A bronchial smooth muscle contains:

Correct Answer: D

Rationale: The correct answer is D: Beta 2 receptor. Bronchial smooth muscle relaxation is mainly mediated by Beta 2 adrenergic receptors when activated by agonists like salbutamol. These receptors stimulate adenylate cyclase leading to increased cAMP levels, which in turn promotes muscle relaxation. Alpha 1 receptors (Choice A) and Alpha 2 receptors (Choice B) are associated with vasoconstriction and decreased sympathetic outflow, respectively, not bronchial smooth muscle relaxation. Beta 1 receptors (Choice C) are primarily found in the heart and play a role in cardiac function, not bronchial smooth muscle relaxation.

Correct Answer: C

Rationale: The correct answer is C: Phenobarbital. Phenobarbital is a long-acting barbiturate that can lead to cumulative and residual effects due to its long half-life and potential for drug accumulation in the body over time. This can result in prolonged sedative effects and increased risk of side effects. Zolpidem (A), Temazepam (B), and Triazolam (D) are shorter-acting hypnotic drugs with less potential for cumulative and residual effects compared to Phenobarbital.

Correct Answer: C

Rationale: Carbamazepine is an antiepileptic drug that acts by blocking voltage-gated sodium channels, similar to Phenytoin. Both drugs inhibit sustained high-frequency repetitive firing of action potentials in neurons. Benzodiazepines (A) enhance inhibitory neurotransmission via GABA receptors, Valproate (B) inhibits GABA transaminase and increases GABA levels, and Ethosuximide (D) blocks T-type calcium channels, making them incorrect choices.

Correct Answer: B

Rationale: The correct answer is B: Clozapine. Clozapine is an atypical antipsychotic that can help counteract the behavioral complications of levodopa therapy, such as hallucinations and psychosis, without compromising the efficacy of levodopa. Tolkapone (A) is a COMT inhibitor used to prolong the effect of levodopa, not counteract behavioral complications. Carbidopa (C) is a dopa decarboxylase inhibitor that enhances levodopa's effectiveness but does not address behavioral complications. Pergolide (D) is a dopamine agonist used to treat Parkinson's disease symptoms, but it does not specifically target levodopa's behavioral complications.

Correct Answer: C

Rationale: Buprenorphine is a partial mu receptor agonist, meaning it activates the mu receptors but to a lesser extent compared to full agonists like morphine. Buprenorphine's unique pharmacological profile includes partial agonist activity at mu receptors, along with antagonist activity at kappa receptors. This combination results in a ceiling effect on respiratory depression and a lower risk of abuse potential compared to full agonists. Methadone is a full mu receptor agonist, morphine is a full mu receptor agonist, and sufentanyl is a potent full mu receptor agonist but is not a partial agonist like buprenorphine.