Autonomic Nervous System Flashcards
Describe the basic function of the autonomic nervous system.
Unconscious control of structures with smooth muscle, cardiac muscle, and certain glands.
Can the autonomic nervous system be modulated by conscious drive?
You bet it can!
What 3 systems are included in the autonomic nervous system?
Sympathetic, parasympathetic, and enteric nervous system.
Where are the efferent structures of the sympathetic fibers located?
In the “thoracolumbar division”.
Originate at T1-L3 lateral horns.
Where are the efferent structures of the parasympathetic fibers located?
In the “craniosacral division”
Fibers from CN 3, 7, 9, and 10 originate in brainstem
Also originates at S2-S4 lateral horns
What are the 4 major features of the somatic NS?
- Have specialized afferent and efferent fibers with reflex connections within CNS.
- Have connections with higher levels of CNS via pathways
- Thalamus is major structure that receives afferent info
- Cerebral cortex is the major source of descending pathways
What are the 4 major functions of the autonomic NS?
- Have specialized afferent and efferent fibers with reflex connections within CNS.
- Have connections with higher levels of CNS via pathways
- Hypothalamus is major structure that receives afferent info
- Hypothalamus is also major source of descending pathways
What is a major difference of the ANS?
The efferent link between CNS and viscera innervated by ANS involves 2 neurons.
Preganglionic axon exit CNS via ventral roots and synapse in ganglia with postsynaptic neurons, which then project to smooth muscle, cardiac muscle, or gland tissue of visceral organs
What type of synapses are in the ANS?
Electrical synapses (gap junctions) - Allows for steady and widespread contractions of visceral tissue
Describe the myelination of the pre and postganglionic ANS fibers.
Preganglionic fibers = lightly myelinated
Postganglionic fibers = NO myelin
Describe the axons of sympathetic fibers.
Postganglionic cell bodies (in ganglia) are positioned close to the spinal cord.
Have SHORT preganglionic and LONG postganglionic axons.
Describe the axons of parasympathetic fibers.
Postganglionic cell bodies (in ganglia) positioned close to target effector.
Have LONG preganglionic and SHORT postganglionic axons.
What is the sympathetic trunk?
Describes the stacked presentation of the ganglion of the sympathetic NS. Runs parallel to the spinal cord.
What are the neurotransmitters of the sympathetic NS?
- Acetylcholine = released at terminals of preganglionic fibers
- Norepinephrine = released at terminals of postganglionic fibers
*Both ionotropic and metabotropic receptors
What are the neurotransmitters of the parasympathetic NS?
Acetylcholine = released at terminals of pre and postganglionic fibers
*Both ionotropic and metabotropic receptors
What is the function of the SNS?
To increase activity during times of physical or emotional stress.
4 E’s = exercise, emergency, excitement, and embarrassment
What is your targets for the preganglionic neurons in the upper/mid thoracic and lower thoracic/upper lumbar?
Extends from T1-L2/3 in lateral horn of spinal gray matter.
Upper/mid thoracic = head and thorax
Lower thoracic/upper lumbar = abdominal organs, pelvic organs, and LE targets
When the neuron exits the spinal cord via the ventral rami it can take 3 different routes. What are they?
- Travel to sympathetic trunk via white communicating rami and SYNAPSE IMMEDIATELY with postganglionic neurons at the same level of spinal cord.
- Travel to sympathetic trunk via white communicating rami and either ASCEND or DESCEND to synapse in more cranial or caudal ganglia
- Continue through trunk without synapsing, and latera synapse with postganglionic neurons in PREVERTEBRAL ganglia.
Since SNS fibers go onto synapse with multiple postganglionic fibers, what kind of results will there be?
Means that a single preganglionic neuron have multiple target tissues!
Allows for SNS to mass activate targets in response to stress!
What are the targets of the postganglionic fibers of the SNS?
- Blood vessels and skin via gray communicating rami
- To viscera (organs) via prevertebral ganglia
- To lower extremities (sweat secretion, vasoconstriction, piloerection)
What is the function of the parasympathetic NS?
Functions to increase activity during “rest and digest” periods to conserve energy use and build energy stores.
Where are the preganglionic neurons of the PNS found?
Found in the brainstem and sacral spinal cord and travel to parasympathetic ganglia located close to target muscles and glands.
What are the brainstem preganglionic nuclei of the PNS?
- EW nuclei
- Superior and inferior salivary nuclei
- Nucleus ambiguous
- Dorsal motor nucleus of vagus nerve
Where are the sacral preganglionic nuclei of the PNS located?
Lateral horns of S2-S4
Where do the postganglionic nuclei of the brainstem project to?
- EW nuclei TO ciliary muscles
- Superior & inferior salivary nuclei TO salivary and lacrimal gland
- Nucleus ambiguous TO cardiac muscle
- Dorsal motor nucleus of vagus nerve TO thorax/abdomen, cardiac muscle, lungs, and the gut
Where do the postganglionic nuclei from the sacrum project to?
From lateral horns TO colon, rectum, bladder, and reproductive organs
Are most structures innervated by BOTH SNS and PNS?
Yep!
What are the exceptions to the dual innervation?
(sympathetic only)
- Sweat glands
- Erector pili muscles
- Most blood vessels
- Adrenal medulla
Why do sympathetic responses last longer than parasympathetic responses?
Due to:
- Divergence of preganglionic neurons
- Longer myelinated postganglionic neurons
- Slower activation of NE in the synapse
- Presence of NE and eipnephrine from adrenal medulla in blood
What can accelerate parasympathetic responses?
Paradoxical fear
What controls the functions of the ANS?
- Hypothalamus
- Brainstem nuclei
- Amygdala + other limbic structures
- Medial prefrontal cortex
- Insular cortex
What regulates the functions of the ANS?
- Baroreceptors
- Chemoreceptors
- Osmoreceptors
- Thermoreceptors
What are the two main functions that afferent input serves for the ANS structures?
- Feedback input via solitary nucleus for local autonomic reflexes.
- Inform higher integrative centers of more complex patterns of stimulation that may signal danger and/or may require more multi-system control
Describe visceral pain
So some second order neurons in the dorsal horn that receive visceral sensory input are part of the anterolateral system –> since these neurons are also in charge of relaying input about superficial pain, visceral pain often gets perceived as cutaneous pain –> REFERRED PAIN
*Travel to VPL of thalamus then project to insular cortex for integration
