PT2: Pharmacology of Autonomic Nervous System Flashcards
what is the function of the autonomic nervous system
contraction and relaxation of smooth muscle in blood vessels and organs
regulation of glandular secretion (exocrine and some endocrine)
control of heart rate
metabolism
what organs have both sympathetic and parasympathetic action
smooth muscle of gut and bladder
heart
airways
what organs only have sympathetic action
sweat glands
blood vessels
what organs only have parasympathetic action
ciliary muscles of the eye
what are the two neuron types involved in sympathetic and parasympathetic action
pre- and post-ganglionic
what are the features of a preganglionic neuron
cell body in the CNS, small diameter and myelinated, synapses at autonomic ganglia, preganglionic fibres release ACh which acts on nicotinic receptors in the post-synaptic neuron
what neurotransmitter do preganglionic fibres release
ACh
which receptors does ACh act on
nicotinic
what are the features of a postganglionic neurone
cell body in autonomic ganglion, small diameter and unmyelinated, synapse close to target organ
what are the is considered to be a specialised ganglion
adrenal medulla
what are considered to be specialised post-synaptic neurons
chromaffin cells
what is the primary transmitter between pre- and post-ganglionic neurons
ACh
what ganglion type do most actions occur via
nicotinic ACh receptors
nAChR
what are the three classes of nicotinic receptors
muscle, neuronal (CNS), neuronal (autonomic ganglion)
what are nicotinic receptors
ligand gated ion channels that generate a fast excitory post synaptic potential
most ganglia are innervated by several preganglionic nerve fibres - simultaneous firing required to generate action potential
what are the features of nicotinic receptors in autonomic ganglia
ligand gated ion channel, containing alpha3 subunit, cation channel (NA+ in, K+ out; fast EPSP)
when threshold potential is reached an action potential is generated in post-ganglionic cell
via what receptors does primary ganglionic signalling occur
ACh acting on nicotinic receptors
how do M1 muscarinic receptors on post-synaptic bodies modulate signal
K+ channels closing, slow excitatory PSP (epsp)
how do M2 muscarinic receptors on post-synaptic bodies modulate signal
increased K+ conductance, hyperpolarisation, slow inhibitory PSP (ipsp)
what is released from preganglionic fibres during transmission
neuropeptide co-transmittors
late slow EPSP
what are the physiological consequences of nicotinic receptor stimulation (periphery)
stimulation of voluntary muscle (somatic system)
stimulation of autonomic ganglia (sympathetic and parasympathetic)
secretion of adrenaline from the adrenal medulla
what neurotransmitter do most postsynaptic sympathetic fibres release
noreadrenaline
exceptions are sweat glands (ACh) and renal vessels (dopamine)
what neurotransmitter do postsynaptic parasympathetic fibres release
ACh (to act on muscarinic receptors)
what is the sensory nerve pathway in the airway
vagal sensory afferent nerve -> CNS -> vagal afferent nerve -> airway smooth muscle -> airway constriction
what is the pathway of cholinergic signalling
parasympathetic nerve -> (airway) ACh -> M3, Gq and PLS receptors on airway smooth muscle, causing contraction
what inhibits neuronal ACh release
M2 receptor feedback
M2 receptor on parasympathetic nerve
what neurotransmitter do most postsynaptic fibres release
noreadrenaline
what is the function of noreadrenaline
synthesised, stores and released from sympathetic nerves
very sparse sympathetic innervation of the airways and sympathetic control via circulating adrenaline (from adrenals)
how selective are adrenoreceptors
relatively unselective (similar affinity) for two endogenous adrenergic neurotransmitters (adrenaline and noreadrenaline)
what receptors do noreadrenaline and adrenaline activate
both alpha and beta adrenoreceptors
adrenaline more potent at b2 and a2
noreadrenaline more potent at a1 and b1
what is the function of the a1 adrenoreceptor
constrict smooth muscle (except in GI where it relaxes)
what is the function of the a2 adrenoreceptor
presynaptic inhibition of neurotransmitter release (sympathetic and parasympathetic neurones)
what is the function of the b1 adrenoreceptor
increases heart rate and force of constriction
what is the function of the b2 adrenoreceptor
dilates/relaxes smooth muscle
what is the function of the b3 adrenoreceptor
thermogenesis in skeletal muscle
what are co-transmitters
neurotransmitters released from the same neurones as ACh/NA
involved in pre- and post-synaptic modulation
what does NANC transmitter stand for
non-adrenergic non-cholinergic transmitters
what are three examples of NANC transmitters
ATP, neuropeptides, NO
