Basic Sciences - Autonomic Nervous System Physiology Flashcards
Global constituents of autonomic nervous system (ANS)
Afferent pathways
Efferent pathways
Role of afferent pathways in ANS
Transmit sensory information from visceral structures
Also chemical and mechanical data from chemo- and baro- receptors
Role of efferent pathways in ANS
Control cardiac muscle, smooth muscle and glands
Central components of the ANS
Midbrain
Medulla
Limbic system
Hypothalamus
Brainstem
Spinal cord
Limbic system
Emotion
Two main divisions of the ANS
Sympathetic nervous system (SNS)
Parasympathetic nervous system (PNS)
Often antagonistic
Parts of the body supplied by SNS
All parts of body including trunk and limbs
Parts of the body supplied by PNS
Viscera only
(except adrenal glands and gonads - only SNS supply)
Efferent pathways of both SNS and PNS structure
Preganglionic neurones
Intermediary ganglion
Postganglionic neurones
Preganglionic neurones features
Cell bodies in brain or lateral horns of spinal cord
Myelinated axons
Slow conducting B fibres
Number of postganglionic neurones innervated by each preganglionic neurone
8 to 9 postganglionic cells
Produces diffuse responses characteristic of ANS
Postganglionic neurones features
Unmyelinated
C fibres
Outflow of sympathetic efferent neurones
Thoracolumbar outflow
T1 - L2
Methods of preganglionic neurone axon termination
1) Most synapse in paravertebral sympathetic chain
2) Some pass through sympathetic chain via splanchnic nerves to synapse in a peripheral autonomic ganglion in abdo / pelvis
3) Few preganglionic fibres synapse directly with chromaffin cells in medulla of adrenal gland
Examples of peripheral autonomic ganglions in the abdomen or pelvis
Coeliac ganglion
Superior mesenteric ganglion
Inferior mesenteric ganglia
Location of preganglionic cell bodies in SNS
Lateral horns of spinal cord levels T1 - L2
Outflow of efferents in PNS
Cranio-sacral outflow from:
- Cranial nerves 3, 7, 9 and 10
- Spinal roots S2-4
Location of preganglionic cell bodies of PNS
Cranial nerve nuclei or lateral horns of sacral spinal cord
Parasympathetic ganglia sites from vagus an sacral efferents where preganglionic neurones synapse
Diffusely located in the walls of the viscera they supply
Eg. heart, gut, lungs
Parasympathetic ganglia sites from cranial nerve 3, 7 and 9 efferents where preganglionic neurones synapse
4 discrete intermediary ganglia:
- Ciliary
- Sphenopalatine
- Submaxillary
- Otic ganglion
Sympathetic efferent outflow to head and neck
Indirect through sympathetic chain via superior, middle or inferior cervical ganglia
Location of inferior cervical ganglion
Often fused with 1st thoracic ganglion to form the stellate ganglion at level C6
Just anterior to neck of first rib
Approximate spinal level origin of sympathetic supply of different organs
Visceral autonomic afferent and pain fibre course of travel
Travel with autonomic efferent nerves:
- Pain fibres from lungs, bronchi and pelvis travel with PNS nerves
- Pain fibres from abdo an heart travel with SNS nerves
Referred pain
Pain from viscera is poorly localised and often ‘referred’ to corresponding somatic segment
Use of thoracic sympathectomy
Treat severe Reynaud’s or hyperhidrosis of palms
Use of lumbar sympathectomy
Treat circulatory insufficiency of lower limb or phantom limb pain
Use of coeliac plexus bloack
Treat pain associated with upper GI malignancy or acute / chronic pancreatitis
Neurotransmitters in the ANS
Acetylcholine
Noradrenaline
Neurones in ANS which use ACh as neurotransmitter
- All preganglionic neurones
- All postganglionic PNS neurones
- Postganglionic SNS neurones that innervate sweat glands and skeletal muscle blood vessels
Neurones in ANS which use noradrenaline as neurotransmitter
All postganglionic SNS neurones EXCEPT postganglionic SNS neurones that innervate sweat glands and skeletal muscle blood vessels
Types of ACh receptor
Muscarinic (M1 - M5)
Nicotinic
Muscarinic ACh receptor location
Smooth muscle, glands, heart and the brain
Muscarinic ACh receptor type
G protein linked
Blocked by atropine
Nicotinic ACh receptor location
Sympathetic ganglia
Motor end plates of skeletal muscle
Nicotinic ACh receptor type
Ligand gated ion channel
Unaffected by atropine
Nicotinic ACh receptor actions mimicked by…?
Nicotine
Muscarinic ACh receptor actions mimicked by…?
Muscarine
Types of adrenergic receptor, their site and G protein type
Alpha 1, Vascular smooth muscle, Gi
Alpha 2, Brain, Gq
Beta 1, Heart, Gs
Beta 2, Lungs, Gs
Beta 3, Adipose tissue, Gs
Adrenergic receptors and secondary messengers
Adrenergic receptors with higher affinity for Noradrenaline
Alpha receptors
Adrenergic receptors with higher affinity for Adrenaline
Beta receptors
Effects of ANS on cardiovascular system
Effects of ANS on lungs, GI and skin
Side effects of atropine
Pyrexia
Confusion
Bronchodilation
Dry mouth
Dilated pupils
Tachycardia
Dry secretions
Side effects of neostigmine
GI spasms
Bradycardia
Nausea
Salivation
Bronchorrhoea
Bronchoconstriction
Side effects of propranolol
Cold extremities
Worsened intermittent claudication
Wheeze
Mechanism of action of propranolol (and therefore reason for side effects caused)
Non selective beta antagonist
Reason for regional anaesthesia inducing sympathetic block
Sympathetic nerves travel with the somatic nerves
