Pharmacology Quiz: Drugs and Their Effects

Drugs Affecting the Nervous System

• This module discusses drugs that impact the nervous system, focusing on autonomic pharmacology.
• The nervous system is divided into peripheral and central nervous systems, further categorized into afferent and efferent divisions.
• The autonomic system controls involuntary functions, including the enteric system (intestines). The somatic system controls voluntary movements.
• The parasympathetic nervous system (PNS) is associated with "rest and digest" functions, while the sympathetic nervous system (SNS) is associated with "fight or flight" responses.
• Different actions are seen in various organs when sympathetic vs. parasympathetic responses dominate.

Autonomic Pharmacology

• The nervous system's response to drugs is a critical aspect of study.
• Neurotransmitters like norepinephrine, epinephrine, acetylcholine, dopamine, serotonin, histamine, glutamate, and GABA are frequently regulated through drugs impacting receptors.
• Cholinergic transmission is paramount in autonomic ganglia, parasympathetic postganglionic neurons' interactions with effector cells, and somatic (voluntary) skeletal muscle neuromuscular junctions.
• Acetylcholine (ACh) is a crucial primary neurotransmitter in these systems.
• Norepinephrine (NE) is the primary neurotransmitter at sympathetic postganglionic neuron-effector synapses in most tissues.
• Dopamine can act as a vasodilator in renal blood vessels, whereas norepinephrine is a vasoconstrictor.

Actions of Sympathetic and Parasympathetic Nervous Systems on Effector Organs

• Specific organs respond differently to sympathetic and parasympathetic stimulation.
• The eye, salivary glands, heart, kidneys, ureters and bladder, and genitals (both male and female) have specific actions with neurotransmitter involvement.
• Sympathetic stimulation often results in increased heart rate, pupil dilation, and bronchodilation.
• Conversely, parasympathetic responses typically decrease heart rate, constrict pupils, and contract bronchioles.

Fight or Flight Response vs. Rest and Digest

• The sympathetic nervous system activates in response to perceived danger ("fight-or-flight").
• Diffuse output to multiple organs is characteristic of the sympathetic nervous system.
• The parasympathetic nervous system promotes "rest and digest," with specific and individual outputs to individual organs.

Sympathetic vs. Parasympathetic Nervous Systems

• Autonomic branches balance each other, maintaining homeostasis.
• Parasympathetic activity generally dominates during calm situations; sympathetic activity typically dominates in response to stress.

Neuron Signaling

• Neurons transmit signals via synaptic signaling, through neurotransmitters.
• A nerve cell, receiving neurotransmitter signals from a presynaptic axon terminal, transmits the signal to a target cell.

Types of Neurotransmitters

• Numerous neurotransmitters, but specific ones frequently play roles in drug actions.
• Norepinephrine, epinephrine, acetylcholine, dopamine, and others are involved.

Cholinergic Transmission

• Acetylcholine (ACh) is the primary neurotransmitter, influential across the nervous system.
• Crucial in autonomic ganglia, parasympathetic postganglionic synapses, and the thermoregulatory sweat glands, along with the somatic skeletal muscle junction.

Adrenergic Transmission

• Norepinephrine (NE) is the critical sympathetic transmitter at most effector synapses.
• Important exceptions involve thermoregulatory sweat glands and potentially vasodilating fibers in skeletal muscle, utilizing acetylcholine.

ANS Receptors

• Different receptors for neurotransmitters (ACh, NE, EPI, etc.) determine specific responses.
• Receptors vary in target organs (e.g., heart, lungs, arteries).
• Cholinergic receptors: muscarinic and nicotinic.
• Adrenergic receptors: alpha and beta.
• Dopamine receptors are also involved.

Drugs Affecting the ANS

• Agonists and antagonists influence the sympathetic and parasympathetic nervous systems.
• Agonists mimic the effects; antagonists block them.

Adrenergic Agonists (Sympathomimetic Drugs)

• Drugs stimulating adrenergic receptors, including norepinephrine (Levophed), epinephrine (Adrenaline).
• Albuterol (Ventolin) is a beta2 agonist, often used for bronchospasm (e.g. asthma).
• Dopamine can be critical in emergency situations, to elevate blood pressure.

Adrenergic Antagonists (Sympatholytic Drugs)

• Drugs that block adrenergic receptors, including phentolamine (Regitine) to counter hypertension and potential tissue necrosis linked to extravasated norepinephrine.

Cholinergic Agonists (Parasympathomimetic Drugs)

• Drugs stimulating cholinergic receptors.
• Physostigmine (Antilirium) is an exception, crucial in severe atropine poisoning situations.

Cholinergic Antagonists (Blocking, Parasympatholytic Drugs)

• Drugs blocking cholinergic receptors, like atropine, affecting heart rate and other responses.
• Atropine is prevalent in prehospital settings due to its role in treating bradycardia and counteracting nerve agent poisoning.

Drugs Affecting the CNS

• Classes of drugs impact the central nervous system, including analgesics, anesthetics, anxiolytics, CNS stimulants, antipsychotics, antidepressants, and neurodegenerative drugs.

Analgesics

• Reduce pain sensation, via opioid and non-opioid categories.
• Opioids include morphine, codeine, and others, affecting receptors like mu and kappa.
• Non-opioids, like salicylates (aspirin) and NSAIDs (ibuprofen, naproxen), impact prostaglandin synthesis or related pathways.

Opioids

• Act on endorphin receptors (primary mu and kappa), impacting pain, breathing, sedation, and euphoria.
• Pure agonists, agonist-antagonists, and pure antagonists (e.g., naloxone) have differing roles.

Actions at Opioid Receptors

• Actions of opioids at mu and kappa receptors: analgesia, respiratory depression, sedation, euphoria, and physical dependence.

Anesthetics

• General anesthetics affect consciousness; local anesthetics, like lidocaine, act at the injection site.

Anti-Anxiety & Sedative-Hypnotic Drugs

• Act on GABA and other receptors in the CNS, impacting mood, sleep, and anxiety, including barbiturates, benzodiazepines, and alcohol.

Mechanism of Action (GABA Receptors)

• Drugs affect the GABA receptor system. Benzodiazepines enhance its activity; barbiturates promote and (at high doses) stimulate it.

Benzodiazepines vs. Barbiturates

• Differences in safety, maximum CNS depression, respiratory depression, and potential for abuse are key. Benzodiazepines typically have advantages regarding safety and abuse, compared to barbiturates.

Anti-Seizure Medications

• Target hyperactive brain areas, decreasing propagation of action potentials.

CNS Stimulants

• Amphetamines, methylphenidate (Ritalin), and methylxanthines (e.g., caffeine) impact neurotransmitter release (norepinephrine, dopamine).

Psychotherapeutic Medications

• Regulate neurotransmitter imbalances.

Antipsychotic Drugs (Neuroleptics)

• Treat schizophrenia (disorganized thoughts); primarily target dopamine receptors. 

Antidepressants

• Treat conditions linked to inadequate monoamine levels. Tricyclic antidepressants (TCAs) and selective serotonin reuptake inhibitors (SSRIs) affect neurotransmitter levels.

MAOIs

• Monoamine oxidase inhibitors (MAOIs) impact monoamine breakdown, leading to potential safety interactions with dietary tyramine.

Other

• Various other substances are listed, and data are provided about mechanisms, actions, and indications for their use.