ANS Flashcards
General vs special
General
- In spinal and cranial regions
Specific
- Only in cranial regions
Somatic vs visceral
Somatic
- Innervate structures derived from somatopleure
Visceral
- Innervate structures derived from splachnopleure
Afferent vs Efferent
Afferent
- Input to CNS
Efferent
- Output from CNS
Autonomic efferent fibers innervate __________, _________ and _________; these fibers can be called _______________
Cardiac muscle, smooth muscles and secretory cells (in mucosa, dermis & glands)
General Visceral Efferents (GVE)
Somatic (and branchiomotor) motor fibers innervate _________ that is derived from ___________ and ___________; these fibers can be called ____________
striated muscle; somites and head mesoderm
General Somatic Efferents (GSE)
In ANS, the preganglionic neuron cell body _______ the CNS, with its axon synapsing on a ganglion __________ of the CNS.
Inside; outside
Somatomotor vs brachiomotor
Somatomotor
- GSE
- Innervate: Striated muscles
- Develop from myotomes or dorsal portions of the cranial paraxial mesoderm
Brachiomotor
- GVE
- Innervate: Striated muscles
- Develop from cranial paraxial mesoderm that has migrated into the pharayngeal arches
Somatomotor and Brachiomotor vs Visceral motor
Somatomotor and Brachiomotor
- 1 neuron from CNS to target
- Transmitter: Acetylcholine
- Fibers are highly myelinated
Visceral Motor
- 2 neurons (preganglionic and postganlionic)
- Transmitter: 1st is acetylcholine; 2nd is norepinephrine
- Preganglionic fibers are myelinated; postganglionic fibers are unmyelinated
NOTE: Postganglionic sympathetic fibers that innervate sweat glands ONLY secrete acetylcholine
Visceral Motor
- Innervate: Smooth muscle, cardiac muscle and secretory cells
- These target tissues devel from splanchnopleure mesoderm, neural crest, and dermal mesenchyme
Which organ in the sympathetic nervous system acts as a ganglia?
The adrenal glands sit on top of the kidneys. The adrenal medulla acts as a sympathetic ganglia with neuron like cells in it. These cells receive synapses and when activated they release norepinephrine into the bloodstream
___________ is referred to as the Cranio-Sacral “outflow”.
Parasympathetic nervous system
___________ is referred to as the Thoraco-Lumbar “outflow”.
Sympathetic nervous system
Where are central neurons for the parasympathetic nervous system located?
- brainstem (CN III, VII, IX, X) and
- sacral spinal cord (S2-4)
Where are central neurons for the sympathetic nervous system located?
Sympathetic central neurons are found only in the thoracic and lumbar spinal cord between T1 and L2.
Preganglionic sympathetic neurons are located in the _____________ in the lateral horn of the spinal cord, from T1- L2.
Intermediolateral cell column
Where do the postganglionic motor neurons of the parasympathetic nervous system synapse?
- Parasympathetic ganglia of the head
- Ciliary (Cranial nerve III)
- Submandibular (Cranial nerve VII)
- Pterygopalatine (Cranial nerve VII)
- Otic (Cranial nerve IX)
- In or near the wall of an organ innervated by the Vagus (Cranial nerve X) or Sacral nerves (S2, S3, S4)
Where do the postganglionic motor neurons of the sympathetic nervous system synapse?
-
Paravertebral ganglia of the sympathetic chain (these run on either side of the vertebral bodies)
- Cervical ganglia
- Thoracic ganglia
- Rostral lumbar ganglia
- Caudal lumbar ganglia and sacral ganglia
- Prevertebral ganglia (celiac ganglion, aorticorenal ganglion, superior mesenteric ganglion, inferior mesenteric ganglion)
- Chromaffin cells of adrenal medulla
Examples of structures/ functions that receive both sympathetic and parasympathetic input
Cardiac function
Pupillary reflexes
Cerebral vascular resistance
Which structures receive on sympathetic innervation?
- most arterial smooth muscle
- effectors in the skin such as arrector pili mm. and glands
- chromaffin cells in adrenal medulla.
Which structures receive only parasympathetic innervation?
- Ciliary body which helps change lens shape
- Lacrimal gland
- Salivary glands
Cerebral control of visceral motor activity is mediated through descending projections of the _________, especially by those of the ____________ nucleus
hypothalamus, paraventricular
Paraventricular nucleus of the hypothalamus
- A group of neurons that can be activated by physiological changes including stress.
- The PVN receives afferent inputs from many brain regions and different parts of the body, by hormonal control.
Where do the neurons in the paraventricular nucleus project?
- Hypothalamic-pituitary-adrenal (HPA)-axis
- The parasympathetic and sympathetic visceral motor nuclei of the brainstem and spinal cord.
Sympathetic trunk ganglia also known as______________
(a.k.a. sympathetic chain ganglia; paravertebral ganglia)
Prevertebral ganglia also known as___________
(a.k.a. preaortic ganglia)
The __________________projects to the preganglionic sympathetic visceral motor neurons in the intermediolateral cell column.
hypothalamospinal tract
Hypothamospinal tract
- Connects the hypothalamus to the ciliospinal center of the intermediolateral cell column in the spinal cord (T1 to L2).
- Lesions of the hypothalamospinal tract cause ipsilateral Horner’s syndrome.
Prevertebral ganglia
- Sympathetic ganglia which lie between the paravertebral ganglia and the target organ.
- Some of the targets present in the pelvic viscera include the enteric nervous system, as well as the renal system, bladder, and any other organs present in the abdomen.
The ganglion cells project postganglionic fibers through gray rami communicans to spinal nerves for distribution to ___________ and ____________.
blood vessels and dermis
Paravertebral sympathetic ganglia are derived from ______________
embryonic neural crest cells
What are the 3 possible pathways of preganglionic fibers?
- Preganlionic fibers exit the ventral root, floow spinal nerve, and then white ramus communicans to either:
1. Synapse at the same level. Postganglionic fibers exit in gray ramus communicans to join ventral or dorsal ramus at the same spinal level
2. Travel up or down the sympathetic chain to synapse at a different level. Post ganglionic fibers exit in gray ramus at the level of the synapse
3. Transverse the ganglion without synapsing to travel in a splanchnic nerve. It will synapse in a prevertebral ganglion. Postganglionic fibers travel on blood vessels to reach target.
Preganglionic sympathetic fibers leave the spinal cord via ventral roots and then reach the sympathetic trunk through ____________on their way to synapse on cells in _____________ ganglia.
Postganglionic sympathetic fibers leave the sympathetic trunk through ______________ to join ___________ for distribution to peripheral targets like smooth muscle and glands in the body wall and extremities.
White rami communicantes; paravertebral
Gray rami communicantes; spinal nerves
Autonomic plexuses are formed from ______________, ____________, and ___________.
sympathetic postganglionic axons
parasympathetic preganglionic axons
visceral sensory axons.
What type of fibers are carried by splanchnic nerves?
These splanchnic nerves carry:
-
Preganglionic sympathetic fibers (GVE) axons from T1-L2 intermediolateral neurons that extend through the trunk and terminate at synaptic sites on:
- Preaortic sympathetic ganglion cells (Prevertebral) in coeliac, superior mesenteric, inferior mesenteric
- Dorsal root ganglion afferent fibers (GVA) to the same viscera as supplied by the postganglionic sympathetic fibers
Pelvic splanchnic nerves extend between __________ and _________.
spinal nerves s2-S4 and pelvic viscera.
What type of fibers do pelvic splanchnic nerves carry?
They carry parasympathetic fibers from s2-s4 spinal cord to small parasympathetic ganglia in the walls of the hindgut and pelvic viscera
How do sympathetics innervate the heart?
Postganglionic sympathetic fibers from cervical and thoracic paravertebral ganglia run in sympathetic cardiac nerves, which run from the sympathetic trunk to the cardiac plexus
NOTE: Increased sympathetic activity results in acceleration and strengthening of the heart beat
Which type of fibers are found in the cardiac plexus?
The Cardiac Plexus also contains preganglionic parasympathetic (Vagus) fibers as well as Dorsal Root Ganglion and vagus sensory fibers
What are steps to sympathetic innervation of the GI tract?
- Splanchnic nerves carry preganglionic sympathetic fibers (and related sensory fibers) from the sympathetic trunks to the abdominal viscera.
- The preganglionic sympathetic fibers synapse onto prevertebral ganglia (= preaortic ganglia) located on the trunks of major aortic branches supplying the viscera.
List types of preaortic ganglion
Coeliac ganglion
Superior Mesenteric ganglion
Inferior mesenteric ganglion
NOTE: Preaortic ganglion are named for the large arterial branches they surround
- Input from greater splanchnic nerves innervates _________. Which preaortic ganglion is involved?
- Input from lesser splanchnic nerves innervates ________. Which preaortic ganglion is involved?
- Input from lumbar splanchnic nerves innervates ___________. Which preaortic ganglion is involved?
Foregut: stomach, liver, spleen, pancreas; Coeliac ganglion
Midgut: jejunum, illium, proximal colon; Superior mesenteric ganglion
Hindgut: colon, rectum; Inferior mesenteric ganglion
Catecholamine-secreting chromaffin cells in the adrenal medulla are directly innervated by pre-ganglionic sympathetic fibers. How is this possible?
Adrenal medulla acts as a ganglia
When stimulated, the chromaffin cells secrete___________ into the blood stream (mainly via _____________ veins) thus providing the neurohormone to cells throughout the body.
adrenaline (epinephrine); suprarenal
There is no parasympathetic innervation to the limbs. True or false.
TRUE
*This means that the only way blood vessels in the skin are dilated is by diminished sympathetic activity, NOT increased parasympathetic activity
Vagus (cranial nerve X) preganglionic efferent fibers innervate small parasympathetic ganglia throughout the innervation field of the vagus nerve. Where are these ganglia found?
These ganglia are found in the walls of the GI tract from the esophagus to middle of the colon.
Preganglionic efferent fibers in cranial nerves III, VII and IX innervate large parasympathetic ganglia in the head. What do these ganglia innervate?
These ganglia innervate tear & salivary glands, smooth muscles in the eye and cerebral blood vessels.
Preganglionic efferent fibers from the sacral spinal cord (s2-S4) innervate small parasympathetic ganglia. Where are these ganglia found?
In the lower part of the colon (hindgut) and in the walls of pelvic viscera.
Preganglionic neurons of the parasympathetic nervous system are derived from the ___________.
Neural tube
Which ganglion is apart of CN III?
Ciliary ganglion
Which ganglion is apart of CN VII?
Pterygopalantine ganglion
Which ganglion is apart of CN IX?
Otic ganglion
Which fibers are provided by the vagus nerve?
Visceromotor (GVE)
Vagal afferent fibers (GVA)
The visceromotor fibers that provide parasympathetic innervation come from which nucleus of the vagus nerve? What are the targets?
Visceromotor (GVE) fibers from the Dorsal Motor Nucleus of the Vagus target parasympathetic ganglia in the heart, lungs and abdominal viscera, as far down as the beginning of the descending colon
The vagal afferent fibers of the vagus nerve are from which ganglion? What are the targets?
Vagal afferent fibers (GVA) from the Inferior Vagal Ganglion (possibly superior as well) serve all of the organs that receive vagal efferents (heart, lungs and abdominal viscera, as far down as the beginning of the descending colon)
Vagal preganglion parasympathetic neurons (CN X GVE) are located in two very elongated visceral motor nuclei in the ___________.
medulla oblongata.
Where are most of vagal preganglion parasympathetic neurons located?
Dorsal vagus motor nucleus
Stimulation of the dorsal vagus motor nucleus upregulates secretion of ________, __________, and ___________-.
Gastric acid, insulin, glucagon
Aside from the dorsal vagus motor nucleus, vagal preganglionic parasympathetic neurons can be found where?
In the nucleus ambiguus
What type of nucleus is the dorsal vagus motor nucleus?
Visceral motor nucleus (GVE)
The nucleus ambiguus is what type of nucleus?
Branchiomotor nucleus
NOTE: A groups of preganglionic (GVE) neurons projecting to the heart are present in the caudal half of NA.
Nucleus Ambiguus is predominantly a branchiomotor nucleus (SVE) and mainly innervates striated muscles in the _________, ________, and __________.
pharynx, larynx and esophagus.
Vagal sensory neurons located in the ___________ ganglion convey afferent input (except pain) concerning distention of hollow organs, blood gases, pH, etc. to the visceral afferent nucleus of the medulla, the Nucleus of the Solitary Tract (NST).
nodose
The visceral afferent nucleus of the medulla is known as the _______________.
Nucleus of the solitary Tract
The continuation of the sympathetic trunks and preaortic plexuses into the pelvis is called the______________
“hypogastric plexus”.
Nerves running from the hypogastric plexus into the pelvic viscera are called ____________. These carry sympathetic fibers to the pelvic viscera.
“Sacral splanchnic nerves”.
Nerves running from S2-S4 to the pelvic viscera are called_______________. These carry _____________fibers.
“Pelvic splanchnic nerves”; parasympathetic
Sacral splanchnics are ____________
Pelvic splanchnics are _________
Sympathetic
Parasympathetic
In the head, the visceral sensory fibers are found in sensory ganglia of ________ and ___________-.
CN IX and CN X
*Respond to pressure or stretch specialized chemosensitive cells or to pain produced by damaging degrees of stretch, ischema or irritation.
What is the general “rule of thumb” for visceral sensory innervation?
The general “rule of thumb” for visceral sensory innervation is that the sensory fibers to a particular visceral target area travel the same overall path as the efferent fibers that supply that area.
*So, to trace visceral afferent pathways, follow the visceral efferent pathway in reverse.
The vagus nerve conveys pain. True of False.
False
*The vagus nerve (vagus sensory ganglia) conveys sensory information from targets receiving parasympathetic input, but does not convey pain.
In contrast, DRG afferents to visceral organs do convey pain signals, mostly from stretch and pressure on internal organs. Because this “visceral pain” is not highly localized it gets “referred” to somatic regions supplied by the same spinal nerves as the visceral target. Why?
This is because visceral pain receptors enter the spinal cord along the same route as somatic pain.
The most famous example is the referral of cardiac pain occurring during a heart attack to somatic regions supplied by the same DRG and spinal cord levels. Which nerve is implicated?
Phrenic nerve
More neurons are located in the GI tract than in the whole spinal cord. True or false.
True
*So true that it has it’s own nervous system
Enteric Nervous System
- The myenteric and submucosal plexuses comprise a semi-independent sensory-motor nervous system for the gut (enteron).
- Enteric neurons include both sensory (afferent) and motor (efferent) types, which synapse with one another and also receive synapses from/to classical sympathetic, parasympathetic and sensory fibers.
What role do parasympathetics and sympathetics play in the enteric nervous system?
Parasympathetics activate peristalsis in the gut.
Sympathetics slow down peristalsis in the gut.
*This occurs through a plexus in the walls of the GI tract.
NOTE: Enteric neural connections are sufficient to carry out basic GI activity without input from the CNS (not well though)
