Introduction to Autonomic Pharmacology Flashcards
(19 cards)
Autonomic Division: Homeostasis
Rest-and-digest vs flight-or-flight
Rest-and-digest: parasympathetic activity dominates.
Fight-or-flight: sympathetic activity dominates
Autonomic vs somatic
Autonomic:
- CNS connected to periphery via two neurons arranged in series with peripheral ganglia
- Involuntary control of visceral organs
- Sympathetic and parasympathetic afferent and efferent nerves overlap
- Smooth muscle has intercellular bridges, so stimulating one can depolarise 100 others
Somatic:
- Single motor neuron connects CNS to periphery
- Voluntary control of skeletal muscle
- Nerves end in discrete motor-end-plates on muscle fibres
- Muscle fibres are depolarised discretely
Comparison of the 2 ANS systems
Preganglionic fibres
- Sympathetic - short
- parasympathetic - long
Postganglionic fibres
- symp -long
- para - short
Transmitter (at ganglia)
- symp - ACh
- para - ACh
Transmitter (at organs)
- symp - NA
- papa - ACh
Receptors
- symp - N at ganglia, alpha and beta at effectors (M, D)
- para - N at ganglia, M at effectors
Antagonistic control of ANS
Most internal organs are under antagonistic control, in which one autonomic branch is inhibitory and teh other is excitatory.
Exceptions - sweat glands and smooth muscle in most blood vessels
Autonomic activities - antagonistic regulation
heart (baroceptor reflex)
Para: decreased heart rate, decreased cardiac output
Symp: increased heart rate, increased cardiac output
Autonomic activities - antagonistic regulation
blood vessels
Para: no effect
Symp: Viscera, skin - constriction. Skeletal muscle - dilatation
Autonomic activities - antagonistic regulation
eye
Para: constricts pupil, adjusts for near vision
Symp: dilates pupil. adjusts for far vision
Autonomic activities - antagonistic regulation
stomach and intestine
Para: increased gastric acid secretion, gland secretion, motility and defecation
Symp: contracts sphincter, decreased motility and secretion
Autonomic activities - antagonistic regulation
liver
Para: increased bile secretion
Symp: decreased glycogenesis (glycogen synthesis), increased glucose production (glycogenolysis)
Autonomic activities - antagonistic regulation
urinary bladder
Para: relaxes spihncter, increases contraction of detrusor muscle, increased urination
Symp: constricts sphinceter, decreased relaxes detrusor, decreased urination
Autonomic activities - antagonistic regulation
male sex organs
Para: erection
Symp: Ejaculation
What is cholinergic?
Cholingernic: A neuron or axon capable of releasing the neurotransmitter, acetylcholine (ACh) when a nerve impulse passes
Which neurons are cholinergic?
- The entire parasympathetic system
- The preganglionic neurons of the sympathetic nervous system
- The postganglionic sympathetic neurons innervating sweat glands
- Somatic motor neurons
- The CNS
ACh
structual features, therapeutic use
- positively charged quaternary ammonium group
- ester group which has a partial negative charge and is easily hydrolysed
- ACh is virtually of no therapeutic use because it is very quickly hydrolysed, it is not selective for receptor subtypes
Where is ACh a neurotransmitter?
At all autonomic ganglia:
- released by preganglionic nerve endings, ACh stimulates neuronal nicotinic (NsubscriptN) receptors on the ganglionic neurons, and adrenal medulla
At autonomic postganglionic neurons:
- ACh is released from all parasymathetic nerve endings, and sympathetic nerve endings on sweat glands
- Following its release, ACh stimulates muscarinic (M) receptors on the innervated tissues (effectors)
At neuromuscular junctions:
- Following its release from somatic nerves, ACh stimulates muscle-type nicotinic (NsubscriptM) receptors on the motor end plates of skeletal muscles to cause muscle contraction
What is adrenergic?
a neuron or axon that releases noradrenaline at a synapse when a nerve impulse passes (most postganglionic sympathetic neurons)
Adrenergic neurotransmission
At sympathetic synapses:
- NA is the neurotransmitter released from most sympathetic postganglionic neurons
- Once released, it stimulates alpha1, and beta adrenoceptors on the effectors and alpha2 receptors on presynaptic terminals
Autonomic receptors
Cholinergic receptors
- respond to ACh
- nicotinic N
- NsubscriptM (neuromuscular junction)
- NsubscriptN (autonomic ganglia, adrenal medulla,
CNS)
- muscarinic M
- M1 (CNS, glands)
- M2 (heart and smooth muscle)
- M3 (smooth muscle and glands)
- M4 (nerve cells)
- M5 (CNS)
Adrenoceptors
- respond to catecholamines
- alpha-adrenoreceptors
- alpha1 (smooth muscle)
- alpha2 (presynaptic nerves)
- beta-adrenoreceptors
- beta1 (heart)
- beta2 (smooth muscle)
- beta3 (fat tissue, bladder)
Effects of adrenergic receptor types on organs
Blood vessels (arterioles)
- Coronary - constriction - alpha1
- Viscera, skin, brain - constriction - alpha1
- Skeletal muscle - vasodilation - beta2
Heart
- Sinoatrial node, atrioventricular node - increased rate - beta1
- Atrial and ventricular muscle - increased force - beta1
Liver and skeletal muscle - increased glycogenolysis - beta2
