Autonomic Nervous System Flashcards
Define the autonomic nervous system?
Involuntary nervous system
Visceral motor system
What is the purpose of the ANS?
Homeostasis
Allostasis
What sorts of actions can the ANS have?
Part of simple reflexes
Involve coordinated regulation of multiple sites
Associated with more complex behaviour
What are the features of the ANS?
Precise
Flexible
Integrativ
What are the targets of autonomic nerves?
Smooth and cardiac muscle Epithelial transport of ions Hormones and mucous secretions Metabolism Immune cells
What are the components of the ANS?
Sympathetic
Parasympathetic
Enteric
Where are the parts of the sympathetic and parasympathetic nervous systems?
CNS
PNS
Do the sympathetic and parasympathetic nervous systems require the CNS for function?
Yes
Where is the enteric nervous system?
In GIT
Does the enteric nervous system need the CNS to function?
No, can function independently
What neurons make up the enteric nervous system?
Sensory
Motor
Interneurons
Do the sympathetic and parasympathetic nervous systems influence the enteric nervous system?
Yes
How are the sympathetic and parasympathetic nervous systems defined?
By their anatomy - location of their preganglionic neurons
Where are the sympathetic preganglionic neurons?
In thoraco-lumbar region of spinal cord
Where are the parasympathetic preganglionic neurons?
In cranio-sacral region of spinal cord
Which areas of the spinal cord have no visceral fibres?
Cervical and lumbar enlargements
What nucleus in the spinal cord are sympathetic preganglionic cell bodies located?
Intermediolateral nucleus
What are the two types of sympathetic ganglia?
Paravertebral = sympathetic chain Prevertebral = mesenteric ganglia
Other than the sympathetic ganglia, what else do preganglionic sympathetic neurons innervate?
Adrenal medulla
What is the sympathoadrenal system?
Preganglionic sympathetic neurons and adrenal medulla
Where are the preganglionic parasympathetic cell bodies located?
Brainstem nuclei
Sacral spinal cord
What are the preganglionic parasympathetic nuclei of the brainstem?
Edinger-Westphal nucleus
Salivatory nuclei
Dorsal motor nucleus of vagus and nucleus ambiguus
Where do neurons project to from the Edinger-Westphal nucleus, and what do they control?
To ciliary ganglion to control sphincter pupillae and ciliary muscle
Where do neurons project to from salivatory nuclei, and what do they control?
To submandibular, sphenopalatine, and otic ganglia to control lacrimal, salivary, sublingual, nasal, and palatine glands
Where do neurons project to from the dorsal motor nucleus of vagus and nucleus ambiguus, and what do they control?
To microganglia near and on outer surface of thoracic and abdominal organs, controlling many functions
Where in the sacral spinal cord is the parasympathetic preganglionic nucleus?
Interomediolateral nucleus
Where are sacral postganglionic parasympathetic neurons?
In pelvic/inferior hypogastric plexus
Are the pelvic ganglia purely parasympathetic?
No, they contain many sympathetic neurons > mixed ganglia
What is the clinical significance of the long axons of the pelvic plexus?
Vulnerable to surgical injury
Are ANS neurons myelinated or unmyelinated?
Unmyelinated
Where are neurotransmitters stored in postganglionic fibres?
In swellings along axon = varicosities
Can be released from any of them
What is the significance of transmitter release from varicosities?
Transmitter released over large area so it has large effect in coordinated way
What is the preganglionic transmitter, and what receptor does it act on?
ACh
Nicotinic receptors
What is the postganglionic sympathetic neurotransmitter and what receptor does it act on?
NA (most)
Alpha/beta adrenoceptors
ACh (few)
Muscarinic receptors
What is the postganglionic parasympathetic neurotransmitter, and what receptor does it act on
ACh
Muscarinic receptors
How many subtypes of ACh and NA receptors are there?
Many
Are ACh and NA the only transmitters used by the ANS?
No, many others used
How does the ANS gather information?
Caudal part of nucleus of thee solitary tract (NTS) in medulla receives sensory input
What is the major integrative centre of autonomic function?
NTS
Where is sensory information distributed to?
Provide feedback to reflexes > control organ/tissue function
Provide info to higher centres to drive more complex responses
What is the role of the hypothalamus in the ANS?
Receives
- Sensory inputs
- Contextual info from other brain regions
- Hormonal signals
Compares situation to biological set points > adjusts behaviour, autonomic and endocrine function
What does the fight or flight response involve?
Mass activation of many sympathetic pathways at once to overcome/escape from major threat
Why doe mass activation and synchronisation occur in the fight or flight response?
CNS activates many preganglionic pathways at once
Some preganglionic neurons have many axon collaterals > activate many postganglionic neurons at once
When adrenal medulla activated catecholamine hormones spread through bloodstream
When is mass activation of the sympathetic nervous system relevant?
Extreme situation
How does the sympathetic nervous system mediate functions essential for normal living?
Individual cells/tissues/organs precisely and independently activated
Adrenal medulla nerves not always activated
Why is there limited mass activation of different types of parasympathetic pathways?
No equivalent of adrenal gland
Preganglionic neurons don’t have as many axon collaterals to simultaneously activate numerous postganglionic neurons
Most coordination of pathways between different regions occurs by brain mechanisms
