The duration of action of methacholine is longer than that of acetylcholine because

Correct Answer: C

Rationale: In pharmacology, understanding the pharmacokinetics of drugs is crucial in determining their duration of action. In the case of methacholine and acetylcholine, the correct answer is C) Acetylcholine is metabolized more rapidly. Acetylcholine is broken down by the enzyme acetylcholinesterase in the synaptic cleft, leading to its rapid inactivation. This rapid metabolism limits the duration of action of acetylcholine. Option A) Acetylcholine is inactivated by active transport into Schwann cells is incorrect because Schwann cells are involved in the myelination of peripheral nerves, not in the inactivation of acetylcholine. Option B) Acetylcholine is inactivated by active transport into nerve cells is incorrect because acetylcholine is primarily metabolized by acetylcholinesterase in the synaptic cleft, not actively transported into nerve cells for inactivation. Option D) Acetylcholine is excreted more rapidly is incorrect because acetylcholine is primarily broken down within the synaptic cleft rather than being excreted from the body. Understanding the differences in the metabolism and inactivation of neurotransmitters like acetylcholine is vital in pharmacology, as it impacts the effectiveness and duration of action of drugs that target these pathways. Students should grasp these concepts to make informed decisions in drug selection and understand the rationale behind dosing regimens for CNS drugs.

Correct Answer: C

Rationale: The correct answer is C) Regulation of biorhythm. Melatonin is a hormone produced by the pineal gland in the brain that helps regulate the sleep-wake cycle and plays a crucial role in the body's internal clock or biorhythm. Melatonin levels typically rise in the evening, signaling to the body that it is time to sleep. Therefore, its function is primarily related to the regulation of biorhythms and sleep patterns. Option A) Darkening of skin color is incorrect because melatonin does not have a direct role in skin pigmentation. Skin pigmentation is primarily influenced by melanin, a pigment produced by melanocytes in the skin. Option B) Suppression of ovarian function is incorrect because melatonin is not directly involved in the regulation of ovarian function. Ovarian function is primarily regulated by hormones such as estrogen and progesterone produced by the ovaries. Understanding the function of melatonin is essential in pharmacology, especially when considering drugs that target the sleep-wake cycle or circadian rhythm disorders. By knowing that melatonin primarily regulates biorhythms, healthcare professionals can make informed decisions when prescribing medications that influence melatonin levels or activity. This knowledge is crucial for providing effective and safe patient care in conditions related to sleep disorders or disruptions in circadian rhythms.

Correct Answer: B

Rationale: In the context of pharmacology of CNS drugs, local anesthetics are specifically designed to prevent or relieve pain by interrupting nerve conduction. This is because local anesthetics work by blocking voltage-gated sodium channels on the nerve fibers, thereby inhibiting the generation and propagation of action potentials along the nerves. By preventing the transmission of signals along the nerves, local anesthetics effectively block the sensation of pain from reaching the brain. Option A, "Inhibit substance P," is incorrect because substance P is a neurotransmitter involved in transmitting pain signals in the spinal cord and brain, but local anesthetics primarily target nerve conduction rather than neurotransmitters. Option C, "Modify neuronal metabolism," is also incorrect as local anesthetics do not directly alter the metabolic processes within neurons. Their primary mechanism of action lies in blocking nerve conduction as explained earlier. In an educational context, understanding the mechanism of action of local anesthetics is crucial for healthcare professionals, particularly those involved in pain management, anesthesia, and pharmacology. By grasping how local anesthetics interrupt nerve conduction, healthcare providers can make informed decisions regarding the appropriate use, dosing, and potential side effects of these drugs when managing pain in clinical settings.

Correct Answer: C

Rationale: In pharmacology of CNS drugs, understanding the pharmacokinetic properties of different barbiturates is crucial for safe and effective prescribing. In this case, the correct answer is C) Methohexital, which has the shortest half-life among the listed barbiturates. Methohexital is an ultra-short-acting barbiturate primarily used for anesthesia induction due to its rapid onset and short duration of action. Its short half-life means it is quickly metabolized and eliminated from the body, making it suitable for procedures requiring brief sedation periods. Now, let's analyze why the other options are incorrect: - A) Secobarbital: Secobarbital has a longer half-life compared to Methohexital, making it unsuitable for procedures requiring rapid recovery. - B) Pentobarbital: Pentobarbital has a longer half-life as well, making it more suitable for longer sedation or anesthesia maintenance. - D) Amobarbital: Amobarbital also has a longer half-life compared to Methohexital, making it less ideal for short sedation periods. Educationally, understanding the pharmacokinetic differences among barbiturates is essential for healthcare professionals to make informed decisions when choosing the appropriate agent for sedation or anesthesia based on the desired duration of action and clinical context. This knowledge ensures patient safety and optimal outcomes in clinical practice.

Correct Answer: B

Rationale: Sertraline belongs to the class of compounds known as serotonin reuptake inhibitors (SRIs). This means it works by specifically targeting the reuptake of serotonin in the brain, leading to increased levels of serotonin available in the synaptic cleft. This mechanism of action allows sertraline to effectively treat conditions like depression, anxiety disorders, and other mood disorders by modulating serotonin levels. Option A, MAO inhibitors, work by inhibiting the activity of monoamine oxidase enzymes, leading to increased levels of neurotransmitters like serotonin, norepinephrine, and dopamine. Sertraline does not function in this way. Option C, norepinephrine reuptake inhibitors, target the reuptake of norepinephrine specifically, not serotonin like sertraline does. Option D, none of the above, is incorrect as sertraline does belong to the serotonin reuptake inhibitor class. In an educational context, understanding the classification of drugs like sertraline is crucial for healthcare professionals in determining the appropriate treatment for patients with various psychiatric disorders. Knowing the specific mechanisms of action of different classes of CNS drugs is essential for safe and effective prescribing practices. This knowledge also helps in understanding the potential side effects and interactions of these medications.