Neuro Physiology - Autonomic Nervous System Flashcards
AN_BK_22, 23, 24, 25
How is the nervous system organised?
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Central - Divided into spinal cord and brain.
Brain further divided into:
Hindbrain
Pons - Bladder, sleep, breathing, swallowing
Medulla - Breathing, heart & circulation, vomiting
Cerebellum - Balance/Coordination
Midbrain
Tectum - Eye & ear reflexes
Tegmentum - Movement, cranial nerve nuclei
Forebrain
Thalamus - Sleep
Hypothalamus - Metabolism, homeostasis
Basal Ganglia - Voluntary motor control
Amygdala - Emotion, fear, memory
Hippocampus - Memory
Cortex - Higher thought, language & memory
Peripheral divided into Somatic (Sensory and Motor), and Autonomic (Sympathetic and Parasympathetic)
What is the role of the Autonomic Nervous System?
Involuntary, automatic branch of the nervous system concerned with the control and maintenance of homeostasis via reflex pathways, although it may be influenced by higher centres and somatic activity as well.
Describe the anatomy of the Autonomic Nervous System
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Divided into sympathetic and parasympathetic pathways, each starting in the CNS, with a myelinated preganglionic nerve, a ganglion, and then a post-ganglionic unmyelinated nerve to the target organ.
Most organs are supplied by both systems, but some are only supplied by one.
Parasympathetic only:
Lacrimal glands
Sympathetic only:
Juxtaglomerular apparatus, Piloerector muscles, fat, adrenals
CNS Outflow:
Parasympathetic - Cranio-sacral
CN III (Oculomotor), VII (Facial), IX (Glossopharyngeal), and X (Vagus)
S2-S4 supply pelvic organs
Sympathetic - Thoracolumbar
T1-L2 via anterior or ventral nerve roots (white rami)
Location of ganglia:
Parasympathetic
Ganglia are close to target organ - long preganglionic but short post-ganglionic fibres
Oculomotor - Ciliary ganglion
Facial - Pterygopalatine and submandibular ganglia
Glossopharyngeal - Otic ganglion
Vagus - Multiple plexi near target organs
Sympathetic
Ganglia further from target organ, in sympathetic chain, with short preganglionic fibres travelling through white rami, with three main plexi
3 cervical ganglia (Superior, Middle, Lower (Fuses with T1 to form stellate)
12 thoracic ganglia
4 lumbar
4 sacral
Cardiac, Coeliac and Hypogastric plexi
Long post-ganglionic fibres are unmyelinated C fibres.
Classify by organ system
Describe the function of the Autonomic Nervous System
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Most organs are affected by both branches of the autonomic nervous system, but one has a dominant tone.
The parasympathetic governs physiological processes that happen at rest, so there is generally a bakcgound level of activity. The sympathetic system tends to activate in times of stress and high activity.
List the neurotransmitters used by each part of the Autonomic Nervous System
Parasympathetic:
Pre-Ganglionic - ACh at nicotinic receptors
Post-Ganglionic - ACh at muscarinic receptors
Sympathetic:
Pre-Ganglionic - ACh at nicotinic receptors
Post-Ganglionic - NA at muscarinic receptors
c.f. sweat glands (ACh at muscarinic receptors)
Adrenal medulla is unique - the pre-synaptic neuron synapses directly onto the chromaffin cells of the adrenal gland, with ACh as the neurotransmitter
What drugs directly affect the autonomic nervous system?
Parasympathetic
Glycopyrrolate (Peripheral antimuscarinic, Quaternary amine which doesn’t cross BBB or placenta)
Atropine (Peripheral and Central antimuscarinic)
Sympathetic
Adrenaline (A and B agonist)
Noradrenaline (A1 agonist, some B1 activity)
Dobutamine (B agonist, mainly 1 but some B2 hence SVR drops)
Metaraminol/Phenylephrine (A1 agonist)
Ephedrine (A & B agonist, stimulates NA releas from adrenal)
B1 antagonists (Atenolol/Metoprolol)
Describe the sympathetic nervous system
Purpose:
The branch of the autonomic associated with the fight or flight response, induces state of alertness and prepares body for high levels of activity.
Outflow:
T1-L2 thoracolumbar outflow, with short pre-ganglionic nerves in the white rami communicantes, and then long post-ganglionic fibres arising from the sympathetic chain (2cm lateral to vertebrae from occiput to coccyx), targeting specific organs.
Synapses:
Preganglionic: Nicotinic ACh Postganglionic: (Nor)-Adrenergic
Can synapse at same or different spinal level, via synaptic chain to a specific plexus, or via coeliac ganglion to adrenal medulla
Innervation:
Visceral organs via plexi (Cardiac/Coeliac/Hypogastric)
Some organs have unopposed sympathetic input (sweat glands, fat, juxtaglomerular apparatus)
Describe the parasympathetic nervous system
Purpose:
The branch of the autonomic associated with the rest and digest response, reduces cardiac activity, and promotes gut motility/digestion.
Outflow:
Craniosacral outflow, with 75% via vagus. Long pre-ganglionic nerves and short post-ganglionic fibres.
Synapses:
Preganglionic: Nicotinic ACh Postganglionic: Muscarinic ACh
Can synapse at same or different spinal level, via synaptic chain to a specific plexus, or via coeliac ganglion to adrenal medulla
Innervation:
C3 - Ciliary ganglion to pupil
C7 - Pterygopalatine and submandibular ganglion to salivary/lacrimal glands
C9 Otic ganglion to respiratory tree
C1- to heart and GI tract
S2-4 - Distal gut, genitalia, bladder
List the subtypes of muscarinic receptors
M1
Pupil constriction
Gastric acid secretion
M2
Heart
M3
Vascular
Salivary
Lacrimal (Only have parasympathetic input)
Pancreatic
M4
Brain
Adrenal medulla
M5
Brain
How many nuclei does the Vagus nerve have?
Four nuclei in the Medulla
Dorsal motor nucleus
Nucleus Ambiguus
Solitary tract nucleus
Spinal trigeminal nucleus (mostly trigeminal but some vagal input)
Describe the Stellate ganglion and explain its importance in anaesthetic practice
Formed from the fusion of the first thoracic and inferior cervical ganglion, occuring in 75-80% of people
Found at level of C7, anterior to the neck of the first rib, medial to vertebral artery behind the carotid sheath.
Applying local anaesthetic to the brachial plexus can track to the stellate ganglion producing Horner’s syndrome (Ptosis, Miosis, Anhidrosis)
Stellate ganglion block can be used clinically for:
* Vascular insufficiency of the upper limb
* Complex regional pain syndrome
* Severe refractory angina
* Post-herpetic neuralgia
* Refractory VT
