Lecture 13: Autonomic nervous system 1 Flashcards
What is the ANS critical for?
controlling bodily functions, including regulation of all organs and most tissues
What is homeostasis?
maintaining internal set points critical for survival: i.e., keeps us alive
What is allostasis?
maintaining homeostasis through adaptive change of the internal environment, to meet perceived and anticipated demands, e.g., acute stress, exercise
What are the cellular targets of autonomic nerves?
smooth and cardiac muscle epithelial transport of ions hormone and mucous secretion metabolism immune system
Some tissues are supplied by autonomic nerves, but…
no function has been identified for these nerves yet
What can actions of the nervous system be part of?
simple reflexes or involve coordinated regulation of multiple sites or be associated with a more complex behavior (e.g., stress, anxiety, pain)
What do the sympathetic and parasympathetic components of the ANS comprise?
neurons of the central nervous system (CNS) and the peripheral nervous system (PNS): they cannot function without the CNS
Where are neuronal cell bodies of the ENS contained and how can they function?
neuronal cell bodies are entirely within the gastrointestinal tract: can function independently of CNS
What does the ENS comprise?
complete reflex circuits, i.e., the ENS has its own sensory, motor and interneurons
What can some classes of neurons in the ENS be influenced by?
the sympathetic and/or parasympathetic systems
What are sympathetic and parasympathetic nervous systems defined by?
their anatomy, specifically the location of their preganglionic neurons
What is the sympathetic NS described as?
thoraco-lumbar
What is the parasympathetic NS described as?
cranio-sacral
Where are sympathetic ganglia located?
generally closer to CNS
Where are parasympathetic ganglia located?
generally closer to or within organs
What is the primary NT of neurotransmission in the ganglia?
acetylcholine
Which NTs are released by sympathetic ganglia and which receptors do they bind to?
noradrenaline
alpha or beta adrenoceptors
Which NTs are released by parasympathetic ganglia and which receptors do they bind to?
acetylcholine
nicotinic or muscarinic receptors
What is co-transmission?
when more than one transmitter is released from a synapse
There are many ___ of ACh and NA receptors.
subtypes
What are transcriptome analyses identifying?
new subclasses of autonomic ganglion neurons and preganglionic neurons
What is the structure of the sympathetic nervous system?
preganglionic neurons in thoraco-lumbar cord
axons project via spinal nerves
What are the two types of sympathetic ganglia?
paravertebral ganglia (sympathetic chain) and prevertebral ganglia (mesenteric ganglia)
What do sympathetic preganglionic neurons innervate?
the adrenal medulla
What happens if adrenal cells are activated?
adrenal cells secrete the hormones, adrenaline and noradrenaline, into the circulation, having widespread effects
What is “fight-or-flight”? What is the purpose of this response?
mass activation of many sympathetic pathways at once to overcome or escape from a major threat
How does the body change during a “fight-or-flight” response?
increased heart rate, increased contractile force of heart, increased blood flow to skeletal muscle, decreased blood flow to gut, decreased gut motility (can modulate enteric system)
How is mass activation and coordination achieved?
catecholamine hormones can spread through the bloodstream
the CNS activates many preganglionic pathways simultaneously
some preganglionic neurons have many axon collaterals so can activate many postganglionic pathways simultaneously
What is mass activation relevant to in comparison to the SNS?
mass activation is relevant to a more unusual situation, whereas the sympathetic nervous system is essential for normal living (e.g. adjustments of blood pressure, small temperature changes)
Where are preganglionic neurons of the parasympathetic nervous system located?
located in the Edinger-Westphal nucleus, the salivatory nuclei and dorsal motor nucleus of vagus and nucleus ambiguus
Where do preganglionic neurons in the Edinger-Westphal nucleus run to and control?
run to ciliary ganglion to control sphincter pupillae, ciliary muscle
Where do preganglionic neurons in the salivatory nuclei run to and control?
to submandibular, spheno-palatine and otic ganglia to control lacrimal, salivary, sublingual, nasal and palatine glands
Where do preganglionic neurons in the dorsal motor nucleus of vagus and nucleus ambiguus run to and control?
to unnamed microganglia near and on outer surface of thoracic and abdominal organs: numerous functions
Where do sacral postganglionic neurons lie? What do pelvic ganglia contain?
in the pelvic plexus
contain many sympathetic neurons i.e. these are mixed ganglia = very unusual
Why are sacral postganglionic neurons vulnerable to surgical injury?
many of these ganglion neurons have unusually long axons
What is the role of parasympathetic nerves?
inducing “rest-and-digest” which involves decreased heart rate, decreased contractile force of heart and increased gut motility
Is there mass activation of parasympathetic pathways? Why or why not?
no, because there is no equivalent of adrenal gland i.e. no release of ACh into the bloodstream to affect all organs at once
How does most coordination of parasympathetic pathways between different regions occur?
by brain mechanisms
What are the limitations of the “rest-and-digest” model?
parasympathetic pathways can be activated under many situations, not just rest/digest
underestimates diversity of parasympathetic
function
assumes a rather extreme situation when nothing much is happening
Are sympathetic and parasympathetic systems antagonistic?
sometimes: there are very few cases where the two systems are genuinely antagonistic at the cellular level
How does the SNS act in relation to the PNS?
actions on different tissues cause different types of actions (not necessarily opposite)
What are examples of different but not opposite actions?
sympathetic: serous salivary secretion, sweat secretion, lipolysis
parasympathetic: mucous salivary secretion, tear secretion
What are examples of function antagonism in tissue/organ but via different cells?
sympathetic: contract pupil dilator muscle, contract neck of bladder (continence)
parasympathetic: contract pupil sphincter muscle, contract body of bladder (voiding)
What is an example of genuinely antagonistic actions at the cellular level?
sympathetic: increase in heart rate
parasympathetic: decrease in heart rate
