ANS Pharmacology Path physiology Disease State Management Medicinal Chemistry Therapeutics PREPARED BY ANIRUDH JOSHI ASST PROFFESOR BRNCOP MANDSAUR Organization of The Nervous System Central Nervous System ID: 632261
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Slide1
Why Study the Autonomic Nervous System?
ANS
Pharmacology
Path physiology
Disease State
Management
Medicinal
Chemistry
Therapeutics
PREPARED BY ANIRUDH JOSHI
ASST PROFFESOR
BRNCOP
MANDSAURSlide2
Organization of The Nervous System
Central Nervous System
Peripheral Nervous System
Autonomic Nervous System
Sympathetic
ParasympatheticSlide3
ANS
How do we define neuron types in the ANS?
Parasympathetic
Sympathetic
Acetylcholine
Muscarine
Nicotine
Norepinephrine
(
Noradrenaline
)
Epinephrine
(Adrenaline)Slide4
ANS
Action Potential
Na
+
Ca
2+
a
a
b
ACH
Acetylcholinesterase
Na
+
Parasympathetic Ganglionic Synapse
Preganglionic neuron
Nicotinic
ReceptorSlide5
Sympathetic Organ Synapse
ANS
Action Potential
Ca
2+
Na
+
NE
Sympathetic Organ
Synapse
G
Postganglionic neuronSlide6
Summary of sympathetic neurons and synapses
Preganglionic
neuronsShort
Synapse with postganglionic neurons near spinal cordRelease acetylcholine (ACH) to activate nicotinic receptors on postganglionic neurons
Postganglionic neuronsLong
Synapse on the target organRelease norepinephrine to activate adrenergic receptors on target organsSlide7
Exceptions in the sympathetic nervous system:
Sweat glands:
Postganglionic neurons involved with stress-related excretion release norepinephrine (“sweaty palms”)Postganglionic neurons involved with thermoregulation release
acetylcholineSlide8
Exceptions in the sympathetic nervous system
Kidneys:
Postganglionic neurons to the smooth muscle of the renal vascular bed release dopamineAdrenal gland:
Preganglionic neurons do not synapse in the paraverterbral sympathetic ganglion
Preganglionic neurons synapse directly on the adrenal gland, release acetylcholine, and activate nicotinic receptors on the adrenal gland
Adrenal glands release epinephrine into systemic circulation
Most postganglionic sympathetic
neurons release what
neurotransmitter?Slide9
How do drugs influence the ANS?
Mimic or block the effects of the two primary neurotransmitters, Acetylcholine and
Norepinephrine/EpinephrineDrugs that
mimic neurotransmitters are referred to as “receptor agonists”
These drugs activate receptors
Drugs that block neurotransmitters are referred to as “receptor antagonists
”These drugs block the endogenous neurotransmitters
from activating receptorsSlide10
Classification of drugs affecting the ANS
Parasympathetic nervous system
Mimic acetylcholine = cholinergic =
muscarinic agonists = parasympathomimetic
Block acetylcholine = anticholinergic
= muscarinic antagonist = parasympatholytic
Sympathetic nervous system
Mimic
norepinephrine = adrenergic = adrenergic agonist = sympathomimetic
Block norepinephrine =
antiadrenergic = adrenergic antagonist = sympatholyticSlide11
SYNAPSES AND DRUGS
PREPARED
BY ANIRUDH JOSHI ASST PROFFESOR BRNCOP
MANDSAURSlide12
What is a synapse?
A synapse is the junction between 2 neurones.
There is a very narrow gap of about 20nm between neurones called the synaptic cleft.An action potential cannot cross the synaptic cleft, so nerve impulses are carried by chemicals called neurotransmitters.Slide13
A Synapse
Pre-synaptic neurone = neurone sending impulse
Post-synaptic neurone = neurone receiving impulseSlide14
Neurotransmitter is made by the pre-synaptic neurone
and is stored in synaptic vessels at the end of the axon.The membrane of the post-synaptic neurone has chemical-gated ion channels called
neuroreceptors. These have specific binding sites for neurotransmitters.NeurotransmitterSlide15
Acetylcholine is a common transmitter.
Synapses that have acetylcholine transmitter are called cholinergic synapses.Some neurones form more than 1 synapse.
This is an electron micrograph of synapses between nerve fibres and a neurone cell body.
Cholinergic SynapsesSlide16
What happens at a cholinergic synapse? Stage 1
An action potential arrives at presynaptic membrane. Voltage gated calcium channels in the presynaptic membrane open, calcium ions enter the presynaptic neurone.Slide17
What happens at a cholinergic synapse? Stage 2
Calcium ions cause synaptic vesicles to fuse with the presynaptic membrane, releasing acetylcholine into the synaptic cleft.Slide18
What happens at a cholinergic synapse? Stage 3
Acetylcholine diffuses cross the synaptic cleft and binds to specific neuroreceptor sites in the post synaptic membrane.Slide19
What happens at a cholinergic synapse? Stage 4
Sodium channels open. Sodium ions diffuse into the postsynaptic membrane causing depolarisation, which may initiate an action potential.Slide20
What happens at a cholinergic synapse? Stage 5
Acetylcholinesterase breaks down acetylcholine. The products diffuse back into the presynaptic neurone where acetycholine is resynthesised using ATP from the mitochondria.Slide21
Neuromuscular Junctions
Same stages as cholinergic synapses, but in this case the postsynaptic membrane is the muscle fibre membrane, (Sarcolemma). Depolarisation of the sarcolemma leads to contraction of muscle fibre.Slide22
Drugs
Drugs which have molecules of similar shape to transmitter substances can affect protein receptors in postsynaptic membranes.Drugs that stimulate a nervous system are called AGONISTS
Drugs that inhibit a nervous system are called ANTAGONISTS.Slide23
Various effects of drugs on synapses:
DRUG ACTION
EFFECT
Mimic a neurotransmitter
Switch on a synapse
Stimulate the release of a neurotransmitter
Switch on a synapse
Open a neuroreceptor channel
Switch on a synapse
Block a neuroreceptor channel
Switch off a synapse
Inhibit the breakdown enzyme
Switch on a synapse
Inhibit the Na
+
K
+
ATPase pump
Stop action potentials
Block the Na
+
or K
+
channels
Stop action potentials
Slide24
Effect of nicotine and atropineSlide25
A synapse is the point where 2 nerve cells meet. Tiny gap = synaptic cleft.
Chemical transmitter released from presynaptic neurone diffuses across synaptic cleft & fits into receptors on postsynaptic membrane. May cause postsynaptic neurone to depolarise & set up action potential.Neuromuscular junction = motor neurone connects with muscle fibre – similar to a synapse.
Many drugs affect synapses.Summary