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MindMap Gallery Introduction to Pharmacology of the Efferent Nervous System
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Introduction to Pharmacology of the Efferent Nervous System
Introduction to pharmacology of the efferent nervous system. Pharmacology content includes: 1. Nervous system 2. Efferent nervous system transmitters 3. Efferent nervous system receptors 4. Efferent nervous system receptor functions and their molecular mechanisms 5. Biological effects of efferent nerve receptors 6. Basic modes of action and classification of efferent nervous system drugs
Edited at 2023-07-29 11:17:36
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Introduction to Pharmacology of the Efferent Nervous System
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Introduction to Pharmacology of the Efferent Nervous System
1. Nervous system
Central Nervous System
peripheral nervous system
afferent nervous system
efferent nervous system
Classified by anatomy
Autonomic nervous system (vegetative sympathetic nervous system)
Innervates effectors such as internal organs, smooth muscles, and glands
parasympathetic nerve
Sympathetic nerve
motor nervous system
Motor nerves are not divided into preganglionic and postganglionic fibers, and can directly reach the skeletal muscles they control without changing their origin.
Classification by transmitter
cholinergic nerves
All sympathetic and parasympathetic preganglionic fibers
motor nerve
All parasympathetic postganglionic fibers
Very few sympathetic postganglionic fibers (nerves that control sweat gland secretion and skeletal muscle vasodilation)
noradrenergic nerves
Almost all sympathetic postganglionic fibers
dopaminergic nerve
Peripheral sympathetic postganglionic fibers innervating renal and mesenteric vessels
Release dopamine to relax renal blood vessels and mesenteric blood vessels
2. Efferent nervous system transmitters
AcetylcholineACh
characteristic
Transmitters of peripheral and central cholinergic nerves
The aqueous solution is unstable, difficult to penetrate the blood-brain barrier, and has low selectivity.
synthesis
parts
cholinergic nerve endings
raw material
Choline, acetyl-CoA
condition
Catalyzed by choline acetyltransferase
store
Vesicles (stored with ATP and vesicle proteins)
freed
Nerve impulse → Nerve membrane depolarization → Ca ion influx → vesicle advancement → ACh cell cleavage efflux → binding to choline receptors → effect
metabolism
Hydrolyzed by acetate cholinesterase AChE into acetic acid and choline
Norepinephrine NA
synthesis
parts
noradrenergic nerve endings
raw material
Tyrosine
condition
Catalyzed by tyrosine hydroxylase, dopa decarboxylase, dopamine β-hydroxylase
process
Tyrosine → Dopa → Dopamine DA → Norepinephrine NA
store
Stored in vesicles bound to ATP and chromogranin
freed
Nerve impulse → Nerve membrane depolarization → Ga ion influx → vesicle advancement → NA cell cleavage efflux → binding receptor → effect
metabolism
uptake mechanism
Ingest 1
Active transport, amine pump provides energy
75%-90% is taken up by the presynaptic membrane and stored in vesicles
Ingest 2
Post-synaptic membrane uptake 10%-15% (taken up and destroyed by non-nervous tissues (myocardium, smooth muscle, etc.))
Enzyme catalysis
Diffuses into the blood 5%, and is destroyed and inactivated by catechol oxygen methyltransferase COMT and monoamine oxidase MAO
3. Efferent nervous system receptors
choline receptor
M receptors (M cholinergic receptors, muscarinic receptors)
Sensitive to muscarine
It is a G protein-coupled receptor, an effector distributed in the postganglionic fibers of cholinergic ganglia.
effector
myocardium
Heart rate, myocardial contractility↑→cardiac output↓→blood pressure↓
smooth muscle
pupillary sphincter contraction → miosis
Ciliary muscle contraction → myopia
Bronchoconstriction→Ventilation↓, dyspnea
Gastrointestinal smooth muscle contraction→peristalsis↑
Bladder detrusor contraction → urination ↑
Vascular smooth muscle (less distribution) → relaxation
glands
Secretion↑
Classification
M1
Gastric parietal cells, peripheral neurons, central nervous system CNS (cerebral cortex, hippocampus, striatum, etc.), glands
Also known as: "neural wall" receptor; specific blocker: pirenzepine
M2
myocardium, presynaptic membrane
Also known as: "neurocardiac" receptor; specific blocker: galiodonium
M3
Glands, smooth muscle, vascular endothelium, pupillary sphincter, ciliary muscle
Also known as: "smooth muscle-glandular" receptor; specific blocker: HHSD
M4
Eyes (retina, etc.), central nervous system CNS
Also known as: "eye" receptor
M5
CNS and peripheral nervous tissue, cardiac smooth muscle and various glands
N receptors (N cholinergic receptors, nicotinic receptors)
Sensitive to nicotine, an ion channel-coupled receptor
It is a ligand-gated cation channel receptor; after the N receptor binds to ACh, its structure changes, the channel opens, and sodium ions and calcium ions enter the cell. Local depolarization, causing sodium channels to open and triggering action potentials
Classification
Ganglionic synaptic N receptor: Nn receptor (N1)
distributed
sympathetic ganglion
Sympathetic nervous excitement
parasympathetic ganglion
parasympathetic nervous system
adrenal medulla
secrete adrenaline
Neuromuscular junction N receptor: Nm receptor (N2)
distributed
Neuromuscular junction (skeletal muscle cell motor end plate, skeletal muscle membrane)
Excitation → extracellular calcium influx and intracellular calcium release → skeletal muscle contraction
adrenergic receptors
G protein-coupled receptors that bind norepinephrine and epinephrine, etc.
Classification
alpha receptor
α1 (post-synaptic membrane receptor)
distributed
Skin, mucous membranes, visceral vascular smooth muscle
Vasoconstriction, blood pressure ↑
pupillary dilator muscle
dilate pupils
heart, liver, kidneys and brain
Gastrointestinal and bladder sphincters
sphincter contraction
Sweat glands and salivary glands on hands and feet (small distribution)
glandular secretion
drug
Agonists: phenylephrine, methoxyamine (bright)
Blocker: Prazosin
α2 (presynaptic membrane receptor)
distributed
Presynaptic membrane of noradrenergic and cholinergic nerve terminals
Negative feedback regulates the release (inhibition) of norepinephrine NA, acetylcholine and other transmitters
Also present in liver cells, platelets, adipocytes, vascular smooth muscle postsynaptic membrane, brain
drug
Agonist: clonidine
Blocker: Yohimbine
beta receptor
β1
Mainly distributed in the heart (accounting for 80% of total cardiac receptors)
Activation → cardiac excitement → cardiac output ↑ → blood pressure ↑
juxtaglomerular cells
Excitement → renin release
β2
Mainly distributed on bronchial and vascular smooth muscle cells
Bronchial smooth muscle → relax
Gastrointestinal smooth muscle, bladder detrusor → relaxation
Skeletal muscle blood vessels, coronary blood vessels → diastole
Skeletal muscle →contraction
Liver, heart (20% beta2)
presynaptic membrane
Positive feedback regulates the release (promotion) of neurotransmitters such as NA
β3
Distributed in fat cells → promote lipolysis
dopamine receptor
D receptor
D1
distributed
Juxtaglomerular cells, proximal small organs, distal tubules, cortical collecting ducts, gastrointestinal tract, and mesenteric arteries
Excitement → causes vasodilation
D2 (widely distributed in the brain)
distributed
Dopaminergic neuron cell body-dendritic terminal
postsynaptic nondopaminergic neuron
On non-dopaminergic neurons that have no synaptic connections with dopaminergic neurons
presynaptic receptor
Mainly regulates transmitter release from nerve terminals
4. Efferent nervous system receptor functions and their molecular mechanisms
Receptor-ion channel coupling
N receptors: coordination-gated ion channel-type receptors
Can be activated by neurotransmitters or agonists to open ion channels to produce effects
Nm receptor (on the skeletal muscle cell membrane at the neuromuscular junction)
ACh binds to Nm receptor → channel opens → sodium ions and calcium ions flow in → generates end plate potential
Exceeds the threshold → voltage-dependent ion channels on the cell membrane are opened → generates action potential → massive release of intracellular calcium ions → stimulates excitation-contraction coupling → muscle contraction
Nn receptors (on ganglia and adrenergic medulla)
Activated by ACh → depolarization of postganglionic neurons and medulla → release of epinephrine
receptor-enzyme coupling
M, α, and β receptors are all G protein-coupled receptors. After being activated by neurotransmitters or agonists, they trigger the signaling pathway through adenylyl cyclase and phospholipase C to produce effects.
Receptor-adenylate cyclase coupling
β-receptor activation→increased AC activity through Gs protein→↑cAMP levels→cAMP-dependent protein kinase phosphorylates specific protein substrates→effect
α2 receptor activation → inhibits AC activity through Gi protein → ↓ intracellular cAMP → plays a role and inhibits voltage-dependent calcium channels and opens potassium channels
M2 receptor activation → inhibits AC through Gi protein → ↓cAMP → activates potassium channels and inhibits voltage-dependent calcium channels → inhibits cardiac function
Receptor-phospholipase C (PLC) coupling
After Gq protein activates PLC, it can catalyze the hydrolysis of 4,5-bisphosphoinositide (PIP2) into 1,4,5-trisphosphate inositol (IP3) and diacylglycerol (DAG), two messenger molecules, and then produce a series of effects
After M1 or M3 receptors are activated:
IP3 induces intra-cell calcium release from the endoplasmic reticulum (calcium-induced calcium release: CICR) →↑ intra-cell calcium ion concentration
DAG activates downstream protein kinase C (PKC)
After α1 receptor activation: the mechanism is the same as M receptor
5. Biological effects of efferent nerve receptors
cholinergic receptor effects
M receptor
Mainly distributed in effector cells innervated by parasympathetic postganglionic fibers. The effect produced by stimulation of this receptor is called: M-like effect
effect
cardiovascular function depression
Stimulates the presynaptic membrane M1 of sympathetic nerve terminals, inhibits the release of NA from noradrenergic nerves, and indirectly participates in the vasodilatory and cardiac inhibitory effects of ACh.
Excites heart M2 → produces negative muscle force, negative frequency, and negative conduction
Stimulates M3 in vascular endothelial cells → ↑ NO synthesis and release → stimulates vascular smooth muscle to synthesize cGMP → vascular smooth muscle relaxation → vasodilation
Smooth muscle contraction (M3)
Excites the smooth muscles of the gastrointestinal tract, bronchus, uterus and other areas, and enhances contraction
Excites urinary tract smooth muscles: detrusor contraction, urethral sphincter relaxation
pupillary sphincter (M3) and ciliary muscle contraction (M3, β2)
Pupil constriction, adjusting to myopia
Promote glandular secretion (M3)
Increased secretion of salivary glands, sweat glands, lacrimal glands, digestive tract glands, and respiratory tract glands
N receptor
Mainly distributed in the postsynaptic membrane of autonomic ganglion neurons and the motor endplate membrane of neuromuscular junctions. The effect produced by the stimulation of this receptor is called: N-like effect
effect
High-dose ACh stimulates ganglion N1 receptors, and simultaneously stimulates postganglionic cholinergic nerves and noradrenergic nerves, but has a dominant neural determinant effect.
Gastrointestinal tract, bladder, glands – cholinergic innervation predominates
Myocardium, small blood vessels - noradrenergic nerves dominate
ACh stimulates the N1 receptor of adrenal medulla chromaffin cells - releasing epinephrine
ACh stimulates N2 receptors on the motor endplate - diffuse skeletal muscle contraction and muscle spasm
adrenergic receptor effects
The transmitter released by most sympathetic postganglionic fibers is NA, which has both excitatory and inhibitory effects on effectors. The main mechanism of different effects is the different receptors on effector cells.
alpha receptor
α1
Distributed in postsynaptic membranes such as vascular smooth muscle, heart, liver, pupillary dilator muscle, gastrointestinal tract, bladder sphincter, etc.
excited
Vascular smooth muscle, uterine smooth muscle, pupillary dilator muscle, bladder sphincter, gastrointestinal sphincter contraction
Gastrointestinal smooth muscle relaxation, ciliary muscle relaxation
α2
Distribution: presynaptic membrane of noradrenergic nerve terminals, postsynaptic membrane of blood vessels
excited
Negative feedback regulates NA release and indirectly affects effector responses
beta receptor
Acting when excited
Smooth muscle relaxation
Vasodilation, uterine relaxation, gastrointestinal smooth muscle relaxation, bronchial smooth muscle relaxation
myocardial contraction
β1
Main distribution: heart
excited → contraction
β2
Main distribution: bronchus, gastrointestinal tract, uterus, vascular smooth muscle
excited → relaxed
β3
Main distribution: adipocytes
Excitement → Promote fat metabolism
Replenish
Myocardial cells have alpha receptors and beta receptors, but beta receptors are stronger
α1 receptor stimulation → strengthened contraction force, but weaker than β1 receptor
Excitation of β1 receptors → increases heart rate, but not α1 receptors
6. Basic modes of action and classification of efferent nervous system drugs
act directly on receptors
Drugs can bind directly to cholinergic receptors or adrenergic receptors
Two functions
Agitation (mimetics or agonists)
Produces the same effect as that of nerve terminal transmitters
Antagonist (blocker or antagonist)
It produces no effect or less effect after binding, and can prevent the transmitter from binding to the receptor and produce the opposite effect to the transmitter.
influence transmitter
Affect transmitter synthesis
Alpha-methyltyrosine inhibits tyrosine hydroxylase and prevents the conversion of tyrosine to dopa
Carbidopa and benserazide inhibit peripheral dopa decarboxylase and prevent dopa from forming dopamine. They can be used as auxiliary drugs in combination with levodopa to treat Parkinson's disease.
Affects transmitter storage
Reserpine inhibits the uptake of norepinephrine by norepinephrine nerve terminal vesicles and exerts an antagonizing effect on norepinephrine nerves.
Affects transmitter release
Ephedrine and metahydroxylamine promote NA release; carbachol promotes ACh release
Guanetidine and benzyl bromide can stabilize the cell membrane of noradrenergic nerve terminals and reduce the release of NA
Affects transmitter metabolism and reuptake
Cholinesterase inhibitors can interfere with the metabolism of ACh in the body (neostigmine, organophosphates inhibit the degradation of ACh)
Desipramine, an inhibitor of cocaine ingestion
Tricyclic antidepressants are non-selective monoamine uptake inhibitors that block the reuptake of NA transmitters.
Drug Classification
Mimic drugs (agonists)
choline receptor agonists
M, N receptors: carbachol
M receptor: pilocarpine
N receptor: nicotine
cholinesterase inhibitors
neostigmine
adrenoceptor agonists
Alpha and beta receptors: adrenaline
Alpha receptor: norepinephrine
β1, β2 receptors: isoproterenol
β1 receptor: dobutamine
β2 receptor: albuterol
Antagonist
Choline receptor blockers
M receptor: atropine
N1 receptor: mecamylamine
N2 receptor: tubocurarine
cholinesterase reactivating drugs
pralidoxime chloride
adrenoceptor blocking drugs
α1, α2 receptors: phentolamine
Alpha 1 receptor: Prazosin
β1, β2 receptors: propranolol
β1 receptor: atenolol
Alpha, beta receptors: labetalol