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CVS 2023 > Autonomic nervous system > Flashcards

Autonomic nervous system Flashcards

1
Q

What does Autonomic Nervous System regulate?

A

Physiological functions

(e.g. Heart rate, temperature, BP)

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2
Q

Give some examples of the physiological functions that the ANS controls

A

– Heart rate, BP, body temperature… etc (homeostasis)
– Co-ordinating the body’s response to exercise and stress

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3
Q

In ANS regulation largely voluntary or involuntary?

A
  • Involuntary
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4
Q

What types of tissues does ANS exert control over? (3)

A
  • Smooth muscle (Vascular and visceral)
  • Exocrine secretion
  • Rate and force of contraction in heart (HR)
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5
Q

2 divisions of ANS and what are these based on?

A

Sympathetic and Parasympathetic

Based on Anatomical grounds

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6
Q

Some text books include a 3rd division of the ANS, describe this

A
  • Enterinc nervous system
  • Network of neurones surrounding the GI Tract
  • Is normally controlled via sympathetic and parasympathetic fibres (mix of both)
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7
Q

What is the parasympathetic NS responsible for?

A

‘rest and digest’ / basal conditions

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8
Q

What is the sympathetic nervous system responsible for?

A

‘fight or flight’ / stressful conditions (can be coordinated or independent in diff. tissues)

(s for stress and sympathetic)

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9
Q

Sympathetic ganglionic arrangement

A

Short preganglionic neurone

Long post ganglionic neurone to target tissue

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10
Q

Parasympathetic ganglion organisation

A

Long preganglionic neurone

Short postganglionic neurone (within target tissue walls)

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11
Q

What happens under stress?

A

Sympathetic system activity is increased

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12
Q

What autonomic system is more dominant under normal body conditions (basal)?

A

PNS - dominates under normal circumstances

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13
Q

What is the anatomical origin of the SNS?

A
  • Thoracolumbar origin
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14
Q

What is the anatomical origin of the PNS?

A
  • Craniosacral origin
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15
Q

What do preganglionic neurones of both PNS and SNS divisions release?

A
  • Acetylcholine (ACh)
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16
Q

What does the acetylcholine released from the preganglionic neurones act on?

A
  • Nicotinic acetylcholine receptors on the postganglionic cell (neuromuscular junction)
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17
Q

What do nicotinic MACh receptors have?

A
  • An Ion channel
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18
Q

Describe how action potentials are fired to act on the effector cells

A
  • Pre ganglionic neurone fires action potentials
  • Causes release of acetylcholine from the terminal
  • They act on the nicotinic acetylcholine receptors at the neuromuscular junction
  • These receptors have an integral ion channel
  • The acetylcholine binds to the receptor
  • This opens the ion channel
  • The ion channel is permeable to sodium and potassium ions but at resting membrane potentials, overwhelming you get an inward movement of sodium ions
  • This depolarises the post ganglionic neurone to threshold
  • And it can then fire action potentials
  • The postganglionic neurone then releases a neurotransmitter (noradrenaline) onto the effector cell
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19
Q

Where are preganglionic cell bodies found in?

A
  • CNS
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20
Q

What is the primary neurotransmitter in the parasympathetic neurotransmitter?

A

Acetylcholine

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21
Q

Where are preganglionic synapses found?

A
  • Periphery
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22
Q

What receptor does sympathetic system usually act on and how?

A

Adrenaline/noradrenaline released and acts on Adrenergic receptors (eg a1/b1 or b2)

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23
Q

What receptor does parasympathetic system usually act on and how?

A

Ach binds to muscarinic receptors usually (eg M3/M2)

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24
Q

What happens if you denervate a heart?

A

Still beats but faster

Vagal influence from parasympathetic usually slows down

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25
Q

Parasympathetic supply to heart is via…

A

Preganglionic fibres of Vagus nerve (10th cranial nerve)

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26
Q

Where do preganglionic fibres synapse to postganglionic fibres in parasympathetic system?

A

On epicardial surface/within heart (SA/AV NODE!)

27
Q

What do post ganglionic fibres release in parasympathetic heart stimulation and what does this bind to?

A

Ach

Binds to M2 receptors

28
Q

Effects of Ach binding to M2 receptor

A 
Decrease HR (-ve chronotropic effect)
Decrease AV node conduction velocity
29
Q

Sympathetic input to heart

A

Postganglionic fibres travel from sympathetic chain

30
Q

What do the post ganglionic fibres of sympathetic system innervate?

A

SA NODE, AV NODE, MYOCARDIUM

different to parasympathetic as myocardium is included here

31
Q

How does the sympathetic input occur in heart?

A

Release of Noradrenaline

NA binds to B1 adrenoreceptors

32
Q

What effect does NA binding to B1 adrenoreceptors have on the heart?

A 
Increase HR (+ve chronotropic effect)
Increase force of contraction (+ve inotropic effect)
33
Q

What sets the rhythm of the heart?

A

AP firing in the SA node (steadily depolarise towards threshold)

34
Q

Sympathetic effects on AP firing in SA node

A

Noradrenaline binds to B1 receptors (Gs receptors)
Increase cAMP
Speeds up pacemaker potential (If - funny current)

35
Q

Parasympathetic effects on AP firing SA node

A

Ach binds to M2 receptors (Gi receptors)
Decrease cAMP
Increase K+ conductance
decreases pacemaker potential slope

36
Q

How does noradrenaline increase force of contraction?

A

NA acts on B1 receptors
Increase cAMP
Activates PKA
= phosphorylation of Ca2+ channels

37
Q

What does phosphorylation of Ca2+ channels lead to?

A

Increase Ca2+ entry during plateau

Increase uptake of Ca2+ in SR (more available to release)

38
Q

what innervation type do most vessels receive?

A

Sympathetic

39
Q

What receptors are present in most vessels?

A

a1 adrenoreceptors

40
Q

What vessels have B2 receptors?

A

skeletal muscle
myocardium
liver

41
Q

What do you need to ensure you can have vasoconstriction and vasodilation?

A

Vasomotor tone

Already some constriction to allow vasodilation if needed

42
Q

How does sympathetic output effect vessels?

A

Increased output = vasoconstriction

decreased output = vasodilation

43
Q

How does circulating adrenaline affect vessels?

A

High affinity for b2 receptors than for a1

At high levels adrenaline can affect a1

44
Q

What binds to what to allow for vasoconstriction/vasodilation?

A

More Noradrenaline will bind to a1

adrenaline binds to b2 but a1 in high levels

45
Q

What effect does activating b2 adrenoreceptors have?

A

Vasodilation

46
Q

What effect does activating a1 adrenoreceptors have?

A

Vasoconstriction

47
Q

How does vasodilation occur from activating b2 receptor?

A 
Increase cAMP
PKA
Open K+ channels
inhibits MLCK (cannot phosphorylate MLC)
Relaxation of smooth muscle
48
Q

How does vasoconstriction occur from activation of a1 receptor?

A

IP3 production
Increase in Ca2+ from SR stores and influx
= Contraction
(DAG inhibits MLC phosphatase so stays phosphorylated)

49
Q

What has the largest impact on ensuring adequate perfusion?

A 
Metabolite concentration (eg adenosine, H+)
STRONG vasodilator effect
50
Q

How are changes in system communicated to brain?

A 
Afferent nerves (towards brain)
eg baroreceptors or atrial receptors

this then alters efferent pathway

51
Q

What are baroreceptors?

A 
Stretch receptors
(increased arterial pressure = stretch)
52
Q

Where are baroreceptors found?

A

Carotid sinus and aortic arch

53
Q

What happens if baroreceptors detect stretch of blood vessels?

A

Stretch = high BP
Fire more action potentials towards medulla
Inhibit SNS, Activate PNS

=Bradycardia and Vasodilation

54
Q

What is baroreceptor for?

A

Maintaining blood pressure over SHORT time

moment to moment

55
Q

What happens to baroreceptors if there is continuous hypertension?

A

Reset to ‘new normal’

reset to higher levels

56
Q

drugs acting on ANS

A

Sympathomimetics (a and b receptor agonists)
Adrenoreceptor antagonists
Cholinergics (muscarinic antagonists/agonists)

57
Q

Sympathomimetics eg

A

Adrenaline
Dobutamine
salbutamol

58
Q

Adrenaline function

A

Restore function and support circulation in cardiac arrest
Anaphylactic shock

(you get widespread vasodilation when this occurs, HIGH LEVELS of adrenaline stimulates a1 receptor)

59
Q

Dobutamine

A 
B1 agonist 
cardiogenic shock (pump failure)
60
Q

Salbutamol

A 
b2 agonist
treats asthma (relaxes bronchioles0
61
Q

a adrenoreceptor antagonists

A

Anti-hypertensive
eg a1 antagonist PRAZOSIN
Inhibits NA action on a1 receptors = vasodilation

62
Q

B adrenoreceptor antagonists example

A

Propranolol = non selective
slows HR
reduce force of contraction
but BRONCHOCONSTRICTION

63
Q

problem with propranolol

A

non selective
NOT GOOD for Asthmatic patient (causes bronchoconstriction from b2)

(use selective b1 like atenolol)

CVS 2023 (26 decks)

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