Autonomic nervous system Flashcards
What afferents can the PNS be split into
Motor afferents, sensory afferents
What are the 2 sections of the PNS
Autonomic, somatic
What are the 3 sections of the autonomic nervous system
Sympathetic, enteric, parasympathetic
What does the somatic system control
Voluntary control of skeletal muscles
Examples of bodily functions the ANS is involved in
Sweating, drooling, tearing up, hairs standing on end
When does discovery of the ANS date back to
Mid 1600s, Thomas Willis relied on obsevation of carcasses
What structure do the ganglia of the sympathetic nervous system form
Form segmental chain ganglia, organised segmentally according to lumbar and thoracic aspects in the organisation of the body
Where in the CNS do NO sympathetic neurons emerge from
Brain, cervical or sacral spinal cord
How does the sympathetic nervous system supply the gut
Three midline ganglia supply the gut
What are the length of the pre- and postganglionic nerves of the sympathetic nervous system
Preganglionic neurons are short
Postganglionic nerves tend to be very long
What are preganglionic neurons
Preganglionic neurons have cell bodies in the spinal cord that send out axons to the ganglion
What are postganglionic neurons
Run from the ganglion to the effector organ
What are the length of the pre- and postganglionic nerves of the PARAsympathetic nervous system
Preganglionic neurons are long
Post-ganglionic nerves are short
Why do preganglionic nerves tend to be shorter in the sympathetic nervous system than in the parasympathetic nervous system
Sympathetic ganglia are often closer to the spinal cord (making them shorter) while parasympathetic preganglionic fibers tend to project to and synapse with the postganglionic fiber close to the target organ.
What neurotransmitters do both sympathetic and parasympathetic neurons receive as input
Receives cholinergic input from the preganglionic neuron (ACh) that binds to nicotinic receptors
Why is there a segmental chain ganglia organisation
The neural crest migrates through the rostral half of each somite, forming the segmental sympathetic chain ganglia
Where is the output of the parasympathetic nervous system
Output in cranial nerves and sacral spinal cord
What is the organisation of the ganglia in the parasympathetic nervous system
No segmental ganglia, ganglia close to targets
What neurotransmitters does the postganglionic neuron of the sympathetic nervous system release onto target cells
Mostly releases noradrenaline onto alpha/beta adrenergic receptors
Sometimes releases ACh
What neurotransmitters does the postganglionic neuron of the parasympathetic nervous system release onto target cells
Releases mainly ACh onto muscarinic ACh receptors
What do autonomic nerves end in instead of synaptic junctions
Varicosities, form as a series of enlargements that release neurotransmitter
What can autonomic nerves release in addition to the main neurotransmitters
Neuromodulators- modulate the action of primary transmitters
Examples of neuromodulators released by sympathetic nerves
Enkephalin, ATP
Examples of neuromodulators released by parasympathetic nerves
Somatostatin, nitrous oxide (NO)
How is the innervation of sweat glands unusual
Sweat glands receive cholinergic sympathetic innervation(sympathetic neurons don’t usually release cholinergic transmitters)
Why do the sweat glands recieve cholinergic sympathetic innervation instead of noradrenaline
Target derived factors in development cause NA cells to switch to ACh cells in a late phenotypical switch (post-natal)
Examples of the target derived factors that cause NA cells to switch to ACh cells
Leukaemia inhibitory factor, ciliaric neurotrophic factor
How was the switch of the innervation of sweat glands discovered- procedure
By transplanting foot pad tissue (has a cholinergic neurotransmitter identity) onto a patch of skin dominated by noradrenergic innervation (Schotzinger and Landis, 1988)
How was the switch of the innervation of sweat glands discovered- results
The innervation for the transplanted tissue remained cholinergic (switch did not occur) because it receives transcription factor signals from the sweat glands themselves (Schotzinger and Landis, 1988)
What can be done if you sweat a great deal (hyperhidrosis)
The sympathetic chain innervating the sweat glands can be cut or regionally infected with Botulinum toxin to prevent sympathetic stimulation
How are piloerector muscles innervated and what is the result of input
Receive noradrenergic inputs that cause the hair shaft to move into an erected position
What is peripheral vasoconstriction
Sympathetic nerves innervating the smooth muscle cause them to contract which reduces blood flow to the fingers and heat loss (shown by, Pirzgalska et al 2015)
Paravertebral chain of sympathetic ganglia- what supplies head
Superior cervical ganglion at the top of the sympathetic chain
Paravertebral chain of sympathetic ganglia- what supplies heart and lungs
Middle cervical and stellate ganglia
Paravertebral chain of sympathetic ganglia- what supplies abdominal and pelvic organs
Pre-vertrebal ganglia
What are the 3 ways the sympathetic ganglia are innervated
Terminate in ganglia, pass along chain before terminating, some synapse with midline ganglia
How do some preganglionic nerves synapse with midline ganglia before innervating the ganglia
Synapse with midline/pre-vertebral ganglia via the splanchnic nerves eg celiac ganglia and mesenteric ganglia, which in turn project to the gut and internal organs
How do the preganglionic neurons enter and the postganglionic nerves leave the sympathetic ganglia
Preganglioic neurons enter via the white ramus
Postganglionic nerves leave via the grey ramus
Where do the preganglionic and postganglionic sympathetic neurons synapse
In the sympathetic ganglion
What innervates the gut
The main pre-vertebral ganglia innervate the gut
- celiac
- superior mesenteric
- inferior mesenteric
- inferior hypogastric
What are the pre-vertebral ganglia that innervate the gut suppled by
The greater, lesser and least splanchnic nerves
What are the 3 main pre-vertebral ganglia that innervate the gut
The celiac ganglion, the superior mesenteric ganglion, the inferior mesenteric ganglion
What supplies the foregut
The celiac ganglion
What supplies the midgut
The superior mesenteric ganglion
What supplies the pelvic organs
The inferior mesenteric ganglion
What does the rostral-most porttion of the parasympathetic nervous system consist of
Cranial nerves 3, 7, 9 and 10
What is cranial nerve 3 from the parasympathetic nervous system
Oculomotor, the iris
What is cranial nerve 7 from the parasympathetic nervous system
Facial, tear and salivary glands
What is cranial nerve 9 from the parasympathetic nervous system
Glossopharyngeal, salivary gland
What is cranial nerve 10 from the parasympathetic nervous system
Heart, lungs and viscera
Pupil reflex- parasympathetic input
Parasympathetic input stimulates post-ganglion fibres from the ciliary ganglion that innervate the iris constrictor muscles, constricting the pupil and decreasing light passage to the retina
Pupil reflex- sympathetic input
Sympathetic input stimulates post-ganglion fibres from the superior cervical ganglion, causing pupil dilation and increasing light passage to the retina
What drugs can cause parasympathetic stimulation of the eye
Opiates, making pinpoint pupils
What drugs can cause sympathetic stimulation of the eye
Sympathomimetic drugs eg Amphetamines dilate pupils (cycloplegic effect)
What are the symptoms of Horner’s syndrome
Pupils constricted, eyelid droops, dry flushed facial skin
What can cause Horner’s syndrome
Can be caused by lesion of sympathetic superiori cervical ganglion, damaging the axons between the ganglion and the target organ eg due to tumour, carotid artery lesions
Which facial nerve controls lacrimation and salivation
Facial nerve VII
What is lacrimation
Tearing up
How does facial nerve VII control lacrimation
Parasympathetic innervation of the pterygopalatine ganglion regulates secretions of the lacrimal gland and nasal mucosa
How does facial VII control salivation
Parasympathetic innervation of the submandibular ganglion regulates secretions of submandibular and sublingual salivary glands
How does cranial nerve 9 control salivary secretion
Parasympathetic of the otic ganglion leads to increased secretion of saliva from the parotid glands
How do CNS control centres drive cardiovascular effects
CNS control centres project from the brain down the spinal cord to the ventral horn, where preganglionic sympathetic neurons innervate the stellate ganglia which innervate the heart
What is the result of increased sympathetic input into the heart
Increased heart rate, force of contraction and conduction
What is the main effect of sympathetic activation on the lung
Bronchodilation- sympathetic innervation of bronchi leads to bronchodilation which causes increased respiratory capacity
What leads to neurotransmitter release by the sympathetic nervous system during fight or flight
Greater splanchnic nerve carries descending inputs from the brain down the spinal cord- stimulation of the adrenal medulla causes a huge systematic release of noradrenaline and adrenaline
What is known to phenocopy the flight/fight state and how
Adrenal medulla tumours cause the adrenal medulla to massively increase, causing a huge increase of catecholamines in circulate that phenocopy the fight/flight state
Why does a phenocopy happen as a result of adrenal medulla tumours
Chomaffin cells in the adrenal medulla have a common embryonic origin with SNS neurons, meaning they release the same neurotransmitters
Sympathetic stimulation- pupils
Dilate
Sympathetic stimulation- heart
Heart rate increases
Sympathetic stimulation- blood vessels
Peripheral vasoconstriction
Muscle vasodilation
Sympathetic stimulation- bronchi/lung
Bronchodilation
Sympathetic stimulation- liver
Glycogenolysis, gluconeogenesis
Sympathetic stimulation- salivary glands
Viscous salivary secretions
Sympathetic stimulation- GI tract
Contraction of sphincters, decreased motility
What is the vagus nerve
The 10th cranial nerve, major PNS nerve that supplies thorax and abdomen (vagus means wandering)
What does the vagus nerve control
Gut reflexes and motility, blood pressure, heart rate
What neurons attached to the vagus nerve control blood pressure and heart rate
Sensory neurons in the petrosal ganglia and nodose ganglia attached to the vagus nerve
Study showing the role of Piezeo2 channels in the neurons controlling the baroreflex
Neurons subject to optogenetic stimulation had a sharp decrease in blood pressure and heart rate, showing the importance of Piezo2 in monitoring BP and HR
What channel was discovered in the neurons that control blood pressure and heart rate in the vagus nerve
Piezeo2, a mechanosensory channel- senses stretch in the aortic arch and carotid sinus
What is the baroreflex
How sensory nerves that run along the vagus nerve control blood pressure
What is the micturition reflex- P1, sensing
Sensory nerves sense bladder stretch and send signals to the CNS (somatic nervous system), causing the urge to urinate
What is the micturition reflex- P2, contraction
Parasympathetic stimulation (by Beta3) of the smooth muscle of the bladder walls causes contraction
What is the mictuition reflex- P3, expulsion
The sphinctre muscles are voluntarily relaxed via the pudendal and the sphinctre opens
What happens to the micturition reflex during sympathetic stimulation
The micturition reflex is suppressed
What is micturition
The ejection of urine from the urinary bladder to outside the body
What 2 nerve types are involved in male genital ‘reflexes’
Afferent via spinal and autonomic nerves
What is the effect of parasympathetic nervous system stimulation on male genital ‘reflexes’
PSNS stimulation onto helicine arteries causes them to dilate, causing erection
What is the effect of sympathetic nervous system stimulation on male genital ‘reflexes’
Sympathetic stimulation leads to emission of seminal fluid and closure of bladder sphincter, leading to ejaculation
What controls ejaculation
Pudendal (spinal) control over penile muscles causes ejaculation
Defecation reflex- why are the anal sphincters normally closed
Closed by sympathetic tonic (continuous low level) stimulation
Defecation reflex- what triggers the defecation reflex
Detection of a full sigmoid rectum by visceral sensory afferents
Defecation reflex- what causes defecation
Peripheral nervous system stimulates of bowel smooth muscle, tonic sympathetic control of sphinctres is inhibited, voluntary opening of sphincters
What 2 networks comprise the enteric nervous system
Submucosal plexus, myenteric plexus (Rao and Gershon, 2016)
What comprises the enteric nervous system
Intrinsic nerve networks (plexi) in the intestinal wall
How does peristalsis occur via the enteric nervous system
Food in gut casues serotonin release -> stimulates submucosal plexus -> stimulates myenteric plexus (shown by Hibberd et al, 2018)
Study showing role of enteric nervous system in controlling peristalsis
Optogenetic stimulation of calretinin expressing myenteric neurons promotes peristalsis
How does the enteric system develop
Enteric crest arises only from cervical levels and colonises the entire gut
What disorders can be caused if invading crest cells don’t make it to the end of colonising the gut
Hirschprung’s disease and congenital megacolon
What causes a megacolon
If invading crest cells don’t enter the gut wall or fail to survive it leads to a defective nerve plexus, causing a megacolon
What controls the autonomic nervous system
The hypothalamus
Rest and digest responses produced by the parasympathetic division
Slowed heart rate, decreased blood presure, increased digestive functions, reduced sweating
How are the actions of the ANS unlike those of the somatic motor system
ANS actions are typically multiple, widepsread and relatively slow
Where are the soma of preganglionic neurons
Spinal cord (localise in lateral horn) and brain stem
What does it mean to say the ANS is a disynaptic pathway
It involves 2 synapses, one between the pre and post ganglionic neuron, and one between the post ganglionic neuron and the target organ
Where are the soma of postganglionic neurons located
The autonomic ganglia
Can the sympathetic and parasympathetic divisions act simultaneously?
Yes, operate in parallel by complementary distinct pathways and neurotransmitter systems
Where do the preganglionic neurons of the sympathetic division lie
Sympathetic preganglionic neurons- interomediolateral grey matter of spinal cord
Where do the preganglionic neurons of the parasympathetic division lie
Parasympathetic preganglionic neurons- variety of brain stem nuclei and lower spinal cord
What 3 types of tissue does the ANS innervate
Glands, smooth muscle, cardiac muscle
How do the physiological influence of the sympathetic and parasympathetic divisions interact
Generally oppose one another and are reciprocal, as neural circuits in the CNS inhibit activity in one division while the other is active
What behaviours are related to the PNS
Digestion, growth, immune reponses and energy storage
Which time span are the SNS vs PNS aimed at
SNS mobilises the body for short-term emergency at the expese of processes aimed at long-term health, while the PNS works for the long-term good
What is the effect of the parasympathetic vs sympathetic sysyem on smooth muscles of the gastrointestinal tract
Smooth muscle of gastrointestinal tract is dually innervated- intestinal motility (thus digestion) is stimulated by parasympathetic axons and inhibited by sympathetic axons
Which glands are innervated by only one division of SNS vs PSNS
Sweat glands innervated by sympathetic axons alone, lacrimal glands innervated only by parasympathetic input
What is the enteric division
A unique neural system embedded in the lining of the esophagus, stomach, intestines, pancreas and gallbladder
What are both the enteric networks supplies by
Sensory nerves, interneurons, autonomic motor neurons
What does the enteric division control
Many physiological processes involved in the trasport and digestion of food, from oral to anal openings
What do enteric sensory neurons monitor
Tension and stretch of the gastrointestinal walls, chemical status of stomach and intestinal contents, blood hormone levels
What is the info supplied by enteric sensory neurons used for
Info used by motor and interneurons in the gut to govern muscle motility, the production of mucus and digestive secretions, and the diameter of local blood vessels
Where does the enteric division receive indirect input from
The brain- PNS and SNS axons provide supplementary control and can supercede the functions of the enteric division in some circumstances
Example of a circumstance where the brain may supercede the function of the enteric division via PNS and SNS axons
Enteric nervous system and digestive stress are inhibited by the strong activation of the SNS that occurs during acute stress
How does the hypothalamus control the ANS
Integrates the info about body status it receives, anticipates some of its needs, provides a coordinated set of neural and hormonal outputs
What connects the hypothalamus to the autonomic nervous system
Connections of the periventricular zone (in hypothalamus) to the brain stem and spinal cord nuclei that contain the preganglionic neurons of the SNS and PNS
What area of the brain other than the hypothalamus is important for autonomic control
The nucleus of the solitary tract, located in the medulla and connected to the hypothalamus
What does the solitary tract nucleus do
Integrates sensory information from the internal organs and coordinates output to the autonomic brain stem nuclei
What happens if the brain stem is disconnected from all structures above it including the hypothalamus
Autonomic functions still operate well
How does ACh activate postganglionic neurons
ACh bind to nAChRs, evoking a fast EPSP that usually triggers an action potential in the postganglionic cell
Evidence for ACh activating postganglionic neurons
Drugs that block nAChRs eg curare can block autonomic output
What can ACh released by pregabglionic neurons activate as well as nAChRs
mAChRs and GPCRs that can cause the opening/closing of ion channels that lead to very slow EPSPs and IPSP
How evident are the effects of ACh on mAChRs and GPCRs
Effects are usually not evident unless that preganglionic nerve is activated repeatedly
How can neuromodulators affect the action of neurotransmitters
Can interact with GPCRs and trigger EPSPs that can last for several minutes- can make postsynaptic neurons more responsive to the fast nicotinic effects when they come along
How is the pattern of firing in preganglionic neurons important in determining postganglionic activity
More than one action potential is required to stimulate the release of neuromodulators
Why do postganglionic cells use different neurotransmitters in the SNS and PSNS
Postganglionic cells are autonomic motor neurons that actually trigger glands to secrete, sphincters to contract or relax etc
Which postganglionic neurons release ACh vs NS
Parasympathetic postganglionic neurons- ACh
Sympathetic postganglionic neurons- NA
What does parasympathetic ACh bind to on its targets
Binds entirely to mChRs
How widespread are the effects of parasympathetic ACh vs sympathetic NA released by postganglionic neurons
Parasympathetic ACh has very local effects
Sympathetic NA often spreads very far, even into the blood where it can circulate widely
What are sympathomimetic drugs
Drugs that promote the actions of NA or inhibit the muscarinic actions of ACh, aka mimicing activation of the SNS
Example of sympathomimetic drug
Atropine is an antagonist of mAChRs that causes signs of SNS like pupil dilation, because blocking PNS actions shifts ANS activity towards the SNS
What are parasympathomimetic drugs
Drugs that promote the muscarinic effects of ACh or inhibit the actions of NA aka mimic activation of PNS
Example of a parasympathomimetic drug
Propanolol- antagonist of the beta receptor for NA, slows heart rate and lowers blood pressure, sometimes used for physiological efefcts of stage fright
Where is adrenaline realised from
Adrenal medulla
How is the adrenal medulla nothing more than a modified sympathetic ganglion
As it releases adrenaline (made from NA), a it efefcts target tissues almost identically to the SNS, causing a body-wide set of sympathetic effects
