Intro to the ANS Flashcards
What would an increase in Arterial Baroreceptor firing lead to with regards to the ANS?
Stimulations of parasympathetic nerve; inhibits heart contraction
Inhibition of sympathetic innovation of heart and arteries to lower blood pressure and HR
Describe the balance of the ANS in the eye at rest:
Dominated by the Parasympathetic at rest.
You need your smooth muscle to be partially constricted so it can change in both directions
Where do parasympathetic nerves originate?
Cranial or Sacral regions
What is the neurotransmitter used in the Parasympathetic Nervous system?
ACh
What does the Preganglionic fibre of the SNS usually release?
ACh
What dies the Post-ganglionic fibre of the SNS usually release?
Noradrenaline
What post-ganglionic neurotransmitter may be secreted to innovate sweat glands?
ACh
What is the function of the SNS and PNS in the eye?
SNS: Pupil dilation
PNS: Constriction of pupil, Contraction of ciliary muscle
What is the balance of the ANS in the lungs at rest?
Dominated by the Parasympathetic;
There is a partial level of constriction so that it can both constrict further and dilate
What is the dominant branch of the ANS in the liver and what does it control?
Sympathetic
Glycogenolysis + Gluconeogenesis
You want glucose to be available in a fight or flight situation so sympathetic discharge will stimulate an increase in glycogenolysis and gluconeogenesis.
What are the effects of the SNS in the Kidneys, Bladder and Ureters?
Kidney: Increased renin secretion
Ureters and Bladder: Relaxes detrusor; constriction of trigone and sphincter
What are the effects of the ANS in the heart, and which is dominant at rest?
SNS: Increased rate and contractility
PNS: Decreased rate and contractility
PNS dominant at rest
Describe the ANS innovation of arteries and arterioles:
There is no parasympathetic innovation
The sympathetic is totally in control of the arterioles it controls constriction and dilation of the arterioles.
Where do the post-ganglionic neurones in the sympathetic limb project from, and what does this mean for their organisation?
Sympathetic trunk
Very divergent (1:20) neurones so the sympathetic responses are coordinated and divergent; because of the sympathetic trunk, there is a mass discharge of the SNS.
What are the consequences of the organisation and origins of the Parasympathetic trunk of the ANS?
Little divergence of neurones, so its effects tend to be discreet and localised.
Recall the organisation of the ANS and the neurotransmitters it uses:
What are the two types of ACh receptor?
Nicotinic and Muscarinic
Where are nicotinic receptors found?
At ALL autonomic ganglia
What is the speed of Nicotinic receptors and why?
Rapid as they transfer the stimulus from the pre-ganglionic to the post-ganglionic neurone.
What type of receptor is the Nicotinic receptor?
Type 1 - Ionotropic
How do nicotinic receptors work?
Acetylcholine binds to the receptor and opens an ion channel that allows sodium/calcium influx and allows transmission.
Where are Muscarinic receptors found?
At any tissue that is innervated by a post-ganglionic parasympathetic fibre
What type of receptors are Muscarinic receptors?
Type 2 - G-protein coupled
What is the speed of a muscarinic receptor?
Much slower than nicotinic
What are the sub-types of Muscarinic receptors?
- M1 – Neural (Forebrain – learning & memory)
- M2 – Cardiac (Brain – inhibitory autoreceptors)
- M3 – Exocrine & smooth muscle (Hypothalamus – food intake)
Where are Adrenoceptors located?
Most effector organs innovated by post-ganglionic sympathetic fibres
What type of receptors are adrenoceptors?
Type 2 - G-protein coupled
What are the four types of Adrenoceptors?
- Alpha 1
- Alpha 2
- Beta 1
- Beta 2
What are the functions of Alpha 1 and Beta 2 adrenoceptors, and what does this mean in terms of the ANS?
Alpha 1 Constricts
Beta 2 Dilates
- The SNS controls vasculature by itself
Describe the synthesis of ACh:
Acetyl CoA + Choline (from diet)
with Choline Acetyl Transferase
(within presynaptic bulb)
Describe the metabolism of ACh:
Acetylcholinesterase converts ACh in the synapse to Choline and acetate. The Choline then reenters the bulb to from more ACh.
What three enzymes are involved the biosynthesis of Noradrenaline, and what do they convert?
Tyrosine hydroxylase: Tyrosine to DOPA
DOPA decarboxylase: DOPA to Dopamine
Dopamine beta-hydroxylase: Dopamine to NA
What is the main difference betweent he metabolism of ACh and NA?
NA is not metabolised in the synapse!
How is noradrenaline removed from the synapse?
Uptake-1: Back into neuronal tissue
Uptake-2: into extraneuronal tissue
How is NA metabolised, and where?
In neuronal tissue: Monoamine oxidase (MAO)
In extraneuronal tissue: Catechol-O-Methyl Transferase (COMT)
