Autonomic Nervous System Flashcards
What is the autonomic nervous system (ANS) a subdivision of?
Peripheral nervous system
What non-skeletal peripheral functions does the ANS control? (4)
Cardiac muscle
Smooth muscle
Internal organs
Skin
Not under conscious control
What are the 2 afferent neurones of the sensory division, and which of these is part of the ANS?
- Somatic sensory → responds to external stimuli e.g. skeletal muscle responding to you walking
- Visceral sensory afferent (part of ANS) → responds to internal stimuli
What are the 2 efferent neurones of the motor division, and which of these is part of the ANS?
Visceral motor efferent
Somatic motor
Parasympathetic vs sympathies
Rest and digest
Fight or flight
How do the 2 systems interact with pupils, heart, stomach, lungs?
- Pupil → sympathetic causes dilation, para causes constriction
- Heart → sympathetic increases rate and contractility, para decreases rate and contractility
- Stomach → sympathetic decreases motility and secretions, para increases motility and secretions
- Lungs → sympathetic causes dilation, para causes constriction
Effect of SNS and PNS on liver
- Liver → sympathetic increases glucose release, para increases bile release
effect of SNS and PNS on bladder
Bladder → sympathetic causes relaxation, parasympathetic causes contraction
When do para and sympathetic not have opposing effects?
e.g. SNS controls blood vessel tone → both constriction and dilation
Explain how the 2 systems balanced (e.g. with heart rate & bp)?
With autonomic control, generally either para or sympathetic is dominant over the other, particularly when both innervate the same tissue e.g. baroreceptors detect high blood pressure, send this to brain, brain sends signal to para neurones to lower bp and turns sympathetic off to stop further increase in bp
If bp drops, baroreceptors fire less often (baroreceptor firing is proportional to bp) so there is less signal through visceral motor neurones so parasympathetic effect drops and the SNS that is normally inhibited by baroreceptor firing, aren’t anymore as that stimulus has decreased, so SNS switches on (disinhibition) so now SNS is dominant
Where is the autonomic sensory (afferent) info relayed to
Hypothalamus
Where do visceral motor nuclei originate
Hypothalamus
Project to the brain stem or spinal chord
What do autonomic neurones consist of?
2 neurones → a pre-ganglionic (originating in brain/spinal cord) and a post-ganglionic neurone
Ganglion
A group of nerve cell bodies in PNS
What does the paraNS look like in terms of these?
- Long pre-ganglionic fibres
- Ganglions close to/embedded within effector tissues
- Short post-ganglionic fibres
What does the SNS look like in terms of these?
- Short pre-ganglionic fibres (sympathetic)
- Ganglions close to spinal cord
- Long post-ganglionic fibres
Exception to 2 neurone arrangement
Adrenal gland
Only has single sympathetic nerve innervating adrenal gland
Which neurotransmitters do pre-ganglionic nerves of both SNS & PNS release, and what are the receptors?
Acetylcholine (ACh)
nicotinic ACh receptor
Parasympathetic NS, what neurotransmitter is released from the post-ganglionic nerve, and what are the receptors?
ACh but detected by the muscarinic ACh receptors
In SNS, what neurotransmitter is released from the post-ganglionic nerve, and state the exception to this rule?
Noradrenaline (NA) is released into effector organ
The sweat glands where ACh is the neurotransmitter released
What does the adrenal gland secrete?
Does not release neurotransmitter
Instead secretes hormone, Adrenaline (and some noradrenaline)
Released into bloodstream NOT a synapse
After smelling food, is the PNS or the SNS more dominant?
PNS - gastrointestinal tract needs to be ready to undergo process of digesting
What is the name of the complex neural network within the gut?
Enteric nervous system - largely responds to gut function and stimuli received within the gut without engaging the brain
What is the unusual situation with the lung in terms of innervation?
There are parasympathetic neurons in the lung which cause bronchocontrictuon via ACh but in synoayhic neurones
Adrenaline causes bronchodilation
Describe the micturition reflex
Bladder slowly fills and moderate pressure in the bladder, SNS is in charge at this point
Internal sphincter controlled by SNS is contracted to prevent urine leaving the bladder
Once pressure gets to certain point, sensory information is relayed to the brain
PNS switched on and SNS is switched off
PNS contracts detrusor muscle to squeeze bladder and force urine out
Internal Sphincter is relaxed as SNS is turned off so urine can leave the bladder
- Somatic NS also gives voluntary level of control for when you want to empty bladder through control of external sphincter
Which receptors mediate the effects at all autonomic ganglia?
Nicotinic acetylcholine (nACh) receptor- is an ion channel linked receptor that gives fast response
These are found at all ANS ganglion- need that fast propagation of signal
Which receptors mediate the effects of NT released from postganglionic fibres?
- G protein coupled receptors- muscarinic receptors for ACh (in PNS) and adrenergic receptors for NA (in SNS)
- G protein coupled receptors have a slower onset than ion channel linked receptor
How is ACh made at synapses and released etc?
- etc?
- Choline and acetyl CoA enzymatically converted by choline acetyl transferase (into ACh)
- ACh is packaged into vesicles
- Action potential causes Ca2+ influx and exocytosis
- Exocytosis and neurotransmitter release
- ACh binds onto muscarinic/nicotinic receptors
- Acetylcholine rapidly degraded by acetylcholinesterase in the synapse. Choline taken up into presynaptic terminal by choline uptake protein (or in a glial cell)
- What happens if acetylcholinesterase is blocked?
ACh accumulates in synaptic cleft and there is a much more powerful ACh effect
How is NA made at synapses and released etc?
Tyrosine hydroxylated to form Dopa, by tyrosine hydroxylase
Dopa decarboxylated to form Dopamine, by DOPA decarboxylase
Dopamine hydroxylated to form noradrenaline, by dopamine Beta hydroxylase, noradrenaline packaged into vesicles
Action potential causes Ca2+ influx and exocytosis
Exocytosis and neurotransmitter release
Receptor activation (Adrenergic)
Removal of neurotransmitter from synapse via uptake into pre-synaptic terminal or glial cell; can be metabolised in the synapse prior to uptake
What are the 2 enzymes that metabolise noradrenaline into breakdown products, and where are they found?
Monoamine oxidase A within pre-synaptic terminal
Catechol-O-methyltransferase (COMT) in glial cells
- Describe the biosynthesis & action & release of Adrenaline in the nerve innervating the Adrenal gland
Tyrosine hydroxylated to form Dopa, by tyrosine hydroxylase
Dopa decarboxylated to form Dopamine, by DOPA decarboxylase
Dopamine hydroxylated to form noreadrenaline, by dopamine Beta hydroxylase
Noradrenaline methylated to form adrenaline, by phenylethanol methyltransferase
Action potential causes Ca2+ influx & Exocytosis
Exocytosis & Neurotransmitter release
Adrenaline diffuses into capillaries and is transported to tissues in the blood
