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Autonomic Nervous System Organization of Nervous System: Nervous system Integration Central nervous system Peripheral nervous system (CNS) (PNS) Motor output Brain Spinal cord Sensory input Motor division Sensory division (Efferent) (Afferent) “self governing” Autonomic Nervous System Somatic Nervous System (Involuntary; smooth & cardiac muscle) (Voluntary; skeletal muscle) Stability of internal environment depends largely on this system Marieb & Hoehn – Figure 14.2 Autonomic Nervous System Ganglion: A group of cell bodies located in the PNS Comparison of Somatic vs. Autonomic: Somatic NS Cell body location Effector organs NTs Single neuron from CNS to effector organs CNS Effect + ACh Stimulatory Heavily myelinated axon Skeletal muscle ACh = Acetylcholine Two-neuron chain from CNS to effector organs CNS Sympathetic NE Ganglion Postganglionic axon (unmyelinated) Preganglionic axon (lightly myelinated) + Parasympathetic Autonomic NS ACh CNS Ganglion ACh ACh Smooth muscle, glands, cardiac muscle Postganglionic axon (unmyelinated) Preganglionic axon (lightly myelinated) Stimulatory or inhibitory (depends on NT and NT receptor Type) NE = Norepinephrine Autonomic Nervous System Organization of Nervous System: Nervous system Integration Central nervous system Peripheral nervous system (CNS) (PNS) Motor output Brain Spinal cord Sensory input Motor division Sensory division (Efferent) (Afferent) Autonomic Nervous System Somatic Nervous System (Involuntary; smooth & cardiac muscle) (Voluntary; skeletal muscle) Sympathetic division Parasympathetic division 1 Autonomic Nervous System Divisions of Autonomic Nervous System (ANS): 1) Sympathetic Division: (“fight or flight”) • Readies body for stressful situations • Heightens mental alertness • metabolic rate • heart rate / blood pressure • respiratory rate / bronchiole dilation • Activates energy reserves • Activates sweat glands • Dampens non-essentials (e.g., digestion) 2) Parasympathetic Division: (‘rest and digest”) • Conserves energy at rest • metabolic rate • digestive motility / blood flow • Stimulates defecation / urination • heart rate / blood pressure • digestive gland secretions Autonomic Nervous System Sympathetic division also called the thoracolumbar division Sympathetic Division Anatomy: • Sympathetic pathways have short preganglionic fibers and long postganglionic fibers • Preganlionic fibers originate in spinal cord between cord segments T1 – L2 • Autonomic ganglia located close to spinal cord (arranged as sympathetic chain) • 23 ganglia / chain T1 (3 cervical, 11 thoracic, 4 lumbar, 4 sacral, 1 coccygeal) L2 Sympathetic chain Marieb & Hoehn – Figure 14.5 / 14.6 Autonomic Nervous System Pathways in sympathetic chain: Sympathetic Division Anatomy: 1) Terminate directly in sympathetic chain • Postganglionic axons exit out gray ramus communicans Spinal nerve (unmyelinated axons) Lateral horn of spinal cord 2) Ascend / descend several segments before terminating Gray ramus communicans Ventral root Sympathetic chain ganglion (paravertebral ganglion) White ramus communicans (myelinated axons) Marieb & Hoehn – Figure 14.5 • May ascend / descend to ganglia located outside T1 – L2 Cervical ganglia: (fed via T1 – T6) Rami communicantes only associated with sympathetic division Serve head / thorax Sacral ganglia: (fed via T10 – L2) Serve genitalia / urinary bladder 2 Autonomic Nervous System Pathways in sympathetic chain: Sympathetic Division Anatomy: 3) Exit sympathetic chain before terminating in collateral (prevertebral) ganglia Cervical ganglia Collateral ganglion T1 Celiac ganglion L2 Adrenal medulla Spanchnic nerves • Form splanchnic nerves (fed via T5 – L2) Celiac ganglion: Sacral ganglia Serves upper abdominal cavity Mesenteric ganglia • Pass-through point for splanchnic nerve feeding adrenal medulla Mesenteric ganglia: Serve lower abdominal cavity Marieb & Hoehn – Figure 14.5 / 14.6 Autonomic Nervous System Paraympathetic division also called the craniosacral division Parasympathetic Division Anatomy: • Sympathetic pathways have long preganlionic fibers and short postganlionic fibers • Terminal ganglia located near effector tissue • Preganglionic fibers originate in brain stem and S2 – S4: Vagus nerve • Occulomotor Nerve (III) • Ciliary ganglia: Pupillary sphincters / ciliary muscles • Facial Nerve (IIV) • Pterygopalatine ganglia: Nasal / lacrimal glands • Submandibular ganglia: Salivary glands • Glossopharyngeal Nerve (IX) S2 • Otic ganglia: Salivary gland S4 Splanchnic nerves 90% of PNS fibers • Vagus Nerve (X) • Intramural ganglia: Visceral organs • Sacral Segments (S2 – S4): Marieb & Hoehn – Figure 14.4 • Intramural ganglia: Large intestine / bladder / genitalia Autonomic Nervous System ANS Physiology: Fiber Types: • Cholinergic Fibers: Synthesize / secrete acetylcholine (NT) • All preganglionic fibers (sympathetic and parasympathetic divisions) • Postganglionic fibers of parasympathetic division • Adrenergic Fibers: Synthesize / secrete norepinephrine (NT) • Postganglionic fibers of sympathetic division (sans sweat glands / piloerector muscles) Synthesis of Neurotransmitters: • NTs synthesized / stored in varicosities of nerve fibers 3 Autonomic Nervous System • Postganglionic neuron forms diffuse, branching networks at synapse ANS Physiology: • NTs released from varicosities (“beads”) Neuroeffector Junction of ANS: • Innervation by multiple ANS fibers may occur • Postsynaptic receptors spread across target Varicosities Smooth muscle cells Autonomic nerve fiber Remember: Precision strike vs. Saturation bombing Synaptic vesicles Neuromuscular junction Marieb & Hoehn – Figure 9.27 Autonomic Nervous System ANS Physiology: Fiber Types: • Cholinergic Fibers: Synthesize / secrete acetylcholine (NT) • All preganglionic fibers (sympathetic and parasympathetic divisions) • Postganglionic fibers of parasympathetic division • Adrenergic Fibers: Synthesize / secrete norepinephrine (NT) • Postganglionic fibers of sympathetic division (sans sweat glands / piloerector muscles) Synthesis of Neurotransmitters: • NTs synthesized / stored in varicosities of nerve fibers Acetyl-CoA + Choline Removal: Tyrosine hydroxylation choline acetyltransferase Dopa 1) Reuptake (~ 80%) 2) Diffusion (~ 20%) 3) Destruction (> 1%) monoamine oxidase decarboxylation Acetylcholine Dopamine • Catalyzed by acetylcholinesterase • Choline recycled… hydroxylation Norepinephrine Autonomic Nervous System Nature of receptor dictates effects of NTs ANS Physiology: Receptor Types: A) Adrenoreceptors (bind E / NE): G protein-linked receptor systems • Located on target tissues of sympathetic nervous system 4 Autonomic Nervous System ANS Physiology: Receptor G – protein Receptor Systems: Effector G protein • Receptors interact with G-proteins to trigger cellular event Cellular response A. Receptors: • 7 trans-membrane segments (each segment = similar –helix sequences) • Interact with various G-proteins depending on sequence of 3rd intracellular loop Wolfe – Figure 4.3 Autonomic Nervous System ANS Physiology: Receptor G – protein Receptor Systems: Effector G protein • Receptors interact with G-proteins to trigger cellular event Cellular response B. G proteins: • Composed of three unique sub-units (, , ) • No intrinsic enzymatic activity; activates enzymes G protein Activation: 1) Ligand binds to receptor 2) Receptor / G protein interact • GDP (-subunit) replaced by GTP; dissociation occurs 3) -subunit activates effector Hydrolysis of GTP to GDP causes –subunit to dissociate from effector and rejoin other subunits Autonomic Nervous System ANS Physiology: G – protein Receptor Systems: Receptor Effector G protein • Receptors interact with G-proteins to trigger cellular event Cellular response C. Effectors: A) Adenylate cyclase (2nd messenger – cAMP) Activated by GS proteins Inhibited by GI proteins Lodish – Figure 20.20 5 Autonomic Nervous System ANS Physiology: Receptor G – protein Receptor Systems: Effector G protein • Receptors interact with G-proteins to trigger cellular event Cellular response C. Effectors: A) Adenylate cyclase (2nd messenger – cAMP) • Synthesizes cAMP from ATP Methylxanthines (e.g., caffeine) Inactivates cAMP Autonomic Nervous System ANS Physiology: Receptor G – protein Receptor Systems: Effector G protein • Receptors interact with G-proteins to trigger cellular event Cellular response C. Effectors: A) Adenylate cyclase B) Phospholipase C (2nd messenger – cAMP) Diacylglycerol (DAG) (2nd messengers – IP3 / DAG) • IP3 activates release of Ca++ (ER) • DAG activates protein kinase Inositol triphosphate (IP3) Phosphoinositol (PIP) Wolfe – Figure 6.6 / 6.9 Autonomic Nervous System Nature of receptor dictates effects of NTs ANS Physiology: Receptor Types: A) Adrenoreceptors (bind E / NE): G protein-linked receptor systems • Located on target tissues of sympathetic NS • Divided into two types: and β receptors (most common) 1 receptors Effect: Location: (+) Excitatory (+) 2 receptors Effect: (constricts blood vessels) Membrane of adrenergic axon terminals Gastrointestinal tract / bladder Gastrointestinal tract Vascular smooth muscle - skin Location: (-) Inhibitory (-) (inhibits NE release) (constricts sphincters) Phenylephrine (1 agonist) Mechanism of Action: (inhibits GI function) Iris of eye Pancreas (dilates pupil of eye) (inhibits insulin secretion) G protein coupled to phosphorylase C Mechanism of Action: GI protein coupled to adenylate cyclase 6 Nature of receptor dictates effects of NTs Autonomic Nervous System ANS Physiology: Receptor Types: G protein-linked receptor systems A) Adrenoreceptors (bind E / NE): • Located on target tissues of sympathetic NS • Divided into two types: and β receptors 1 receptors 2 receptors (+) Excitatory (+) Effect: Location: Effect: Predominately in the heart (-) Inhibitory (-) Vascular smooth muscle - skeletal (dilates vessels) muscle Location: (increases contraction rate / strength) Kidney Lungs (triggers renin (hormone) release) (dilates bronchioles) Propanolol Albuterol (β-blocker) ( 2 agonist) Mechanism of Action: Gastrointestinal tract (relaxes GI tract) Mechanism of Action: GS protein coupled to adenylate cyclase GS protein coupled to adenylate cyclase Nature of receptor dictates effects of NTs Autonomic Nervous System ANS Physiology: Receptor Types: A) Adrenoreceptors Activated by nicotines Activated by toxins (bind E / NE): from toadstools atropine (muscarinic antagonist) B) Cholinoreceptors (bind ACh): • Located on postganglionic neurons / target tissues of parasympathetic NS • Divided into two types: nicotinic & muscarinic Nicotinic Effect: Location: Muscarinic (+) Excitatory (+) Effect: Motor end plate – skeletal muscle (+) Excitatory (+) & (-) Inhibitory (-) Parasympathetic organs – sans heart Location: (contracts skeletal muscle) (excites organ activity) G protein coupled to K+ channel… All postganglionic neurons (activate postgangionic neurons) Chromaffin cells – adrenal medulla Sweat glands – sympathetic NS (triggers release of E / NE) Mechanism of Action: Heart (inhibits heart rate) (activates sweat glands) Mechanism of Action: Ligand-gated ion channel G protein coupled to phosphorylase C (Majority of locations) Autonomic Nervous System ANS Physiology: Parasympathetic Muscarinic receptors Autonomic ganglion Visceral dffector cell Cholinergic fibers Nicotinic receptors Visceral effector cell Autonomic ganglion Sympathetic Adrenergic fibers Adrenergic receptors (α / β) 7 Autonomic Nervous System ANS Physiology: Costanzo – Figure 2.1 Autonomic Nervous System ANS Physiology: Control of Autonomic Functioning: A) Brain stem / Spinal cord • Vasomotor center (cardiovascular) • Respiratory center • Micturition center (urination) • Swallowing / coughing / vomiting B) Hypothalamus • Main integration center • Body temperature • Water balance • Food intake • Links emotion with ANS C) Cortical control • Links emotional past with ANS • Voluntary cortical ANS control possible Costanzo – Figure 2.4 Autonomic Nervous System Sympathetic = “fight or flight” Parasympathetic = “rest and digest” ANS Physiology: Interactions of Autonomic Divisions: A) Antagonistic Interactions: • Pupil: Systems do not ‘compete’ with each other; coordinated by nervous system • Parasympathetic = Constriction (circular fibers) • Sympathetic = Dilation (meridional fibers) • Heart (sinoatrial node): • Parasympathetic = Decrease heart rate • Sympathetic = Increase heart rate B) Synergistic Interactions: • External genitalia • Parasympathetic = Vasodilation of blood vessels (erection of tissue) • Sympathetic = Smooth muscle contraction (ejaculation / reflex contraction) * Tone: • Basal rate of activity present in a system • Allows increase / decrease by single system Blood vessels under sympathetic tone Decrease output = vasodilation of vessel Increase output = vasoconstriction of vessel 8 Autonomic Nervous System Sympathetic = “fight or flight” Parasympathetic = “rest and digest” ANS Physiology: Interactions of Autonomic Divisions: Sympathetic C) Coordinated Function within Organ: Parasympathetic • Bladder: • Filling = Relaxed detrusor muscle; contracted internal sphincter • Emptying = Contracted detrusor muscle; relaxed internal sphincter Costanzo – Figure 2.4 Autonomic Nervous System Adrenal Medulla: • Large sympathetic ganglion Cortex Medulla • Postganglionic cells = Chromaffin cells • Releases catecholamines (epinephrine (80%) and norepinephrine (20%)) methylation • Catecholamines transported via blood (= hormone) • Delayed effect (3 – 5 sec.); prolonged effect (2 – 4 min. to clear from system) • Stimulation of cardiovascular function / metabolic rate (helps deal with stress) • Perceived purpose: 1) Safety factor (dual mechanism – backs up sympathetic nervous system) 2) Stimulate structures not directly innervated (e.g., every cell of body…) 9