Autonomic nervous system Flashcards
What is the purpose of the autonomic nervous system?
Maintaining homeostasis and survival
Which tissue types does the CNS innervate?
Everything except the CNS tissue and skeletal muscle
What are the three divisions of the ANS?
Sympathetic NS
Parasympathetic NS
Enteric NS
Describe the general pattern of innervation of the sympathetic and parasympathetic NS?
Most organs are innervated by both sympathetic and parasympathetic nerves, but each system usually innervates different tissues.
Which spinal cord segments are the sympathetic and parasympathetic nerves derived from?
Sympathetic: thoraco-lumbar
Parasympathetic: cranio-sacral
Where in the spinal cord do autonomic pathways NOT originate from?
Cervical or lumbar enlargements
Why don’t autonomic pathways originate from cervical or lumbar enlargements?
Upper and lower limb nerves originate from here
Describe the location of sympathetic and parasympathetic ganglia?
Sympathetic ganglia are more distant from organs
Parasympathetic ganglia are closer to or within organs
What are the two divisions of sympathetic ganglia?
Prevertebral ganglia
Paravertebral ganglia
Describe the general organisation of sympathetic and parasympathetic nerves (in terms of strucutre, ganglia, etc.)?
Sympathetic: short preganglionic, long postganglionic fibres
Parasympathetic: long preganglionic, short postganglionic fibres
Preganglioinc fibres are lightly myelinated or unmyelinated, whereas all postganglionic fibres are unmyelinated
Which NTs are used by sympathetic and parasympathetic nerves?
What are non-classical transmitters?
Give some examples?
NTs that are not Ach or NA
aka ‘non-adrenergic, non-cholinergic’
eg. NO, ATP, NPY
What is co-transmission?
More than one NT can be released at one time
How does the ANS differ from the CNS in terms of the primary transmitters?
ANS: Ach and NA
CNS: glutamate and GABA
Describe the junctions of ANS nerves and their target organs?
No easily visible junction
More than one transmitter release site per axon
Extra-junctional receptors present
Where are sympathetic preganglionic neurons found?
Interomediolateral cell column of spinal cord
Where are sympathetic postganglionic neurons located?
Two locations and functional classes:
Paravertebral
Prevertebral
What is the function of sympathetic ganglia?
Essential for integration and coordination of sympathetic control between organs/tissues
What are the functions of paravertebral and prevertebral sympatheitc ganglia?
Paravertebral: primary source of vasoconstrictor neurons
Prevertebral: primary source of neurons innervating non-vascular smooth muscle
Describe the concept of convergence and divergence of sympathetic postganglionic neurons?
Convergence: particularly prevertebral ganglion neurons integrate signals from multiple inputs
Divergence: up to 200 ganglion neurons can be activated by one preganglionic neuron
Why is divergence in postganglionic neurons important?
Allows coordination of effects in many tissues at once
What is the major function of the sympathetic nervous system?
‘Fight or flight’ functions
Also activation of adrenal gland > release A and NA, broad activation of adrenoceptors
List the three nuclei in the cranial component of preganglionic parasympathetic neurons?
Edinger-Westphal nucleus
Salivatory nuclei
Dorsal motor nucleus of vagus and nucleus ambiguus
Where are the sacral preganglionic parasympathetic neurons located?
Sacral spinal cord
Describe the special features of autonomic supply to the pelvic organs?
Project in pelvic splanchnic nerves to pelvic ganglia (pelvic plexus)
Extensions of this plexus lie close to or within pelvic organs
Many of the PS ganglion neurons have unusually long axons
Also contain many sympathetic neurons: mixed ganglia
What is the function of the parasympathetic nervous system?
‘Rest and digest’ functions
Do the sympathetic and parasympathetic nervous systems always act antagonistically?
No
There are very few cases when the two systems are genuinely antagonistic at the cellular level
More commonly, actions are on different tissues to cause different types of actions
Give examples of situations when the sympathetic and parasympathetic nervous systems are not acting genuinely antagonistically?
What is the best way to distinguish between the sympathetic and parasympathetic nerves?
Anatomically: location of preganglionic neurons
Sympathetic: thoracic, lumbar spinal cord
Parasympathetic: cranial nuclei, sacral spinal cord
Describe a typical autonomic reflex?
Visceral afferent neurons provide input to local interneurons and projection neurons
Most autonomic reflexes are supraspinal, and involve brain input
Output to periphery via autonomic ganglion
Describe the nucleus of the solitary tract?
Caudal part located in medulla
Major integrative centre for autonomic function
Second order sensory neurons
Describe the inputs and outputs of the nucelus of the solitary tract?
Input: visceral afferents
Output: 1. feedback to local reflexes that control organ function; or 2. provide info to higher centres to drive more complex responses
Why is the hypothalamus important in the ANS?
Most importnant brain region for coordination of autonomic output
What are the inputs to the hypothalamus?
Sensory pathways
Intrinsic sensory stuctures
Circularting hormones
What is the major role of the hypothalamus in the ANS?
Compares situation to biological set points, and adjusts behaviour and autonomic function if necessary
What does the hypothalamus integrate with to determine its output?
Higher cortical and limbic systems
