Introduction to the ANS Flashcards
Principal target organs of the sympathetic nervous system
- pupil dilation
- thick, viscous secretion from salivary glands
- piloerection
- glycogenolysis and gluconeogenesis in liver
- lipolysis in adipose tissue
- detrusor muscle relaxation, constriction of trigone and sphincter (ureters and bladder)
- vasoconstriction for skin, mucous membranes and splanchnic area
- vasodilation for skeletal muscle
- increase heart rate and contractility
- increased renin secretion from kidneys
- increased gastrointestinal motility and tone, sphincter contraction
- bronchodilation
Principal target organs of the parasympathetic nervous system
- pupil constriction
- ciliary muscle contraction
- copious, watery secretion from salivary glands
- decreased heart rate and contractility
- increased gastrointestinal motility and tone, increased secretions
- detrusor muscle contraction, relaxation of trigone and sphincter (ureters and bladder)
- bronchoconstriction
Autonomic nervous system
- exocrine glands
- smooth muscle
- cardiac muscle
- metabolism
- host defence
- split into sympathetic and parasympathetic nervous system
Somatic nervous system
-skeletal muscle (including the diaphragm and respiratory muscle)
Neuroendocrine system
- growth
- metabolism
- reproduction
- development
- salt and water balance
- host defence
Sympathetic nervous system (autonomic)
‘fight and flight’
Parasympathetic nervous system (autonomic)
‘rest and digest’
-linked to secretions
Enteric nervous system
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Nicotinic receptors
- found in all autonomic ganglia
- type 1 receptor (ion channel-linked)
- stimulated by nicotine/acetylcholine
- transfer stimulus from pre-ganglionic to post-ganglionic
- VERY FAST
Muscarinic receptors
- found at all effector organs innervated by post-ganglionic parasympathetic fibres
- stimulated by muscarine/acetylcholine
- type 2 receptor (G-protein coupled)
- SLOWER
Sub-types of muscarinic cholinoceptors
- M1: neural
- M2: cardiac
- M3: exocrine and smooth muscle
- M4: periphery=prejunctional nerve endings
- M5: striatal dopamine release
Adrenoceptors
- stimulated by noradrenaline/adrenaline
- type 2 receptors (G-protein-coupled)
- four adrenoceptor subtypes (alpha 1, alpha 2, beta 1 and beta 2)
Biosynthesis of acetylcholine
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Release of acetylcholine
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Metabolism of acetylcholine
Acetylcholinesterase breaks down acetylcholine in synapse to give choline and acetate which reenters presynaptic neurone
-contact with enzyme leads to rapid breakdown
Biosynthesis of noradrenaline/adrenaline
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Release of noradrenaline/adrenaline
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Metabolism of noradrenaline/adrenaline
- No enzyme in synapse so noradrenaline is not broken down in the synapse
- Uptake 1 protein remove noradrenaline back into neuronal tissue
- Uptake 2 protein remove noradrenaline into extra-neuronal tissue
- slower removal by uptake proteins so noradrenaline has long lasting effect
- MAO-A present in neuronal tissue-> breaks down noradrenaline after removal from synapse by uptake 1
- COMT present in extra-neuronal tissue-> breaks down noradrenaline after removal from synapse by uptake 2
Parasympathetic nerves
- Originate in cranial/sacral region of the spinal cord
- Long preganglionic fibre usually projecting to tissue with short postganglionic fibre
- ACh always neurotransmitter
Sympathetic nerves
- Originate in thoracic/lumbar region of the spinal cord
- Short preganglionic fibre and long postganglionic fibre
- Main sympathetic nerve arrangement has ACh between pre and postganglionic fibres and noradrenaline at the effector organ
- Rare sympathetic nerve arrangement has ACh being released at the effector organ (sweat secretion)
Adrenal medulla
- Only peripheral tissue innervated by one autonomic nerve releasing ACh
- Adrenal medulla releases adrenaline and noradrenaline via the bloodstream (80%:20%)
