Autonomics 3 Flashcards
What type of receptor do preganglionic parasympathetic fibers synapse on?
nicotinic
What type of receptor do postgangilonic parasympathetic fibers synapse on?
muscarinic receptors
Two Types of Cholinergic Receptors
- Nicotinic
- Muscarinic
Describe the path of ACh in the synapse.
- Aceytlcholine made in presynaptic neuron from choline and acetyl CoA
- Released from a vesicle into the synapse
- Some ACh will bind to receptors, other will be broken down by acetylcholinesterase
- Choline transported back into axon terminal to make more ACh
Are nicotinic receptors always excitatory?
yes
What type of receptor is a nicotinic receptor?
ligand-gated ion channel (ACh binds and causes channel to open, Na+ rushes in and membrane depolarizes)
What type of receptor will you find in neuromuscular junctions?
nicotinic
Nicotine
mimics ACh at nicotinic receptors
How many types of muscarinic receptors are there?
five (5)
Muscarine
mimics ACh at muscarinic receptors; water-soluble toxin derived from a mushroom
Are muscarinic receptors always excitatory?
NO, they can be excitatory or inhibitory, depending on type and where it binds
What are muscarinic receptors bound to?
G-proteins, and second messenger systems (therefore slower acting and more local)
Gq
excitatory G protein
Gi
inhibitory G protein
Which muscarinic receptors are excitatory?
M1, M3, and M5
Which muscarinc receptors are inhibitory?
M2, M4
What parasympathetic muscarinic receptor is found in the heart?
M2
What parasympathetic muscarinic receptor is found in arteries, veins, eyes, lungs, GI tract, urinary system, and salivary glands?
M3
Parasympathetic System Effect on Bladder
contract the detrusor muscles (promote urine)
Parasympathetic System Effect on Stomach and Intestines
increase gastric acid secretion, contract smooth muscle and increase motility
Parasympathetic System Effect on Heart
decrease heart rate and blood pressure
Parasympathetic Effect on Arteries and Veins
vasodilation, decrease blood pressure
Parasympathetic System Effect on Bronchioles
bronchial contraction
Parasympathetic System Effect on Eyes
contraction of pupil due to relaxation of the CIRCULAR msucles of the iris
Asthma and the Parasympathetic System
relaxing means bronchioles contract, therefore breathing difficulty increases leading to coughing at night
Does the parasympathetic system have any effect on bladder or intestinal sphincters?
no, sphincters are only affected by the sympathetic nervous system (a1 contraction)
Which two receptors are never located in the same region? Why?
a1 and M3 - two dfferent systems but the same contracting function
In what special case will M3 have no contracting function?
arteries (blood vessels)
M3 will act on endothelial cells and trigger nitric oxide synthesis which binds to something in smooth muscle to make cGMP which reduces calcium and therefore relaxes the smooth muscle cells
Direct Acting cholinergic agonists
act on muscarinic receptors to activate a tissue response
Pilocarpine
cholinergic agent used to treat glaucoma by constricting the pupil by stimulating M receptor with minimal effect on N receptor
SLUD effect
salivation, lacrimation, urination, defecation
Indirect Acting Cholinergic agonists
inhibit acetylcholinesterase
2 Types of Indirect Acting Cholinergic agonists
- Reversible Inhibitors
- Irreversible Inhibitors
Can cholinergic agonists pass the blood brain barrier?
some of them
Should you ever use an organophospahte as medicine?
NO!
It is used in pesticides and nerve gasses!
Anticholinergics
inhibit muscarinic ACh receptors and allow sympathetic system to take over
Ganglionic receptor agonists
block both sympathetic and parasympathetic transmission of nerve impulses (act on nicotinic receptors)
Why don’t we use ganglionic receptor agonists in vet med?
because they are not selective
