Chapter 15: The Autonomic Nervous System

Transcription

1 Chapter 15: The Autonomic Nervous System Chapter Objectives COMPARISON OF SOMATIC AND AUTONOMIC NERVOUS SYSTEMS 1. List the structural and functional characteristics of the autonomic nervous system. 2. Distinguish between the pre- and postganglionic neurons, in terms of location. 3. Specify the different origins and destination ganglia for the sympathetic (thoracolumbar) and parasympathetic (craniosacral) preganglionic neurons. 4. Describe the differing locations of the ganglia of the sympathetic and parasympathetic systems. PHYSIOLOGICAL EFFECTS OF THE ANS 5. Discuss the primary purpose of the sympathetic division and the general body functions it directs. 6. Describe specific responses of effectors due to increased sympathetic stimulation. 7. Discuss the primary purpose of the parasympathetic division and the general body functions it directs. 8. Describe specific responses of effectors due to increased parasympathetic stimulation. ANS NEUROTRANSMITTERS AND RECEPTORS 9. Identify the cholinergic neurons,, and neurotransmitters. 10. Identify the adrenergic neurons,, and neurotransmitters. Chapter Lecture Notes Characteristics of the autonomic nervous system (Table 15.1) Involuntary control Sensory input mostly from interoceptors Motor pathways divided into sympathetic and parasympathetic divisions Two-neuron pathway (Fig 15.1) Preganglionic Postganglionic Neurotransmitters Preganglionic acetylcholine

2 Postganglionic acetylcholine (parasympathetic and sympathetic to sweat glands (except on palms and soles), blood vessels in skeletal muscle and arrector pili muscles) or norepinephrine (remainder of sympathetic) Effects smooth muscle, cardiac muscle and glands Physiological effects of the autonomic nervous system (Table 15.4) Sympathetic E situations (exercise, emergency, excitement and embarrassment) - fight or flight response Pupils dilate Heart rate, force of contraction and blood pressure increase Airways dilate Blood vessels to kidneys and gastrointestinal tract constrict Blood vessels to skeletal muscles, cardiac muscle, liver and adipose tissue dilate Liver cells perform glycogenolysis and lipid cell perform lipolysis Release of glucose by the liver Parasympathetic rest and digest response Increased salivation, lacrimation, urination, digestion and defecation Decreased heart rate, diameter of airways and diameter of pupils (constriction) Anatomical Differences between the Parasympathetic and Sympathetic Divisions (Table 15.3) Characteristics Parasympathetic Sympathetic Origin (Fig 15.2 & 15.3) Craniosacral outflow: brainstem nuclei of cranial nerves III, VII, IX and X; spinal cord segments S2-S4 Thoracolumnar outflow: lateral horn of gray matter of spinal cord segments T1-L2 Location of ganglia Relative length of pre- and postganglionic fibers Ganglia in (intramural= terminal) or close to visceral organ served Long preganglionic; short postganglionic Sympathetic ganglia (Fig 15.5) Ganglia within a few cm of CNS: alongside vertebral column (paravertebral ganglia=chain) and anterior to vertebral column (prevertebral ganglia) Short preganglionic; long postganglionic

3 Paravertebral ganglia = chain ganglia Innervate organs above the diaphragm like the heart and lungs Prevertebral ganglia = collateral ganglia Prevertebral ganglia surround the following arteries that branch from the aorta Celiac artery (celiac ganglia forms the solar plexus) Superior mesenteric artery Inferior mesenteric artery Neurotransmitters and (Table 15.2 & Fig 15.7) Cholinergic neurons release acetylcholine (all preganglionic neurons, select sympathetic postganglionic neurons and all parasympathetic postganglionic neurons) Cholinergic on the postsynaptic membrane that bind acetylcholine Nicotinic receptor Found in the dendrites and cell bodies of sympathetic and parasympathetic postganglionic neurons, the motor end plate in the neuromuscular junction and adrenal medullary cells (excitatory) Is mimicked by nicotine Muscarinic receptor Found in all parasympathetic target organs (excitatory in all but cardiac muscle where it is inhibitory), sweat glands (activation) and some blood vessels in skeletal muscle (inhibition; vasodilation) and arrector pili muscle (excitatory) Is mimicked by muscarine (a mushroom poison) Adrenergic neurons release norepinephrine (most sympathetic postganglionic neurons) Adrenergic bind norepinephrine and epinephrine α 1 Smooth muscle of blood vessels (excitation; vasoconstriction)

4 radial muscles of eye (dilation of pupil) sphincter muscles of stomach and urinary bladder (closing) salivary gland cells (decreased salivation) sweat glands on palms and soles (increased sweating) α 2 Smooth muscle in some blood vessels (inhibition; vasodilation) beta cells in pancreatic islets (decrease insulin secretion) pancreatic acinar cells (inhibition of digestive enzyme secretion) blood platelets (aggregation) β 1 Cardiac muscle (excitation; increased force and rate of contraction) posterior pituitary (secretion of antidiuretic hormones) adipose cells (breakdown of triglycerides) β 2 Smooth muscle in airways (relaxation; bronchodilation) blood vessels (relaxation; vasodilation) walls of internal organs (relaxation) cillary muscles (inhibition; relaxation) hepatocytes (glycogenolysis) β 3 Brown adipose tissue (thermogenesis)

5 Sympathetic Responses Target Organ Ganglia Effect Location Blood vessels of skeletal and Paravertebral Dilation cardiac muscle Blood vessels of skin, gut Paravertebral Constriction and kidneys Arrector pili muscle Sweat Glands Eyes Lungs Heart Paravertebral Contraction Paravertebral Sweat production Paravertebral Dilates pupils and relaxes ciliary muscles for far vision Paravertebral Dilates bronchi Paravertebral Increased rate and force of contraction Liver Prevertebral Breakdown of glycogen to glucose and triglycerides to fatty acids Small and Large Intestines Paravertebral Slows digestion, stops secretions and contracts sphincters Urinary Bladder Paravertebral Contracts sphincter Adrenal Medulla Stimulates release of norepinephrine and epinephrine Parasympathetic Responses Target Organ Origin Effect Eyes Cranial Nerve III Constricts pupils and ciliary muscles for near vision and stimulates tears Salivary Glands Cranial Nerve VII&IX Stimulate salivation Lungs Cranial Nerve X Constricts bronchi and stimulates secretion Heart Cranial Nerve X Decreased rate and force of contraction Gall Bladder Cranial Nerve X Constriction Pancreas Cranial Nerve X Stimulation of exocrine secretions and release of insulin Small and Large Intestines Cranial Nerve X and Sacral Nerves Increases motility and secretions and relaxes sphincters for increase defecation Urinary Bladder Sacral Nerves Contracts bladder (micturition) and relaxes sphincter Genitals Sacral Nerves Erection Drugs that Effect the Autonomic Nervous System

6 Drug Mechanism Action Uses Drugs that Stimulate the Sympathetic Nervous System (Sympathomimetic) Phenylephrine Stimulates α 1 Elevates blood pressure; stimulates smooth muscle Lowers blood Clonidine Stimulates α 2 pressure Isoproterenol Stimulates β Stimulates heart rate; dilates respiratory passages Albuteral, terbutaline Stimulates β 2 Ephedrine, psuedoephedrine MAO Inhibitors Tricyclic antidepressants (Moxadil, Endep) Stimulates NE release at synapses Increases NE levels in the synapse by inhibiting the enzyme that breaks it down Increases NE levels in the synapse by blocking reuptake Dilates respiratory passages Nasal decongestant and to elevate blood pressure Treatment of high blood pressure Treatment of respiratory disorders and as a cardiac stimulant during cardiac resuscitation Treatment of asthma, severe allergies and other respiratory disorders Similar to epinephrine Nasal decongestant and to elevate blood pressure or dilate respiratory passages Boosts mood in the brain Boosts mood in the brain Antidepressant Antidepressant Drugs that Stimulate the Parasympathetic Nervous System (Parasympathomimetic) Muscarine, pilocarpine, Stimulates muscarinic Similar to effects of Ach methacholine pupil contraction Physostigmine, neostigmine, malathion, nerve gases Block action of acetylcholinesterase Increase Ach concentrations at synapses Drugs that Block the Sympathetic Nervous System Prazosin (Minipress) Blocks α 1 Lowers blood pressure Tamsulosin (Flomax) Blocks α 1a Relaxes smooth muscle surrounding the urethra Yohimbine (herbal supplement) Blocks α 2 Propranolol (Inderal) Blocks β 1 and β 2 Dilates blood vessels and relaxes smooth muscles Reduces metabolic activity in cardiac muscle but may constrict respiratory passageways: slows heart rate Applied topically to cornea of eye to cause Stimulate digestive tract and smooth muscles of urinary bladder Treatment of high blood pressure Treatment of benign prostrate hyperplasia Aphrodisiac Treatment of high blood pressure: used to reduce heart rate and force of contraction in heart disease

7 Metoprolol (Lopressor), atenolol Blocks β 1 Reduces metabolic activity in cardiac muscle Drugs that Block the Parasympathetic Nervous System Atropine, related drugs Block muscarinic Inhibit parasympathetic activity Similar to those of Inderal but has less of an effect on respiratory muscles Treating diarrhea; dilating pupils; raising heart rate; blocking secretions of digestive and respiratory tracts prior to surgery; used to treat accidental exposure to anticholinesterase drugs, such as pesticides or military nerve gases