What kind of substances can’t permeate membranes by passive diffusion?

Correct Answer: D

Rationale: The correct answer is D because hydrophilic substances cannot permeate membranes by passive diffusion due to their polarity and inability to dissolve in the hydrophobic lipid bilayer. This prevents them from crossing the membrane without the assistance of transport proteins. A, B, and C are incorrect because lipid-soluble, non-ionized substances, and hydrophobic substances can easily pass through membranes by passive diffusion as they can dissolve in the lipid bilayer.

Correct Answer: A

Rationale: The correct answer is A because Type A delta and C fibers are known to participate in high-frequency pain transmission. Type A delta fibers transmit sharp, localized pain signals, while Type C fibers transmit dull, aching pain signals. Choice B, Type A alpha fibers, are responsible for transmitting proprioceptive information. Choice C, Type B fibers, are not involved in pain transmission. Choice D, Type A beta fibers, are responsible for touch and pressure sensations, not high-frequency pain transmission. Therefore, based on the characteristics of each fiber type, Type A delta and C fibers are the correct choice for high-frequency pain transmission.

Correct Answer: A

Rationale: The correct answer is A: Physostigmine, which penetrates the blood-brain barrier. Physostigmine is a reversible cholinesterase inhibitor that can cross the blood-brain barrier, allowing it to exert its effects on cholinesterase enzymes in the central nervous system. This property makes it useful in conditions where increasing cholinergic activity in the brain is desired, such as in the treatment of Alzheimer's disease. Choice B, Edrophonium, is a reversible cholinesterase inhibitor but does not effectively penetrate the blood-brain barrier. Choice D, Neostigmine, is also a reversible cholinesterase inhibitor but is primarily used for its effects on peripheral cholinesterase enzymes and does not cross the blood-brain barrier effectively.

Correct Answer: D

Rationale: The correct answer is D: Atracurium. Atracurium is metabolized to laudanosine, which readily crosses the blood-brain barrier and may cause seizures. Pancuronium (A) does not readily cross the blood-brain barrier. Succinylcholine (B) does not have a breakdown product that crosses the blood-brain barrier. Tubocurarine (C) does not produce a breakdown product that causes seizures.

Correct Answer: B

Rationale: Step 1: Norepinephrine is a neurotransmitter that acts on both alpha and beta receptors. Step 2: Norepinephrine has more potent effects on alpha receptors compared to epinephrine. Step 3: Choice A is correct as norepinephrine has similar effects on beta1 receptors in the heart and similar potency at alpha receptors. Step 4: Choice C is incorrect as tissue necrosis is associated with dopamine, not norepinephrine. Step 5: Choice D is incorrect as norepinephrine increases both diastolic and systolic blood pressure. Step 6: Choice B is correct as norepinephrine does not decrease mean pressure below normal before returning to the control value, making it the exception among the effects listed.