lecture 9 : physiology and pharmacology of the ANS Flashcards
what does the autonomic nervous system consist of?
the sympathetic and the parasympathetic nervous system
what is the sympathetic nervous system needed for?
what is the para sympathetic nervous system needed for?
how do they work ?
fight or flight
rest and digest
they work together
- what are some of the functions of the parasympathetic system?
- constriction of the pupil
- constriction of the trachea
- contraction of the sphincter of the bladder
- heart rate slows
- the GI works more
- what are some of the functions of the sympathetic system?
- dilation of the pupil
- dilation of the trachea
- dilation of the sphincter
- the heart rate increases
- GI slows
- gluconeogenesis and glycogenlysis increases by the liver
where is the sympathetic nervous system on the spinal cord?
how does the sympathetic nervous arm work?
T1 -L3 - no cranial
nerves exit the spinal cord and synapse in sympathetic chain (ganglion)
- thoracolumbar outflow
- Pre-ganglionic fibres leave the spinal cord and join together into sympathetic ganglia in a sympathetic chain
- to allow mass discharge
where is the parasympathetic nervous system?
how does the parasympathetic arm work?
- cranial and sacral
no nerves emanating from the spinal cord
- the cranio-sacral outflow: there are 4 main cranial nerves - Oculomotor Nerve - Facial Nerve - Glossopharyngeal Nerve
- vagus nerve
goes to an array of organs
what is the difference about adrenal medula
The adrenal medulla only receives pre-ganglionic fibres
there are no post ganglionic fibres
what are ganglia?
site where cell bodies exist
what are pre ganglionic neurones
the fibres coming out of the spinal cord - synapse onto cells on the spinal cord
what are post ganglionic neurones
these are fibres that synapse onto cells in the ganglia
where is the ganglia in the sympathetic and parasympathetic nervous systems?
parasympathetic - inside the target organ
sympathetic - outside the target organ
what are the pre and pos ganglionic nerves like in para and sympathetic systems
sympathetic
what kind of neurotransmitter controls the parasympathetic nervous system ?
cholinergic
acetylcholine and the pre and post neurones
what kind of neurotransmitter controls the sympathetic nervous system ?
glutamate
what neurotransmitter is always used in the ganglia?
acetylcholine
why is the adrenal medulla different?
what does it release?
- this is because the adrenal medulla doesn’t go through the sympathetic ganglia
- then releases adrenaline and noradrenaline
how are the structures of parasympathetic and sympathetic nerves different?
- parasympathetic :
pre-ganglionic
fibres are long.
The post-ganglionic fibres are then short.
- sympathetic :
post-ganglionic fibre is long.
and pre ganglionic fibre is short
how is the somatic nervous system different?
- somatic supplies the skeletal muscle
- glutamate comes down to the spinal cord and synapses to the effector neurones which then release acetyl choline
*how is noradrenaline biosynthesised?
- L-phenylalanine
- L-tyrosine
- L-DOPA
Dopamine (cytoplasm) then in vesicles converted to noradrenaline
how is acetylcholine biosynthesised?
acetate + choline uses choline acetyltransferase to produce ACh, broken down by acetylcholinesterase
what is the intermediolateral cell column?
- found T1-L3 and target of presympathetic neurones
where sympathetic neurones eminate from - travelling to the sympathetic ganglia outside of the cord
- synapsing to post-ganglionic neurones
how does the autonomic nervous system regulate blood pressure?
- baroreceptors in the aorta respond to mechanical pressure
- When BP threshold reached, baroreceptors start to fire
- Aortic baroreceptors send impulses down vagus afferents, to brain
- this causes impulses down the vagus efferents to decrease the stroke volume and also the output
- also causing vasodilation
what is the baroreflex?
- the set point is normal blood pressure
- a tiny change in blood pressure can cause significant change in baroreceptor firing
- sketch the graph
(sigmoid curve )
baroreceptor firing vs blood pressure
how is the GI function regulated?
- this is innovated by the vagus nerve
- the sight, small, taste of food causes secretion of acid in the stomach
- sensory input enters hypothalamus
- output goes out of the spinal cord
what is the cephalic response
- cephalic response is the response of the body to food before you have ingested it
- the pancreas pumps insulin into the body
(happens even before food is ingested) - also there is a release of gastric juices in the stomach
- the mechanoreceptors then detect the stomach wall distension which send info via the vagus nerve to the brainstem to alert the brain that the person has eaten
- gut hormones are released by GI tract to activate chemoreceptors to signal to the brain to stop eating via the vagus nerve
what happens to satiety hormones in obesity?
obesity decreases the response from mechanoreceptors for a given pressure and loses satiety hormones
what are satiety hormones
the GI releases these hormones which via the chemoreceptors on vagus nerve signals to the brain stem that one is full now and to stop eating
what makes up the central respiratory centre?
Pontine respiratory centre (rate and pattern) in the pons and the ventral (coordinating rhythmicity)/dorsal (inspiration and diaphragm control) groups in the medulla make up the central respiratory centre
how is respiration regulated?
- aortic chemoreceptors transmit down vagus nerve
- carotid chemoreceptors transmit down 9th cranial nerve
they detect decreases O2, decreased PH and increased CO2
- Central chemoreceptors respond to decreased pH and increased CO2
- All chemoreceptors communicate with the dorsal group of the medulla to increase respiration
- the lung mechanoreceptors are stretched and transmit down the vagus nerve which prevents respiration
Mechanoreceptors communicate with the dorsal group
- how do the different parts of the spinal cord innovate?
C1-C3 = accessory muscles
C3-C5 = diaphragm control
T1-T11 = intercostals
T6-L1 = abdominals
explain how is the bladder controlled by the autonomic nervous system
- regulation of the bladder is associated with the pressure inside the bladder
- stretch receptors in the wall have influence on the afferent pathways along the pelvic nerve which is part of the micturition reflex
- there is parasympathetic control over the muscle in the bladder wall which means it contracts
- there is sympathetic control over the internal sphincter via the hypogastric nerve
- as the parasympathetic system increases activity the sympathetic system will decrease activity
what is the signal pathway through the brain stem?
- signal travels up the vagus nerve to the nucleus tracts solitarius
- this signal then moves up the brain stem into the hypothalamus
- information is then sent back down the vagus nerve to the dorsal motor nucleus of the vagus nerve
what receptors does the sympathetic system use?
adrenoreceptors
alpha and beta
alpha 1- ABD
alpha 2 - ABC
beta 1
beta 2
what receptors does the parasympathetic system use?
cholinoceptors
- nicotinic
- muscarinic
what types of receptors are there?
how do they work ?
ion channels - binding ligands therefore conformational change
G protein coupled receptors
- binding of ligand to outer membrane which activates down stream process
what are the PSNS receptors?
-Synapse 1 = ACh in nicotinic
Synapse 2 = ACh in muscarinic
what are the SNS receptors?
Mostly NA/DA postganglionic
All ganglionic synapses are nicotinic ACh receptors
Sweat glands use ACh muscarinic receptors
what are examples of cholinergic drugs?
what do they do?
- Atropine: competitive muscarinic receptor antagonist
- Tubocurarine: nicotinic receptor antagonist - also used as NMJ so would paralyse muscles
what does adrenergic mean?
working on adrenaline or noradrenaline
where are adrenergic receptors found?
- Alpha1 receptors located on most effector organs to cause smooth muscle contraction
- Alpha2 receptors present on presynaptic neurones to limit NA release to synapse
- Beta1 receptor exclusively found on the heart to increase cardiac output
- Beta2 receptors can relax smooth muscle in noradrenaline synapses
what odes doxazosin do?
Alpha1 receptor antagonist to cause smooth muscle dilation
what does medetomidine do?
Alpha2 receptor agonist to decrease NA release
what does atenolol do?
Beta1 receptors antagonist to decrease HR
what does salbutamol do?
Beta2 receptor agonist to relax smooth muscle
what is shy drager syndrome?
(Multiple System Atrophy)
- Synucleopathy - associated with loss of intermediolateral cell bodies and striatonigral brain areas
orthostatic hypotension, impotence, dry mouth, urinary retention and incontinence
what is 1 hypotension ?
Exaggerated sympathetic nerve activity to blood vessels and renal bed leads to increased circulating volume and vascular tone
what is heart failure?
- Inability of heart to pump sufficient blood to meet oxygen demand
- Associated with increased sympathetic nerve activity to renal bed,
what is parkinsons disease?
- autonomic dysfunction
- vagus nerve affected
