Gross Anatomy Lecture 5Peripheral Nervous System: Autonomic DivisionPeripheral Nervous System (PNS)

Overview of Autonomic Nervous System Innervates viscera - unconscious control Mediates Homeostasis Visceral sensory and visceral motor neurons which function in visceral reflexes Takes at least two motor neurons connected in series to innervate organs. Necessitates peripheral ganglia A ganglion is a collection of neuronal cell bodies, often grossly visible Three divisions: Parasympathetic, Sympathetic and Enteric Dual Innervation of organs: Parasympathetic and Sympathetic divisions Enteric division is special for GI tract.

Homeostasis: Maintenance of critical physiological parameters of the internal environment within the limits compatible with life

General Functional Attributes Sympathetic Division Prepares body for action Mobilizes energy stores (Catabolic) Mediates responses to stress Fight or flight Anatomically: Originates from a restricted part of Spinal Cord Has its own set of peripheral gangliaGeneral Functional Attributes Parasympathetic Division Conserves and restores energy reserves (Anabolic) Promotes digestion, absorption and storage Protective - miosis - constriction of pupil Rest and Digest i.e., assimilate Anatomically: Originates from a restricted part of Brain and restricted part of the Spinal Cord Has its own set of peripheral ganglia

Dual Innervation Many organs have a Sympathetic and a Parasympathetic innervation One excites and the other inhibits function of the organ Some organs dont!! Sweat glands, arrector pili muscle of hair follicles, vascular smooth muscle, adrenal gland and adipose tissue get only a Sympathetic innervation

Opposition in Dual Innervation by ANSThe Sympathetic division controls: Mydriasis - opens pupil to let light in Decreases GI motility Closes sphincters of GI tract/bladder Decreases salivary gland secretion Accelerates heart rate Increases blood pressure Increases blood glucose Increases lipolysis Dilates bronchioles Piloerection to conserve heat Ejaculation - contracts smooth muscle of associated penile structures Operates all the time and capable of massive response in emergencies - "sympathetic discharge" in the "flight or fight" reaction

The Parasympathetic division controls: Miosis - close the pupil -protects retina from excess light Increases GI motility to promote digestion and absorption of nutrients Opens sphincters (stomach, rectum, bladder) Increases salivary gland and mucosal gland secretions - digestion Slows heart rate - rest Vasodilation in erectile tissue of penis and clitoris - erection Stimulates bladder muscle for micturition Operates all the time.What is the Pattern of Spinal Nerve Branching? Branches of a Spinal Nerve - Thoracic level

Branches of a Spinal Nerve: Fiber (meaning axons) types (or neuron types) that are in spinal nerves and their branchesNerve fiber types in spinal nerves and their roots and ramii. Somatic Afferent fibers (SA) Sensory axons from somatic tissue - somatic nervous systemii. Visceral Afferent fibers (VA)Sensory axons from visceral tissue autonomic nervous systemiii. Somatic Efferent fibers (SE)Motor axons to skeletal muscle - somatic nervous system iv. Visceral Efferent fibers (VE)Motor axons to smooth muscle, cardiac muscle, glands and adipose tissue autonomic nervous systemGeneral Components to ANS :

Sensory neurons - one neuron to reach the CNS Motor neurons Takes two motor neurons in series to innervate an organ This requires a synaptic connection in the periphery between the two motor neurons This occurs in peripheral ganglia that are usually grossly visible Many organs have dual innervation: Parasympathetic Sympathetic Generally, they oppose each other. One excites, the other inhibits

Dog ANS in sagittal view

The slide of the ANS diagram is very complex - Lets break the ANS down The next series of slides build up to the final figure, Division by Division; Preganglionic by Preganglionic axons and Postganglionic by Postganglionic axons First, well do Parasympathetic Second, well do Sympathetic

Origins of ANS in CNSSites of ANS gangliaCraniosacral division because it originates in brain and sacral spinal cordParasympathetic pre- and postganglionic fibers together and synapsing in Head or Terminal ganglia

Sympathetic preganglionic fibers for organs of Head, Neck, Thoracic, Abdominal and Pelvic Cavities

Thoracolumbar division because it originates from thoracic and upper lumbar spinal cordSympathetic pre- and postganglionic fibers for organs of Head, Neck, Thorax, Abdominal and Pelvic Cavities

Sympathetic preganglionic fibers for sudomotor (sweating), pilomotor (erecting hair), and vasomotor (managing blood pressure and blood distribution ) controls

Sympathetic pre- and postganglionic fibers for sudomotor, pilomotor and vasomotor function

Dog ANS in sagittal view

Routing of Sympathetic fibers in Spinal NervesRouting of sympathetic fibers

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Summary: ANS Innervates Organs Involuntary Homeostasis At least two motor neurons in series Necessitates peripheral ganglia Three divisions: Parasympathetic, Sympathetic and Enteric Dual Innervation of organs by Parasympathetic and Sympathetic divisions Enteric division is special for GI tract.