Session 8.2: ANS: Neurotransmitters in the ANS Flashcards
what is the basic neurochemistry of ANS
neurones communicate at ganglia where a neurotransmitter is released which is received by post ganglionic neurone which in turn releases signal at neuromuscular junction
what are the principle neurotransmitters within ANS
ACh (acetylcholine), NA (noradrenaline/norepinerphrine)
what is the preganglionic transmitter
acetylcholine, as they are cholinergic neurons (from both parasympathetic and sympathetic)
what does the release of ACh cause in preganglionic fibre
binds to nicotinic ACh receptor and causes activation of post ganglionic nicotinic ACh receptors post ganglionic neurone
what are nicotinic acetylcholine receptors and what is their role
ligand gated ion channels and cause depolarisation of cell body of post ganglionic neurone
how do action potentials pass along the sympathetic NS
depolarisation begins in cell body of sympathetic NS -> action potential causing release of ACh which is received by the nicotinic receptor, causes cell body of post ganglionic fibre to depolarise -> action potential arrives at neuroeffector junction
what is the parasympathetic postganglionic transmitter
ACh (cholinergic)
what does the release of ACh cause in postganglionic fibre of parasympathetic neurons
ACh acts on muscarinic ACh receptors in target tissue
what are muscarinic ACh receptors
G protein coupled receptors
what is the sympathetic postganglionic transmitter
noradrenaline (noradrenergic) or adrenaline (cholinergic)
what does the release of noradrenaline cause in postganglionic fibre of the sympathetic neurons
interacts with alpha -adrenoreceptors or beta-adrenoreceptors
which can be divided into a1, a1, b1, b2, b3 subtypes
what are adrenoreceptors
G protein coupled receptors
what does the release of adrealine cause in postganglionic fibre of the sympathetic neurons
act at muscarinic ACh receptors - those innervating sweat glands and hair follicles - causes piloerection
what other transmitters are released in ANS when activated
either non-adrenergic or non-cholinergic
eg: ATP, NO, serotinin, neuropeptides
what is the somatic efferent system
cell body in CNS -> single axon -> -> ACh -> nicotinic receptors in skeletal muscle
what is the parasympathetic nervous system
two neurones in series. ACh released at ganglia to act on nicotinic receptors and ACh released in post ganglionic fibre to act on muscarinic, acting on salivary glands etc
what is the sympathetic nervous system
- release ACh preganglionically, binds to nicotinic receptor, release of noradrenaline at post ganglionic junction to adrenoreceptors which affect blood vessels.
- release ACh preganglionically, binds to nicotinic receptor, release of ACh which binds to muscarinic receptors, which affects sweat glands
- hormonal release of adrenaline fromadrenal medulla
how does hormonal release occur in sympathetic nervous system
some postganglionic neurons innervate cells within adrenal gland:
in the adrenal medulla there are chromaffin cells which are like post ganglionic neurons. they contain nicotinic ACh receptors which depolarize the chromaffin cells, which release adrenaline into blood stream, rather than target tissue
what are the physiological consequences of parasympathetic stimulation in the heart
release of ACh which causes:
SA node contains M2 - bradycardia
AV node - Reduced cardiac conduction velocity
what are the physiological consequences of parasympathetic stimulation in the smooth muscle
release of ACh which causes:
bronchiole/bronchi to contract in lungs, at M3
increased intestinal mobility/secretion in GI tract
bladder contraction (detrusor) and relaxation (trigone/sphincter) in GU tract
penile erection in GU tract
cillary muscle and iris sphincter contraction in eye
what are the physiological consequences of parasympathetic stimulation in the glands
releasse of ACh causes:
increased sweat/salivary/lacrimal secretion - at M1/M3
how is NO used
NO is generated locally, caused by parasympathetic release of ACH, which causes localised vasodilation in penis to cause erection
what are the physiological consequences of sympathetic stimulation in the heart
release of noradrenaline causes:
SA node - tachycardia (positive chonotropy)
venticles - positive inotropy
all at beta 1 adrenoreceptors
what are the physiological consequences of sympathetic stimulation in the smooth muscle
release of noradrenaline:
arteriolar contraction/venous contraction (arteriolar relaxation in some vascular beds) - vasoculature - alpha 1 adrenoreceptor = contraction and beta 2 adrenoreceptots = relaxation
bronciolar/intestine/uterine relaxation - lungs, GI, GU tract at beta 2 adrenoreceptor
bladder sphincter contraction - GU tract
radial muscle contraction - eye
what are the physiological consequences of sympathetic stimulation in the glands
release of noradrenaline:
increased secretion - salivary
what are the physiological consequences of sympathetic stimulation in the kidney
renin release
why do different tissues contain different adrenoreceptor
to coordinate appropriate responses to autonomic control in correct tissues
increase sympathetic activity results in release of adrenaline/noradrenaline to cause
positive chronotropic and inotropic effects in heart -beta 1 adrenoreceptors
vasoconstriction of most blood vessels to digestion - alpha 1 adrenoreceptors
vasodilation of blood vessels to exercising muscles and airways - beta 2 adrenoreceptors
