Intermediate Pharmacology (PHAR0009) Notes - Autonomic Nervous System

Autonomic Nervous System – Summary
Peripheral Nervous System
 Nervous system = CNS + PNS
o CNS
 Brain + spinal cord – receives, processes, outputs
o PNS
 Somatic nervous system – sensory system + somatosensory system
 Autonomic nervous system – sympathetic + parasympathetic + enteric systems
 Autonomic nervous system
o Sympathetic nervous system
 Dilates pupil
 Inhibits flow of saliva
 Accelerates heartbeat
 Dilates bronchi
 Inhibits peristalsis and secretion
 Conversion of glycogen to glucose
 Secretion of adrenaline and noradrenaline
 Inhibits bladder contraction
o Parasympathetic nervous system
 Constricts pupil
 Stimulates flow of saliva
 Slows heartbeat
 Constricts bronchi
 Stimulates peristalsis and secretion
 Stimulates release of bile
 Contracts bladder
o Enteric nervous system
 Innervation from autonomic system – via vagus nerve + prevertebral ganglia
 Neurons control motor functions of the system + secretion of gastrointestinal
enzymes
 Structure
 Embedded in the lining of the gastrointestinal system
 Neurons are collected in two types of ganglia = myenteric + submucosal plexuses
o Myenteric plexus
 Provides motor innervation to both layers of the muscular layer of
the gut
 Activation  increases tonic contraction + intensity of rhythmic
contraction + rate of rhythmic contractions + velocity of conduction
o Submucosal plexus
 Activation  increases secretory activity + modulates intestinal
absorption
 Brain processes can alter autonomic events
o Hypothalamus
 Provide large hormonal output through pituitary
 Innervated by limbic system = emotional part of the brain
o Brain stem nuclei
 Controls autonomic outflow
o Nucleus solitary tract
 Receives and sends information to the brain stem nuclei and limbic system
 Acetylcholine and noradrenaline in the autonomic nervous system
o Structure = preganglionic neuron  ganglion  postganglionic neuron  effector organ

,Autonomic Nervous System – Summary
o Sympathetic





 Short cholinergic preganglionic neuron + long adrenergic postganglionic neuron
 ACh at ganglion – acts on fast cholinergic nicotinic receptors
o Fast nicotinic excitation at ganglion
 NA at target – acts on slow adrenergic alpha and beta receptors
o Excitatory alpha 1 receptor  inhibitory alpha 2 receptor  excitatory beta
1 receptor  inhibitory beta 2 receptor
o Parasympathetic





 Long cholinergic preganglionic neuron + short cholinergic postganglionic neuron
 ACh at ganglion – acts on fast cholinergic nicotinic receptors
o Fast nicotinic excitation at ganglion
 ACh at target – acts on slow cholinergic muscarinic receptors
o Excitatory muscarinic 1 receptor  inhibitory muscarinic 2 receptor 
excitatory muscarinic 3 receptor
 Synaptic transmission
o Stages
 Action potential arrival in axon of presynaptic neuron  depolarises nerve terminal
 Opening of voltage-gated Ca2+ channels in terminal membrane
 Ca2+ enters cell  binds to vesicles containing neurotransmitter
 Secretion of neurotransmitter from vesicles by exocytosis
 Diffusion of neurotransmitter across synaptic cleft
 Neurotransmitter binds to post-synaptic receptors  resulting in change in membrane
potential
 Removal of neurotransmitter from synapse
 Degraded by enzymes
 Endocytosed into pre-synaptic cell
 Diffuses away from synaptic cleft
o Transmission at the ganglion
 For every preganglionic neuron – 20 postganglionic neurons
 Acetylcholine – fast depolarisation
 Opioid peptides – slow hyperpolarisation
 LHRH – slow hyperpolarisation
o Transmission at the target
 Parasympathetic – muscarinic receptors

, Autonomic Nervous System – Summary





 Sympathetic – alpha and beta receptors





o Autoreceptors
 Alpha-2 autoreceptor (sympathetic) + muscarinic-2 autoreceptor (parasympathetic) –
controls release of transmitter
 Endothelium derived relaxation factor – nitric oxide
o NO acts as a transmitter in the endothelium
 Precursor = arginine
 Enzyme = nitric oxide synthase
o NO production in the endothelium  release  works on guanylyl cyclase  relaxes smooth
muscle

Adrenergic Pharmacology
Adrenoceptors
Sympathetic Activity
 Sympathetic nervous system
o Sympathetic outflow
 Short preganglionic axons  release
acetylcholine in the sympathetic ganglia
 stimulates nicotinic receptors on the
long postganglionic axons
 Long postganglionic axons  release
noradrenaline from nerve terminals =
stimulates adrenoceptors on the target tissues
o Exception = sweat glands
 Postganglionic axons release acetylcholine from nerve terminals  stimulates muscarinic
receptors on sweat glands
o Innervation of adrenal medulla