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Autonomic Nervous System Monday, February 2, 2015 9:29 AM ANS is divided into two parts - Sympathetic ○ Fibers originate in Throacolumbar SC levels ○ Active during stress, competition, fear, excitement ○ Functions are Catabolic in nature - Parasympathetic ○ Fibers originate in cranial and sacral levels ○ Active during relaxation, digestion, calm ○ Functions are anabolic in nature Primary functions of ANS Neuroanatomy Page 1 -Even though urination/defecation is via parasympathetic, incontinence during stressful events can be caused by an overshoot of sympathetic stimulation being corrected by parasympathetic -Important notes: - Skin has NO PARASYMPATHETIC Stimulation -> NO BLOOD VESSELS/SWEAT GLANDS/ARRECTOR PILI MUSCLE innervation - Even though sympathetic stimulation causes vasoconstriction, it actually causes DILATION in CORNARY arteries. - Heart has intrinsic ability to beat -> ANS controls heart RATE and Contractility not the actual ability to beat General ANS Organization - Remember that somatic motor neurons have monosynaptic neurons in anterior horn and synapse directly onto the muscle - ANS has Pre-ganglionic (PrG) and Post-ganglionic (PoG) neurons ○ PrG are in CNS and project out to synapse onto PoG ○ The PoG then leaves its respective ganglia and synapses on effectors Effectors include Glands, Cardiac Muscle, smooth muscle, and adipose Most effectors are dual innervated by sympathetic and parasympathetic => antagonistic effects on effectors - ANS PrG axons are MYELINATED ○ Parasympathetic system has LONG PrG axons and synapse at ganglia near effector(target) organs ○ Sympathetic system has SHORT PrG axons and synapse at ganglia near spinal cord Sympathetic Division - ANS fibers leave SC via VENTRAL root - PrG cell bodies for sympathetic are located in intermediolateral cell column of T1-L2/L3 - PoG cell bodies are located in one of two ganglia, named for where they are anatomically ○ Paravertebral Ganglia = sits lateral to vertebral column C1-C4 => Superior Cervical Ganglion □ How sympathetic fibers reach head C5-C6 => Middle Cervical C7-C8 => Inferior Cervical □ If fused at C7-T1 => Stellate Ganglion Thoracic/Lumbar/Sacral Ganglion Ganglion impar (where both chains meet near coccyx) ○ Prevertebral (preaortic) Ganglia = ganglia sits on aorta Celiac Ganglia Superior Mesenteric Ganglia Aorticorneal Ganglia Inferior mesenteric ganglia ○ PrG can also synapse at Adrenal Medulla with Chromaffin Cells which are modified PoG neurons in adrenal gland => releases Epi/NE into blood - Sympathetic Pathways ○ For the most part, the nerves that travel to effector organs are named after the arteries they run with Neuroanatomy Page 2 ○ PrG leave ventral roots and go to either ganglia or adrenal medulla If entering paravertebral ganglion, PrG enter via WHITE RAMI COMMUNICANS (more lateral) □ NO WHITE RAMI ABOVE T1 or BELOW L2, ONLY GRAY RAMI -> neuronal cell bodies are only at T1-L2 so axons have already entered Ganglia PrG can ascend or descend in Paravertebral ganglia before synapsing ○ PoG leave ganglion and synapse at effector organ If leaving paravertebral ganglion, PoG leave via GRAY RAMI COMMUNICANS (more medial) PoG can project to: □ Body Surface -> by following spinal nerve going to its target dermatome Effectors include Sweat gland, blood vessels, arrector pilli □ Head -> by following Carotid nerve above superior cervical ganglion Effectors include Iris and face/head □ Thoracic Viscera -> by following Cardiopulmonary splanchnic nerve Effectors include heart and respiratory tree These nerves are near CERVICAL region due to organ migration during embryological development *POST-Ganglionic travels via Cardiopulmonary splanchnic nerve □Abdominopelvic Viscera -> by following abdominal splanchnic nerve Effectors include GI Tract and other viscera *NOTE*: PRE-Ganglionic travels via abdominal splanchnic nerve THEN synapses - Sympathetic nuclei have Somatotropic distribution in terms of origination ○ Upper Limbs -> T1-T6 Eye -> T1-T2 Heart/Lungs/Esophagus -> T4-T6 ○ Body Wall -> T7-T11 ○ Lower Limbs -> T11-L2 Parasympathetic Division - PrG neuron bodies are in: Neuroanatomy Page 3 ○ Brainstem Nuclei Axons travel via □ CN 3 to Ciliary Ganglion => constricts iris □ CN 7 to Pterogopalatine ganglion and submandibular ganglion => Lacrimal glands and submandibular/sublingual glands respectively □ CN 9 to Otic Ganglion => Parotid salivary glands □ CN 10 to intrinsic ganglia of organs => Parasympathetic control of Thorax (lungs/heart) and upper 2/3 of abdominal organs CRANIAL NERVES HAVE NO SYMPATHETIC FUNCTION ONLY PARASYMPATHETIC ○ Lateral horn of Sacral Spinal cord (S2-4) Axons of PrG leave via pelvic splanchnic nerve Exert Parasympathetic control over GU and distal digestive tract Abdominal (Autonomic) Plexus - Are networks of nerve fibers typically consisting of the Long axons of the ANS aka PrG PARASYMPATHETIC axons and PoG SYMPATHETIC axons with some afferent axons (not part of ANS) -ANS is autonomic but still controlled by higher levels in CNS -> Hypothalamus - Hypothalamus is main integration center of ANS ○ Signals for change in response to osmoreceptors, temperature changes, and feeding/satiety centers ○ Sends signals to Vagal nucleus and PrG cell bodies in Spinal Cord Dr. Ochs talks more about neurotransmitters of ANS but briefly - Somatic is single axon system -> ACh - All PrG of ANS -> ACh - All PoG of Parasympathetic and sweat glands of sympathetic -> ACh - Most PoG to organs for Sympathetic -> NE - Chromaffin cells from Medulla -> Epi/NE Neurotransmitter Pathway of the ANS Neuroanatomy Page 4