Lecture 6: Autonomic Nervous System Flashcards
What does the autonomic nervous system control?
Controls non-skeletal peripheral function:
- cardiac muscle (heart)
- smooth muscle
- internal organs
- skin
What is the autonomic nervous system a sub-division of?
The peripheral nervous system (motor/efferent division –> visceral motor)
What is the ANS split into?
- parasympathetic (rest and digest - PNS)
- sympathetic (fight and flight - SNS)
What sort of effects does the PNS have on the body?
- constricts pupil
- increases secretion in salivary gland
- decreases heart rate/contractility
- constricts lungs
- increases motility and secretions in GIT
- increases bile release in liver
- contracts bladder
What sort of effects does the SNS have on the body?
- dilates pupils
- decreases secretion in salivary glands
- increases heart rate/contractility
- dilates lungs
- decreases motility and secretions in GIT
- increases glucose release in liver
- relaxes bladder
What is an exception to the antagonistic effects of the PNS and SNS?
SNS controls blood vessel tone - both constriction and dilation (due to diff receptors)
What does the ANS react to?
sensory information received in the integrating centre (hypothalamus)
Where do the visceral motor nuclei originate?
in the hypothalamus
What is a ganglion?
a nerve cell cluster or group of nerve cell bodies
What 2 types of neurones do autonomic neurones consist of?
a pre-ganglionic and a post-ganglionic neurone
What type of ganglion would you find in the PNS?
- long pre-ganglionic fibres
- ganglions close to (or embedded within) effector tissues
- short post-ganglionic fibres
What type of ganglion would you find in the SNS?
- short pre-ganglionic fibres
- ganglions close to originating site of pre-ganglionic fibre
- long post-ganglionic fibres
(sympathetic nerves often work together)
What is the one exception to the 2 neurone arrangement in the ANS?
- adrenal gland (only 1 sympathetic nerve)
In which synapses is acetylcholine released?
- pre- and post-ganglionic nerve fibres of parasympathetic
- pre-ganglionic nerve fibre of sympathetic
In which synapse is noradrenaline released?
post-ganglionic nerve fibre of sympathetic
What does the adrenal gland secrete instead of neurotransmitter and where does this substance go?
- hormone (adrenaline) and some noradrenaline that is secreted into bloodstream rather than a synapse
How does the sympathetic nervous system influence lung function?
- by adrenal gland producing adrenaline which affects lung rather than neurotransmitter
What does the ANS respond to?
sensory input
What is unusual about the nerves going to the lungs?
There are parasympathetic nerves innervating the lung tissue but no sympathetic neurons innervating the lung tissue.
Where does the enteric nervous system work?
In GIT
What type of receptor would you want at autonomic ganglia?
acetylcholine receptor (nicotinic acetylcholine receptor - ion channel linked receptor)
What do nicotinic acetylcholine (nACh) receptors do?
- mediate responses to ACh released from preganglionic fibres at ALL autonomic ganglia
- also mediate response to ACh released by sympathetic nerves innervating adrenal medulla (adrenal gland)
Which receptors are used for the post-ganglionic neurones in the PNS?
muscarinic receptors (G-protein coupled) - for ACh
Which receptors are used for the post-ganglionic neurones in the SNS?
adrenergic receptors (G-protein coupled) - for noradrenaline (NA) or adrenaline via blood
Outline the general biosynthesis and metabolism of neurotransmitter.
- Precursor enzymatically converted to neurotransmitter
- packaged into vesicles
- action potential causes Ca2+ influx and exocytosis
- exocytosis and neurotransmitter release
- receptor activation
- removal of NT from synapse via uptake into pre-synaptic terminal or glial cells. can be metabolised in synapse prior to uptake.
Where does the precursor for neurotransmitters usually come from?
usually from diet
How is acetylcholine produced?
choline + acetyl CoA enzymatically converted by choline acetyl transferase
What receptors may acetylcholine bind to?
muscarinic (G-coupled) or nicotinic (ion channel)
What happens to acetylcholine after it’s been used to activate receptors on the post-synaptic terminal?
- ACh rapidly degraded by acetylcholinesterase in the synapse
- Choline taken up into presynaptic terminal by choline uptake protein
What would happen if you blocked acetylcholinesterase?
over accumulated ACh
How is noradrenaline produced?
- tyrosine converted to DOPA by tyrosine hydroxylase
- DOPA converted to dopamine by DOPA decarboxylase
- dopamine packaged into vesicles and dopamine B hydroxylase produces noradrenaline
What receptor does noradrenaline bind to?
adrenergic
How is adrenaline produced?
noradrenaline converted to adrenaline in the cytoplasm by phenylethanol methyl transferase
What happens once adrenaline is released into the synaptic cleft?
Adrenaline diffuses into capillary and is transported to tissues in the blood
What happens to noradrenaline after it has activated receptors on the post-synaptic terminal?
It is transported back to pre-synaptic neuron via reuptake channels and then metabolised.
