ICPP - Autonomic Nervous System Flashcards
The autonomic nervous system and the somatic nervous system form part of what?
The peripheral nervous system
What does the autonomic nervous system split into?
Sympathetic and para-sympathetic
Where is the term “autonomic” derived from?
Greek ‘autos’ (self) and ‘nomos’ (law), meaning self-governing
Does the ANS control voluntary or involuntary functions?
Involuntary, eg heart rate, blood pressure, GI motility
Is the ANS efferent or afferent?
Entirely efferent, but regulated by afferent inputs
Briefly outline the roles of the sympathetic and parasympathetic nervous systems.
Sympathetic - responds to stressful situations, “fight or flight” response, increases heart rate/force of contraction/blood pressure
Parasympathetic - regulates basal activities, “rest and digest”
What are the five sections that the ANS is divided into? What do they control?
Medullary - eye, lacrimal + salivary glands
Cranial
Thoracic - Structures in head and neck, heart, lungs, adrenal medulla, liver, GI tract, bladder, genitalia
Lumbar - also controls bladder and genitalia
Sacral - Lower GI tract, bladder, genitalia
Which sections of the brain and spinal cord are under sympathetic control and which are under parasympathetic?
Sympathetic - thoracic and lumbar
Para-sympathetic - medullary, cranial and sacral
Where do parasympathetic nerves originate?
Lateral horn of the medulla
Describe the pre- and postganglionic fibres in the PNS.
- long myelinated pre-ganglionic fibres
- short unmyelinated post-ganglionic fibres
Where are the ganglia located in the PNS?
Within innervated tissues
Where do sympathetic nerves originate?
In the lateral horn of the lumbar and thoracic spinal cord
Describe the pre- and post-ganglionic fibres of the SNS.
- short myelinated preganglionic fibres
- long unmyelinated post-ganglionic fibres
Where are the ganglia located in the SNS?
In the paravertebral chain close to the spinal cord
What are the principal neurotransmitters in the ANS?
Acetylcholine (ACh) and noradrenaline (NA)
What sort of channels are nicotinic ACh receptors?
Ligand-gated ion channels
What neurotransmitter do all pre-ganglionic neurones use?
ACh
Which neurotransmitter do post ganglionic sympathetic and parasympathetic neurons use?
PNS - ACh
SNS - NA
Which receptors does ACh act on?
Muscarinic ACh receptors (GCPRs) - m1, m2, m3, m4, m5 and nAChR
Which receptors does NA interact with?
Alpha-adrenoceptors and beta-adrenoceptors (a1, a2, b1, b2, b3)
Can some specialised sympathetic post-ganglionic neurons be cholinergic rather than noradrenergic?
Yes, eg sweat glands and hair follicles
What are NANC transmitters?
Non-adrenergic, non-cholinergic transmitters. Examples include ATP, nitric oxide, serotonin and VIP
Why are sympathetic post-ganglionic neurons in the adrenal glands different?
They form neurosecretory chromaffin cells, which can be considered as post-ganglionic sympathetic neurons. On sympathetic stimulation, they release adrenaline into the bloodstream.
Give some consequences of parasympathetic release of ACh.
- heart slows
- bronchial contraction
- increased intestinal mobility
- increased sweat/salivary/lacrimal secretion
Give some consequences of sympathetic release of noradrenaline.
- tachycardia and positive inotropy
- bronchiolar relaxation
- increased salivary secretion
- renin release from kidneys
What is the umbrella term for distinct malfunctions of the ANS?
Dysautonomia
Which parts of neurotransmission across a synapse can be targeted by drugs?
- degradation of transmitter
- interaction with post-synaptic receptors
- inactivation of transmitter
- re-uptake of transmitter
- interaction with pre-synaptic receptors
How is acetylcholine synthesised?
Acetylcholine CoA + choline -> acetylcholine + coenzyme A
This uses choline acetyltransferase (CAT)
How is acetylcholine degraded?
Acetylcholine -> acetate + choline
This uses acetylcholinesterase (AChE)
Why is it difficult to treat disorders with drugs that affect muscarinic receptors?
There are five mAChR subtypes, but few subtype-selective agonists/antagonists, meaning they have a large amount of side effects
What side effects would a non-selective, muscarinic ACh receptor agonist be likely to cause?
- decreased heart rate and cardiac output
- increased bronchoconstriction and GI tract peristalsis
- increased sweating and salivation
What are the pathological effects indicative of massive discharge of the parasympathetic nervous system? (SLUDGE)
Salivation Lacrimation Urination (relaxation of sphincter) Defecation Gastrointestinal upset Emesis
When are the SLUDGE symptoms usually encountered?
- drug overdose
- ingestion of magic mushrooms
- exposure to organophosphorus insecticides or nerve gases (theses covalently-modify AChE, so ACh levels are raised)
Treated with atropine, palidoxime or other anti-cholinergic agents
Give some clinical uses of mACh receptor agonists/antagonists.
- pilocarpine and bethanechol (agonists) treat glaucoma and stimulate bladder emptying respectively
- ipratropium and tiotropium (antagonists) treat athsma and COPD
What is a “varicosity” in a post-ganglionic sympathetic neuron?
A bulge in the axon which serves as a specialised site for Ca2+ dependent noradrenaline release
How is noradrenaline synthesised?
Tyrosine -> DOPA -> dopamine (passes from cytosol to vesicle) -> noradrenaline
Within adrenal medulla, an enzyme converts noradrenaline to adrenaline
Which ion is required for exocytosis release of NA?
Ca2+
What is the difference between uptake 1 and uptake 2 in noradrenergic transmission?
Uptake 1 - NA actions terminated by re-uptake into pre-synaptic terminal by Na+ dependent, high affinity transporter
Uptake 2 - left over NA is taken in by lower affinity, non-neuronal mechanism
What happens to NA once it’s taken into the pre-synaptic terminal?
- some goes into vesicles where it’s stored for re-use
- remainder is susceptible to metabolism by monoamine oxidase (MAO) or COMT
