM: Those nerve cells with long axons -- the ones that go a meter or so from your spine to your feet and control how you walk -- suddenly take 20 times as long to transmit information.

DrCMcM: Your brains says do this....and some time later your feet do it.

DrCMcM: Your coordination will be affected -- your brain is used to you doing things in a certain response time.

DrCMcM: Your instinctive responses -- like pulling away from the fire -- will be affected.

DrCMcM: So yes, slowing down signal transmission is going to mess everything up.

Lucy: ?

DrCMcM: It would be like the internet and phones going down and everyone having to rely on snail mail for communication again.

DrCMcM: Lucy, ga

Lucy: I'm a little confused- so dendrites pass active potentials just as described in the book, and myelin-sheathed axons don't?

DrCMcM: Well, the book describes both: the structure and method of passing the signal along the axon of a motor neuron is covered in 28.2 (p. 565), but that's the outward bound signal.

DrCMcM: Notice that the dendrites don't have the myelin sheath.

DrCMcM: The incoming signal has to be high enough to hit the threshhold potential.

DrCMcM: And locally at the nodes, you are still going to get the shift in resting potential -- it's just that the node kicks the signal back out.

Lucy: so do the motor neurons pass info without worrying about potentials?

DrCMcM: It's almost as though each node of Ranvier saw itself as a separate neuron passing the electrical energy to another neuron -- effectively, the myelin provides the insulation for the separation.

DrCMcM: No -- the potential issue is still there.

DrCMcM: You know how you get a spark of electricity if the air is dry and you walk across a (usually synthetic) rug and touch metal?

mycroft hates that.

Lucy: yes

Lucy: err, kind of

DrCMcM: Okay.

DrCMcM: Now, say something disturbes the electric potential of spot A1 on the tip of the dendrite.

DrCMcM: The potential jumps up enough to hit threshold, the gates open, the potential goes even higher.

DrCMcM: This is like sending off fireworks.

mycroft: Or lighting the beacons of Amon Hen.

Susan: lol

DrCMcM: The neighbors notice.

DrCMcM: The change in electric potential starts to spread; they see their own go up, and their Na+ gates open.

DrCMcM: Their gates are wide open -- and the neighbors further down the street start to see the effects -- at the same time that the original spot at A1 on the end of the dendrite is starting to go back to normal.

DrCMcM: So the signal continues down to the body of the neuron, and out the axon.

DrCMcM: Now when it gets to the axon it runs into a barrier.

DrCMcM: It can't move forward because the sheath is in the way, but all this charge is coming crowding up behind.

DrCMcM: The collected charge gets large.

DrCMcM: We have a situation like an electrical capacitor: charge in one spot.

DrCMcM: It can't go back because there is still a lot of residual charge behind "pushing" it forward.

DrCMcM: It can't go directly forward because of the insulation.

DrCMcM: So it jumps to the first node, just like a capacitor discharging (it *is* a capacitor discharging).

DrCMcM: The node is just like any other membrane-surfaced area of the neuron; the incoming charge disturbs its resting potential, the gates open, the potential jumps up, and the collected charge has to go somewhere, so it jumps to the next node.

DrCMcM: So at each node, all the stuff we've seen about resting potentials changing, voltage-gated channels opening/closing -- all that occurs AT THE NODEs along the axon.

DrCMcM: But not between them: between them the electrical energy is jumping OVER the Schwann cell.

DrCMcM: That help?

Lucy: very much :)

DrCMcM: Instead of walking, it's using a pogo stick.

DrCMcM: Lucy, Susan, Peter, anything else?

Lucy: nope

Susan: No ma'am.

Peter: nope

DrCMcM: Okay -- see you Monday then.