Autonomic Nervous System Flashcards
Peripheral Nervous System
“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
Cell Bodies of GSA vs. GSE
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.
Nuclei of GSA, GSE, GVE, and GVA
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
Dorsal and Ventral Rami Innervation
Dorsal/post rami innervate: skin on back & deep (intrinsic) muscles of back
Ventral/ant rami innervate: all other somatic tissues
(in torso and limbs)
GVE and Glands
Directly increase secretion in exocrine glands
Some endocrine glands mostly vasomotor tone
Sympathetic vs. Parasympathetic
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
Differences in Efferent Pathways
Autonomics (Sympathetic and Parasympathetic)= 2 neuron chain (pre and post); between CNS and target cells
Somatic = 1 neuron chain; project directly to skeletal muscle
Principle of Divergence of Stimuli
One preganglionic neuron (central neuron) can have a larger influence on the target by synapsing on many postganglionic neurons
Visceral vs. Somatic Preganglionic Synapse Types
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
Visceral vs. Somatic Postganglionic Synapse Types
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
Visceral vs. Somatic Postganglionic NT Types
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
Somatic vs. Visceral Sources of Efferent Innervation
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
Somatic vs. Visceral Effects on Organs
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
Origin of Preganglionic Neurons in Sympathetic vs. Parasympathetic
Sympathetic: thoracolumbar, T1-L2
Parasympathetic: craniosacral, CN 3, 7, 9, 10 (vagus) + S2-4
*CN X (vagus) is more important for this block
Locations of Cell Bodies for Sympathetic vs. Parasympathetic
IML/Lateral horn: where preganglionic cell bodies of sympathetic or parasympathetics come from
Location of Autonomic Ganglia
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
Common Sympathetic Preganglionic Pathway
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
Sympathetics to Body Wall
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
White vs. Gray Rami Levels
White Rami: only at levels T1-L2
Gray Rami: at all 31 levels, C1 - Co1
Sympathetics to Cardiopulmonary Organs
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
Sympathetics to Abdominopelvic Organs
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
Sympathetic Thoracic vs. Abdominopelvic Summary
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
Sympathetic Adrenal Medulla
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)
Parasympathetic CN
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)
Parasympathetic Pelvic Splanchnics
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
Autonomic Control of Cardiac Function
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
Sympathetic Response
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)
Sympathetic Response in Muscle, Liver, Lungs, Peripheral Vessels, and Pupils
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)
GSA
Somatic Sensory
Skeletal m., tendon, ligaments, periosteum, skin, parietal pleura, pericardium
GVA
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
Vagus Nerve Function and Structure
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
Internal Sensory Organs
Baroreceptors: other stretch receptors (lung inflation/deflation; gut distension)
Chemoreceptors
Thermoreceptors
Visceral Sensory System
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%)
Visceral Sensory Pathways
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
Referred Pain
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
