Lecture 1 - Introduction to the ANS Flashcards
What are the two general functions of the sympathetic and parasympathetic nervous systems?
Sympathetic - Fight or flight
Parasympathetic - Rest and digest
Is the liver largely sympathetic or parasympathetic and what effects are altered by the stimulation?
Largely sympathetic
Glycogenolysis and gluconeogenesis are increased by stimulation as available glucose needed during sympathetic response
What organ do arterial baroreceptors have a large influence over the autonomic control of?
The heart
What are the two branches of the autonomic nervous system (ANS)?
Sympathetic
Parasympathetic
How do sympathetic and parasympathetic nerves affect the heart?
Sympathetic - stimulatory effect, increase rate and contractility
Parasympathetic - inhibitory effect, decrease rate and contractility
What do baroreceptors detect and produce a response to?
Blood pressure
How do baroreceptors influence autonomic control of responses to changing blood pressure?
Baroreceptors are stimulatory to parasympathetic nerves and inhibitory to sympathetic nerves to the heart.
When baroreceptors fire due to increased blood pressure, they activate the parasympathetic limb and inhibit the sympathetic limb thus leading to reduced heart rate and contractility, thus reducing blood pressure until they stop firing.
Which limb of the ANS dominates the heart at rest?
Parasympathetic (rest and digest)
Which limb of the ANS dominates the heart during exercise?
Sympathetic (fight or flight)
How are the arterioles innervated regarding presence of sympathetic/parasympathetic fibres?
No parasympathetic innervation of arterioles
JUST sympathetic
What neurotransmitters are used pre and post-ganglion in parasympathetic neurones?
Acetylcholine in both cases
Difference in pre-ganglionic neurones in sympathetic and parasympathetic nervous systems?
Parasympathetic - Long pre-ganglionic
Sympathetic - Short pre-ganglionic
What neurotransmitters are used pre and post-ganglion in sympathetic neurones?
Acetylcholine pre-ganglion
Noradrenaline, Adrenaline, Acetylcholine post-ganglion
How do the sympathetic and parasympathetic responses differ in localisation and how wide they reach?
Sympathetic - Coordinated and divergent (happen same time in multiple organs with one pre-ganglionic fibre resulting in multiple post-ganglionic fibres)
Parasympathetic - Discrete and localised (1:1 ratio pre to post-ganglionic fibres, very focused response single target)
How is the somatic nervous system different to the others?
Not influenced by the ANS at all, entirely voluntary, neurones don’t have ganglia, just single neurone from brain to muscle releasing acetylcholine
Where are nicotinic receptors found and what neurotransmitter are they receptive to?
Found at ALL autonomic ganglia
Acetylcholine
How do nicotinic receptors work in relaying signal and how fast are they?
They are Type 1 ionotropic - linked to an ion channel
ACh binds, ion channel opens which allows sodium/calcium influx and transmission of the signal - VERY FAST
Where are muscarinic receptors found and what neurotransmitter are they receptive to? (what is the exception to the usual rule for these receptors?)
Found in any tissue innervated by post-ganglionic parasympathetic fibre
(exception are sweat glands which are sympathetically innervated)
How do muscarinic receptors work in relaying signal and how fast are they?
They are Type 2 G-protein Coupled
G-protein handle relay of transmission
Much slower than nicotinic
What are the subtypes of muscarinic receptors and where are they generally found/what do they do?
M1 - Neural M2 - Cardiac M3 - Exocrine and smooth muscle M4 - Periphery M5 - Striatal dopamine release All found in the brain to some degree
Where are adrenoceptors found and what are the different types?
Found at the end of the sympathetic nervous system on the effector organs.
Four subtypes, a1, a2, b1, b2
What do the adrenoceptors control and what do the different types do specifically?
Control vasculature
- Alpha 1 constricts
- Beta 2 dilates
What are adrenoceptors stimulated by and what are they linked to?
Stimulated by noradrenaline and adrenaline
G-Protein Coupled
What is the 8 step process for the synthesis, release and metabolism of acetylcholine?
1) Acetyl CoA + Choline (catalysed by choline acetyl transferase) produces ACh + CoA
2) ACh packaged into vesicles
3) Ca2+ influx stimulates vesicle movement and fusion
4) Vesicle fuses and ACh released
5) ACh moves across synapse
6) ACh binds with receptor on post-synaptic membrane
7) ACh broken down in the synapse by acetylcholinesterase into Choline + Acetate
8) Choline moves back into pre-synaptic neurone to be recycled into step 1
What is the 8 step process for the synthesis, release, reuptake and metabolism of noradrenaline?
1a) Tyrosine enters presynaptic neurone and is converted to DOPA by tyrosine hydroxylase
1b) DOPA is converted to dopamine by DOPA decarboxylase (still in neurone)
1c) Dopamine is packaged into vesicles
2) Dopamine is converted to noradrenaline by dopamine beta hydroxylase
3) Ca2+ influx stimulates vesicle movement and fusion
4) Vesicle fuses and NA is released
5) NA moves across synapse
6) NA binds to receptor on postsynaptic membrane.
7) NA reuptake via Uptake 1 transport protein into presynaptic neurone or Uptake 2 transport protein into extraneuronal tissue.
8) NA degraded by COMT in extraneuronal tissue or metabolised by Monoamine Oxidase A (MAO-A) in presynaptic neurone or returns to vesicle for recycling
