Intro the to ANS 9/20

Question 1

Autonomic Nervous System

Answer 1

• the portion of the central and peripheral nervous system that is responsible for unconscious control of visceral function.

Two divisions:

• parasympathetic = “craniosacral” - constant control of visceral function
• Sympathetic = “thoracolumbar” visceral reaction in response to immediate stress

Question 2

Parasympathetic division

Answer 2

• Craniosacral
• cranial: motor nuclei of cranial nerves III, VII, IX, X and
• Sacral: lateral horn (Intermediolateral cell column - IMLCC) of spinal levels S2,3,4
• responsible for constant control of visceral function (vegetative state) i.e. decreased heart rate, decreased rate and depth of respiration, increased gut motility, shunting of blood toward the gut away from skeletal muscle

Question 3

Sympathetic Division

Answer 3

• thoracolumbar: (IMLCC) lateral horn of spinal cord levels T1-L2
• responsbible for control of visceral reaction in response to immediate stress - fight or flight - i.e. increased heart rate, increased rate and depth of respiration, decreased gut motility, shunting of blood from gut to skeletal muscles, etc.

Question 4

Autonomic Neurons

Answer 4

• two neuron chain: regardless of the division, the first neuron resides in CNS nucleus, the second neuron resides in a peripheral ganglion

1. Parasympathetic ganglia
2. Sympathetic ganglia (two types)

Question 5

Parasympathetic Ganglia

Answer 5

• Cranial portion: four individually named ganglia associated with cranial nerves: ciliary (CNIII), pterygopalateine ganglion and submandibular (CNVII) and otic ganglion (CN IX)
• these innervate the eye, lacrimal gland, nasal, palatine, and pharyngeal glands - synapse near the organ they affect
• Vagal and Sacral portion - unamed peripheral ganglia that reside in the wall of organs innervated
• i.e heart, lungs, liver, gallbladder, stomach, kidney, intestines, sexual organs

Question 6

Sympathetic Ganglia

Answer 6

• Para-vertebral Ganglia: sympathetic trunk or “chain ganglia”. attached to spinal nerves by trunks (rami) which conduct specific nerve fibers

1. White Ramus Communicans: conduct myelin preganglionic sympathetic fibers from a spinal nerve to a paravertebral ganglion
2. Gray Ramus Communicans: conduct unmyelinated post-ganglionic sympathetic fibers from a paravertebral ganglion to a spinal nerve

- Pre-vertebral ganglia (collateral)

1. Located ANTERIOR to the vertebral column (anterior to the aorta)
2. include: celiac, aorticorenal, superior and inferior mesenteric ganglia as well as scattered ganglial cells which exist in autonomic plexuses of the kidney and pelvis

Question 7

Autonomic Nerve Fibers

Answer 7

1 - Preganglionic fiber: efferent fiber from the preganglioic neuron (cell bodies located within the CNS)

2 - Postganglionic fiber - fiber from the second neuron (cell bodies located within peripheral ganglion)

NOTE: in general parasympathetic has long preganglionic and short postganglionic and sympathetic has short preganglionic and long postganglionic fibers because their postganglionic neurons are located away from the organs which they innervate

3. Splanchnic Nerve: a sympathetic preganglionic fiber that does not synapse in a paravertebral ganglion; synapses distally in a prevertebral ganglion closer to the organs which they innervate

Question 8

Distribution of Fibers of the Sympathetic ANS

Answer 8

• Preganglionic sympathetic fibers distribute through thoracolumbar spinal nerves T1-L2 via white rami communicantes to sympathetic chain ganglia where they can:

1. synapse on a postganglionic neuron at the level of entry, exit the ganglion via a gray ramus communicans and distribute through dorsal or ventral rami of a spinal nerve to peripheral targets
2. Enter the chain, ascend or descend a few segments, synapse in a ganglion, exit the ganglion via a gray ramus communicans and distribute through dorsal or ventral rami of a spinal nerve to peripheral targets
3. Pass through the sympathetic chain and ganglion without synapsing and pass via a splanchnic nerve to a prevertebral ganglion, synapse there and send a postganglionic fiber via a plexus on the surface of arterial blood

Question 9

Origin of Preganglionic sympathetic distribution ot specific regions of the body

Answer 9

1. Head and Neck: T1-T4
2. Thorax: T1-6
3. Upper LImb: T2-T7
4. Abdomen: T5-L2
5. Pelvis and Perimeum: T11-L2
6. Lower Limb: T10-L2/3

Question 10

Distribution of Fibers of the Parasympathetic ANS

Answer 10

• preganglionic parasympathetic fibers distribute through cranial nervesa dn via plexuses on the surface of organis or arteries to target visceral organs where they will synapse in ganglia located within their walls
• they are normally not found in spinal nerves (exception: pelvic splanchnic nerve)
• note, in many areas of the body both sympathetic branch fibers travel together as autonomic plexuses (aside from the paraympathetic post-ganglionic, which is in organ walls)

NOTE: the ratio of postganglionic to preganglionic fibers is much greater in the sympathetic division of the ANS than it is in the PS division. this correlates with the overall ‘global’ effect that is seen with sympathetic innervation compared to the ‘local’ effects, which result from parasympathetic innervation

Question 11

synapses and neurotransmitters

Answer 11

• synapse at pre-ganglionic fiber on the postganglionic neuron (preganglionic synapse) is mediated by acetylcholine (Ach) for both divisions

Synapses of postganglionic fibers on the effector organs (postganglionic synapse)

• Parasympathetic: Acetylcholine (Ach)

- Sympathetic: Norepinephrine (NE)

Question 12

Visceral Pain

Answer 12

• either acute (sharp) pain or dull/nauseous pain (due to the distention of a hollow organ - not localized due to cranio-sacral innervation)
• Acute or shapr pain is registered by visceral afferent fibers which retunr to the spinal cord along routes which parallel the sympathetic system. since preganglionic sympathetic fibers arise from specific segments of the spinal cord and travel within all spinal nerves, pain fibers which parallel them enter the spinal cord at the exact sam spinal levels as the origin of sympathetic efferent fibers. Because of this arrangemtn, acute pain is welllocalized when compared to pain registered by the PS and forms the basis for referred pain mechanisms and viscerosomatic reflexes.

Question 13

Referred Pain

Answer 13

• linings of body’s cavities are not precisely innervated as is the outside “mapped” cuteanous portion of the body.
• Viscera are innervated by branches of spinal nerves that correlate to the dermatomes (Recall: afferent fibers for pain travel with the sympathetic visceral motor system. dermatomes which are implicated in referred pain syndromes are limited to levels T1-L2)
• afferent (sensory) tract neurons conduct both cutaneous and visceral sensation centralward.
• normally stimulateion of visceral afferent fibers is sub-threshold — but in a diseased state the visceral afferents fire more often, thereby stimulating ascending tract neurons to the point that their stimulation is percieved. Because these tract neurons are being fired more often, the brain incorrectly interprets the pain as coming from the surface of the body at the same spinal level as the incoming visceral afferents
  ex. .. angina pectoris

Question 14

Viscerosomatic Reflexes

Answer 14

• Recall: visceral efferent and visceral afferent fibers to specific viscera or portions of viscera originate from identical spinal levels…. see description……