1.10A. Parasympathetic efferent mechanisms. Flashcards

1
Q

I. Basics
1. What are divisions of autonomic nervous system?

A

the sympathetic (SYM) and parasympathetic (PARA) nervous systems

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2
Q

I. Basics
2. What is the main function of the autonomic nervous system (ANS)

A

To maintain a constant internal environment (homeostasis).
-> ANS unconsciously receives sensory inputs and sends signals to effectors.

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3
Q

I. Basics
3. What are the effectors of the autonomic nervous system (ANS)

A

smooth muscle, cardiac muscle, and glands.

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4
Q

II. PARA nervous system
1. What are the characteristics of parasympathetic nervous system?

A

1/ PARA effects are generally associated with ‘’rest and digest’’ functions of the body
2/ The preganglionic PARA neuron cell bodies are located either in cranial or sacral regions
3/ The preganglionic fibers of the PARA nerves are relatively long to the ones of SYM system
4/ Many of the cranial preganglionic fibers lead to ganglia within the cranium, while others lead to ganglia located near or within the walls of effector visceral organs
5/ In these ganglia, the preganglionic fibers synapse with ACh sent to the nicotinic ACh receptors of the postganglionic neuron
6/ The postganglionic neurons in PARA are short, and also send ACh, which binds to muscarinic cholinergic receptors of the target effector muscle/gland

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5
Q

II. PARA nervous system
2. What are PARA cranial nerve nuclei?

A

Accessory, Oculomotor, Superior inferior salivatory nuclei, Dorsal vagal nucleus, Nucleus ambiguous

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6
Q

III. Anatomy of PARA nervous system
1. Origin of PARA nervous system

A

CRANIAL - CN (III, VII, IX, X)
Sacral
Spinal Cord S2-S4

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7
Q

III. Anatomy of PARA nervous system
2. Ganglion of PARA nervous system

A

Near or within organ

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8
Q

III. Anatomy of PARA nervous system
3. Size of Preganglionic and Postganglionic axons

A

Pre - Long
Post - short

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9
Q

III. Anatomy of PARA nervous system
4. What is the Preganglionic Transmitter?

A

ACh

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10
Q

III. Anatomy of PARA nervous system
5. What is the Preganglionic receptor?

A

nAChR (nicotinic)

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11
Q

III. Anatomy of PARA nervous system
6. What is the Postganglionic Axon Transmitter?

A

ACh
(Also VIP and NO)

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12
Q

III. Anatomy of PARA nervous system
7. What are Receptors of the effector cells?

A

1) mAChR (M1-M5)
2) M1,M3,M5 (IP3 & Ca2+)
3) M2,M4 (cAMP↓)

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13
Q

III. Anatomy of PARA nervous system
8. What are the 3 mechanisms of Elimination of Transmitters

A
  1. ACh esterase
  2. Reuptake of choline
  3. Diffusion
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14
Q

III. Anatomy of PARA nervous system
9. What are the 3 mechanisms of Modulating Transmitter Balance

A
  • Blocking transmitter release (ACh)
  • Blocking choline reuptake
  • Blocking ACh esterase
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15
Q

V. Muscarinic receptors
1. What are the 2 types of muscarinic receptors

A

1/ muscarinic receptors (M1, M3, M5)
have Gq-effects
2/ muscarinic receptors (M2, M4) affect Gi GPCRS

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16
Q

V. Muscarinic receptors
2. How do muscarinic receptors (M1, M3, M5) work?

A
  • Odd-numbered muscarinic receptors (M1, M3, M5)
    have Gq-effects
    -> M1, M3, M5 receptor activation leads to an activation of phospholipase C (PLC), which generates IP3 and diacylglycerol (DAG)
    -> IP3 releases stored [Ca2+]IC and DAG produces tissue-specific physiological actions
17
Q

V. Muscarinic receptors
2. How do muscarinic receptors (M2, M4) work?

A

Even-numbered muscarinic receptors (M2, M4) affect Gi GPCRS
-> Activation of Gi GPCR = inhibits adenylyl cyclase
-> decreasing [cAMP]

18
Q

VI. What are the PARA effects on heart:?

A
  • Within the heart, stimulation of the right vagus nerve leads to PARA effects of the SA node
    -> negative chronotropy (decreased HR)
  • Stimulation of the left vagus nerve effects the AV node
    -> negative dromotropy (slower AV node conductance) = can also decrease the HR
  • Unlike the SYM nervous system, there is not really PARA innervation of the ventricular muscle of the heart
    -> PARA effects do not include weaker muscle contraction
19
Q

VII. Effects of the Parasympathetic nervous system on Organs
1. What are PARA effect(s) on heart?

A
  • Receptor: M
  • Decreasing activity of SA node, heart rate, AV nodal conduction and Contractility (atria only!)
20
Q

VII. Effects of the Parasympathetic nervous system on Organs
2. What are PARA effect(s) on Vascular Smooth Muscle?

A

No parasympathetic innervation

21
Q

VII. Effects of the Parasympathetic nervous system on Organs
3. What are PARA effect(s) on Endothelium?

A

Action: releases EDRF
Receptor: M

*Note: The Endothelium-derived relaxing factor (EDRF) is a strong vasodilator produced by cardiac endothelial cells in response to stress signals

22
Q

VII. Effects of the Parasympathetic nervous system on Organs
3. What are PARA effect(s) on Bronchioles?

A

Action: Constricts
Receptor M

23
Q

VII. Effects of the Parasympathetic nervous system on Organs
4. What are PARA effect(s) on Smooth Muscle in GI tract?

A

Actions:
- Contraction of smooth muscle in walls
- Relaxation of smooth muscle in sphincters

Receptor: M

24
Q

VII. Effects of the Parasympathetic nervous system on Organs
5. What are PARA effect(s) on Circular sphincter muscle of iris?

A

Constrict pupils (miosis, M receptor)

25
Q

VIII. Pharmacology of PARA
1. Examples of direct Parasympathomimetic drugs (parasympathetic stimulation)

A
  • Direct
    1. Ach – short-lived
    2. muscarinic receptor agonist (pilocarpine)
26
Q

VIII. Pharmacology of PARA
2. Examples of indirect Parasympathomimetic drugs (parasympathetic stimulation)

A

Indirect „potentiating” effect:
- Inhibit acetylcholinesterase (neostigmine)
- Organophosphate poisoning
- pesticides: parathion, malathion; nerve gases: soman, sarin, novicsok

27
Q

VIII. Pharmacology of PARA
2. Examples of drugs that block cholinergic activity

A
  • Direct
  • competitive inhibitor of m-AchRs (atropine)