Autonomic Nervous System PDF

Autonomic Nervous System Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  Nervous System Central Nervous...

Autonomic Nervous System Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  Nervous System Central Nervous Peripheral System Nervous System Somatic Autonomic Enteric Sympathetic Parasympathetic Nervous System Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings   The autonomic nervous system (ANS) is part of the peripheral nervous system and it controls many organs and muscles within the body.  In most situations, we are unaware of the workings of the ANS because it functions in an involuntary, reflexive manner.  For example, we do not notice when blood vessels change size or when our heart beats faster. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  Autonomic Nervous System (ANS)  The ANS consists of motor neurons that:  Innervate smooth and cardiac muscle and glands  Make adjustments to ensure optimal support for body activities  Operate via subconscious control  Have viscera as most of their effectors Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  ANS Versus Somatic Nervous System (SNS)  The ANS differs from the SNS in the following three areas  Effectors  Efferent pathways  Target organ responses Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  Effectors  The effectors of the SNS are skeletal muscles  The effectors of the ANS are cardiac muscle, smooth muscle, and glands Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  Efferent Pathways  Heavily myelinated axons of the somatic motor neurons extend from the CNS to the effector  Axons of the ANS are a two-neuron chain  The preganglionic (first) neuron has a lightly myelinated axon  The ganglionic (second) neuron extends to an effector organ Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  Neurotransmitter Effects  All somatic motor neurons release Acetylcholine (ACh), which has an excitatory effect  In the ANS:  Preganglionic fibers release ACh  Postganglionic fibers release norepinephrine or ACh and the effect is either stimulatory or inhibitory  ANS effect on the target organ is dependent upon the neurotransmitter released and the receptor type of the effector Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  Comparison of Somatic and Autonomic Systems Figure 14.2 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  Divisions of the ANS  The three divisions of the ANS are the sympathetic, parasympathetic and enteric nervous system  The sympathetic mobilizes the body during extreme situations  The parasympathetic performs maintenance activities and conserves body energy  The two divisions counterbalance each other’s activity Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  Role of the Parasympathetic Division  Concerned with keeping body energy use low  Involves the D activities – digestion, defecation, and diuresis  Its activity is illustrated in a person who relaxes after a meal  Blood pressure, heart rate, and respiratory rates are low  Gastrointestinal tract activity is high  The skin is warm and the pupils are constricted Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  Role of the Sympathetic Division  The sympathetic division is the “fight-or-flight” system  Involves E activities – exercise, excitement, emergency, and embarrassment  Promotes adjustments during exercise – blood flow to organs is reduced, flow to muscles is increased  Its activity is illustrated by a person who is threatened  Heart rate increases, and breathing is rapid and deep  The skin is cold and sweaty, and the pupils dilate Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  Anatomy of ANS Location of Division Origin of Fibers Length of Fibers Ganglia Sympathetic Thoracolumbar Short preganglionic Close to the region of the spinal and long spinal cord cord postganglionic Parasympathetic Brain and sacral Long preganglionic In the visceral spinal cord and short effector organs postganglionic Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  Anatomy of ANS Figure 14.3 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  Parasympathetic Division Outflow Cranial Outflow Cranial Nerve Ganglion Effector Organ(s) Occulomotor (III) Ciliary Eye Facial (VII) Pterygopalatin Salivary, nasal, and Submandibular lacrimal glands Glossopharyngeal Otic Parotid salivary glands (IX) Vagus (X) Located within the Heart, lungs, and most walls of target organs visceral organs Sacral Outflow S2-S4 Located within the Large intestine, urinary walls of the target bladder, ureters, and organs reproductive organs Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  Parasympathetic Division Outflow Figure 14.4 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  Sympathetic Outflow  Arises from spinal cord segments T1 through L2  Sympathetic neurons produce the lateral horns of the spinal cord  Preganglionic fibers pass through the white rami communicantes and synapse in the chain (paravertebral) ganglia  Fibers from T5-L2 form splanchnic nerves and synapse with collateral ganglia  Postganglionic fibers innervate the numerous organs of the body Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  Sympathetic Outflow Figure 14.5 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  Sympathetic Trunks and Pathways  A preganglionic fiber follows one of three pathways upon entering the paravertebral ganglia  Synapse with the ganglionic neuron within the same ganglion  Ascend or descend the sympathetic chain to synapse in another chain ganglion  Pass through the chain ganglion and emerge without synapsing Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  Neurotransmitters and Receptors  Acetylcholine (ACh) and norepinephrine (NE) are the two major neurotransmitters of the ANS  ACh is released by all preganglionic axons and all parasympathetic postganglionic axons  Cholinergic fibers – ACh-releasing fibers  Adrenergic fibers – sympathetic postganglionic axons that release NE  Neurotransmitter effects can be excitatory or inhibitory depending upon the receptor type Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  Cholinergic Receptors  The two types of receptors that bind ACh are nicotinic and muscarinic  These are named after drugs that bind to them and mimic ACh effects Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  Nicotinic Receptors  Nicotinic receptors are found on:  Motor end plates (somatic targets)  All ganglionic neurons of both sympathetic and parasympathetic divisions  The hormone-producing cells of the adrenal medulla  The effect of ACh binding to nicotinic receptors is always stimulatory Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  Muscarinic Receptors  Muscarinic receptors occur on all effector cells stimulated by postganglionic cholinergic fibers  The effect of ACh binding:  Can be either inhibitory or excitatory  Depends on the receptor type of the target organ Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  Adrenergic Receptors  The two types of adrenergic receptors are alpha and beta  Each type has two or three subclasses (1, 2,  1, 2 , 3)  Effects of NE binding to:   receptors is generally stimulatory   receptors is generally inhibitory  A notable exception – NE binding to  receptors of the heart is stimulatory PLAY InterActive Physiology®: Nervous System II: Synaptic Transmission Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  Interactions of the Autonomic Divisions  Most visceral organs are innervated by both sympathetic and parasympathetic fibers  This results in dynamic antagonisms that precisely control visceral activity  Sympathetic fibers increase heart and respiratory rates, and inhibit digestion and elimination  Parasympathetic fibers decrease heart and respiratory rates, and allow for digestion and the discarding of wastes Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  Sympathetic Tone  The sympathetic division controls blood pressure and keeps the blood vessels in a continual state of partial constriction  This sympathetic tone (vasomotor tone):  Constricts blood vessels and causes blood pressure to rise as needed  Prompts vessels to dilate if blood pressure is to be decreased  Alpha-blocker drugs interfere with vasomotor fibers and are used to treat hypertension Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  Parasympathetic Tone  Parasympathetic tone:  Slows the heart  Dictates normal activity levels of the digestive and urinary systems  The sympathetic division can override these effects during times of stress  Drugs that block parasympathetic responses increase heart rate and block fecal and urinary retention Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  Cooperative Effects  ANS cooperation is best seen in control of the external genitalia  Parasympathetic fibers cause vasodilation and are responsible for erection of the penis and clitoris  Sympathetic fibers cause ejaculation of semen in males and reflex peristalsis in females Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  Unique Roles of the Sympathetic Division  Regulates many functions not subject to parasympathetic influence  These include the activity of the adrenal medulla, sweat glands, arrector pili muscles, kidneys, and most blood vessels  The sympathetic division controls:  Thermoregulatory responses to heat  Release of renin from the kidneys  Metabolic effects Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  Release of Renin from the Kidneys  Sympathetic impulses activate the kidneys to release renin  Renin is an enzyme that promotes increased blood pressure Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings