A patient is given an experimental drug that prolongs the opening of calcium channels in cardiac muscle cells. Which of the following is the most likely effect on heart function?
Topic: action potential duration In this diagram we see here how the changing membrane permeabilities determine the shape of the action potential as well as the duration of the contraction. Notice that the action potential of a cardiac contractile cell represented here in red lasts for almost as long as the contraction of the cardiac muscle itself, represented in blue here. Now this is good for the heart. I want you to remember that tetanus was what we observed in the skeletal muscle. What we don't want our heart to do is to tetanize. In other words, we don’t want the heart to contract just once with great force and stay that way because it will no longer perform the actions of a pump. So there's a mechanism in place where if you were to fire another action potential in close succession, tetanus won't be generated because by the time you are able to fire another action potential, the cardiac muscle will be in the relaxed state. So summation and tetanus cannot occur in the heart, which is a good thing. Now let's compare the cardiac muscle cell to the skeletal and the smooth muscles. When the cardiac muscle cell membrane is depolarized to threshold. First, sodium channels open within a few milliseconds, just like the skeletal muscles. However, calcium channels also open, but more slowly and stays open for long. This allows calcium to enter from the ECF. To summarize, the action potential is initiated by sudden increase in the permeability of sodium followed by a slower and longer lasting increase in the permeability to calcium. Now, this longer lasting increase in the permeability to calcium like that which happens in the smooth muscle, is what explains the prolonged contraction time in the heart relative to the skeletal muscle. So what happens if we give more than one action potential? In a given period of time, now we're talking about the frequency of action potential in the muscle fiber. We can give multiple action potentials because the muscle action potentials lasts only two milliseconds, whereas the tension can last 400 milliseconds. So if you now increase the frequency of action potential in the muscle fiber, this will increase the tension via the concept that we are familiar with, the summation. As the skeletal muscle as action potential frequency increases. successive twitches begin to fuse with each other, and the contractile force rises. As you stimulate the muscle more frequently on the X axis, the tension generated on the Y axis goes up. Now, this is because the successive twitches add on top of each other. There's no time to relax, and the contractile force rises. Muscle twitch or twitch contraction. A muscle twitch is a single contraction relaxation cycle. Now I think it's important to point out that we are no longer talking about action potentials, but tension or force that is generated by the muscle. And the rise time and the duration of Twitch Force really varies with the different muscle fiber type. For example, fast glycolytic fibers have a rise time of about 50 milliseconds and duration of about 120 milliseconds, and for all intents and purposes, an isolated single twitch is pretty much useless. A single twitch will not generate enough tension or force to cause your muscles to do anything to generate force, you need to have many twitches working together. This is the time required for calcium to be released and binding to troponin before the muscle can generate tension, force. The next phase, the period of contraction, occurs as the intracellular calcium levels are getting high and crossbridge cycling is occurring now. This allows the muscle cells to produce tension, to produce force.
Here's a multiple choice question targeting application of knowledge about action potential duration: A patient is given an experimental drug that prolongs the opening of calcium channels in cardiac muscle cells. Which of the following is the most likely effect on heart function? A) The heart will beat more forcefully but maintain its normal rhythm B) The heart will be unable to relax properly between contractions C) The heart rate will increase significantly D) The heart will require less oxygen to maintain normal function Correct Answer: B Explanation: This question requires students to apply their understanding of how calcium channel duration affects cardiac muscle function. Since cardiac action potential duration is closely tied to contraction duration, and normal heart function requires complete relaxation between beats, prolonging calcium channel opening would prevent proper relaxation. The question tests understanding of the relationship between action potential duration, calcium channel activity, and the cardiac cycle while avoiding tetanus.
A researcher is studying a patient with an unusual cardiac condition where their heart muscle cells have a significantly shorter action potential duration than normal. Which of the following is the most likely consequence of this condition?
Topic: action potential duration In this diagram we see here how the changing membrane permeabilities determine the shape of the action potential as well as the duration of the contraction. Notice that the action potential of a cardiac contractile cell represented here in red lasts for almost as long as the contraction of the cardiac muscle itself, represented in blue here. Now this is good for the heart. I want you to remember that tetanus was what we observed in the skeletal muscle. What we don't want our heart to do is to tetanize. In other words, we don’t want the heart to contract just once with great force and stay that way because it will no longer perform the actions of a pump. So there's a mechanism in place where if you were to fire another action potential in close succession, tetanus won't be generated because by the time you are able to fire another action potential, the cardiac muscle will be in the relaxed state. So summation and tetanus cannot occur in the heart, which is a good thing. Now let's compare the cardiac muscle cell to the skeletal and the smooth muscles. When the cardiac muscle cell membrane is depolarized to threshold. First, sodium channels open within a few milliseconds, just like the skeletal muscles. However, calcium channels also open, but more slowly and stays open for long. This allows calcium to enter from the ECF. To summarize, the action potential is initiated by sudden increase in the permeability of sodium followed by a slower and longer lasting increase in the permeability to calcium. Now, this longer lasting increase in the permeability to calcium like that which happens in the smooth muscle, is what explains the prolonged contraction time in the heart relative to the skeletal muscle. So what happens if we give more than one action potential? In a given period of time, now we're talking about the frequency of action potential in the muscle fiber. We can give multiple action potentials because the muscle action potentials lasts only two milliseconds, whereas the tension can last 400 milliseconds. So if you now increase the frequency of action potential in the muscle fiber, this will increase the tension via the concept that we are familiar with, the summation. As the skeletal muscle as action potential frequency increases. successive twitches begin to fuse with each other, and the contractile force rises. As you stimulate the muscle more frequently on the X axis, the tension generated on the Y axis goes up. Now, this is because the successive twitches add on top of each other. There's no time to relax, and the contractile force rises. Muscle twitch or twitch contraction. A muscle twitch is a single contraction relaxation cycle. Now I think it's important to point out that we are no longer talking about action potentials, but tension or force that is generated by the muscle. And the rise time and the duration of Twitch Force really varies with the different muscle fiber type. For example, fast glycolytic fibers have a rise time of about 50 milliseconds and duration of about 120 milliseconds, and for all intents and purposes, an isolated single twitch is pretty much useless. A single twitch will not generate enough tension or force to cause your muscles to do anything to generate force, you need to have many twitches working together. This is the time required for calcium to be released and binding to troponin before the muscle can generate tension, force. The next phase, the period of contraction, occurs as the intracellular calcium levels are getting high and crossbridge cycling is occurring now. This allows the muscle cells to produce tension, to produce force.
Let me create a multiple choice question following those steps: 1. Key concept to test: Understanding how action potential duration in cardiac muscle prevents tetanus and relates to muscle contraction timing 2. Required knowledge and approach: - Understanding of action potential duration in cardiac vs skeletal muscle - Relationship between action potential timing and muscle contraction - Why tetanus can occur in skeletal but not cardiac muscle - Common misconception: Students might confuse cause and effect relationships 3. Question stem: A researcher is studying a patient with an unusual cardiac condition where their heart muscle cells have a significantly shorter action potential duration than normal. Which of the following is the most likely consequence of this condition? 4. Response options: A) The heart would be at risk of tetanus due to the possibility of rapid successive contractions B) The heart would contract with greater force due to faster repolarization C) The heart would be unable to contract at all D) The heart would maintain normal function since action potential duration doesn't affect contraction timing 5. Distractor explanations: B) Students might think faster repolarization leads to stronger contractions C) Students might think shorter action potentials prevent any contraction D) Students might not recognize the importance of action potential duration 6. Correct answer: A Explanation: This is correct because the long action potential duration in cardiac muscle normally prevents tetanus by ensuring the muscle is still refractory when the next potential arrives. With shortened duration, rapid successive action potentials could occur, potentially leading to tetanic contraction. This tests application of knowledge because students must predict the physiological consequence of an altered parameter rather than just recall facts.
EVALUATION: 1. Core Item Elements: A. Content Validity (Score: 4) - Accurately represents cardiac physiology - Realistic clinical scenario - Appropriate use of terminology - Scientifically sound premise B. Scope Appropriateness (Score: 4) - Appropriate for medical/physiology students - Tests fundamental cardiac physiology concept - Clear alignment with learning objectives - Reasonable difficulty level C. Item Anatomy (Score: 3) - Clear stem with good context - Single clear question - Appropriate number of options - Distractors are plausible - Minor improvement possible in option parallelism 2. Cognitive Level Assessment: - Successfully targets "Apply" level - Requires understanding and application of physiological principles - Appropriate complexity for application level - Students must predict consequences of altered parameters 3. Item Writing Flaws Check: Content: No significant flaws - Focused on important concept - No unnecessary complexity - Based on factual relationships Style/Format: Minor issues - Options could be more uniform in length - Grammar and punctuation correct - Clear wording Stem: - Well-constructed - Positively phrased - Contains essential information - No grammatical cues Options: - All plausible - No obvious logical cues - Independent options - Could improve parallel construction 4. Feedback Quality (Score: 4) - Comprehensive explanation - Addresses key concept - Clear scientific reasoning - Evidence-based explanation SCORES: Content Validity: 4/4 Scope Appropriateness: 4/4 Item Anatomy: 3/4 Feedback Quality: 4/4 Overall Score: 15/16 DECISION: ACCEPT Strengths: - Tests important physiological concept - Clear clinical relevance - Well-constructed stem - Strong explanatory feedback Minor Suggestions: - Consider making option lengths more uniform - Ensure parallel construction in all options - Could add specific timing details to make scenario more concrete The question effectively tests application of knowledge about cardiac physiology and meets all essential quality criteria with only minor potential improvements.
A physical therapist is developing an exercise program for an elderly patient who is having difficulty with precise movements when writing and buttoning clothes. Based on the age-related changes in motor units, which type of muscle fiber would be MOST affected in this patient?
As the name would imply, the slow twitch oxidative fibers are very slowly contracting but has many mitochondria. Therefore they rely upon oxidative metabolism, hence the name and these are the non fatiguing type of muscle. But they generate small maximal force. As an example, muscles in low level force production such as walking and maintaining posture, Soleus muscle in the lower leg is a good example of a slow twitch. Oxidative fiber. Whereas a fast twitch, glycolytic fibers, they have a very fast twitch time, and they produce tremendous amounts of tension. They have few mitochondria so they rely heavily on the glycolytic metabolism and as a result they fatigue very rapidly in about one minute or so, and this is due to lactic acid accumulation. As an example, muscles being used in sprinting and jumping or for weightlifting, they used fast twitch glycolytic fibers. And Lastly, in between what's called the fast twitch oxidative glycolytic fibers. You can think of them as somewhere in between the slow and the fast twitch muscles. I probably have a lot of these because I'm not good at sprinting or marathoning. The question is which motor neurons innervate the different types of muscles? Well, small diameter motor neurons innervate slowtwitch oxidative fibers and large diameter motor neurons innervate fast twitch, glycolytic fibers and it makes sense that a small diameter motor neurons are more excited or more easily excited by summation of EP SPS. Then the large diameter motor neurons therefore slow oxidative motor units are recruited by relatively low levels of excitatory synaptic. Now there are three broad categories of muscle fibers, which means that there are three categories of motor units, and the distinction is based on their histochemical characteristics. So we have what's called a slow twitch, fast twitch and something in between. And it turns out that the muscle fibers of a motor unit are of the same type. This means that particular motor unit contains muscle fibers of 1 type only. For example motor Unit 1 shown in red here may be a slow twitch and it will only contain the slow twitch fibers. So with age the motor units become larger. This means that the fine motor movements will become much more difficult to perform because of the loss of small motor units. So your life expectancy as a microsurgeon is rather short after having put in 125 years of medical school studying. Now let's have a brief look at the different muscle types. First, slowtwitch oxidative fibers.
Here's a multiple choice question targeting application of knowledge about muscle fiber types: A physical therapist is developing an exercise program for an elderly patient who is having difficulty with precise movements when writing and buttoning clothes. Based on the age-related changes in motor units, which type of muscle fiber would be MOST affected in this patient? A) Fast twitch glycolytic fibers B) Fast twitch oxidative glycolytic fibers C) Slow twitch oxidative fibers innervated by small motor neurons D) Fast twitch fibers innervated by large motor neurons Correct Answer: C This question requires students to: - Apply their understanding of how motor units change with age - Connect the relationship between small motor units and fine motor control - Recognize that loss of small motor units (which innervate slow twitch oxidative fibers) would impact precise movements - Apply this knowledge to a real clinical scenario The distractors are plausible but incorrect because: A) These fibers are mainly involved in powerful movements, not fine motor control B) These intermediate fibers are not primarily responsible for precise movements D) Large motor units are not primarily responsible for fine motor control
EVALUATION: 1. Core Item Elements: A. Content Validity (4/4) - Accurately reflects age-related changes in motor units - Clinically realistic scenario - Appropriate use of terminology (motor units, fiber types) - Realistic patient presentation B. Scope Appropriateness (4/4) - Appropriate for health science students - Difficulty level matches application requirements - Tests fundamental concepts of muscle physiology - Clear alignment with clinical application objectives C. Item Anatomy (4/4) - Well-structured stem with clinical context - Clear single question - Appropriate number of options (4) - One clearly correct answer - Distractors are scientifically valid alternatives 2. Cognitive Level: - Successfully targets Application level - Question structure requires knowledge transfer to clinical scenario - Complexity appropriate for application-level thinking 3. Item Writing Flaws: Content: No flaws detected - Focused complexity - Clinically significant content - No unnecessary information - Fact-based Style/Format: No flaws detected - Clear grammar and punctuation - Unambiguous wording - Options could be formatted vertically - No bias detected Stem: No flaws detected - Complete - Positive phrasing - Essential information only - No grammatical cues Options: No flaws detected - All distractors plausible - No logical cues - Clear distinctions between options - Appropriate terminology 4. Feedback Quality: (Not provided in original question) SCORES: Content Validity: 4/4 Scope Appropriateness: 4/4 Item Anatomy: 4/4 Cognitive Level Match: 4/4 Technical Quality: 4/4 DECISION: ACCEPT This is an exemplary multiple choice question that successfully: - Tests application of knowledge - Uses a realistic clinical scenario - Has clear, scientifically accurate options - Maintains appropriate difficulty level - Is free from technical flaws The only minor suggestion would be to format options vertically for better readability, but this doesn't affect the question's quality.
A researcher develops a drug that partially blocks RyR channels in skeletal muscle cells. Which of the following would be the most likely immediate effect of this drug?
RyR is a calcium channel that's present on the sarcoplasmic reticulum. DHP opens the RyR and ends up releasing calcium into the cytoplasm. So ultimately the arrival of the action potential will cause the sarcoplasmic reticulum to release calcium into the cytoplasm. Now with calcium present, this calcium binds to troponin and allows for the myosin head to bind the actin and crossbridge cycling and power stroke can finally occur and contraction can begin. In this case, acetylcholine then diffuses across the cleft and binds to nicotinic receptors on the motor end plate. Now binding of this acetylcholine triggers depolarization on the motor end plate and an eventual generation of an action potential in the muscle cell. And this action potential travels down deep into the muscle via the T tubules, and reaches the sarcoplasmic reticulum. Now at the T tubules we find what's called the DHP receptor. Now this is a type of a calcium channel dihydropyridine and with the arrival of an action potential there is a confirmational change in this DHP receptor and this DHP receptor is physically linked to what's called the Ryanodine receptor, RyR. In this diagram you can see the black dots. Now it is covered, but these black dots are the binding sites for myosin. However, you will see that the black dots the binding sites for myosin is covered up by this pink strand pinkish reddish strand called the tropomyosin, so it cannot be interacting with the myosin head at this stage. This means that the muscle is relaxed. However, I want you to notice another structure called the Troponin complex. Digitalis is a cardiac glycoside used to treat certain heart conditions, such as congestive heart failure and it works directly on the heart muscle to strengthen contraction by increasing calcium levels. Digitalis increases the force of cardiac contraction by essentially inhibiting sodium potassium ATPase, sodium potassium pump. By inhibiting sodium potassium ATPase, you will end up with an increase in the intracellular sodium levels and this increase in sodium will affect the sodium calcium membrane exchange to result in decreased sodium influx. And at the same time, results in decreased calcium efflux and this leads to increased intracellular calcium levels and therefore increased strength of contraction. This is analogous to putting in your or in the water and pulling, propelling you then the myosin head and actin detach. This is analogous to your or breaking contact with the water. And finally, the myosin head returns to its initial position. This is analogous to your ore being moved to a new position so that a new cycle can start. Now, with increased systolic calcium levels, which exposes the actin's binding sites for myosin, now they are able to bind the myosin head and the actin filament binds strongly due to the presence of calcium.
Let me create a question following those steps: 1. Key concept to test: Understanding how calcium regulation affects muscle contraction and applying this knowledge to predict effects of calcium channel modifications 2. Required knowledge and approach: - Understanding of calcium's role in muscle contraction - Knowledge of RyR and DHP receptor interaction - Understanding of the relationship between calcium and troponin/tropomyosin - Ability to predict physiological outcomes from channel modifications Common misconceptions: - Confusing the sequence of events in muscle contraction - Misunderstanding the role of calcium channels - Mixing up cause and effect relationships 3. Question stem: A researcher develops a drug that partially blocks RyR channels in skeletal muscle cells. Which of the following would be the most likely immediate effect of this drug? 4. Response options: A) Decreased strength of muscle contractions while maintaining normal action potential conduction B) Complete paralysis of the affected muscles C) Increased frequency of muscle contractions D) Enhanced calcium release from the sarcoplasmic reticulum 5. Explanation of distractors: A) CORRECT - Partial RyR blocking would reduce calcium release, leading to fewer exposed binding sites and weaker contractions, while not affecting nerve signaling B) Tempting but too extreme - partial blocking wouldn't cause complete paralysis C) Tempting because students might think the body would compensate by increasing contraction frequency, but this isn't an immediate effect D) Directly contradicts the effect of blocking RyR channels, but might be chosen if students confuse blocking with activation 6. Correct answer: A This question tests application by requiring students to predict the physiological outcome of a novel drug intervention based on their understanding of calcium's role in muscle contraction.
A researcher is studying two different muscle types and observes that Muscle A can undergo tetanus while Muscle B cannot. Given that Muscle B has an action potential duration that nearly matches its contraction duration, what would happen if you attempted to stimulate Muscle B with rapid, repeated action potentials?
Topic: action potential duration In this diagram we see here how the changing membrane permeabilities determine the shape of the action potential as well as the duration of the contraction. Notice that the action potential of a cardiac contractile cell represented here in red lasts for almost as long as the contraction of the cardiac muscle itself, represented in blue here. Now this is good for the heart. I want you to remember that tetanus was what we observed in the skeletal muscle. What we don't want our heart to do is to tetanize. In other words, we don’t want the heart to contract just once with great force and stay that way because it will no longer perform the actions of a pump. So there's a mechanism in place where if you were to fire another action potential in close succession, tetanus won't be generated because by the time you are able to fire another action potential, the cardiac muscle will be in the relaxed state. So summation and tetanus cannot occur in the heart, which is a good thing. Now let's compare the cardiac muscle cell to the skeletal and the smooth muscles. When the cardiac muscle cell membrane is depolarized to threshold. First, sodium channels open within a few milliseconds, just like the skeletal muscles. However, calcium channels also open, but more slowly and stays open for long. This allows calcium to enter from the ECF. To summarize, the action potential is initiated by sudden increase in the permeability of sodium followed by a slower and longer lasting increase in the permeability to calcium. Now, this longer lasting increase in the permeability to calcium like that which happens in the smooth muscle, is what explains the prolonged contraction time in the heart relative to the skeletal muscle. So what happens if we give more than one action potential? In a given period of time, now we're talking about the frequency of action potential in the muscle fiber. We can give multiple action potentials because the muscle action potentials lasts only two milliseconds, whereas the tension can last 400 milliseconds. So if you now increase the frequency of action potential in the muscle fiber, this will increase the tension via the concept that we are familiar with, the summation. As the skeletal muscle as action potential frequency increases. successive twitches begin to fuse with each other, and the contractile force rises. As you stimulate the muscle more frequently on the X axis, the tension generated on the Y axis goes up. Now, this is because the successive twitches add on top of each other. There's no time to relax, and the contractile force rises. Muscle twitch or twitch contraction. A muscle twitch is a single contraction relaxation cycle. Now I think it's important to point out that we are no longer talking about action potentials, but tension or force that is generated by the muscle. And the rise time and the duration of Twitch Force really varies with the different muscle fiber type. For example, fast glycolytic fibers have a rise time of about 50 milliseconds and duration of about 120 milliseconds, and for all intents and purposes, an isolated single twitch is pretty much useless. A single twitch will not generate enough tension or force to cause your muscles to do anything to generate force, you need to have many twitches working together. This is the time required for calcium to be released and binding to troponin before the muscle can generate tension, force. The next phase, the period of contraction, occurs as the intracellular calcium levels are getting high and crossbridge cycling is occurring now. This allows the muscle cells to produce tension, to produce force.
Let me create a multiple choice question following those steps: 1. Key concept to test: Understanding how the prolonged cardiac action potential duration prevents tetanus in the heart 2. Required knowledge and approach: - Students need to understand the relationship between action potential duration and muscle contraction - They need to grasp why tetanus can occur in skeletal muscle but not cardiac muscle - Common misconception: Students might confuse the mechanisms of skeletal and cardiac muscle contraction 3. Question stem: A researcher is studying two different muscle types and observes that Muscle A can undergo tetanus while Muscle B cannot. Given that Muscle B has an action potential duration that nearly matches its contraction duration, what would happen if you attempted to stimulate Muscle B with rapid, repeated action potentials? A) The muscle would enter a sustained tetanic contraction B) The muscle would not respond to the subsequent stimuli during the ongoing action potential C) The muscle would immediately relax between each stimulation D) The muscle would contract with increasing force with each stimulus 4. Rationale for distractors: A) Incorrect but tempting because tetanus is a common muscle response to rapid stimulation in skeletal muscle C) Incorrect because it suggests no relationship between action potential and contraction duration D) Incorrect but appealing because it describes what happens in skeletal muscle summation 5. Correct answer: B The correct answer is B because during the prolonged cardiac action potential, the membrane cannot be re-excited (refractory period), preventing additional contractions until the current action potential and contraction are complete. This is precisely what prevents tetanus in cardiac muscle. This question tests application because students must take their understanding of action potential duration and apply it to predict the physiological response in a new scenario.