Autonomic Nervous System PDF

Functional Organization of the Peripheral Nervous System Sensory Nervous System AKA Afferent nervous system Convey information (impulses) to the CNS Somatic sensory: Sensory input that is conscio...

Functional Organization of the Peripheral Nervous System Sensory Nervous System AKA Afferent nervous system Convey information (impulses) to the CNS Somatic sensory: Sensory input that is consciously perceived from receptors (special senses, skin, etc.) Visceral sensory: Sensory input that is not consciously perceived from the viscera and blood vessels Motor Nervous System AKA Efferent nervous system Convey information (impulses) from the CNS to the effector organs Somatic motor: Motor output that is consciously or voluntarily controlled. Effector: skeletal muscle Autonomic motor: Motor output that is not consciously or is involuntarily controlled. Functionally maintains homeostasis Effectors: glands, smooth and cardiac muscle. Further divided into sympathetic and parasympathetic systems Functional Organization of the Nervous system Somatic Nervous System Processes that are consciously perceived or controlled Somatic sensory: Detects and transmits information from the special senses, skin, and proprioceptors to the CNS Somatic motor: Initiation and transmission of nerve signals from the CNS to skeletal muscles Autonomic Nervous System Also called the visceral nervous system Processes regulated below the conscious level Functionally maintains homeostasis Visceral sensory: Receptors that detect stimuli from the viscera and blood vessels to the CNS Autonomic motor: Transmit signals from the CNS to cardiac and smooth muscles and the glands Differences between the autonomic & somatic nervous systems Differences between the autonomic & somatic nervous systems Autonomic nerve pathway consists of two- neuron chains Cell body of 1st neuron is located within the CNS Synapses with cell body of 2nd neuron located in a ganglion Axon of 2nd neuron (post-ganglionic fiber) innervates the effector organ Autonomic system has two subdivisions Sympathetic “fight-or-flight” Primarily mobilized during periods of exertion (activity), excitement (stress), or emergency Increases in heart and respiration rate, blood flow to skeletal and cardiac muscle, and sweating Parasympathetic “rest-and-digest” or “feed and breed” Primarily promotes maintenance functions and energy conservation SLUD = salivation, lacrimation, urination, and defection Decreases heart rate and blood pressure Increases motility and secretion in the digestive system, the excretion of waste products, and sexual arousal The body spends most of the time under parasympathetic dominance Anatomic differences between parasympathetic and sympathetic Location of Preganglionic cell bodies Para: Cranial and sacral origins Symp: Thoracic and lumbar origins Length of preganglionic fibers Para: Long Symp: Short Location of ganglia Para: Located near the target organ or within wall of organ Symp: Located near the spinal cord Length of postganglionic fibers Para: Short Symp: Long Number of preganglionic axon branches Para: Few (1 preganglionic fiber to 20 postganglionic fiber) Degree of response Para: local Symp: mass activation (many systems simultaneously) or local Parasympathetic anatomy Oculomotor nerve (CN III) Ciliary muscle of lens for accommodation Sphincter pupillae muscle Facial nerve (CN VII) Lacrimal glands Nasal cavity glands Glands of the palate and oral cavity Submandibular and sublingual salivary gland Glossopharyngeal nerve (CN IX) Parotid salivary gland Vagus nerve (CN X) Thoracic viscera Abdominal viscera Splachnic nerves (S2-S4) Lower abdominal viscera Pelvic viscera Sympathetic anatomy More complex than parasympathetic Cell bodies are housed in the lateral horn of the spinal cord (between T1 and L2) and fibers exit through anterior roots Sympathetic fibers leave the spinal nerve to enter either the left or right sympathetic trunk (immediately lateral to the spinal cord) The trunks contain the sympathetic ganglia The sympathetic ganglia are interconnected by bundles of axons to form the trunk Roughly one sympathetic ganglia per spinal nerve Sympathetic anatomy One of three things can happen 1. A fiber can synapse with neurons in the same trunk ganglion 2. It can ascend or descend to synapse with another trunk ganglion 2 3. It can pass through without synapsing (collateral ganglia) 3 1 2 Sympathetic anatomy Cervical ganglia Superior: postganglionic fibers to head and neck, some thoracic Middle: postganglionic fibers to thoracic viscera Inferior: postganglionic fibers to thoracic viscera Rami Communicantes Connect the spinal nerves to each sympathetic trunks Two types: White ramus communicans Gray ramus communicans Sympathetic splanchnic nerves Preganglionic fibers that do not synapse in a sympathetic trunk ganglion Travel to most of the abdominal and pelvic viscera Terminate in collateral (prevertebral) ganglia Rami communicantes Rami (s. ramus): Connect the spinal nerves to each sympathetic trunks White ramus communicans Carry pre-ganglionic axons from T1-L2 to the sympathetic trunk Gray ramus communicans Carry post-ganglionic axons from the sympathetic trunk to the spinal nerve Post-ganglionic fibers lack myelin, hence color and name Sympathetic splanchnic nerves Greater thoracic splanchnic nerve Preganglion fibers originate from T5 – T9 Synapse in Celiac ganglion Lesser thoracic splanchnic nerve Preganglion fibers originate from T10 – T11 Synapse in superior mesenteric ganglion Least thoracic splanchnic nerve Preganglion fibers originate from T12 Synapse in superior mesenteric ganglion Lumbar splanchnic nerve Preganglion fibers originate from L1 – L2 Synapse in inferior mesenteric ganglion Sacral splanchnic nerves postganglion fibers originate from sympathetic sacral ganglion Prevertebral (collateral) ganglia Located anterior to the vertebral column on the anterolateral wall of the aorta Located only in the abdominopelvic cavity Celiac ganglion Postganglionic fibers innervate stomach, spleen, liver, gall bladder and proximal portion of duodenum and part of pancreas Superior mesenteric ganglion Postganglionic fibers innervate distal half of duodenum, the rest of small intestine, proximal portion of large intestine, part of pancreas, kidneys and proximal part of ureters Inferior mesenteric ganglion Postganglionic fibers innervate distal part of large intestine, rectum, urinary bladder, distal ureters, and most of the repro organs Sympathetic pathway The path by which a sympathetic fiber exits the sympathetic ganglion Four types of pathways Spinal nerve pathway Postganglionic sympathetic nerve pathway Splanchnic nerve pathway Adrenal medulla pathway Spinal nerve pathway Preganglionic fiber Synapses in the sympathetic trunk ganglion with postganglionic fiber Postganglionic fiber Travels out of the ganglion via the gray ramus at the same “level” The fiber joins the spinal nerve and extends to its target organ Targets Skin of the torso, neck and limbs including sweat glands, blood vessels of the skin, and arrector pili muscles Postganglionic sympathetic nerve pathway Preganglionic fiber Synapses in the sympathetic trunk ganglion with postganglionic fiber Postganglionic fiber Does not use gray ramus The fiber exits the ganglion and directly extends to its target organ Targets Esophagus, heart, lungs, and thoracic blood vessels Innervated structures of the head including sweat glands and blood vessels Also some eye muscles Splanchnic nerve pathway Preganglionic fiber Pass through the sympathetic trunk ganglion without synapsing Extend to the collateral (prevertebral) ganglia to synapse with postganglionic fiber Postganglionic fiber Travels out of the collateral ganglion and extends to its target organ Targets Abdominal and pelvic organs Adrenal medulla pathway Preganglionic fiber Directly innervates the adrenal medulla Extends through the sympathetic trunk and collateral ganglion Terminate on neurosecretory cells Postganglionic fiber No postganglionic fibers Targets adrenal medulla Modified sympathetic ganglion Does not give rise to postganglionic fibers Secretes hormone into the bloodstream 20% NorE 80% Epinephrine (Epi) Reinforces the activity of the sympathetic nervous system Adrenal medulla Adrenal gland is located superior to the kidney Two parts: Cortex = outer portion Medulla = inner portion Modified sympathetic ganglion Does not give rise to postganglionic fibers Secretes hormone into the bloodstream 20% NorE 80% Epinephrine (Epi) Reinforces the activity of the sympathetic nervous system Neurotransmitters of the ANS The two main neurotransmitters of the ANS are Norepinephrine (NorE) and acetylcholine (ACh) Neurons are named for which NT they synthesize and release Cholinergic fibers release ACh All sympathetic and parasympathetic preganglionic fibers All parasympathetic postganglionic fibers Sympathetic postganglionic fibers that innervate sweat glands in skin and blood vessels in muscle Adrenergic fibers release NorE Pre Post Almost all sympathetic postganglionic fibers Receptors are named for what they bind Sym Cholinergic receptors bind Ach Found on cell bodies of cells responding to ACh Para Adrenergic receptors bind NorE Found on cell bodies of cells responding to NorE Varicosity Terminal end of a sympathetic fiber Analogous to a synaptic knob Network of swellings along the terminal branch that overlays the innervated tissue NT is released along the terminal length of the axon as opposed to the terminal end Yields a greater response Cholinergic Receptors: Nicotinic Named because they are sensitive to nicotine Location Post-ganglionic cell bodies Adrenal medulla Skeletal muscles Activated by ACh Post Target Binding of ACh to nicotinic Sym receptor is always excitatory Para Produces EPSPs Cholinergic Receptors: Muscarinic Named because they are sensitive to muscarine, a mushroom toxin Location Effector cell membranes in parasympathetic system Selected cells in sympathetic system Activated by ACh From parasympathetic postganglionic fibers From some sympathetic fibers innervating sweat glands and blood Post Target vessels (of skeletal muscle) Binding of ACh to muscarinic receptor Sym can be either excitatory or inhibitory Depending on the subclass of receptor Para Adrenergic receptors α1 α2 β1 β2 β3 Ligand NorE NorE NorE, Epi Epi NorE, Epi Response excitatory inhibitory excitatory inhibitory excitatory Tissue Favor smooth Favor Favor heart Favor smooth Favors muscle ↑glucagon & contraction & muscle increased contraction ↓insulin; increased relaxation lipolysis & inhibition of blood pressure increased digestion thermogenesis Two major types Alpha (α) receptors: α1 & α2 Beta (β) receptors: β1, β2, & β3 Bound by either Epi or NorE depending on subtype Can be excitatory or inhibitory depending on subtype All are coupled with G-protein Interactions within the ANS Tone Basal level of activity of both systems Both systems are always active but the dominant level of activity is dependent on the homeostatic need at a given time When one system is increased above its tonic level with a simultaneous decrease in the other system, called dominance Different organ systems have different types of dominance that exhibit the tone of the dominant system Antagonistic effects Sympathetic and Parasympathetic frequently innervate the same organ Generally exert opposite effects on a particular organ Called dual reciprocal innervation Autonomic reflexes Also called visceral reflexes Similar to the somatic reflex arc, but has two neurons in the motor component Cardiovascular reflex Reduction of blood pressure Gastrointestinal reflex Prepare the body for digestion and elimination Micturition reflex Leads to urinary elimination Control of the ANS Top level is the Hypothalamus Signals from hypothalamus are relayed through the brainstem and spinal cord Cortex provides input to the hypothalamus so that the proper response is performed