1. Introduction to the ANS Flashcards
Which ANS limb dominates the lungs and why?
- Parasympathetic
- Partial level of constriction
- Can therefore constrict or dilate further when needed
Which ANS limb dominates the eyes and why?
- Parasympathetic
- Smooth muscle partially constricted
- Change in both directions when needed
Why ANS limb slows the heart down and how?
- Parasympathetic
- These nerves activate inhibitory neurone
- Heart slows down
Which ANS limbs can act on the heart and arterioles?
- Heart - both
* Arterioles - only sympathetic
Why ANS limb are baroreceptors stimulatory/inhibitory to and why?
- Stimulatory - parasympathetic
- Inhibitory - sympathetic
- Baroreceptor firing activates parasympathetic limb
Why ANS limb dominates the heart at rest?
Parasympathetic
Why are sympathetic responses ‘coordinated’ and ‘divergent’ and how can parasympathetic responses be described in comparison?
- All post-ganglionic neurones project out from the sympathetic trunk (in the sympathetic limb)
- Parasympathetic are more ‘discrete’ and ‘localised’
How are somatic motor neurones different to autonomic?
- Just one motor neurone
- Innervating a muscle
- Only releasing ACh
Where can nicotinic receptors be found?
All autonomic ganglia (between pre and post-ganglionic - therefore very fast)
What type of receptor is a nicotinic receptor and how does it work?
- Ion channel linked
- Ionotropic - Type 1
- ACH binds and opens an ion channel
- Sodium/calcium influx - allows transmission
Where can muscarinic receptors be found?
- Innervated by post-ganglionic parasympathetic fibres
* Sweat glands are the odd one - sympathetic but releases ACh
What type of receptor is a muscarinic receptor?
Type 2 - G-protein coupled (slow)
What effect would a blockade of nicotinic acetylcholine receptors have on heart rate at rest?
- Parasympathetic dominates
* Therefore blockade would increase heart rate
What effect would a blockade of nicotinic acetylcholine receptors have on heart rate during exercise?
- Sympathetic dominates
* Therefore blockade would decrease heart rate
What changes occur in the lungs, sweat production, gut (motility), urinary frequency and sightedness, after the blockade of nicotinic acetylcholine receptors at rest?
Reduced parasympathetic effects so…
• Lungs: bronchoconstricted => bronchodilated
• Sweat: (parasympathetic predominates but not involved in this) => reduced sweat
• Gut: increased motility => constipation
• Urinary frequency: Increased => decreased
• Sightedness: short => long-sightedness
Describe the 5 subtypes of muscarinic receptor?
- M1 - Neural (forebrain - learning and memory)
- M2 - Cardiac (brain - inhibitory auto-receptors)
- M3 - Exocrine and Smooth Muscle (hypothalamus - food intake)
- M4 - Periphery: prejunctional nerve endings (inhibitory)
- M5 - Striatal dopamine release
Where (in which limb) are adrenoceptors predominantly found?
End of sympathetic limb
With reference to adrenoceptor subtypes, how does the sympathetic nervous system control vasculature by itself?
- Alpha 1 - constricts
* Beta 2 - dilates
What type of receptor are adrenoceptors?
• G-protein coupled
What stimulates the adrenoceptors?
- Noradrenaline
* Circulating adrenaline from adrenal medulla
The blockade of which of the following receptor sub-types would induce both an increased heart rate and reduction in sweat production during exercise?
- Muscarinic
- Each of the 4 adrenoceptors
• Muscarinic
Describe the synthesis (and breakdown) of ACh
- Acetyl CoA + Choline => ACh + CoA [choline acetyltransferase]
- ACh packaged into vesicles
- Action potential triggers calcium influx
- ACh released and acts on receptor
- Acetylcholinesterase can convert ACh to Choline + Acetate
Describe the synthesis of NA
- Tyrosine taken up
- Tyrosine => DOPA [tyrosine hydroxylase]
- DOPA => Dopamine [DOPA decarboxylase]
- Dopamine packaged into vesicles
- Dopamine => NA [dopamine beta hydroxylase]
- Action potential triggers calcium influx
- NA released and acts on adrenoceptor
Describe the breakdown of NA
- Uptake 1 - back into neuronal tissue and broken down by MAO (Monoamine Oxidase)
- Uptake 2 - into extra-neuronal tissue and broken down by COMT (Catechol-O-Methyl Transferase)
The blockade of which of the following targets would cause the most significant rise in synaptic noradrenaline concentrations?
• Tyrosine hydroxylase
• Uptake 1 transport protein
• Monoamine Oxidase
• Uptake 1 transport protein
- Blocking tyrosine hydroxylase reduces NA
- Blocking MAO increases NA
- Blocking of uptake 1 transport protein causes more significant rise
