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Neurophysiology > Autonomic nervous system > Flashcards

Autonomic nervous system Flashcards

1
Q

What afferents can the PNS be split into

A

Motor afferents, sensory afferents

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2
Q

What are the 2 sections of the PNS

A

Autonomic, somatic

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3
Q

What are the 3 sections of the autonomic nervous system

A

Sympathetic, enteric, parasympathetic

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4
Q

What does the somatic system control

A

Voluntary control of skeletal muscles

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5
Q

Examples of bodily functions the ANS is involved in

A

Sweating, drooling, tearing up, hairs standing on end

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6
Q

When does discovery of the ANS date back to

A

Mid 1600s, Thomas Willis relied on obsevation of carcasses

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7
Q

What structure do the ganglia of the sympathetic nervous system form

A

Form segmental chain ganglia, organised segmentally according to lumbar and thoracic aspects in the organisation of the body

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8
Q

Where in the CNS do NO sympathetic neurons emerge from

A

Brain, cervical or sacral spinal cord

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9
Q

How does the sympathetic nervous system supply the gut

A

Three midline ganglia supply the gut

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10
Q

What are the length of the pre- and postganglionic nerves of the sympathetic nervous system

A

Preganglionic neurons are short

Postganglionic nerves tend to be very long

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11
Q

What are preganglionic neurons

A

Preganglionic neurons have cell bodies in the spinal cord that send out axons to the ganglion

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12
Q

What are postganglionic neurons

A

Run from the ganglion to the effector organ

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13
Q

What are the length of the pre- and postganglionic nerves of the parasympathetic nervous system

A

Preganglionic neurons are long

Post-ganglionic nerves are short

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14
Q

Why do preganglionic nerves tend to be shorter in the sympathetic nervous system than in the parasympathetic nervous system

A

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.

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15
Q

What neurotransmitters do both sympathetic and parasympathetic neurons receive as input

A

Receives cholinergic input from the preganglionic neuron (ACh) that binds to nicotinic receptors

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16
Q

Why is there a segmental chain ganglia organisation

A

The neural crest migrates through the rostral half of each somite, forming the segmental sympathetic chain ganglia

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17
Q

Where is the output of the parasympathetic nervous system

A

Output in cranial nerves and sacral spinal cord

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18
Q

What is the organisation of the ganglia in the parasympathetic nervous system

A

No segmental ganglia, ganglia close to targets

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19
Q

What neurotransmitters does the postganglionic neuron of the sympathetic nervous system release onto target cells

A

Mostly releases noradrenaline onto alpha/beta adrenergic receptors
Sometimes releases ACh

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20
Q

What neurotransmitters does the postganglionic neuron of the parasympathetic nervous system release onto target cells

A

Releases mainly ACh onto muscarinic ACh receptors

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21
Q

What do autonomic nerves end in instead of synaptic junctions

A

Varicosities, form as a series of enlargements that release neurotransmitter

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22
Q

What can autonomic nerves release in addition to the main neurotransmitters

A

Neuromodulators- modulate the action of primary transmitters

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23
Q

Examples of neuromodulators released by sympathetic nerves

A

Enkephalin, ATP

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24
Q

Examples of neuromodulators released by parasympathetic nerves

A

Somatostatin, nitrous oxide (NO)

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25
Q

How is the innervation of sweat glands unusual

A

Sweat glands receive cholinergic sympathetic innervation(sympathetic neurons don’t usually release cholinergic transmitters)

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26
Q

Why do the sweat glands recieve cholinergic sympathetic innervation instead of noradrenaline

A

Target derived factors in development cause NA cells to switch to ACh cells in a late phenotypical switch (post-natal)

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27
Q

Examples of the target derived factors that cause NA cells to switch to ACh cells

A

Leukaemia inhibitory factor, ciliaric neurotrophic factor

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28
Q

How was the switch of the innervation of sweat glands discovered- procedure

A

By transplanting foot pad tissue (has a cholinergic neurotransmitter identity) onto a patch of skin dominated by noradrenergic innervation (Schotzinger and Landis, 1988)

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29
Q

How was the switch of the innervation of sweat glands discovered- results

A

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)

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30
Q

What can be done if you sweat a great deal (hyperhidrosis)

A

The sympathetic chain innervating the sweat glands can be cut or regionally infected with Botulinum toxin to prevent sympathetic stimulation

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31
Q

How are piloerector muscles innervated and what is the result of input

A

Receive noradrenergic inputs that cause the hair shaft to move into an erected position

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32
Q

What is peripheral vasoconstriction

A

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)

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33
Q

Paravertebral chain of sympathetic ganglia- what supplies head

A

Superior cervical ganglion at the top of the sympathetic chain

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34
Q

Paravertebral chain of sympathetic ganglia- what supplies heart and lungs

A

Middle cervical and stellate ganglia

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35
Q

Paravertebral chain of sympathetic ganglia- what supplies abdominal and pelvic organs

A

Pre-vertrebal ganglia

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36
Q

What are the 3 ways the sympathetic ganglia are innervated

A

Terminate in ganglia, pass along chain before terminating, some synapse with midline ganglia

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37
Q

How do some preganglionic nerves synapse with midline ganglia before innervating the ganglia

A

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

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38
Q

How do the preganglionic neurons enter and the postganglionic nerves leave the sympathetic ganglia

A

Preganglioic neurons enter via the white ramus

Postganglionic nerves leave via the grey ramus

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39
Q

Where do the preganglionic and postganglionic sympathetic neurons synapse

A

In the sympathetic ganglion

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40
Q

What innervates the gut

A

The main pre-vertebral ganglia innervate the gut

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41
Q

What are the pre-vertebral ganglia that innervate the gut suppled by

A

The greater, lesser and least splanchnic nerves

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42
Q

What are the 3 main pre-vertebral ganglia that innervate the gut

A

The celiac ganglion, the superior mesenteric ganglion, the inferior mesenteric ganglion

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43
Q

What supplies the foregut

A

The celiac ganglion

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44
Q

What supplies the midgut

A

The superior mesenteric ganglion

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45
Q

What supplies the pelvic organs

A

The inferior mesenteric ganglion

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46
Q

What does the rostral-most porttion of the parasympathetic nervous system consist of

A

Cranial nerves 3, 7, 9 and 10

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47
Q

What is cranial nerve 3 from the parasympathetic nervous system

A

Oculomotor, the iris

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48
Q

What is cranial nerve 7 from the parasympathetic nervous system

A

Facial, tear and salivary glands

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49
Q

What is cranial nerve 9 from the parasympathetic nervous system

A

Glossopharyngeal, salivary gland

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50
Q

What is cranial nerve 10 from the parasympathetic nervous system

A

Heart, lungs and viscera

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51
Q

Pupil reflex- parasympathetic input

A

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

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52
Q

Pupil reflex- sympathetic input

A

Sympathetic input stimulates post-ganglion fibres from the superior cervical ganglion, causing pupil dilation and increasing light passage to the retina

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53
Q

What drugs can cause parasympathetic stimulation of the eye

A

Opiates, making pinpoint pupils

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54
Q

What drugs can cause sympathetic stimulation of the eye

A

Sympathomimetic drugs eg Amphetamines dilate pupils (cycloplegic effect)

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55
Q

What are the symptoms of Horner’s syndrome

A

Pupils constricted, eyelid droops, dry flushed facial skin

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56
Q

What can cause Horner’s syndrome

A

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

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57
Q

Which facial nerve controls lacrimation and salivation

A

Facial nerve VII

58
Q

What is lacrimation

A

Tearing up

59
Q

How does facial nerve VII control lacrimation

A

Parasympathetic innervation of the pterygopalatine ganglion regulates secretions of the lacrimal gland and nasal mucosa

60
Q

How does facial VII control salivation

A

Parasympathetic innervation of the submandibular ganglion regulates secretions of submandibular and sublingual salivary glands

61
Q

How does cranial nerve 9 control salivary secretion

A

Parasympathetic of the otic ganglion leads to increased secretion of saliva from the parotid glands

62
Q

How do CNS control centres drive cardiovascular effects

A

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

63
Q

What is the result of increased sympathetic input into the heart

A

Increased heart rate, force of contraction and conduction

64
Q

What is the main effect of sympathetic activation on the lung

A

Bronchodilation- sympathetic innervation of bronchi leads to bronchodilation which causes increased respiratory capacity

65
Q

What leads to neurotransmitter release by the sympathetic nervous system during fight or flight

A

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

66
Q

What is known to phenocopy the flight/fight state and how

A

Adrenal medulla tumours cause the adrenal medulla to massively increase, causing a huge increase of catecholamines in circulate that phenocopy the fight/flight state

67
Q

Why does a phenocopy happen as a result of adrenal medulla tumours

A

Chomaffin cells in the adrenal medulla have a common embryonic origin with SNS neurons, meaning they release the same neurotransmitters

68
Q

Sympathetic stimulation- pupils

A

Dilate

69
Q

Sympathetic stimulation- heart

A

Heart rate increases

70
Q

Sympathetic stimulation- blood vessels

A

Peripheral vasoconstriction

Muscle vasodilation

71
Q

Sympathetic stimulation- bronchi/lung

A

Bronchodilation

72
Q

Sympathetic stimulation- liver

A

Glycogenolysis, gluconeogenesis

73
Q

Sympathetic stimulation- salivary glands

A

Viscous salivary secretions

74
Q

Sympathetic stimulation- GI tract

A

Contraction of sphincters, decreased motility

75
Q

What is the vagus nerve

A

The 10th cranial nerve, major PNS nerve that supplies thorax and abdomen (vagus means wandering)

76
Q

What does the vagus nerve control

A

Gut reflexes and motility, blood pressure, heart rate

77
Q

What neurons attached to the vagus nerve control blood pressure and heart rate

A

Sensory neurons in the petrosal ganglia and nodose ganglia attached to the vagus nerve

78
Q

Study showing the role of Piezeo2 channels in the neurons controlling the baroreflex

A

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

79
Q

What channel was discovered in the neurons that control blood pressure and heart rate in the vagus nerve

A

Piezeo2, a mechanosensory channel- senses stretch in the aortic arch and carotid sinus

80
Q

What is the baroreflex

A

How sensory nerves that run along the vagus nerve control blood pressure

81
Q

What is the micturition reflex- P1, sensing

A

Sensory nerves sense bladder stretch and send signals to the CNS (somatic nervous system), causing the urge to urinate

82
Q

What is the micturition reflex- P2, contraction

A

Parasympathetic stimulation (by Beta3) of the smooth muscle of the bladder walls causes contraction

83
Q

What is the mictuition reflex- P3, expulsion

A

The sphinctre muscles are voluntarily relaxed via the pudendal and the sphinctre opens

84
Q

What happens to the micturition reflex during sympathetic stimulation

A

The micturition reflex is suppressed

85
Q

What is micturition

A

The ejection of urine from the urinary bladder to outside the body

86
Q

What 2 nerve types are involved in male genital ‘reflexes’

A

Afferent via spinal and autonomic nerves

87
Q

What is the effect of parasympathetic nervous system stimulation on male genital ‘reflexes’

A

PSNS stimulation onto helicine arteries causes them to dilate, causing erection

88
Q

What is the effect of sympathetic nervous system stimulation on male genital ‘reflexes’

A

Sympathetic stimulation leads to emission of seminal fluid and closure of bladder sphincter, leading to ejaculation

89
Q

What controls ejaculation

A

Pudendal (spinal) control over penile muscles causes ejaculation

90
Q

Defecation reflex- why are the anal sphincters normally closed

A

Closed by sympathetic tonic (continuous low level) stimulation

91
Q

Defecation reflex- what triggers the defecation reflex

A

Detection of a full sigmoid rectum by visceral sensory afferents

92
Q

Defecation reflex- what causes defecation

A

Peripheral nervous system stimulates of bowel smooth muscle, tonic sympathetic control of sphinctres is inhibited, voluntary opening of sphincters

93
Q

What 2 networks comprise the enteric nervous system

A

Submucosal plexus, myenteric plexus (Rao and Gershon, 2016)

94
Q

What comprises the enteric nervous system

A

Intrinsic nerve networks (plexi) in the intestinal wall

95
Q

How does peristalsis occur via the enteric nervous system

A

Food in gut casues serotonin release -> stimulates submucosal plexus -> stimulates myenteric plexus (shown by Hibberd et al, 2018)

96
Q

Study showing role of enteric nervous system in controlling peristalsis

A

Optogenetic stimulation of calretinin expressing myenteric neurons promotes peristalsis

97
Q

How does the enteric system develop

A

Enteric crest arises only from cervical levels and colonises the entire gut

98
Q

What disorders can be caused if invading crest cells don’t make it to the end of colonising the gut

A

Hirschprung’s disease and congenital megacolon

99
Q

What causes a megacolon

A

If invading crest cells don’t enter the gut wall or fail to survive it leads to a defective nerve plexus, causing a megacolon

100
Q

What controls the autonomic nervous system

A

The hypothalamus

101
Q

Rest and digest responses produced by the parasympathetic division

A

Slowed heart rate, decreased blood presure, increased digestive functions, reduced sweating

102
Q

How are the actions of the ANS unlike those of the somatic motor system

A

ANS actions are typically multiple, widepsread and relatively slow

103
Q

Where are the soma of preganglionic neurons

A

Spinal cord (localise in lateral horn) and brain stem

104
Q

What does it mean to say the ANS is a disynaptic pathway

A

It involves 2 synapses, one between the pre and post ganglionic neuron, and one between the post ganglionic neuron and the target organ

105
Q

Where are the soma of postganglionic neurons located

A

The autonomic ganglia

106
Q

Can the sympathetic and parasympathetic divisions act simultaneously?

A

Yes, operate in parallel by complementary distinct pathways and neurotransmitter systems

107
Q

Where do the preganglionic neurons of the sympathetic division lie

A

Sympathetic preganglionic neurons- interomediolateral grey matter of spinal cord

108
Q

Where do the preganglionic neurons of the parasympathetic division lie

A

Parasympathetic preganglionic neurons- variety of brain stem nuclei and lower spinal cord

109
Q

What 3 types of tissue does the ANS innervate

A

Glands, smooth muscle, cardiac muscle

110
Q

How do the physiological influence of the sympathetic and parasympathetic divisions interact

A

Generally oppose one another and are reciprocal, as neural circuits in the CNS inhibit activity in one division while the other is active

111
Q

What behaviours are related to the PNS

A

Digestion, growth, immune reponses and energy storage

112
Q

Which time span are the SNS vs PNS aimed at

A

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

113
Q

What is the effect of the parasympathetic vs sympathetic sysyem on smooth muscles of the gastrointestinal tract

A

Smooth muscle of gastrointestinal tract is dually innervated- intestinal motility (thus digestion) is stimulated by parasympathetic axons and inhibited by sympathetic axons

114
Q

Which glands are innervated by only one division of SNS vs PSNS

A

Sweat glands innervated by sympathetic axons alone, lacrimal glands innervated only by parasympathetic input

115
Q

What is the enteric division

A

A unique neural system embedded in the lining of the esophagus, stomach, intestines, pancreas and gallbladder

116
Q

What are both the enteric networks supplies by

A

Sensory nerves, interneurons, autonomic motor neurons

117
Q

What does the enteric division control

A

Many physiological processes involved in the trasport and digestion of food, from oral to anal openings

118
Q

What do enteric sensory neurons monitor

A

Tension and stretch of the gastrointestinal walls, chemical status of stomach and intestinal contents, blood hormone levels

119
Q

What is the info supplied by enteric sensory neurons used for

A

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

120
Q

Where does the enteric division receive indirect input from

A

The brain- PNS and SNS axons provide supplementary control and can supercede the functions of the enteric division in some circumstances

121
Q

Example of a circumstance where the brain may supercede the function of the enteric division via PNS and SNS axons

A

Enteric nervous system and digestive stress are inhibited by the strong activation of the SNS that occurs during acute stress

122
Q

How does the hypothalamus control the ANS

A

Integrates the info about body status it receives, anticipates some of its needs, provides a coordinated set of neural and hormonal outputs

123
Q

What connects the hypothalamus to the autonomic nervous system

A

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

124
Q

What area of the brain other than the hypothalamus is important for autonomic control

A

The nucleus of the solitary tract, located in the medulla and connected to the hypothalamus

125
Q

What does the solitary tract nucleus do

A

Integrates sensory information from the internal organs and coordinates output to the autonomic brain stem nuclei

126
Q

What happens if the brain stem is disconnected from all structures above it including the hypothalamus

A

Autonomic functions still operate well

127
Q

How does ACh activate postganglionic neurons

A

ACh bind to nAChRs, evoking a fast EPSP that usually triggers an action potential in the postganglionic cell

128
Q

Evidence for ACh activating postganglionic neurons

A

Drugs that block nAChRs eg curare can block autonomic output

129
Q

What can ACh released by pregabglionic neurons activate as well as nAChRs

A

mAChRs and GPCRs that can cause the opening/closing of ion channels that lead to very slow EPSPs and IPSP

130
Q

How evident are the effects of ACh on mAChRs and GPCRs

A

Effects are usually not evident unless that preganglionic nerve is activated repeatedly

131
Q

How can neuromodulators affect the action of neurotransmitters

A

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

132
Q

How is the pattern of firing in preganglionic neurons important in determining postganglionic activity

A

More than one action potential is required to stimulate the release of neuromodulators

133
Q

Why do postganglionic cells use different neurotransmitters in the SNS and PSNS

A

Postganglionic cells are autonomic motor neurons that actually trigger glands to secrete, sphincters to contract or relax etc

134
Q

Which postganglionic neurons release ACh vs NS

A

Parasympathetic postganglionic neurons- ACh

Sympathetic postganglionic neurons- NA

135
Q

What does parasympathetic ACh bind to on its targets

A

Binds entirely to mChRs

136
Q

How widespread are the effects of parasympathetic ACh vs sympathetic NA released by postganglionic neurons

A

Parasympathetic ACh has very local effects

Sympathetic NA often spreads very far, even into the blood where it can circulate widely

137
Q

What are sympathomimetic drugs

A

Drugs that promote the actions of NA or inhibit the muscarinic actions of ACh, aka mimicing activation of the SNS

138
Q

Example of sympathomimetic drug

A

Atropine is an antagonist of mAChRs that causes signs of SNS like pupil dilation, because blocking PNS actions shifts ANS activity towards the SNS

139
Q

What are parasympathomimetic drugs

A

Drugs that promote the muscarinic effects of ACh or inhibit the actions of NA aka mimic activation of PNS

140
Q

Example of a parasympathomimetic drug

A

Propanolol- antagonist of the beta receptor for NA, slows heart rate and lowers blood pressure, sometimes used for physiological efefcts of stage fright

141
Q

Where is adrenaline realised from

A

Adrenal medulla

142
Q

How is the adrenal medulla nothing more than a modified sympathetic ganglion

A

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

Neurophysiology (23 decks)

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