L5 - Cholinergics Flashcards
What are the major physiological effects of the parasympathetic system?
- contracts pupil
- slows heart rate
- lowers blood pressure
- constricts bronchi
- stimulates salivation
- stimulates lacrimation
What are the major physiological effects of the sympathetic system?
- dilates pupil
- accelerates heart rate
- strengthens contraction
- elevates blood pressure
- relaxes bronchi
- stimulates sweating
What are the non-selective agonists and antagonists of the muscarinic receptors?
agonists:
- ACh
- muscarine
- pilocarpine
antagonists:
- atropine
- hyoscine
What are the different muscarinic receptors and where are they found?
M1 - brain (neuronal) M2 - cardiac (reduce force of contraction and heart rate) M3 - glands and smooth muscle M4 M5
How is muscarine different to ACh?
- muscarine only works on muscarinic receptor types
- ACh targets nicotinic and muscarinic receptors
What is a feature about atropine related to the BBB?
- atropine can cross the BBB with ease
- methonated atropine = atropine methonitrate is charged and cannot cross BBB
What is a major use of atropine?
- used by opthamologists to dilate pupils during retinal exams
What is a use for pilocarpine?
- used to lower intraocular pressure to relieve symptoms of glaucoma
What are some minor clinical uses of muscarine receptor agonists?
- suppression of atrial tachycardia
- stimulation of GI activity after anaesthesia
- stimulation of bladder emptying after surgery
What are anticholinesterases?
- drugs which inhibit the enzyme acetylcholinesterase
- enhance cholinergic transmission
What are the groups of anticholinesterases?
- short and medium duration inhibitors = reversible
- long duration inhibitors = often irreversible and highly toxic
What is Myasthenia Gravis?
- autoimmune disease causing decreases number of functioning postsynaptic nicotinic receptors on endplates
- characterised by muscle weakness
What are some ACh-E inhibitors drugs + info about duration, site of action, and use?
edrophonium
- short duration
- acts on NMJ
- used in diagnosis of myasthenia gravis
neostigmine
- medium duration
- acts on NMJ
- used in oral treatment of myasthenia gravis
physostigmine
- medium duration
- acts on parasympathetic ganglia
- used as eye drops for glaucoma, also Alzheimer’s disease
dyflos
- very long duration
- acts on postganglionic parasympathetic synapses
- is highly toxic organophosphate
parathion
- very long duration
- acts on postganglionic parasympathetic synapses
- used as insecticide but commonly causes poisoning in humans
What is an example of a nicotinic agonist?
suxamethonium
How does suxamethonium work?
- Phase I block: produces sustained depolarisation
- Phase II block: nicotinic receptors undergo desensitisation and channel closure, RMP restored by muscle paralysed because receptors are unresponsive
