Cholinergic Parasympathetic Nervous System Review

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Questions and Answers

How does the parasympathetic nervous system influence gastrointestinal (GI) motility, and which specific receptor type is primarily involved in this process?

The parasympathetic nervous system increases GI motility through muscarinic cholinergic receptors.

What is the functional outcome of administering a cholinomimetic drug, and how does it relate to the action of acetylcholine (ACh)?

A cholinomimetic drug mimics the action of acetylcholine, enhancing cholinergic neurotransmission.

How do cholinesterase inhibitors affect acetylcholine levels in the synapse, and what are the potential consequences of this action?

Cholinesterase inhibitors increase acetylcholine levels by preventing its breakdown, leading to enhanced cholinergic effects which, if excessive, can cause a cholinergic crisis.

What distinguishes reversible cholinesterase inhibitors from irreversible ones in terms of their mechanism of action and clinical implications?

Reversible inhibitors temporarily bind to cholinesterase, while irreversible inhibitors form a stable, permanent bond, requiring the synthesis of new cholinesterase enzymes. Signup and view all the answers

Describe the dual mechanism through which Atropine influences heart rate at different doses.

At low doses, Atropine can cause bradycardia via CNS effects, while at high doses, it causes tachycardia by blocking vagal activity at the heart. Signup and view all the answers

How does Atropine affect exocrine gland secretions, and what is the underlying mechanism for these effects?

Atropine reduces exocrine gland secretions by blocking muscarinic receptors, thus inhibiting parasympathetic stimulation of these glands. Signup and view all the answers

What is the primary mechanism by which scopolamine induces sedation, and how does its action differ from that of Atropine?

Scopolamine causes sedation by crossing the blood-brain barrier and affecting central muscarinic receptors, whereas Atropine has more limited CNS entry. Signup and view all the answers

Explain how Tiotropium achieves bronchodilation in the treatment of asthma or COPD, and specify which muscarinic receptor subtypes are involved.

Tiotropium primarily blocks M3 receptors in the airways, causing bronchodilation, while its brief binding to M2 receptors has a smaller impact. Signup and view all the answers

How does nicotine affect autonomic ganglia at low and high doses, and what accounts for the differing effects?

At low doses, nicotine stimulates autonomic ganglia, leading to increased sympathetic activity; at high doses, it causes ganglionic blockade due to desensitization. Signup and view all the answers

Describe the physiological effects of nicotine on the cardiovascular system, and explain how these effects are mediated.

Nicotine increases blood pressure and heart rate by stimulating sympathetic ganglia and adrenal activation, leading to increased catecholamine release. Signup and view all the answers

What are ganglionic blockers, and how do they influence the balance between parasympathetic and sympathetic tone?

Ganglionic blockers inhibit neurotransmission at autonomic ganglia, reducing both parasympathetic and sympathetic activity but with effects more pronounced in the dominant system. Signup and view all the answers

What are the expected effects of a ganglionic blocker on ocular function, and how do they relate to the drug's mechanism of action?

Ganglionic blockers cause mydriasis (pupil dilation) by inhibiting parasympathetic tone, which normally constricts the pupil. Signup and view all the answers

How does hemicholinium affect acetylcholine synthesis, and what specific step in the process does it inhibit?

Hemicholinium inhibits the choline transporter, reducing the uptake of choline into the neuron, which is necessary for acetylcholine synthesis. Signup and view all the answers

What enzymatic activity is inhibited by physostigmine, and how does it differ from the mechanism of action of neostigmine?

Physostigmine inhibits acetylcholinesterase and crosses the blood-brain barrier, while neostigmine also inhibits acetylcholinesterase but has direct nAChR activity and does not cross the BBB. Signup and view all the answers

How does the action of pralidoxime (2-PAM) counteract the effects of organophosphate poisoning, and what limitations exist in its effectiveness?

Pralidoxime reactivates acetylcholinesterase inhibited by organophosphates, but it must be administered before 'aging' occurs. Signup and view all the answers

How do irreversible cholinesterase inhibitors such as nerve gases lead to cholinergic crisis, and what are the key signs of such a crisis?

Irreversible cholinesterase inhibitors cause a massive accumulation of acetylcholine, leading to muscle paralysis, excessive secretions, and respiratory failure. Signup and view all the answers

What is the role of cholinesterase in the cholinergic synapse, and how does its function contribute to normal neurotransmission?

Cholinesterase breaks down acetylcholine in the synaptic cleft, terminating the signal and preventing continuous stimulation of receptors. Signup and view all the answers

How does the selectivity of muscarinic receptor antagonists influence their therapeutic applications and side effect profiles?

Selective muscarinic antagonists can target specific tissues, reducing side effects, whereas non-selective antagonists affect multiple systems, increasing the likelihood of adverse reactions. Signup and view all the answers

What are the primary mechanisms by which anticholinergic drugs affect urinary function, and for what conditions might they be used?

Anticholinergic drugs relax the bladder and tighten the vesical sphincter, promoting urinary retention, and are used to treat urinary incontinence. Signup and view all the answers

How does the use of Atropine influence accommodation, and in what medical circumstances is this effect useful?

Atropine blocks accommodation by paralyzing the ciliary muscle, which prevents the lens from focusing, and is used to precisely measure refraction and treat iritis. Signup and view all the answers

Explain how the differing selectivity of pilocarpine and bethanechol impacts their uses.

Pilocarpine has preference for muscarinic over nicotinic receptors and is used for glaucoma, while bethanechol has selectivity for muscarinic receptors, thus its use for urinary retention. Signup and view all the answers

Explain the concept of 'aging' as it relates to the irreversible inhibition of acetylcholinesterase by organophosphates. How does aging affect treatment strategies for organophosphate poisoning?

Aging refers to a chemical modification of the inhibited acetylcholinesterase that makes it resistant to reactivation by pralidoxime. This process limits the treatment window for organophosphate poisoning. Signup and view all the answers

How do the mechanisms of action of scopolamine and dimenhydrinate (Dramamine) differ in preventing motion sickness, and what are the clinical implications of these differences?

Scopolamine, a muscarinic antagonist, acts primarily in the central nervous system (CNS) to block cholinergic neurotransmission, while dimenhydrinate, an antihistamine, targets histamine receptors in the inner ear and CNS. Scopolamine is a more potent antiemetic, but has more pronounced anticholinergic side effects. Dimenhydrinate is less effective. Signup and view all the answers

In the context of anesthesia, what is the rationale for using anticholinergic drugs like glycopyrrolate before surgery, and how does glycopyrrolate's properties make it suitable for this purpose?

Anticholinergic drugs like glycopyrrolate are used to reduce salivary and respiratory secretions before surgery, preventing aspiration and improving airway management. Glycopyrrolate's minimal CNS penetration limits its sedative effects. Signup and view all the answers

Describe the role of M2 muscarinic receptors as autoreceptors in the context of cholinergic neurotransmission in the lungs, and explain how blocking these receptors with a drug like ipratropium affects acetylcholine release and airway function.

M2 receptors act as autoreceptors to inhibit further acetylcholine release, blocking M2 increases Ach release. Signup and view all the answers

How does chronic exposure to nicotine lead to desensitization of nicotinic receptors at autonomic ganglia, and what are the clinical consequences of this desensitization in terms of cardiovascular function and blood pressure regulation?

Chronic nicotine exposure causes sustained depolarization and receptor inactivation, leading to desensitization; this results in autonomic dysfunction, potentially impairing cardiovascular function and blood pressure regulation. Signup and view all the answers

Explain the rationale behind using trimethaphan camsylate in the management of hypertensive crisis, and describe the mechanism of action by which this drug achieves rapid reduction in blood pressure.

Trimethaphan reduces blood pressure by blocking nicotinic receptors at autonomic ganglia, thereby reducing both sympathetic and parasympathetic outflow, leading to vasodilation and decreased cardiac output. Signup and view all the answers

What are the key considerations when treating a patient presenting with the classic 'SLUDGE' symptoms (Salivation, Lacrimation, Urination, Defecation, Gastrointestinal distress, Emesis) indicative of cholinergic toxicity, and how do these considerations guide the choice of antidote and supportive care?

Atropine is the treatment for cholinergic toxicity and supportive care. Signup and view all the answers

Compare and contrast the therapeutic uses of neostigmine and edrophonium in the context of myasthenia gravis, including the mechanisms of action. Why is edrophonium used diagnostically and neostigmine chronically?

Both drugs are acetylcholinesterase inhibitors, but edrophonium is very short acting, so is used for diagnosis, and neostigmine is used to treat muscle weakness. Signup and view all the answers

How does the pathophysiology of glaucoma relate to cholinergic mechanisms, and what is the rationale for using pilocarpine to manage this condition?

In glaucoma, increased intraocular pressure damages the optic nerve. Pilocarpine contracts the ciliary muscle. Signup and view all the answers

A patient with Alzheimer’s disease is prescribed donepezil. What is the cholenergic mechanism of this drug, and what is its purpose for Alzheimer's?

Donepezil inhibits acetylcholinesterase in the brain, increasing acetylcholine levels and improving cognitive function. Signup and view all the answers

How does the mechanism of action of Vesamicol differ from that of Hemicholinium in modulating cholinergic neurotransmission?

Vesamicol inhibits the vesicular transport of acetylcholine into synaptic vesicles, thus depleting store release, while Hemicholinium prevents choline reuptake into the presynaptic neuron. Signup and view all the answers

When are direct cholinergic receptor agonists indicated, and how do they differ from cholinesterase inhibitors in their mechanism of action?

Direct cholinergic receptor agonists are often used when there is a need to stimulate cholinergic receptors directly, such as in the treatment of glaucoma or urinary retention, and they work by directly binding to and activating these receptors. Signup and view all the answers

How does the chemical structure of atropine contribute to its pharmacological effects, particularly in terms of its ability to interact with muscarinic receptors and its distribution in the body?

Atropine's structure allows it to act as a competitive antagonist at muscarinic receptors, blocking acetylcholine binding and preventing receptor activation. Its lipophilic nature enables it to cross the blood-brain barrier, leading to central nervous system effects. Signup and view all the answers

In toxicology, how does the concept of 'muscarinic excess' apply to organophosphate poisoning, and which specific signs and symptoms reflect this excess?

Muscarinic excess in organophosphate poisoning refers to the overstimulation of muscarinic receptors due to the accumulation of acetylcholine. This leads to signs such as miosis, increased salivation, diarrhea, and bronchoconstriction. Signup and view all the answers

In what clinical scenarios would a drug that selectively blocks nicotinic receptors at autonomic ganglia be useful? How would it impact the sympathetic and parasympathetic nervous systems?

Ganglionic blockers have limited clinical use due to their widespread effects. They would block signal transmission at both the sympathetic and parasympathetic ganglia, reducing their individual activities. Signup and view all the answers

How are cholinesterase deficiencies diagnosed and managed, and what role do genetic factors play in the variable expression of cholinesterase activity?

Cholinesterase deficiencies are typically diagnosed based on symptoms and blood tests that measure cholinesterase activity. Management can involve minimizing exposure to cholinesterase inhibitors and using alternative drugs. Genetic factors influence cholinesterase activity, leading to variable expression and response to drugs. Signup and view all the answers

Describe how muscarinic receptors in the sinoatrial (SA) node of the heart mediate the effects of the parasympathetic nervous system on heart rate. Explain the mechanism.

When acetylcholine binds to M₂ muscarinic receptors in the SA node it decreases the heart rate due to increasing $K^+$ permeability, which leads to a hyperpolarization, and decreases $Ca^{+2}$ influx, which slow rates of depolarization. Signup and view all the answers

A patient that overdoses on methacholine shows signs of bronchoconstriction. Why is epinephrine the antidote of choice for the clinician? Explain.

The primary concern is methacholine-induced bronchoconstriction. Epinephrine combats this by activating β₂-adrenergic receptors in the lungs, promoting bronchodilation, and α₁-adrenergic receptors to counteract vasodilation. Signup and view all the answers

A patient with Alzheimer's is taking a cholinesterase inhibitor but their memory is beginning to decline. How might combining muscarinic agonists or antagonists provide a synergistic effect?

This results in cognitive benefits and improvement of daily functioning. They enhance the effect of existing cholinsterase inhibitors. Cholinergic antagonists may be used. The effects differ. Signup and view all the answers

Flashcards

Parasympathetic Nervous System

Parasympathetic nervous system uses long preganglionic neurons and short postganglionic neurons to communicate with target organs using acetylcholine (ACh).

Cholinomimetics

Drugs that mimic the effects of acetylcholine by binding to cholinergic receptors directly.