The central nervous system (CNS) cells, where the impulses for the sympathetic nervous system (SNS) originate, are located where?

A) Increased intraocular pressure: Sympathomimetic drugs stimulate the sympathetic nervous system and promote "fight or flight" responses, often resulting in vasoconstriction and other effects. Some sympathomimetics, especially those that affect alpha-adrenergic receptors, can lead to increased intraocular pressure, which is a concern in conditions like glaucoma.

B) Decreased blood pressure: Sympathomimetic drugs generally increase blood pressure by stimulating alpha and beta receptors that cause vasoconstriction and increased heart rate. In contrast, drugs that would decrease blood pressure are usually parasympathomimetics or other agents designed to block sympathetic responses.

C) Decreased heart rate: Sympathomimetic drugs typically increase heart rate by stimulating beta-1 adrenergic receptors in the heart. These drugs are used in situations requiring increased cardiac output or to counteract bradycardia. Decreased heart rate would typically occur with parasympathomimetic drugs or medications that block sympathetic activity (e.g., beta blockers).

D) Increased respiration: Sympathomimetic drugs can increase respiratory rate by promoting bronchodilation through beta-2 adrenergic receptor activation in the lungs. However, "increased respiration" as a general effect is not as specific or consistent as the other cardiovascular and ocular effects of these drugs. The primary and most prominent physiological change would be related to the cardiovascular effects.

A) It decreases the activity of norepinephrine receptor sites: Cholinergic agonists specifically act on acetylcholine receptors, not norepinephrine receptors. Norepinephrine is associated with the sympathetic nervous system and its receptors (alpha and beta), whereas cholinergic agonists affect the parasympathetic system through acetylcholine receptors.
B) It increases the activity of acetylcholine receptor sites: This is the correct answer. Cholinergic agonists work by stimulating acetylcholine receptors (both muscarinic and nicotinic), thereby enhancing the action of acetylcholine. This can lead to various effects such as decreased heart rate, increased digestion, and muscle contraction, as part of the parasympathetic nervous system response.
C) It decreases the activity of GABA receptor sites: GABA (gamma-aminobutyric acid) is an inhibitory neurotransmitter that acts on GABA receptors, not acetylcholine receptors. Cholinergic agonists have no direct effect on GABA receptor activity.
D) It increases the activity of dopamine receptor sites: Dopamine is a neurotransmitter primarily involved in the reward system, motor control, and mood regulation. Cholinergic agonists do not directly affect dopamine receptors. Instead, they target acetylcholine receptors, which are part of the parasympathetic nervous system.