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DA > ANS applied physiology > Flashcards

ANS applied physiology Flashcards

1
Q

Where do the preganglionic SNS neurons arise from?

A

Lateral horn of the spinal cord

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2
Q

Describe the course of these pre-ganglionic SNS fibres

A

Descend 1 - 2 sebments within the spinal cord before emerge along with the posterior segmental roots. They then synapse in the ganglia of the paravertebral sympathetic chain to give rise to LONG post-ganglionic neurons

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3
Q

As the SNS is ‘thoracolumbar’ how is the head and neck supplied with

A

The cervical (stellate) ganglia:
Superior
Middle
Inferior

Formed from preganglionic fibers emerging from the first 3 thoracic segments

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4
Q

What anatomical course do sympathetic fibres usually follow

A

the arterial blood supply to these organs

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5
Q

Describe the structure and function of the Adrenal medulla

A

It is a specialized sympathetic ganglion in which post-ganglionic cells are modified into secretory cells rather than nerve fibres –> consequently the output of this gland is neuronal rather than neural:

Noradrenalin ± 70 %
Adrenalin ± 29 %
Dopamine ± 1 %

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6
Q

From which cranial nerves does parasympathetic cranial (craniosacral) outflow occur

A

3, 7, 9, 10

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7
Q

Where are PSNS ganglia found and how does the length of preganglionic PSNS fibers compare to postganglionic PSNS fibres

A

Ganglia are near target organs and as such pre-ganglionic neurons are significantly longer than PSNS postganglionic neurons

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8
Q

Where is ACh the neurotransmitter in the ANS and PNS

A
  1. All ANS ganglia (including adrenal medulla)
  2. All PSNS post ganglionic nerve endings
  3. At 2 places in the SNS
    - –> Apocrine sweat glands
    - –> Vasodilation in blood vessels of skeletal muscle

PNS –> Dominant neurotransmitter in the motor system including the neuromuscular junction

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9
Q

Summarize basic function, distribution of the adrenergic receptors

A

alpha 1 - arteriolar smooth muscle + –> VC
alpha 2 - Pre-synaptic + –> - SNS
beta 1 - heart + inotropy and chronotropy
beta 2 - lungs + bronchodilation and reduce secretions

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10
Q

Describe the redistribution of blood flow consequent to the ‘fight or flight response’

A

Redistribution of blood flow to “fight or flight” organs with sustained perfusion of the brain.

Blood diverted away from skin/liver/GIT/kidney via alpha adrenergic vasoconstriction

Blood diverted toward heart, muscle, lungs, brain via Beta beta adrenergic and vasodilation (muscarinic in muscle)

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11
Q

Describe the overall organization of the ANS

A

PSNS (Craniosacral)

  • CN 3,7,9,10 innervate 4 PSNS ganlgia in the head and neck. Ciliary (Eye), Sphenopalatine (lacrimal), Submandibular (Submaxillary and sublingual glands), Otic (parotid glands)
  • The Vagus nerve then supplies the vocal chords to the colon
  • The pelvic nerve supplies the colon/rectum/bladder/sex organs

SNS
The sympathetic chain runs paravertebrally
T1 - T4
Supply head and neck:
3 cervical ganglion (Supplied from T1 - T#3): Superior/middle and inferior supply SNS to head and neck. These nerves follow the course of the carotid artery and its branches.

Also supply heart/lungs

T5 - T12 via the Greater and small splanchnic nerves –> supplies stomach to sex organs via three ganglia: Celiac, Superior mesenteric, inferior mesenteric ganglion

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12
Q

Summarize the organization of the ANS

A

PSNS

  • 4 ganglia in the head
  • CN 3,7,9,
  • Vagus: Subglottic to colon
  • Pelvic: Colon to sex organs

SNS

  • 3 ganglia in the neck
  • 3 ganglia in the abdomen: greater/small splanchnic nerves also here
  • No ganglion for thoracic structures
  • T1 - T4: Head to Lungs
  • T4 - T12: Stomach to sex organs
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13
Q

SNS effects on pulmonary vasculature

A

pulmonary vessel constriction

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14
Q

Does the PSNS effect force of contraction in the heart

A

Yes

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15
Q

What is the heart rate of transplant patients and why?

A

± 110
Vagal nerve transected

Explanation
Adults: PSNS dominates –> Resting heart rate 70 - 80 bpm
Kids: SNS dominates –> HR ± 100

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16
Q

What pharmacological strategies are available to stimulate parasympathetic activity - name the agents and their clinical use

A

Muscarinic agonists - Ophthalmology: Constrict pupil, opening flow to aqueous humor and decreasing IOP.

  • Pilocarpine
  • Carbacol
  • Methacholine

Anticholinesterase - Anaesthetics and myasthenia gravis

  • Increase Ach available at M receptors and at NMJ
  • Neostigmine
  • Pyridostigmine (myasthenia)
  • Organophosphates
17
Q

What pharmacological strategies are available to inhibit parasympathetic activity. Name the drugs and differentiate between them

A

Muscarinic antagonists - from the plant Atropa belladonna (Deadly nightshade)

  • Atropine - crosses BBB with central effects (confusion in elderly)
  • Glycopyrrolate - does not cross BBB
  • Hyoscine - used for GI and HPB colic
  • Homatropine
18
Q

Describe the effects of antimuscarinic drugs on the CNS, CVS, RSP and GIT

A

CNS - atropine is a mild stimulant and can cause confusion in the elderly

CVS - Tachycardia - vagus blocked allowing unopposed SNS. IF brady due to hypoxia - no tachycardia

RSP - Bronchodilatation and reduces secretions

GIT - Anti-sialogogue. Reduced gastrin secretion. Reduced secretions. GI motility is reduced not abolished.

19
Q

Describe the mechanism of action of adrenalin and noradrenalin at different doses

A

Adrenalin
Low doses: beta effects (initial decrease SVR)
High doses: alpha effects increase with increasing dose

Noradrenalin
Predominant alpha 1 effects with some beta effects all doses

20
Q

Describe the mechanism of action of dopamine and dobutamine at different doses

A

Dopamine and dobutamine

Low doses: Stimulate dopamine receptors
High doses: Stimulate adrenergic receptors

Dopamine (similar to adrenalin)
Low dose: Beta 2
High dose: Alpha 1

Dobutamine
Beta 1 (minimal beta 2 and alpha 1 with slight decrease SVR)
–> shift of perfusion from GIT to heart and skeletal muscle but with overall improved splanchnic perfusion

21
Q

What is the mechanism of action, dose, onset and duration of Ephedrine?

A

Dual mechanism of action

  1. Release NA of endogenous noradrenaline from sympathetic terminals
  2. Direct effect on alpha and beta receptors

Dose: 2.5 - 10 mg titrated to BP
Onset: 1 minute
Duration: 1 hour

22
Q

What are the receptor specific adrenegic receptor agonists? What is their mechanism dose, onset, duration of action

A

Phenylephrine
Alpha 1 agonist –> increase SVR
Dose: 50 - 100ug per dose titrated to BP

23
Q

Explain how to use a paediatric infusion set to estimate infusion rate

A

Dimensional analysis

60 drops/ml
_________

1 drop/second

= 60 s/ml

= 60s/ml x 1 min/60s

= 1 min/ml

AND

60 drops/ml
_________

2 drop/s

= 30s/ml

= 30s/ml x 1min/60s

= 1min/2ml

= 2ml/min

SO NUMBER OF DROPS PER SECOND = NUMBER of MLS PER MINUTE

24
Q

What is the mechanism of action of clonidine and dexmedetomidine?

A

Clonidine

  • alpha 2 predominant
  • also alpha 1

Dexmedetomidine (more specific for alpha 2)
- alpha 2 (8 x more selective than clonidine)

Stimulation of alpha 2 receptors

  • -> Sedation (central alpha 2 effects)
  • -> Anxiolytic
  • -> Analgaesia without respiratory depression
  • -> Decrease SVR
25
Q

What is the Richmond Agitation Sedation Score

A

+4 Violent
+3 Aggressive (pulls tubes/catheters)
+2 Agitated (frequent movements/fights vent)
+1 Restless (anxious but movement not vigorous)

0 Alert and calm

  • 1 Drowsy: eyes open with contact to voice >10s
  • 2 Light sedation: eye open with contact to voice < 10s
  • 3 Mod sedation: eye open to voice
  • 4 Deep sedation: eye open to physical stimulation

-5 Unarousable: No response to voice or physical

26
Q

Give examples of selective beta 2 receptor agonist and their use

A

Asthma
Salbutamol
Terbutaline
Fenoterol

27
Q

Give examples of the selective alpha 1 blockers and their use

A

Phenoxybenzamine

  • Great for phaeochromocytoma as the drugs binds covalently to alpha receptor which destroys the receptor
  • Non-competitive alpha 1 antagonist

Prazosin
- alpha 1 antagonist - t1/2 short –> requires QID dosing

Doxazosin

  • Longer half life
  • Used as antihypertensive and preop in phaeo.
28
Q

What is the only available parenteral beta blocker readily available in RSA

A

Labetalol

29
Q

What is the mechanism of action of labetalol

A

10 X greater affinity for beta receptors than alpha receptors but does block both types of receptor

30
Q

How does the dosing of beta blockers differ depending on oral vs intravenous administration and why is this the case

A

Beta blockers have high first pass metabolism

IV doses are therefore significantly lower than oral doses

31
Q

What is the major disadvantage of non-selective Beta antagonists

A

Beta antagonism in the lungs –> increasing airway resistance in asthmatics

32
Q

Describe the metabolic effects of beta bolckers

A
  1. Inhibit lipolysis

2. Inhibit gluconeogenesis (risk of hypoglycaemia)

DA (50 decks)

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