Autonomic Nervous System

Question 1

Peripheral Nervous System

Answer 1

“Somatic” ~ body wall (including limbs)
Somatic tissues = skeletal m. + tissues composed primarily of CT

Somatic Motor (GSE) = skeletal muscle
Somatic Sensory (GSA) = structures composed primarily of skeletal muscle or CT

Question 2

Cell Bodies of GSA vs. GSE

Answer 2

SPINAL NERVES: Cell bodies of all somatic sensory neurons projecting to the CNS are located in the dorsal/post root ganglia.

SPINAL NERVES: Cell bodies of all somatic motor neurons projecting from the spinal cord are located in the ventral/ant horn.

Question 3

Nuclei of GSA, GSE, GVE, and GVA

Answer 3

Somatic sensory: dorsal horn (neurons in DRG)

Somatic motor: ventral horn (neurons also in ventral horn)

Autonomic efferent: lateral horn (sympathetic and parasympathetic)

Visceral sensory: ventral horn

Question 4

Dorsal and Ventral Rami Innervation

Answer 4

Dorsal/post rami innervate: skin on back & deep (intrinsic) muscles of back

Ventral/ant rami innervate: all other somatic tissues
(in torso and limbs)

Question 5

GVE and Glands

Answer 5

Directly increase secretion in exocrine glands

Some endocrine glands mostly vasomotor tone

Question 6

Sympathetic vs. Parasympathetic

Answer 6

Sympathetic: organs of H&N, trunk, external genitalia
PLUS:
-Skin adnexa - sweat & sebaceous glands, arrector pili
-Vascular smooth m.
-Adrenal medulla

Parasympathetic: organs of H&N, trunk, external genitalia

Question 7

Differences in Efferent Pathways

Answer 7

Autonomics (Sympathetic and Parasympathetic)= 2 neuron chain (pre and post); between CNS and target cells

Somatic = 1 neuron chain; project directly to skeletal muscle

Question 8

Principle of Divergence of Stimuli

Answer 8

One preganglionic neuron (central neuron) can have a larger influence on the target by synapsing on many postganglionic neurons

Question 9

Visceral vs. Somatic Preganglionic Synapse Types

Answer 9

Autonomic: discrete synapses at the ganglion where pre synapse on post, but not at end of post ganglionic cell; true synapse

Somatic Motor: discrete sites for synapses with synaptic terminal/bouton

Question 10

Visceral vs. Somatic Postganglionic Synapse Types

Answer 10

Visceral Motor: have varicosities stretched out structure that have many locations where neurotransmitter can be released = broad distribution at its target than synaptic bouton

Somatic Motor: true synapse with synaptic bouton with specific target and not widely distributed

Question 11

Visceral vs. Somatic Postganglionic NT Types

Answer 11

Somatic Motor NT: ACh

Preganglionic Autonomic NT: ACh always including the adrenal medulla

Postganglionic Autonomic NT: ACh is used by parasympathetic, but sympathetics use NE or E, except for sweat glands which use ACh

Question 12

Somatic vs. Visceral Sources of Efferent Innervation

Answer 12

Somatic effectors (skeletal m.) innervated by one source 
(GSE from spinal cord or brainstem)

Most visceral effectors (cardiac m., smooth m., glands) innervated by two sources (GVE): both sympathetic and parasympathetic motor neurons

Question 13

Somatic vs. Visceral Effects on Organs

Answer 13

Somatic motor: release of ACh causes stimulatory; any inhibition happens at CNS

Sympathetic and Parasympathetic: effect of NT can be inhibitory or stimulatory; increase or decrease activity

Functional division: sympathetics has energy expenditure and para is reserving energy

Question 14

Origin of Preganglionic Neurons in Sympathetic vs. Parasympathetic

Answer 14

Sympathetic: thoracolumbar, T1-L2

Parasympathetic: craniosacral, CN 3, 7, 9, 10 (vagus) + S2-4
*CN X (vagus) is more important for this block

Question 15

Locations of Cell Bodies for Sympathetic vs. Parasympathetic

Answer 15

IML/Lateral horn: where preganglionic cell bodies of sympathetic or parasympathetics come from

Question 16

Location of Autonomic Ganglia

Answer 16

Autonomic ganglia = postganglionic cell bodies

Sympathetic: paravertebral ganglion – sympathetic chain = majority of sympathetics
Some that synapse before the aorta = pre-vertebral / pre-aortic
Have short pre, and long post

Parasympathetic: preganglionic – long distance sometimes to/wall of target organ
Have long post, and short pre

Question 17

Common Sympathetic Preganglionic Pathway

Answer 17

Common Pathway: the only way that sympathetic pre ganglionic neurons can leave the spinal cord and go to the sympathetic chain

Cell body is at IML (lateral horn) and pre ganglionic fiber gives off its axon that goes through motor root (ventral/anterior) and enters spinal nerve and enters the paravertebral chain (sympathetic chain) via white communicans = ALL sympathetics do this

Question 18

Sympathetics to Body Wall

Answer 18

Includes extremities

Body wall: mostly composed of somatic, but some visceral; pre ganglionic neuron can leave by synapsing on the same level as the white communicans and exiting via gray ramus (communicans)

Above T1 or below L2: DO NOT synapse as same level as entering white ramus, but then goes up or down and exits via the gray rami on the exiting level

Gray rami communicantes are the “gateway” for postganglionic sympathetics to reach smooth muscle & glands in the body wall

Question 19

White vs. Gray Rami Levels

Answer 19

White Rami: only at levels T1-L2

Gray Rami: at all 31 levels, C1 - Co1

Question 20

Sympathetics to Cardiopulmonary Organs

Answer 20

Common origin: pre-ganglionics go from IML through ventral root, through the white rami, into paravertebral ganglionic (T1-5), and some of them will synapse at that ganglion there, others will ascend up to cervical ganglia (not one for all levels inferior, middle, and superior) and synapse there

Going to internal organs, so once synapse they jump off sympathetic chain (without passing through gray rami) and go to the organ

Question 21

Sympathetics to Abdominopelvic Organs

Answer 21

Outflow is T5-L2 for abdominopelvic and make way to sympathetic chain, and instead of synapsing, they leave as pre ganglionic fibers as splanchnic nerves that synapse on pre-aortic ganglia (pre-vertebral)

They DO NOT synapse on gray rami

Question 22

Sympathetic Thoracic vs. Abdominopelvic Summary

Answer 22

Thoracic (Cardiopulmonary):
Preganglionic fibers (short) synapse in paravertebral ganglia;
Postganglionic fibers travel as sympathetic “organ” nerves and then join plexus

Abdominopelvic:
Preganglionic fibers (long) exist as splanchnic nerves and synapse on prevertebral (preaortic) ganglia;
Postganglionic fibers join plexus

Question 23

Sympathetic Adrenal Medulla

Answer 23

Adrenal medulla~modified sympathetic ganglion

Receives sympathetic preganglion directly with NT being ACh, but when it synapses on adrenal gland, there are chromaffin cells they release something like an NT into blood stream (E and small amounts of NE) and effects the entire body (tissues with adrenergic receptors)

EPI similar to NE but effect 10X as long (not removed from blood as quickly as NE)

Question 24

Parasympathetic CN

Answer 24

Organs in torso down to L colic/splenic flexure = vagus comes out and sacral outflow of parasympathetics kicks in
Boundary between midgut and hindgut = 2/3 across transverse colon

Vagus has very long preganglionic axons (CN X)

Question 25

Parasympathetic Pelvic Splanchnics

Answer 25

Pelvic splanchnic nerves: parasympathetic nerves that come out of lateral horn through S2-4 and leave as pre-ganglionics to go to hindgut and pelvic organs ant then intramural ganglia and miscropic postganglionics Sacral outflow takes over from vagus nerve

Question 26

Autonomic Control of Cardiac Function

Answer 26

Cardiac function: heart has own intrinsic conducting system and gets stimuli from sympathetics and para High parasympathetic: lower HR, decrease myocardial contractility, and vasoconstrict coronary vessels High sympathetic: higher HR, increase contractility, and vasodilate coronary vessels

Question 27

Sympathetic Response

Answer 27

Perception of challenging situation (cerebral cortex) and activation of sympathetic nervous system - Activate adrenal medulla (A1); release EPI (B1) - Activate sympathetic NS throughout body (A2); postganglionics release NE(B2) Heart Activity: Increase rate of contraction and stroke volume (E1): -Increase SA node discharge rate -Decrease conductance time through AV node -Increase excitability of conducting bundles and cardiac muscle cells Vasodilation of coronary vessels (E2)

Question 28

Sympathetic Response in Muscle, Liver, Lungs, Peripheral Vessels, and Pupils

Answer 28

Changes in Other Organs Breakdown glycogen in muscle to produce glucose; vasodilate vessels to muscles (C1, C2) Hepatocytes release glucose (D) Increase respiratory rate and bronchial dilation; vasodilate pulmonary vessels (F1, F2) Vasoconstrict peripheral vessels Pupil dilation; Erection of body hair; Sweating (heat dissipation from muscle activity)

Question 29

GSA

Answer 29

Somatic Sensory Skeletal m., tendon, ligaments, periosteum, skin, parietal pleura, pericardium

Question 30

GVA

Answer 30

Visceral Sensory Sensations derived from structures composed primarily of cardiac m., smooth m., and glands Most visceral afferents are mediated by the parasympathetics (e.g., vagus n.), but are not consciously perceived to regulate visceral function Parasympathetics (vagus n.) set a resting baseline for general organ function

Question 31

Vagus Nerve Function and Structure

Answer 31

Sensing BP, O2 content and mediated by the parasympathetics like the vagus nerve Vagus mostly has GVE fibers but also carries back visceral sensations of organs and doesn’t reach the level of consciousness, but if it does as discomfort or pain, it will go back by way of sympathetics, which have visceral sensory fibers and they go through the same pathway as the visceral motor fibers through ganglia and sympathetic chain, white rami, DRG, then dorsal horn Basically doing same pathway as motor outflow until get to roots because dorsal only has sensory and ventral has motor

Question 32

Internal Sensory Organs

Answer 32

Baroreceptors: other stretch receptors (lung inflation/deflation; gut distension) Chemoreceptors Thermoreceptors

Question 33

Visceral Sensory System

Answer 33

Consciously perceived visceral signals include: Visceral pain (ischemia, build-up of metabolic by-products) Organ distention Hunger/nausea Sexual tension Role: change behavior to deal with stimulus Visceral pain is diffuse & poorly localized (density of sensory endings in viscera is low ~10%)

Question 34

Visceral Sensory Pathways

Answer 34

Most visceral pain mediated by afferent axons in sympathetic nerve* Pass-through (retrograde) sympathetic chain; no synapse until CNS Cell body in dorsal root ganglion

Question 35

Referred Pain

Answer 35

``` Central Convergence (Convergence-Projection) Theory Nociceptive neurons in spinal dorsal horn receive convergence of inputs (somatic, visceral) Higher centers in brain unable to identify actual input source ``` Doesn’t have to be visceral to somatic, but can be somatic to somatic C3-5 - keeps the diaphragm alive; also has sensory nerves (proprioception) but any irritation of diaphragm will be picked up from phrenic nerve and goes up through C3-5, and parts of the body wall are also using this pathway; superclavicular nerve shares these cord levels and the pain will be referred to top of shoulders