1.10A. Parasympathetic efferent mechanisms. Flashcards
I. Basics
1. What are divisions of autonomic nervous system?
the sympathetic (SYM) and parasympathetic (PARA) nervous systems
I. Basics
2. What is the main function of the autonomic nervous system (ANS)
To maintain a constant internal environment (homeostasis).
-> ANS unconsciously receives sensory inputs and sends signals to effectors.
I. Basics
3. What are the effectors of the autonomic nervous system (ANS)
smooth muscle, cardiac muscle, and glands.
II. PARA nervous system
1. What are the characteristics of parasympathetic nervous system?
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
II. PARA nervous system
2. What are PARA cranial nerve nuclei?
Accessory, Oculomotor, Superior inferior salivatory nuclei, Dorsal vagal nucleus, Nucleus ambiguous
III. Anatomy of PARA nervous system
1. Origin of PARA nervous system
CRANIAL - CN (III, VII, IX, X)
Sacral
Spinal Cord S2-S4
III. Anatomy of PARA nervous system
2. Ganglion of PARA nervous system
Near or within organ
III. Anatomy of PARA nervous system
3. Size of Preganglionic and Postganglionic axons
Pre - Long
Post - short
III. Anatomy of PARA nervous system
4. What is the Preganglionic Transmitter?
ACh
III. Anatomy of PARA nervous system
5. What is the Preganglionic receptor?
nAChR (nicotinic)
III. Anatomy of PARA nervous system
6. What is the Postganglionic Axon Transmitter?
ACh
(Also VIP and NO)
III. Anatomy of PARA nervous system
7. What are Receptors of the effector cells?
1) mAChR (M1-M5)
2) M1,M3,M5 (IP3 & Ca2+)
3) M2,M4 (cAMP↓)
III. Anatomy of PARA nervous system
8. What are the 3 mechanisms of Elimination of Transmitters
- ACh esterase
- Reuptake of choline
- Diffusion
III. Anatomy of PARA nervous system
9. What are the 3 mechanisms of Modulating Transmitter Balance
- Blocking transmitter release (ACh)
- Blocking choline reuptake
- Blocking ACh esterase
V. Muscarinic receptors
1. What are the 2 types of muscarinic receptors
1/ muscarinic receptors (M1, M3, M5)
have Gq-effects
2/ muscarinic receptors (M2, M4) affect Gi GPCRS
V. Muscarinic receptors
2. How do muscarinic receptors (M1, M3, M5) work?
- 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
V. Muscarinic receptors
2. How do muscarinic receptors (M2, M4) work?
Even-numbered muscarinic receptors (M2, M4) affect Gi GPCRS
-> Activation of Gi GPCR = inhibits adenylyl cyclase
-> decreasing [cAMP]
VI. What are the PARA effects on heart:?
- 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
VII. Effects of the Parasympathetic nervous system on Organs
1. What are PARA effect(s) on heart?
- Receptor: M
- Decreasing activity of SA node, heart rate, AV nodal conduction and Contractility (atria only!)
VII. Effects of the Parasympathetic nervous system on Organs
2. What are PARA effect(s) on Vascular Smooth Muscle?
No parasympathetic innervation
VII. Effects of the Parasympathetic nervous system on Organs
3. What are PARA effect(s) on Endothelium?
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
VII. Effects of the Parasympathetic nervous system on Organs
3. What are PARA effect(s) on Bronchioles?
Action: Constricts
Receptor M
VII. Effects of the Parasympathetic nervous system on Organs
4. What are PARA effect(s) on Smooth Muscle in GI tract?
Actions:
- Contraction of smooth muscle in walls
- Relaxation of smooth muscle in sphincters
Receptor: M
VII. Effects of the Parasympathetic nervous system on Organs
5. What are PARA effect(s) on Circular sphincter muscle of iris?
Constrict pupils (miosis, M receptor)
VIII. Pharmacology of PARA
1. Examples of direct Parasympathomimetic drugs (parasympathetic stimulation)
- Direct
1. Ach – short-lived
2. muscarinic receptor agonist (pilocarpine)
VIII. Pharmacology of PARA
2. Examples of indirect Parasympathomimetic drugs (parasympathetic stimulation)
Indirect „potentiating” effect:
- Inhibit acetylcholinesterase (neostigmine)
- Organophosphate poisoning
- pesticides: parathion, malathion; nerve gases: soman, sarin, novicsok
VIII. Pharmacology of PARA
2. Examples of drugs that block cholinergic activity
- Direct
- competitive inhibitor of m-AchRs (atropine)
