7 Cholinergic and Adrenergic Mechanisms 3
Last Modified: 2012-01-31
- Acetylcholine - neurotransmitter - stimulates nAChR and mAChR
- Carbachol - similar structure to Acetylcholine - stimulates nAChR and mAChR
- Bethanecol - methyl substituted Carbachol - stimulates ONLY mAChR
- They are not well absorbed by the GI tract because they are hydrolyzed by stomach acid and GI tract, and only acetylcholine is broken down by acetylcholinesterase
- Vasodilation requires to have endothelial cell layer in order for tissue relaxation.
- Required for vasodilation: Endothelial Derived Relaxing Factor (EDRF = NO, Nitric Oxide, not Nitrous Oxide)
- NO causes activation of guanylyl cyclase which produces cGMP. cGMP causes muscle excitation
- 1st response, non-damaged vessel
- 2nd response, endothelia damaged
- Contracts the sphincter muscle of iris - Miosis (pin point pupils).
- Contracts ciliary muscle - accommodation for near vision - myopia.
- Cholinergic effects allow aqueous humour to leave the eye, lowers intraocular pressure - useful for glaucoma
- Nicotine will cause the skeletal muscle cells to be more easily depolarized.
- Depolarization and Excitation - muscle fibres twitching, can range from disorganized (random muscle twitches) to strong contraction of whole muscle.
- Nerve Gases
- Antidysrhythmic Drugs
- Memory Enhancers in Alzheimer's
- Reversible, used therapeutically: Edrophonium
- Carbamic esters of alcohols with quaternary and tertiary ammonium groups: Neostigmine
- Nerve Gases/Insecticides: Malathion/Soman
- Increased strength of contraction, muscle twitches better
- Higher concentrations cause muscle fasciculations
- Highest concentrations cause polarizing neuromuscular blockade followed by a phase of non-depolarizing block.
- Anticholinesterase effects are stronger than direct cholinergic agonists
- Cardiac Arrest
- Fluid in lungs increases and bronchioconstriction
- Blockade of respiratory muscle contraction (respiratory muscle is a voluntary muscle, it will block)
- You will drown in your own lung fluid and you won't be able to breathe.
- Anticholinesterases or muscarinic agonists can be used for Glaucoma - which is a condition of high intraocular pressure.
- Cholinergic contraction of ciliary body allows outflow of aqueous humour.
- Postoperative Ileus - after surgery, activating all the sympathetic outflow to the gut.
- Cholinomimetics will cause a jump start to the GI tract, and cause urinary flow again.
- Myasthenia Gravis - autoimmune disease, antibodies produced which destroy nAChR at neuromuscular junction. Symptoms look similar to neuromuscular block produced by D-tubocurarine.
- Cholinomimetics can be used to increase concentration of ACh for more agonist to act at receptors.
- First neuromuscular blocker - D-Tubocurarine, used by South American endogenous population.
- They used blow darts to paralyze animals, they would then eat the animal, but Tubocurarine didn't paralyze the hunter.
- Tubocurarine is not well absorbed from GI tract.
- Found in snake venom.
- Very similar to D-Tubocurarine, not absorbed by the GI tract.
- α-Bungarotoxin - is a protein and is hydrolyzed in snake venom drinks when served with alcohol.
- Belladonna - "Beautiful Woman" - in 19th century girls would put Belladonna in their eyes, to dilate their pupils.
- It is still used today in opthamology.
- Causes near vision focusing
- Inhibits lacrymal secretion
- Parkinson's is a condition where there is an excess of cholinergic activity and a lack of dopaminergic in the striatum.
- Anti-muscarinic drugs can be used to control tremor associated with Parkinson's
- Motion sickness, involve cholinergic effects, treated with Scopolamine
- Pupillary Constrictor muscle is under muscarinic and parasympathetic tone.
- In presence of atropine, muscarinic effect is blocked and unopposed sympathetic effect dilates pupils.
- Weakening of ciliary muscle, can only focus on near sightedness.
- Produces glaucoma.
- Can't cry!
- Heart is under parasympathetic tone.
- Rate, force of contraction and AV conduction are increased by blockers such as Atropine. This causes cardiac activity to rise.
- Muscarinic Antagonists decrease secretion and motility, decreased salivary secretion.
- M1 selective antagonists such as Pirenzepine was once used in treatment of ulcer.
Words From Our Students
"StudyBlue is great for studying. I love the study guides, flashcards, and quizzes. So extremely helpful for all of my classes!"
Alice, Arizona State University
"I'm a student using StudyBlue, and I can 100% say that it helps me so much. Study materials for almost every subject in school are available in StudyBlue. It is so helpful for my education!"
Tim, University of Florida
"StudyBlue provides way more features than other studying apps, and thus allows me to learn very quickly! I actually feel much more comfortable taking my exams after I study with this app. It's amazing!"
Jennifer, Rutgers University
"I love flashcards but carrying around physical flashcards is cumbersome and simply outdated. StudyBlue is exactly what I was looking for!"