Pharmacology and physiology of the autonomic system Flashcards
What is the role of the autonomic nervous system?
Branch of the CNS which has involuntary control over respiration, digestion and blood pressure.
What are the divisions of the autonomic nervous system?
Sympathetic, parasympathetic and enteric
What is the role of the enteric system?
Involuntary control of the gastric system.
What are M1 receptors?
Found in the CNS and the glands. Gs proteins which increases cAMP activity to activate phospholipase C -> IP3 which increases Ca2+ for increased membrane excitability and K+ conductance. It increases CNS excitability and gland secretion.
What are M2 receptors?
Found in the CNS and the atria of the heart. Gi protein which negatively reduces cAMP activity and reduces heart contraction and CNS excitability.
What are M3 receptors?
Found in the exocrine glands, smooth muscle of the GI tract. It is a Gs protein positively coupled to cAMP to increase Ca2+ availability and induce gland secretion and smooth muscle contraction.
What are M4 receptors?
Found in the CNS. Gi protein negatively coupled to cAMP but increases K+ conductance and reduces CNS excitability
What are M5 receptors?
Found in substantia nigra of the CNS. Gs protein positively coupled to cAMP to increases K+ conductivity. It has unknown effect.
How do nicotinic receptors respond to drugs?
They are previously in a closed state. When a drug binds they open. However, excessive dose over time can lead to it becoming desensitised and remaining closed unless a higher dose is given or withdrawal occurs.
Where are nicotinic receptors located?
In the muscles, ganglia and CNS.
Where is the (a3)2(B2)3 receptor located?
In muscles, ganglia and pre- or post-ganglionic neurons of the CNS. Induces release of acetylcholine and increases excitability and permeability of the membrane to the cations Na+ and K+
What is the (a7)5 receptor?
Present in the pre-or post ganglionic neurons of the CNS. It is a subtype of a nicotonic receptor which allow influx of Na+ or K+. It is implicated in Alzhiemer’s disease.
What are the muscle type nicotinic receptors?
(a3)2(B2)3 receptor which is found in the motor end plate to increase cation permeability and membrane excitability.
What are the ganglion nicotinic receptors located?
(a3)2(b2)3 which is found in ganglia such as pre-vertebral or paravertebral and increase membrane excitability or cation permeability
How do drugs affect the cholinergic system?
Inhibits acetylcholine uptake, packaging into vesicles, exocytosis of vesicles, acetylcholinesterase enzyme or action on post-synaptic receptors.
How is acetylcholine packaged into vesicles?
Via the ATP proton pump exchanger vAchT (vesicular acetylcholine transporter) which allows influx of Ach from synaptic cleft in exchange for H+
What is the rate limiting step in acetylcholine production?
Uptake of acetylcholine into the pre-synaptic cell.
What is vesamicol?
Inhibits the vAchT for packaging acetylcholine into vesicles.
What is hemicholinium?
Inhibits acetylcholine uptake into the pre-synaptic cell and reduces acetylcholine production.
What is botulinium?
Toxin released by bacteria used in beauty industry as botox which reduces exocytosis of vesicles of acetylcholine.
What are the type of cholinesterase inhibitors?
Reversible inhibitor which binds for a period of time to ACHesterase. Irreversible inhibitor which forms covalent bond with the enzyme to irreversibly inactive it.
How do irreversible cholinesterase inhibitors work?
Form covalent bond with ACHesterase which prevents reactivation
What is the role of organophosphate?
A pesticide which forms covalent bond with serine of acetylcholinesterase and irreversibly inactivates it.
What is the role of 2-PAM?
Treatment for pesticide poisoning by binding to organophosphate and prevent formation of covalent bond.
PRALIDOXIME
What are non-depolarising blocking agents and their use?
Non-depolarising blocking agents are muscarinic receptor antagonists which can act as muscle relaxants. They bind to the receptor and do not cause depolarisation, cannot be cleared by ACHesterase and lead to muscle paralysis in excess.
What are fast non-depolarising nicotinic agents?
Mivacurium
What are intermediate non-depolarising nicotinic agents?
Atracurium
What are slow non-depolarising nicotinic agents?
Pancuronium