Introduction: Screening models for skeletal muscle relaxants are essential tools for B. Pharm students to understand pharmacodynamics, pharmacokinetics, and safety pharmacology. These models include in vitro organ bath muscle strip assays, ex vivo phrenic nerve-hemidiaphragm preparations, cell-based calcium flux assays, and in vivo behavioral tests (rotarod, grip strength). Key concepts covered are neuromuscular junction physiology, depolarizing versus non-depolarizing mechanisms, EC50/IC50 determinations, receptor binding, assay validation, high-throughput screening, and toxicity markers. Familiarity with models for drugs such as dantrolene, baclofen, succinylcholine, and aminosteroid blockers prepares students for research and therapeutics. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. What is the primary purpose of screening models for skeletal muscle relaxants?
- To determine color and odor of drug formulations
- To identify potency, selectivity, mechanism of action, and safety of candidate compounds
- To replace clinical trials entirely
- To study only renal elimination
Correct Answer: To identify potency, selectivity, mechanism of action, and safety of candidate compounds
Q2. Which experimental model uses an isolated muscle strip mounted in an organ bath to measure contractile responses?
- Whole-animal behavioral assay
- Organ bath muscle strip assay (in vitro)
- Xenopus oocyte expression system
- Human PET imaging
Correct Answer: Organ bath muscle strip assay (in vitro)
Q3. Which ex vivo preparation preserves nerve stimulation and records muscle contractions to assess neuromuscular blockers?
- Isolated hepatocyte culture
- Phrenic nerve-hemidiaphragm preparation (isolated rodent diaphragm with phrenic nerve)
- Intact whole-brain slice
- Isolated cardiac papillary muscle
Correct Answer: Phrenic nerve-hemidiaphragm preparation (isolated rodent diaphragm with phrenic nerve)
Q4. Which simple electrophysiological endpoint is commonly used to quantify neuromuscular transmission in screening models?
- Single twitch height (twitch tension amplitude)
- Electroencephalogram frequency
- Renal clearance rate
- Skin conductance
Correct Answer: Single twitch height (twitch tension amplitude)
Q5. How do depolarizing and non-depolarizing neuromuscular blockers differ mechanistically?
- Depolarizing agents inhibit ryanodine receptors; non-depolarizing increase calcium release
- Depolarizing agents cause sustained depolarization at nAChR (e.g., succinylcholine); non-depolarizing agents competitively block nAChR
- Both act identically at GABAA receptors
- Non-depolarizing agents permanently activate sodium channels
Correct Answer: Depolarizing agents cause sustained depolarization at nAChR (e.g., succinylcholine); non-depolarizing agents competitively block nAChR
Q6. Which in vivo behavioral model is frequently used to evaluate centrally acting muscle relaxants for motor coordination effects?
- Rotarod test (motor coordination and endurance)
- Tail flick thermal nociception test
- Forced swim test for depression
- Two-bottle preference test
Correct Answer: Rotarod test (motor coordination and endurance)
Q7. Which agent is commonly used to reverse non-depolarizing neuromuscular blockade by inhibiting acetylcholinesterase?
- Sugammadex (encapsulates aminosteroid blockers)
- Neostigmine (acetylcholinesterase inhibitor)
- Procaine (local anesthetic)
- Atropine alone
Correct Answer: Neostigmine (acetylcholinesterase inhibitor)
Q8. Which biochemical assay is widely used to measure acetylcholinesterase inhibition during screening?
- ELISA for cytokines
- Ellman’s colorimetric assay
- Gram staining
- Western blot for actin
Correct Answer: Ellman’s colorimetric assay
Q9. What does EC50 represent in pharmacological screening?
- Concentration required to produce 100% of maximal effect
- Concentration that produces 50% of maximal effect
- Time to half-life elimination
- Maximum efficacy of an antagonist
Correct Answer: Concentration that produces 50% of maximal effect
Q10. Which drug acts as a direct-acting skeletal muscle relaxant by inhibiting sarcoplasmic reticulum Ca2+ release?
- Baclofen
- Dantrolene
- Neostigmine
- Rocuronium
Correct Answer: Dantrolene
Q11. Which heterologous expression system is commonly used to study ion channel and receptor function for screening?
- HEK293 or CHO cell lines and Xenopus oocytes for functional expression
- Whole human liver slices only
- Intact plant cells
- Saline solution without cells
Correct Answer: HEK293 or CHO cell lines and Xenopus oocytes for functional expression
Q12. Tetanic fade during a sustained high-frequency stimulation is a characteristic sign of which type of blockade?
- Depolarizing blockade only
- Non-depolarizing neuromuscular blockade
- Enhanced voluntary contraction
- Complete recovery of neuromuscular function
Correct Answer: Non-depolarizing neuromuscular blockade
Q13. Which parameter derived from Schild analysis quantifies competitive antagonist potency?
- IC100
- pA2
- LD50
- Bioavailability
Correct Answer: pA2
Q14. For high-throughput screening of candidate muscle relaxants, which assay format is most suitable?
- Large animal survival studies
- Cell-based calcium flux assays with fluorescent indicators
- Manual organ bath recordings for each compound
- In vivo PET scans for each compound
Correct Answer: Cell-based calcium flux assays with fluorescent indicators
Q15. Which safety pharmacology parameter is critical to monitor when developing skeletal muscle relaxants?
- Liver enzyme only
- Respiratory function (e.g., tidal volume, respiratory rate)
- Hair color changes
- Urine specific gravity only
Correct Answer: Respiratory function (e.g., tidal volume, respiratory rate)
Q16. What is an advantage of ex vivo phrenic nerve-hemidiaphragm preparations over isolated single-muscle myotubes?
- Lower reproducibility
- Preserves intact neuromuscular junction and nerve stimulation for physiological responses
- Requires no ethical considerations
- Can directly measure brain activity
Correct Answer: Preserves intact neuromuscular junction and nerve stimulation for physiological responses
Q17. Which description best fits non-depolarizing neuromuscular blockers?
- Irreversible activation of acetylcholine release
- Competitive antagonists at nicotinic acetylcholine receptors (nAChR) at the motor endplate
- Agents that block voltage-gated calcium channels in the CNS only
- Drugs that directly destroy muscle fibers
Correct Answer: Competitive antagonists at nicotinic acetylcholine receptors (nAChR) at the motor endplate
Q18. Which centrally acting drug is a GABAB receptor agonist used as a muscle relaxant?
- Baclofen
- Suxamethonium
- Rocuronium
- Doxazosin
Correct Answer: Baclofen
Q19. Which agent is a depolarizing neuromuscular blocker commonly used for rapid sequence intubation?
- Rocuronium
- Succinylcholine (suxamethonium)
- Neostigmine
- Dantrolene
Correct Answer: Succinylcholine (suxamethonium)
Q20. What tetanic stimulation frequency is often used to evaluate fade in neuromuscular preparations?
- 0.5 Hz
- 50 Hz
- 0.05 Hz
- 0.001 Hz
Correct Answer: 50 Hz
Q21. In myography-based screening of skeletal muscle relaxants, which endpoint is most directly measured?
- Twitch tension (force) measurement
- Serum creatinine
- Brain glucose uptake
- Urine output
Correct Answer: Twitch tension (force) measurement
Q22. Which reversal agent specifically encapsulates aminosteroid neuromuscular blockers like rocuronium?
- Sugammadex
- Atropine
- Physostigmine
- Dantrolene
Correct Answer: Sugammadex
Q23. Which pharmacokinetic parameter indicates the time to reach maximal plasma concentration and is useful in correlating PK/PD for relaxants?
- Tmax
- IC50
- pA2
- Volume of distribution only
Correct Answer: Tmax
Q24. Which experimental artifact can reduce twitch responses in organ bath studies and mimic drug-induced blockade?
- High extracellular calcium concentration
- Hypothermia or low temperature leading to decreased twitch height
- Excessive oxygenation
- Use of physiological pH and temperature
Correct Answer: Hypothermia or low temperature leading to decreased twitch height
Q25. A rightward shift in a concentration–response curve without a change in maximal response typically indicates what?
- Increased efficacy
- Decreased potency (e.g., competitive antagonism)
- Noncompetitive irreversible antagonism
- Enhanced intrinsic activity
Correct Answer: Decreased potency (e.g., competitive antagonism)
Q26. Which cell-based screening endpoint would indicate direct inhibition of sarcoplasmic reticulum Ca2+ release?
- Increase in mitochondrial membrane potential only
- Decrease in intracellular Ca2+ transient amplitude in myotubes (calcium imaging)
- Elevated ATP release from neurons
- Enhanced cAMP production in hepatocytes
Correct Answer: Decrease in intracellular Ca2+ transient amplitude in myotubes (calcium imaging)
Q27. Which alternatives align with the 3Rs (replacement, reduction, refinement) for screening muscle relaxants?
- Increasing use of whole-animal acute toxicity without refinement
- In vitro cell models and in silico (computational) screening as alternatives
- Using larger numbers of animals per group to ensure variability
- Replacing all assays with uncontrolled human exposure
Correct Answer: In vitro cell models and in silico (computational) screening as alternatives
Q28. Which analytical approach discriminates competitive from noncompetitive antagonism using shifts in agonist dose–response curves?
- Mass spectrometry quantification
- Schild plot analysis and shifts of agonist concentration–response curves
- Histological staining
- Simple observation without concentration–response data
Correct Answer: Schild plot analysis and shifts of agonist concentration–response curves
Q29. Which experimental conditions must be controlled in organ bath studies to ensure reproducible skeletal muscle responses?
- Temperature, pH, and oxygenation of the organ bath
- Only the investigator’s mood
- Ambient light color exclusively
- Type of plastic used for electrodes only
Correct Answer: Temperature, pH, and oxygenation of the organ bath
Q30. In toxicity screening for muscle relaxants, which serum biomarker indicates potential muscle damage?
- Serum creatine kinase (CK) elevation
- Serum bilirubin decrease
- Platelet count increase only
- Reduced fasting glucose only
Correct Answer: Serum creatine kinase (CK) elevation
I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.
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