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Physiology Part 1 > Lec 8 Cholinergic > Flashcards

Lec 8 Cholinergic Flashcards

1
Q

What is an example of a muscarinic agonist?

A

acetylcholine

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2
Q

What are two examples of nicotinic agonists?

A

nicotine

acetylcholine

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3
Q

What is an example of a muscarinic antagonist?

A

atropine

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4
Q

What is an example of an acetylcholinesterase inhibitor?

A

physostigmine

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5
Q

What is an example of a ganglionic blocker?

A

hexamethonium

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6
Q

What is an example of a neuromuscular blocker?

A

tubocurarine

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7
Q

What are cholinomimetic drugs?

A

Mimic action of acetylcholine

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8
Q

What tissues do muscarinic agonists normally affect?

A
  • nerve
  • heart and smooth muscle
  • glands and endothelium
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9
Q

what tissues to nicotinic agonists normally affect?

A
  • neuromuscular end plate
  • skeletal muscle
  • autonomic ganglion cells
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10
Q

What are two types of direct acting cholinoceptor stimulants?

A

alkaloids

choline esters

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11
Q

M1 muscarinic receptor [location, G protein, cell effect]

A
  • located in neurons
  • Gq/11
  • Activates IP3/DAG
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12
Q

What type of receptors are muscarinic receptors? Where are they located?

A
  • g protein coupled receptors [GPCRs]
  • at end organs primarily of PNS
  • work through secondary messengers
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13
Q

M2 muscarinic receptor [location, G protein, cell effect]

A
  • located in neurons, heart, smooth muslce
  • Gi/o
  • inhibits cAMP production
  • activates K+ channels via B-gamma subunits
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14
Q

M3 muscarinic receptor [location, G protein, cell effect]

A
  • located in glands, endothelium, smooth muscle
  • Gq/11
  • activates IP3/DAG cascade
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15
Q

What type of receptors are nicotinic? Location? Permeable to what ions?

A
  • ligand-gated channels
  • permeable to Na, K, Ca
  • only at ganglia
  • —– postsynaptic neuron of ganglion synapse in both PNS/SNS
  • —– neuromuscular junction of somatic motor nerves
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16
Q

Nicotine as a drug?

A
  • nicotinic agonist

- binds nicotinic receptors on postsynaptic neuron of ganglion synapse in both PNS/SNS divisions of ANS

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17
Q

Nm nicotinic receptors [location, effect]

A
  • in skeletal muscle neuromuscular junction [NMJ]

- causes membrane depolarization [ligand gated Na, K, Ca influx/efflux]

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18
Q

Nn nicotinic receptors [location, effect]

A
  • in CNS, postganglionic neuron of ANS

- causes membrane depolarization [ligand gated Na, K, Ca influx/efflux]

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19
Q

Mech of muscarinic synapse at end organ [heart example]

A
  1. ACh released from varicosities along axon
  2. ACh interacts with M receptor
  3. M receptor linked to K+ channel causes hyperpolarization
  4. Voltage-dependent opening of pacemaker Na current channel shifts to negative potential
    - phosphorylation of L-type Ca channels is reduced
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20
Q

Synthesis of acetylcholine?

A
  • precursor choline actively taken up in terminal by choline transporter [Na/Cl dependent co-transport]
  • ACh synthesized from choline and acetyl CoA in axon terminal by choline acetyltransferase [ChAT]
  • ACh packed in vesicle
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21
Q

Mech of acetylcholine release

A
  • action potential in axon reaches terminal
  • voltage-gated Ca channels open
  • increased intracellular Ca causes protein on vesicle membrane [VAMPs] to form complex with protein on cell membrane [SNAPs]
  • vesicle fuses with cell membrane and releases ACh into synaptic cleft
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22
Q

How does acetylcholine signal terminate?

A
  • acetylcholinesterase [AChE] expressed on postsynatpic membrane
  • hydrolyzes acetylcholine in synapse to acetic acid and choline
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23
Q

What is an example of an anticholinesterase? What is effect?

A
  • physostigmine

- inhibits acetylcholinesterase [which breaks down ACh], thus indirect cholinergic agonist

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24
Q

2 effects of physostigmine on heart?

A
  • slows [SA node]

- decreases atrial contractile force

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25
Q

What is physostigmine?

A
  • An anticholinesterase - inhibits acetylcholinesterase
  • indirect cholinergic agonist since increases amount of ACh in synaptic cleft
  • reversible inhibitor
  • can cross blood brain barrer
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26
Q

2 effects of physostigmine on bronchioles?

A
  • bronchoconstriction

- increased secretions

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27
Q

effect of physostigmine on vascular?

A
  • no effect because no parasympathetic innervation
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28
Q

Effect of physostigmine on GI?

A

more contraction –> increased motility

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29
Q

Effect of physostigmine on eye?

A

miosis [pupil constriction]

30
Q

Effect of physostigmine on sweat glands?

A

increased secretion

31
Q

2 mnemonics for cholinesterase poisoning? what 2 things can lead to this?

A 
caused by insecticides, nerve gases
SLUDGE
- salivation
- lacrimation
- urination
- defecation
- GI upset
- Emesis
Killer B's
- bradycardia
- bronchospasm
- bronchorrhea
32
Q

What does mnemonic Killer Bs mean?

A 
Effect of cholinesterase poisoning
Killer B's
- bradycardia
- bronchospasm
- bronchorrhea
33
Q

What does mnemonic SLUDGE mean?

A 
Effect of cholinesterase poisoning
SLUDGE
- salivation
- lacrimation
- urination
- defecation
- GI upset
- Emesis
34
Q

What is effect of acetylcholine as a drug?

A
  • non-selective with muscarinic and nicotinic, agonist for both
  • its a choline ester - so is a substrate for acetylcholinesterase
  • activates muscarinic and nicotinic receptors
35
Q

What is subunit configuration of Nn vs Nm? Why is this important?

A
  • Different types of a and B subunits

- allows development of drugs specific for one or the other

36
Q

What is effect of nicotine on end organs?

A
  • variable since stimulates both sympathetic and parasympathetic
  • reflects dominant tone for that organ
37
Q

Effect of nicotine given systemically on ANS?

A
  • stimulates sympathetic and parasympathetic postganglionic neurons
38
Q

What is effect of nicotine in somatic nervous system?

A
  • activates Nm receptors to induce contraction [just like when ACh released]
39
Q

Effect of high levels nicotine or other nACHr agonist?

A

flaccid paralysis [relaxation] of skeletal muscle due to depolarization blockade: excessive sustained depolarization so voltage-gated Na channels can’t recover

40
Q

Two sites of action of nicotinic agonists?

A
  1. ganglionic stimulant [activates PNS/SNS]

2. skeletal muscle contraction [Nm, NMJ]

41
Q

What does a ganglionic stimulant do?

A
  • activates nicotinic ganglionic receptors [Nn] in both sympathetic and parasympathetic
  • causes increase in primary tone of each tissue
42
Q

What are two synonyms for muscarinic antagonists?

A
  • antimuscarinic

- parasympatholytic

43
Q

What is the prototype muscarinic antagonist?

A

atropine

44
Q

What is Hexamethonium? Mech?

A
  • selective antagonist at Nn receptors
  • ganglionic blocker
  • blocks transmission at all ganglia [parasympathetic and sympathetic] so target organs denervated
  • effect on each organ is opposite of dominant tone
45
Q

Effect of Hexamethonium on heart?

A

tachycardia [because dominant tone is parasympathetic]

46
Q

Mech of action of muscarinic antagonists

A
  • reversible competitive antagonists at M receptors

- block access of acetylcholine/cholinomimetics

47
Q

Effect of muscarinic antagonist? How does it effect BP?

A
  • blocks M receptors at parasympathetic end organs

- little effect on BP [M receptors exist on blood vessels but no parasympathetic innervations to these receptors]

48
Q

What does a ganglionic blocker do? What type of receptor does it block?

A
  • blocks Nn receptors
  • produces opposite of primary tone
  • effectively removes both sympathetic and parasympathetic input to organs
49
Q

Effect of Hexamethonium on heart?

A

tachycardia

50
Q

Effect of Hexamethonium on arterioles?

A

vasodilation - increased peripheral blood flow, hypotension

51
Q

Effect of Hexamethonium on veins?

A

dilation - peripheral pooling blood, decreased venous return, decreased cardiac output

52
Q

Effect of Hexamethonium on iris?

A

mydriasis

53
Q

Effect of Hexamethonium on ciliary muscle?

A

cycloplegia - focus to far vision

54
Q

Effect of Hexamethonium on GI?

A

reduced tone and motality
constipation
decreased gastric and pancreatic secretions

55
Q

Effect of Hexamethonium on urinary bladder?

A

urinary retention

56
Q

Effect of Hexamethonium on salivary glands?

A

xerostomia

57
Q

Effect of Hexamethonium on sweat glands?

A

anhidrosis

58
Q

Effect of Hexamethonium on genital tract?

A

decreased stimulation

59
Q

Mech of action ganglionic blocker [hexamethonium] on BP

A
  • normally blood vessels have sympathetic tone which causes vasoconstriction to increase BP
  • hexamethonium knocks out the dominant tone so get vasodilation and low BP
60
Q

what side effect of ganglionic blockers is reason they are not clinically used?

A

othostatic hypotension

61
Q

Function of neuromuscular blockers? Primary example?

A
  • competitive antagonists as Nm receptors
  • block binding ACh to Nm, prevent opening of cation channel –> prevent skeletal muscle contraction
  • ex. tubocurarine [curare]
62
Q

What is use of tubocurarine [curare]?

A
  • neuromuscular blocker
  • used as muscle relaxant before surgery/intubation
  • produces flaccid paralysis of skeletal muscle
63
Q

What important cholinesterase inhibitor can cross the blood-brain barrier?

A

physostigmine

64
Q

When is acetylcholine used as a drug clinically?

A

for opthalmic indications

65
Q

Whats another name for muscarinic agonists? [hint starts with a p]

A

parasympathomimetics

66
Q

Why is acetylcholine short lived when administered as IV? What does it activate?

A
  • activates mainly muscarinic receptors = muscarinic agonist

- short-acting because it is a substrate for pseudocholinesterase in plasma and tissues

67
Q

What is effect of muscarininc agonists? [on HR, bronchus, sweating]

A
  • bradycardia
  • bronchoconstriction
  • diaphoresis
68
Q

What main difference between effect of muscarinic agonists and anticholinesterase?

A
  • muscarinic agonists dilate vasculature, decrease diastolic BP
  • vs anticholinesterases have no effect on vasculature
69
Q

Why does exogenous ACh cause vasodilation?

A
  • endothelial cells of intima have M receptors
  • when activated, these cells release NO [aka endothelial derived relaxation factor [EDRF]
  • NO diffuses to surround vascular smooth muscle
  • — activates guanine cyclase, increase cGMP, muscle relaxes, vessel dialtes
70
Q

3 names of rmuscarinic antagonists

A
  • parasympatholytics
  • antimuscarinics
  • atropinics
71
Q

Effect of atropine

A
  • dry mouth, difficulty with near vision, tachycardia, etc
72
Q

Phrase for atropine poisoning

A 
Blind as a bat
mad as a hatter
red as a beet
hot as hell
dry as bone
the bowel and bladder loser their tone
and the heart runs alone

Physiology Part 1 (37 decks)

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