This week, we’re moving on to bio/biochem from Blueprint MCAT full-length 1. We discuss how to shift your mindset after CARS, test-taking strategies, and more!
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Listen to this podcast episode with the player above, or keep reading for the highlights and takeaway points.
[01:57] Tips for Taking Breaks on MCAT Day
Have a light lunch and stay mentally engaged. Give yourself that a few minutes of mindful meditation where you just close your eyes. Focus on your breathing. Don’t think about anything and just be still. Take time to walk around. Drink water, but not enough where you have to get up in the middle of the session and use the restroom. Just know yourself in the next seven hours and be very robotic.'Don't do anything different on test day than you wouldn't normally do.'Click To Tweet
[04:17] Shifting from CARS to a Science Mindset
We have just finished the CARS section. So we’re jumping into bio/biochem, which is the next section that comes on the MCAT. Obviously, we’re going from critical reading and analysis to another science-based passage.
The best thing to do is to practice. Think about some of your favorite science phenomena to get yourself primed, like action potentials and sodium channels opening and an influx and causing potassium channels opening in any flux.
You have to bring in outside information now. All MCAT books are fair game. Now, you get to apply your sciences here. So get yourself ready for that mentality of getting yourself primed.
[05:51] Passage 1 (Questions 1 – 5)
“Transcranial magnetic stimulation (TMS) of the motor cortex uses a powerful, focused magnetic field to depolarize brain neurons and elicit motor-evoked potentials (MEPs) from the skeletal muscle. An MEP may be defined as a recording of the electrical muscular response elicited by artificially stimulating the motor cortex, which can cause muscle movement as well. MEPs are useful as a method for assessing the integrity of the central to peripheral nervous system path. MEP amplitude is taken as an indicator of cortical-motor excitability.”
Note: We’re learning about the inner workings of TMS. Then MEP amplitude is taken as an indicator of cortical motor excitability. So just keep that in mind. You definitely want to be careful to not highlight a lot of things.
[07:54] Paragraph 2
“Pathological conditions that affect the efferent and afferent paths are varied. For example, spinal cord injuries may result in a severing of a section of the spinal cord that relays impulses to the muscle. In Parkinson’s disease, dopaminergic cells in the brain die and motor movements become slow, shaking, and increasingly difficult. TMS can be used to differentiate if the communication problem is in the brain or in the periphery.”
Note: In this paragraph, we didn’t really introduce a lot of new ideas. As an MCAT student, you’re familiar with the efferent and afferent paths, going out of the brain and coming back to the brain. We’re familiar with the pathology of Parkinson’s, specifically with the lack of dopamine. If anything, the only important thing would be that TMS differentiate communication problems in the brain or the periphery.
The next thing that we see here is a figure. And whenever we approach figures, graphs, and all that good stuff on the MCAT, the only thing that we want to focus on is answering one question and that question is: why did the author waste their life putting this here? What was the point? Start off by reading the finger description. And then look at any of the legends, the axes, the titles, and whatnot.
Figure 1 The effect of six different motor protocols on MEP amplitude; Dyn = dynamic, the subject was moving during the task; Sta = static, the subject’s hand remained at rest during the task
Observation: You could probably notice a decrease in that amplitude each time when it’s static versus dynamic. You can keep this in mind but don’t spend any more time than that because you’ll come back to it as needed.
But this definitely tells us a little bit about MEP amplitude in the context of static or dynamic and then they introduce AO or MI and we’re going to keep that in mind.
[11:15] Paragraph 3
“A TMS experiment was conducted to test the excitatory effects of motor imagery (MI) and action observation (AO) in the first dorsal interosseous (FDI), the muscle responsible for flexing (closing) the index finger when making a fist. Five healthy subjects were asked to perform three pairs of motor protocols, each comprising 20 trials over five minutes. In the first protocol, the subject observed a video (AO) of a stranger opening and closing a fist. Next the subject was asked to imagine opening and closing his/her own fist (MI). Finally, the subject both observed and imagined movements of the hand (AO + MI). Each protocol was performed once with the subject’s own hand at rest and separately with the subject actively opening and closing his hand. During each protocol, in ten of the 20 trials, MEPs were elicited from the FDI. The group results are shown in Figure 1.”
Note: It is showing us the amplitude of what they were doing in this trial of observing or imagining the movements. They were actually moving their hands themselves.
Whenever we approach experiments, we want to focus on the purpose of the experiment. Look at the independent and dependent variables. What are we measuring and what’s changing? And then any results, and here, Figure 1 is definitely our results.
Have a good understanding of the experiment. It’s a TMS experiment where we’re measuring amplitudes. And in that last paragraph, you could probably highlight the variables.
[15:59] Question 1
Which sequence properly indicates the transmission path of impulses as a direct result of transcranial magnetic stimulation?
- Sensory neurons, cerebral cortex, afferent neurons, skeletal muscle cells
- Skeletal muscle cells, afferent neurons, spinal cord, cerebral cortex
- Cerebral cortex, spinal cord, efferent neurons, skeletal muscle cells
- Efferent neurons, afferent neurons, interneurons, cerebral cortex
Reworded Question: Why was the conquest of the South Pole the ultimate test?
Based on the discussion of what TMS is, it’s of the motor cortex depolarizing brain neurons to elicit MEPs by the skeletal muscles. So we know it’s coming from the motor cortex to the skeletal muscle. And just based on that answer choice C is the only one that goes on that path. We’re going from the brain to the skeletal muscle. So we’re starting at the brain and everything in between. This is an example of what will cause muscle contraction.
Correct Answer: C
[17:56] Question 2
L-DOPA is a common medication administered to treat the symptoms of Parkinson’s disease. What is the likely mechanism of L-DOPA?
- L-DOPA increases dopamine concentration.
- L-DOPA decreases dopamine concentration.
- L-DOPA breaks down the blood-brain barrier.
- L-DOPA converts glucose to dopamine.
Reworded Question: Approach this with a prediction mentality. What’s wrong with Parkinson’s?
In Parkinson’s disease, dopaminergic cells die and motor movements become slow shaking and increasingly difficult. So dopaminergic means there’s something going on with dopamine.
When dopaminergic cells die, dopamine levels go down. So how are we going to treat Parkinson’s? We have to get it back up.
L-DOPA is used to treat Parkinson’s so it increases dopamine. Looking at the answer choices, A is the most likely answer.
Correct Answer: A
If you make a prediction, you see it in the answer choices, pick it, and move on. Don’t even look at the other answer choices. Don’t even consider the remainders. And that’s how you save on time.“One of the techniques of a very efficient test-taker is to read a question, rephrase it, predict what the correct answer is, look at the answer choices, match it, click it, and move on.”Click To Tweet
[20:50] Question 3
Which of the following processes is involved in the motor-evoked potential elicited by transcranial magnetic stimulation?
- Na+ influx
- Ca2+ release
III. Cl- efflux
- I only
- II only
- II and III only
- I and II only
Thought Process:“There's a particular strategy on how to approach Roman numeral questions. First, look at the answer choices and find the Roman numeral that pops up the most.”Click To Tweet
For this question, II pops up three times. And if II is wrong, then we know the answer and move on. The question is asking what is involved in MEPs elicited by transcranial magnetic stimulation to motor-evoked potentials elicited by TMS? II is Ca2+ release and there is calcium release whenever we have a motor-evoked potential.
Remember, skeletal muscle contraction is caused by the release of calcium from the sarcoplasmic reticulum, and calcium binds to tropomyosin. To remove tropomyosin out of the way helps the contraction to occur. So calcium release is true. So we can definitely cross out answer choice A.
Let’s now take a look at I. Whenever we have a motor-evoked potential, there is sodium influx due to voltage-gated sodium channels opening. It allows for the sodium from the extracellular space to be rushed into the intracellular space. And that causes depolarization. So sodium influx is a true statement. So Roman numerals I and II are true.
Therefore, the correct answer is D because there’s no way that I, II, and III could be true because there’s no answer choice allowing that. So the answer is D, we click it, and move on. Besides, there’s no chloride efflux, a potassium efflux.
Correct Answer: D
[24:10] Question 4
Would the leg muscles of a patient paralyzed due to spinal cord transection be expected to exhibit MEPs?
- No, because the motor cortex is damaged
- No, because a muscle response requires an intact pathway
- Yes, if the stimulation intensity can be made sufficiently high
- Yes, because the motor cortex is intact
Reworded Question: We know what MEPs are which are these motor-evoked potentials. Would the leg muscles of someone who’s paralyzed exhibit them?
A – The motor cortex isn’t damaged, but the spinal cord is damaged. So we throw this one out.
B – No, because a muscle response requires an intact pathway. And so this one is interesting, because I agree with part of it, but not the other part of it.
C – The stimulation intensity can NOT be made sufficiently high It’s transected so it’s not going to be fixed. With the technology that we have now, transection means there’s no pathway there.
D – This doesn’t make sense.
B is the correct answer here because of the lack of communication from the motor cortex to the skeletal muscle.
Correct Answer: B
[30:23] Question 5
The student in charge of the experiment wishes to present his/her findings in support of the theory that motor imagery and action observation together facilitate a greater increase in motor excitability than either protocol alone. Which of the following would be the best reason to withhold this presentation?
- The procedure used did not include MEP recordings prior to each task.
- MEP amplitudes in an individual are typically highly consistent.
- The motor tasks performed in the experiment were too simple.
- The six different conditions were run in random order.
Reworded Question: What would cause this student to not want to discuss this, which is what we found in Figure I because the combination together seems like a bigger amplitude here. So what would cause that to not be true or cause it to be a false finding?
By randomizing within an experiment, we’re removing confounding variables. Imagine a muscle continuously contracting or being imagined to contract or staying steady. These muscles eventually develop muscle memory. So if we mix things up, we’re able to evoke potentials and measure these MEPs specifically at what it was designed to, and not because of repetition.
For A, we don’t have any controls. In order for us to make a definitive conclusion, we need something to compare it against. We need a baseline. So A is the correct answer.
Correct Answer: A
[34:44] Final Thoughts and Tips
It’s confusing and frustrating to spend so much time trying to learn the passage and understand the passage and then be asked questions that had nothing to do with the passage. This is why you need these kinds of tips and tricks and shortcuts so you could do well on the MCAT.
The way you should approach the passage in the sciences is, why is the author mentioning this. If they provide any type of background information, that’s just background information. Don’t spend too much time highlighting that.
Instead, focus on the experiment and be able to identify three major things.
- The purpose of the experiment and/or hypothesis
- The dependent and independent variables – What are the researchers changing or measuring?
- Results, if any.
If in every experiment, you’re able to identify those three pieces on your first pass, you should be doing good.
And again, we’re not going to spend too much time breaking down the experiments in the passage. Just get a brief idea of what the experiment did, what’s the purpose of these particular figures. Then jump into the questions and if the question is required, you can come back and hone in on that particular area.
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