Atropine causes:

Correct Answer: A

Rationale: Atropine causes spasmolitic activity by blocking acetylcholine receptors, leading to relaxation of smooth muscles. This is beneficial in conditions like irritable bowel syndrome. Intestinal hypermotility, stimulation of gut contraction, and secretory activity are all effects opposite to what atropine causes due to its anticholinergic properties. Atropine's mechanism of action supports choice A as the correct answer.

Correct Answer: B

Rationale: The correct answer is B: Phentolamine. This drug is a nonselective alpha receptor antagonist, blocking both alpha-1 and alpha-2 receptors. It is used to treat hypertensive emergencies. Prazosin (A) is a selective alpha-1 receptor antagonist, used for hypertension and BPH. Metoprolol (C) is a beta blocker, mainly blocking beta-1 receptors for heart conditions. Reserpine (D) inhibits the uptake of norepinephrine into vesicles, reducing sympathetic activity.

Correct Answer: D

Rationale: The correct answer is D because all three options (A, B, and C) are used in the treatment of insomnia. Benzodiazepines, such as diazepam, help induce sleep. Imidazopyridines, like zolpidem, also aid in sleep. Barbiturates, such as phenobarbital, have sedative effects. Therefore, all of the above options are valid treatments for insomnia.

Correct Answer: C

Rationale: The correct answer is C: Clonazepam. Clonazepam is a benzodiazepine commonly used for myoclonic seizures due to its ability to enhance the inhibitory neurotransmitter GABA in the brain, reducing seizure activity. Primidone (A), Carbamazepine (B), and Phenytoin (D) are more commonly used for other types of seizures like focal or generalized tonic-clonic seizures, not specifically for myoclonic seizures.

Correct Answer: A

Rationale: The correct answer is A because levodopa, as a precursor of dopamine, can cross the blood-brain barrier and be converted to dopamine in the brain, while dopamine itself cannot cross the blood-brain barrier when administered peripherally. Choice B is incorrect because dopamine-induced psychotic reactions are not the main reason for choosing levodopa. Choice C is also incorrect as levodopa is metabolized in the periphery before reaching the brain. Therefore, the correct choice is A as it addresses the main reason for using levodopa over dopamine.