Parasympathetic Nervous System and Cholinergic Receptors Flashcards
What are the primary ANS neurotransmitters?
Acetylcholine and Norepinephrine
Where are Acetylcholine and Norepinephrine synthesized and stored?
They are both synthesized in nerve terminals and stored in synaptic or varicosity vesicles until released by nerve impulse.
Where is acetylcholine found in the peripheral nervous system?
ACh is the primary neurotransmitter at 3 different sites:
1) All preganglionic synapses in both the parasympathetic and sympathetic ganglions
2) Most parasympathetic postganglionic nerve endings/neuroeffector junctions
3) All somatic motor end-plates on skeletal muscle
All neurons/axons/fibers that release ACh are called:
Cholinergic
Where is the NT norepinephrine found in the ANS?
1) Most sympathetic postganglionic neuroeffector junctions
2) Adrenal Medulla cells (chromatin) release both norepinephrine and epinephrine
Neurons/axons/fibers that release NE are called:
Adrenergic
Cholinergic neurons release:
ACh
What are drugs that mimic the action of ACh called?
Cholinergic, cholinomimetic, parasympathomimetic
What are drugs that antagonize the action of ACh called?
Anticholinergic, cholinergic blockers, parasympatholytic
What are receptors on which ACh or cholinergic drugs act called?
Cholinergic receptors or cholinoreceptors
Adrenergic neurons release:
Norepinephrine
Drugs that mimic the action of NE are called?
adrenergic, adrenomimetic, sympathomimetic
Drugs that antagonize the cation of NE are called?
antiandrenergic, adrenergic blockers, sympatholytic
What are receptors on which NE or adrenergic drugs act called?
adrenergic receptors, adrenoceptors
What is the primary NT of the parasympathetic nervous system?
ACh
What are the steps of ACh synthesis and storage?
- Synthesized in the axonal cytoplasm from acetylCoA and choline via ChAT
- AcetylCoA comes from mitochondria
- Choline comes from extracellular fluid via choline transporter (CHT)
- ACh is transported into neuronal vesicles via vesicle-associated transporter (VAT)
What can block choline transporter (CHT)?
hemicholiniums
What can block vesicle-associated transporter (VAT)?
vesamicol
How is ACh released?
1) Vesicle-associated membrane proteins (VAMPs) - align vesicle with release sites on inner nerve terminal membrane
2) Synaptosomal nerve-associated proteins (SNAPS) - located on the inner nerve terminal and interact with VAMPs
3) Action potential reaches nerve terminal that triggers Ca++ influx via calcium channels
4) Ca++ interacts with VAMPs synaptotagmin (Ca++ sensor), triggering fusion of vesicle membrane with terminal membrane
5) ACh is then released via exocytosis into the synaptic cleft
What can block ACh release into the synaptic cleft?
botulinum toxin
What happens the ACh in the synaptic cleft?
It can bind to ACh receptors to result in effector response
All ACh molecules are rapidly metabolized by acetylcholinesterase (AChE)
AChE rapidly hydrolyzes ACh into acetate and choline, which terminates the action of ACh
What is critical to the fine control of neurotransmission?
Rapid removal of the NT
What are the ACh receptor subtypes?
Muscarinic receptors and Nicotinic receptors
Where are Muscarinic receptors located?
Smooth muscle, cardiac muscle, exocrine glands
What type of receptors are muscarinic receptors and what kind of responses do they exhibit?
GPCR – they have slower responses and may be either inhibitory or excitatory
Where are Nicotinic receptors located?
Three places:
1) Postganglionic neurons in both sympathetic and parasympathetic
2) Adrenal medulla
3) Skeletal muscle
What type of receptors are nicotinic receptors and what kind of responses do they exhibit?
Ligand-gated ion channels – they always cause a rapid increase in permeability to Na+ and K+, depolarization and excitation
What is the function of Gs in GPCRs?
Increase in adenylyl cyclase activity, then increase in Ca++ currents
What is the function of Gi in GPCRs?
Decrease in adenylyl cyclase activity, then increase in K+ currents
What is the function of Go in GPCRs?
Decrease in Ca++ currents
What is the function of Gq in GPCRs?
Increase in phospholipase C activity
