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Cholinergics are compounds that mimic the action of acetylcholine, a neurotransmitter that sends messages within the parasympathetic nervous system. Cholinergic drugs can inhibit, enhance, or mimic acetylcholine's actions, which include contracting smooth muscles, dilating blood vessels, increasing secretions, and slowing the heart rate. Cholinergic medications have a wide range of applications, from treating motion sickness and muscle weakness to enhancing cognition and global functioning in patients with dementia. They can also be used to dilate the pupils during ophthalmological procedures and dry up secretions during anesthesia. While cholinergics have many benefits, they can also cause side effects such as blurred vision, constipation, and muscle relaxation. This response primarily focuses on the impact of cholinergics on muscle function, particularly the role of acetylcholine in muscle contraction and its implications for various medical conditions.
| Characteristics | Values |
|---|---|
| Definition | Cholinergic drugs are compounds that inhibit, enhance, or mimic the action of acetylcholine, the primary transmitter of nerve impulses within the parasympathetic nervous system. |
| Types | Direct-acting and indirect-acting. |
| Direct-acting examples | Choline esters (acetylcholine, methacholine, carbachol, bethanechol) and alkaloids (muscarine, pilocarpine, cevimeline). |
| Indirect-acting examples | Reversible agents (physostigmine, neostigmine, pyridostigmine, edrophonium, rivastigmine, donepezil, galantamine) and irreversible agents (echothiophate, parathion, malathion, diazinon, sarin, soman). |
| Uses | Cholinergics are used to treat glaucoma, myasthenia gravis, motion sickness, and mild to moderate Alzheimer's disease. They are also used during surgery to produce muscle relaxation and prevent skeletal muscles from contracting. |
| Side effects | Blurred vision, constipation, impotence, inability to urinate, cardiac arrhythmias, lethargy, seizures, central respiratory depression, coma. |
| Mechanism of action | Cholinergics bind to and activate muscarinic and nicotinic receptors. |
| Receptors | Muscarinic and nicotinic receptors have been identified in the brain and throughout the body, including the neuromuscular junction, preganglionic neurons of the sympathetic nervous system, the basal forebrain, and brain stem complexes. |
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What You'll Learn
- Cholinergic drugs can suppress the parasympathetic nervous system, causing bodily secretions to dry up
- Acetylcholine, the primary neurotransmitter within the parasympathetic nervous system, is blocked by botulinum toxin
- Anticholinesterase drugs can treat muscle weakness disorders by increasing acetylcholine levels
- Cholinergic agents can improve cholinergic transmission within the CNS and are called cholinergic agonists
- Cholinergic drugs can be used to treat motion sickness and dilate pupils during ophthalmological procedures
Cholinergic drugs can suppress the parasympathetic nervous system, causing bodily secretions to dry up
Cholinergic drugs are pharmaceutical agents that act upon the neurotransmitter acetylcholine, the primary neurotransmitter within the parasympathetic nervous system (PNS). The parasympathetic nervous system is the "rest and digest" response, which contracts smooth muscles, dilates blood vessels, increases bodily secretions, and slows the heart rate.
Cholinergic drugs can inhibit, enhance, or mimic the action of acetylcholine. Anticholinergic drugs, on the other hand, inhibit the parasympathetic nervous system by blocking the action of acetylcholine, preventing it from binding to receptor sites. Cholinergic drugs have many side effects associated with paralysis of the autonomic nervous system, such as blurred vision, constipation, impotence, and inability to urinate.
Cholinergic blocking agents compete with acetylcholine and block it at the receptors in the PNS, preventing it from binding to the receptor site and causing a cholinergic effect. Most anticholinergic drugs interact with muscarinic cholinergic receptors in the brain, secretory glands, heart, smooth muscle, and eyes. Anticholinergic drugs can be used to treat conditions such as Parkinson's disease, overactive bladder, and motion sickness.
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Acetylcholine, the primary neurotransmitter within the parasympathetic nervous system, is blocked by botulinum toxin
Acetylcholine (ACh) is a neurotransmitter, a chemical that carries messages from the brain to the body through nerve cells. It is an excitatory neurotransmitter, which means it "excites" the nerve cell and causes it to "fire off the message".
In the autonomic nervous system, acetylcholine is the neurotransmitter in the preganglionic sympathetic and parasympathetic neurons. It is also the neurotransmitter at the adrenal medulla and serves as the neurotransmitter at all the parasympathetic innervated organs. In the peripheral nervous system, acetylcholine is released into the neuromuscular junction, where nerves meet muscle cells.
Acetylcholine is found in the central nervous system (CNS), the brain, and the spinal cord. It plays a significant role in the autonomic nervous system, a branch of the peripheral nervous system. Acetylcholine is the primary neurotransmitter within the parasympathetic nervous system, which uses acetylcholine almost exclusively to send its messages.
Botulinum toxin is a neurotoxin produced by the bacterium Clostridium botulinum. It is one of the most poisonous biological substances known. Botulinum toxin interferes with neural transmission by blocking the release of acetylcholine, causing muscle paralysis. The toxin binds selectively and irreversibly to high-affinity receptors at the presynaptic surface of cholinergic neurons, and the toxin-receptor complex is taken up into the cell by endocytosis. The blockage of neurotransmitter release is irreversible, and function can only be recovered by the sprouting of nerve terminals and the formation of new synaptic contacts, which usually takes two to three months.
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Anticholinesterase drugs can treat muscle weakness disorders by increasing acetylcholine levels
Cholinergic drugs, or cholinergics, are a category of pharmaceutical agents that act upon the neurotransmitter acetylcholine, the primary transmitter of nerve impulses within the parasympathetic nervous system. Anticholinesterase drugs, or acetylcholinesterase inhibitors, are a group of cholinergic drugs that inhibit acetylcholinesterase from breaking down acetylcholine, thereby increasing acetylcholine levels.
Acetylcholine is a chemical messenger that nerves release to signal muscles to contract. In people with myasthenia gravis, a muscle weakness disorder, the body attacks the neuromuscular junction, which is the area where acetylcholine flows. This decreases the muscle's response to acetylcholine, causing the muscles to tire quickly upon use. Anticholinesterase drugs work to stop the breakdown of acetylcholine, increasing its levels and, subsequently, muscle function.
A small cross-over randomised trial using intranasal neostigmine, an acetylcholinesterase inhibitor, showed that symptoms of myasthenia gravis improved in nine out of ten participants after a two-week treatment phase. However, there is controversy regarding the long-term efficacy, dosage, and side effects of acetylcholinesterase inhibitors. In addition, acetylcholinesterase inhibitors generally do not work for people with MuSK-positive myasthenia gravis.
Acetylcholinesterase inhibitors are also used to treat other muscle weakness disorders such as Alzheimer's disease, Parkinson's disease, and Lewy body dementia. These drugs increase acetylcholine levels and improve the function of neural cells. However, it is important to note that the potential toxicity of acetylcholinesterase inhibitors varies from patient to patient, and they may cause adverse effects such as headaches, insomnia, gastrointestinal issues, lightheadedness, weakness, and weight loss.
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Cholinergic agents can improve cholinergic transmission within the CNS and are called cholinergic agonists
Cholinergic agents are compounds that mimic the action of acetylcholine and/or butyrylcholine. Acetylcholine is the primary neurotransmitter within the parasympathetic nervous system (PNS), which is a part of the autonomic nervous system. The PNS is responsible for contracting smooth muscles, dilating blood vessels, increasing bodily secretions, and slowing the heart rate.
Direct-acting cholinergic agents include choline esters (acetylcholine, methacholine, carbachol, bethanechol) and alkaloids (muscarine, pilocarpine, cevimeline). Pilocarpine, for example, is used in eye drops to constrict the pupil and decrease intraocular pressure in glaucoma. Indirect-acting cholinergic agents include reversible agents like physostigmine, neostigmine, and pyridostigmine, and irreversible agents like echothiophate, parathion, and malathion.
Cholinergic agents have a wide range of uses, including the treatment of glaucoma, myasthenia gravis, and dementia. However, they can also cause adverse effects, particularly in organs controlled by the parasympathetic nervous system. For example, nicotinic effects of cholinergic agents can lead to muscle weakness, fasciculations, and paralysis through acetylcholine stimulation at the neuromuscular junction. Anticholinesterase drugs, a type of cholinergic agent, can also lead to muscle twitching and fasciculations by increasing acetylcholine levels in skeletal muscles.
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Cholinergic drugs can be used to treat motion sickness and dilate pupils during ophthalmological procedures
Cholinergic drugs are any of various drugs that inhibit, enhance, or mimic the action of the neurotransmitter acetylcholine, the primary transmitter of nerve impulses within the parasympathetic nervous system. Cholinergic drugs can be used to treat motion sickness and dilate pupils during ophthalmological procedures.
Motion sickness is an unpleasant condition that occurs when a person is subjected to motion or the perception of motion, resulting in symptoms like nausea, nonvertiginous dizziness, and malaise. Scopolamine, an anticholinergic, is used for the prevention and treatment of motion sickness. Its effectiveness is likely due to its central anticholinergic properties. It is most commonly prescribed as a transdermal patch that should be placed behind the ear on clean, hairless skin at least 30 minutes prior to exposure to motion stimuli. Common adverse effects can include dry mouth/nose/throat, drowsiness, loss of visual accommodation, and sensitivity to bright light.
Cholinergic drugs are also used to dilate the pupils during ophthalmological procedures. This is achieved through the suppression of the parasympathetic system, which results in the drying up of the secretions of the body, an increase in heart rate, and dilation of the pupils. One example of a drug used for this purpose is pilocarpine, a selective muscarinic-receptor agonist that is used in eyedrops to constrict the pupil and to decrease the intraocular pressure that is raised in the disease glaucoma.
In addition to the above-mentioned uses, cholinergic drugs have a variety of other applications. For example, they were the first effective agents to reduce high blood pressure (antihypertensive drugs) and anticholinesterase drugs are used to treat myasthenia gravis, a disorder characterized by muscle weakness. Furthermore, cholinergic drugs are used to treat dementia and Alzheimer's disease, with medications such as rivastigmine, donepezil, and galantamine available for improving cognition and global functioning in patients.
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Frequently asked questions
Cholinergic is a term used to refer to the molecule acetylcholine. It is usually employed to define neurons, receptors or synapses that use acetylcholine. Cholinergic drugs inhibit, enhance, or mimic the action of the neurotransmitter acetylcholine, the primary transmitter of nerve impulses within the parasympathetic nervous system.
Cholinergics increase muscle function by improving cholinergic transmission within the CNS. Acetylcholine, the primary neurotransmitter within the parasympathetic nervous system, is involved in muscle movement and function.
Cholinergic drugs include direct-acting and indirect-acting agents. Direct-acting cholinergic agonists include choline esters (acetylcholine, methacholine, carbachol, bethanechol) and alkaloids (muscarine, pilocarpine, cevimeline). Indirect-acting cholinergic agents include reversible agents (physostigmine, neostigmine, pyridostigmine) and irreversible agents (echothiophate, parathion, malathion).
Cholinergics have many side effects, including blurred vision, constipation, impotence, and inability to urinate. They can also cause muscle weakness, fasciculations, and paralysis.
