Systems Physiology 9

SYSTEMS PHYSIOLOGY 9 THE AUTONOMIC NERVOUS SYSTEM (ANS) ? Controls the Body's Internal Environment in a Coordinated Manner ? The ANS helps control the heart rate, blood pressure, digestion, respiration, blood pH and other bodily functions through a series of complex reflex actions ? These controls are done automatically, below the conscious level ? To exert this control the activities of many different organs must be coordinated so they work to accomplish the same goal AUTONOMIC NERVOUS SYSTEM In emergencies that cause stress and require us to "fight or flight" (run away) In nonemergencies that allow us to " rest and digest " . AUTONOMIC NERVOUS SYSTEM Sympathetic Division Preganglionic fibers of SNS emerge from the spinal cord at levels T1- L2. The sympathetic nervous system involves spinal nerves T1 to L2. SNS and PNS work together in reciprocal fashion to regulate body function Parasympathetic Division Preganglionar fibers of PNS are associated with cranial nerves III, VII, IX, X and also emerge from sacral spinal cord at S2- S4. Parasympathetic system is involved in vegetative processes such as digestion as well as homeostatic functions. SNS and PNS work together in reciprocal fashion to regulate body function The ANS: Sympathetic and Parasympathetic Differ in Anatomy and Function The sympathetic nerves come from the thoracic and lumbar regions of the spinal cord. The preganglionic nerves are short and synapse in paired ganglia adjacent to the spinal cord ? The adrenal medulla, technically an endocrine gland, is functionally a part of the sympathetic nervous system Adrenal medulla is like a modified autonomic ganglion + postsynaptic nerve The parasympathetic nerves come from the cranial and sacral regions of the CNS. They have long preganglionic nerves which synapse at ganglia near or on the organ innervated Animation: Autonomic nerves Chapter 7 The Peripheral Nervous System: Efferent Division Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning ANS ? Adrenal medulla is a modified part of sympathetic nervous system ? Modified sympathetic ganglion that does not give rise to postganglionic fibers ? Stimulation of preganglionic fiber prompts secretion of hormones into blood ? About 20% of hormone release is norepinephrine ? About 80% of hormone released is epinephrine (adrenaline) Autonomic Targets ? Smooth Muscle ? Cardiac Muscle ? Exocrine Glands ? Some Endocrine glands ? Lymphoid Tissue ? Adipose AUTONOMIC NERVOUS SYSTEM AUTONOMIC NERVOUS SYSTEM ? The 2 branches use the same transmitter, acetylcholine (ACh), in the ganglia. At the organ quite different transmitters are used: ? Parasympathetic = ACh ? Sympathetic = norepinephrine (NE). Note: norepinephrine is the same thing as noradrenaline. ? Note: there are a few sympathetic nerves where the transmitter at the organ is ACh ? Sympathetic fibers releasing ACh: sweat glands, piloerector muscles, some blood vessels Chapter 7 The Peripheral Nervous System: Efferent Division Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning ANS ? Exceptions to general rule of dual reciprocal innervation by the two branches of autonomic nervous system ? Most arterioles and veins receive only sympathetic nerve fibers (arteries and capillaries are not innervated) ? Most sweat glands are innervated only by sympathetic nerves ? Salivary glands are innervated by both ANS divisions but activity is not antagonistic ? both stimulate salivary secretion Chapter 7 The Peripheral Nervous System: Efferent Division Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning ANS- Autonomic Efferent Neurons ? Autonomic nerve pathway ? Extends from CNS to an innervated organ ? Two-neuron chain ? Preganglionic fiber neuron- cell body in CNS and synapses with cell body of second neuron. ? Postganglionic fiber (innervates effector organ) Thoracolumbar division (T1 to L2) ? Preganglionic neurons (N1)from thoracolumbar region of spinal cord ? Pre and paravertebral ganglia ? Long postganglionic neurons (N2) secrete NE onto adrenergic receptors Craniosacral Division ? Long preganglionic axons from brain & S2- S4 ? Intramural ganglia ? Postganglionic (nonmyelinated) neurons secrete ACh onto cholinergic muscarinic receptors Chapter 7 The Peripheral Nervous System: Efferent Division Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning SNS and PSNS features Chapter 7 The Peripheral Nervous System: Efferent Division Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning Autonomic Neurotransmitter Receptors ? Tissues innervated by autonomic nervous system have one or more of several different receptor types for postganglionic chemical messengers ? Cholinergic receptors ? bind to ACh ? Nicotinic receptors ? found on postganglionic cell bodies of all autonomic ganglia ? Muscarinic receptors ? found on effector cell membranes ? Adrenergic receptors ? bind to norepinephrine and epinephrine ? Alpha (?) receptors ? Beta (?) receptors Cholinergic and Adrenergic Synapses SYMPATHETIC PATHWAY AT SPINAL CORD Most Common Autonomic NTs: ? Acetylcholine (ACh) ACh neurons & ACh receptors are called cholinergic (nicotinic or muscarinic). Located at autonomic preganglionic & para-sympathetic postganglionic synapses ? Norepinephrine (NE) NE neurons & receptors are called (nor) adrenergic (? and ?). Located at sympathetic postganglionic synapses Chapter 7 The Peripheral Nervous System: Efferent Division Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning ANS ? Two subdivisions ? Sympathetic nervous system ? Parasympathetic nervous system Sympathetic Nervous System Parasympathetic Nervous System Fibers originate in thoracic and lumbar regions of spinal cord Fibers originate from cranial and sacral areas of CNS Most preganglionic fibers are short Preganglionic fibers are longer Long postganglionic fibers Very short postganglionic fibers Preganglionic fibers release acetylcholine (Ach) Preganglionic fibers release acetylcholine (Ach) Most postganglionic fibers release noradrenaline (norepinephrine) Postganglionic fibers release acetylcholine Fig. 7-2, p. 239 AUTONOMIC NERVOUS SYSTEM Chapter 7 The Peripheral Nervous System: Efferent Division Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning AUTONOMIC NERVOUS SYSTEM CONTROL ON VARIOUS ORGANS NTs of Autonomic NS ? and ?N1 N1 N2 N2 NEUROEFFECTOR JUNCTION Synapse between postganglionic cell and target ? Most are different from model synapse ? ANS synapse: axon has varicosities containing neurotransmitter ? May supply many cells, resulting in less specific communication ? Synthesis of NT is in the varicosity Fig 11-8 Pre- & Postganglionic Parasympathetic Neurons Release ACh muscarinicnicotinic Receptors N1 N2 Two Types of Cholinergic Receptors: Nicotinic and Muscarinic 1. Nicotine = agonist 2. In autonomic ganglia & somatic NS 3. Directly opens a Na+ & K+ channel: ? ? 4. Curare = antagonist 1) Nicotinic cholinergic receptor 2) Muscarinic cholinergic receptor ? Muscarine = agonist ? Found in neuro-effector junctions of parasympathetic branch ? G-protein coupled mechanisms ? Atropine = antagonist N1 N2 Muscarinic ACh are G-protein Mediated Receptor Mechanism of Sweat Glands: Also some 2nd messenger mechanisms Adrenergic Receptors ? Found in neuroeffector junctions of sympathetic branch ? G protein linked, with various 2nd mess. Mech ? NT is NE ? ?- and ?- Receptors NE Action Sympathetic Receptors ? Receptors: ?NT is NE ?(most common) ? Excitation [Ca2+] In? ? muscle contraction or secretion by exocytosis. ?? Inhibition of GI tract and pancreas Sympathetic Receptors ? - Receptors Clinically more important ? ?1 ? Excitation heart ([E] = [NE]) ? ?? - blockers? = Antagonists (e.g.: Propranolol) ? ?2 usually inhibitory: smooth muscle relaxation of some blood vessels and bronchioles ([E] > [NE]) ? ?3 Adipose; [NE]>[E] ? ?? -blockers? = Antagonists (e.g.: Propranolol) Termination of NT Activity ? ACh: Acetylcholinesterase ? Catecholamine reuptake ?repackaging ?degradation (MAO) ?blocked by cocaine Fig 11-9 Fig 8-22 Table 7-4, p. 244 Chapter 7 The Peripheral Nervous System: Efferent Division Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning Autonomic Agonists and Antagonists ? Agonists ? Bind to same receptor as neurotransmitter ? Elicit an effect that mimics that of neurotransmitter ? Antagonists ? Bind with receptor ? Block neurotransmitter?s response Direct (Ant)agonist = mimic or block the NT receptor (Ant)agonist = mimic or block secretion, reuptake or degradation of NT Chapter 7 The Peripheral Nervous System: Efferent Division Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning CNS AND CONTROL OF AUTONOMIC FUNCTION ? Can be influenced by prefrontal association complex through its involvement with emotional expression characteristic of individual?s personality ? Hypothalamus plays important role in integrating autonomic, somatic, and endocrine responses that automatically accompany various emotional and behavioral states ? Medulla within brain stem is region directly responsible for autonomic output ? Some autonomic reflexes, such as urination, defecation, and erection, are integrated at spinal cord level CONTROL THE URINARY BLADDER Three sets of muscles are used to control the bladder: Detrusor muscle: used to empty bladder, has beta 2 and muscarinic receptors Internal sphincter muscle: used to retain fluid in bladder, has alpha 1 and muscarinic receptors External sphincter muscle (not shown): also retains fluid, under voluntary control During filling sympathetic system is active: Internal sphincter contracts and closes Detrusor relaxes During emptying (micturition or "peeing") parasympathetic system is active Internal sphincter relaxes (external sphincter must also relax) Detrusor muscle contracts, forcing urine out HYPOTHALAMUS NUCLEIThe hypothalamus is involved in the coordination of ANS responses Temperature regulation Regulation of food intake Regulation of water intake Emotional behavior FIGHT OR FLIGHT RESPONSE Fight or Flight Response THE PAPEZ CIRCUIT Limbic system helps control emotional behavior, in part by influence of Hypothalamus. The circuit connects the limbic lobe with hypothalamus and regulates emotional behavior. roseli Slide 1