Autonomic Nervous System Notes

Contents

Osmosis High-Yield Notes

This Osmosis High-Yield Note provides an overview of Autonomic Nervous System essentials. All Osmosis Notes are clearly laid-out and contain striking images, tables, and diagrams to help visual learners understand complex topics quickly and efficiently. Find more information about Autonomic Nervous System:

Sympathetic nervous system

Parasympathetic nervous system

Adrenergic receptors

Cholinergic receptors

NOTES NOTES AUTONOMIC NERVOUS SYSTEM ▪ Part of peripheral nervous system (PNS); regulates basic visceral processes necessary to homeostasis ▪ Autonomic nervous system (ANS) affects visceral organs, glands, involuntary muscles → regulates heart rate, respiration rate, digestion, urination, salivation, sexual arousal, etc. ▪ Divided into two systems ▫ Sympathetic, parasympathetic ▪ Unlike somatic nervous system, in ANS ▫ Neurotransmitters synthesized, stored, released in varicosities (analogous to presynaptic nerve terminals in somatic nervous system) ▫ Target organ’s tissue can be innervated by multiple postganglionic neurons ▫ Postsynaptic receptors widely scattered on target organ NEURONS ▪ Two neuron types in both sympathetic, parasympathetic systems ▫ Preganglionic, postganglionic ▪ Preganglionic neurons → preganglionic fibers → synapse with autonomic ganglia (postganglionic neurons) → postganglionic fibers → target organ Preganglionic neurons ▪ General visceral efferent (GVE) neurons ▪ Located in central nervous system (CNS) (spinal cord) ▪ Release acetylcholine (ACh) Postganglionic neurons ▪ GVE, general visceral afferent (GVA) neurons ▪ Located outside central nervous system ▪ Release acetylcholine/norepinephrine/ neuropeptides Autonomic ganglia ▪ Contain neuron cell body clusters (postganglionic neurons) ▪ Synapse points between preganglionic fibers, postganglionic fibers SYMPATHETIC NERVOUS SYSTEM osms.it/sympathetic-nervous-system ▪ ANS component; controls visceral functions requiring fast response (i.e. “fight or flight”) ▪ Ganglia close to spinal cord → short preganglionic fibers, long postganglionic fibers Preganglionic neurons ▪ Located: thoracolumbar spinal cord’s intermediate horn (T1–L2) ▪ Cholinergic neurons → release ACh Postganglionic neurons ▪ Located close to spinal cord ▫ Paravertebral ganglia (cervical, thoracic, rostral lumbar, caudal lumbar, pelvic ganglia) ▫ Prevertebral ganglia (celiac, aorticorenal, superior mesenteric, inferior mesenteric ganglion) ▫ Chromaffin cells of adrenal medulla (modified sympathetic ganglion) OSMOSIS.ORG 445
▪ Either adrenergic/cholinergic ▫ Adrenergic neurons → release norepinephrine/epinephrine (adrenal medulla) ▫ Cholinergic → release ACh ▪ Effector organ receptors: ɑ1, ɑ2, β1, β2, β3 Sympathetic nervous system effects ▪ Cardiovascular: ↑ heart rate, ↑ cardiac output, vasoconstriction ▪ Respiratory: bronchodilation ▪ Gastrointestinal: ↓ motility, ↓ secretions ▪ Genitourinary: ↓ bladder’s detrusor muscle activity, ejaculation ▪ Metabolic: ↑ gluconeogenesis ▪ Glands: ↓ salivation, ↑ sweating ▪ Pupils: mydriasis Figure 51.1 Neurons originating in the hypothalamus synapse with sympathetic pre-ganglionic cells bodies in spinal cord nuclei. Some pre-ganglionic neurons synapse in the paravertebral ganglia of the sympathetic chain; others synapse in the pre-vertebral ganglia. Figure 51.2 Sympathetic preganglionic neurons release acetylcholine, which bind to nicotinic receptors on postganglionic neurons. Postganglionic neurons release catecholamines, which are received by adrenergic receptors on target organs. 446 OSMOSIS.ORG
Chapter 51 Neurology: Autonomic Nervous System PARASYMPATHETIC NERVOUS SYSTEM osms.it/parasympathetic-nervous-system ▪ ANS component controls visceral functions not requiring fast response (i.e. “rest and digest”) ▪ Ganglia close to target organ → long preganglionic fibers, short postganglionic fibers Preganglionic neurons ▪ Located in brainstem (nuclei of cranial nerves II, VII, IX, X), sacral spinal cord (S2– S4) ▪ Cholinergic neurons → release ACh Postganglionic neurons ▪ Located close to target organs ▫ Ciliary ganglion (cranial nerve III) ▫ Submandibular ganglion (cranial nerve VII) ▫ Otic ganglion (cranial nerve IX) ▫ Near/inside target organ (cranial nerve X, sacral nerves) ▪ Mostly cholinergic, but some nonadrenergic, non-cholinergic → release neuropeptides ▪ Effector organ receptors are muscarinic Parasympathetic nervous system effects ▪ Cardiovascular: ↓ heart rate, ↓ cardiac output ▪ Respiratory: bronchoconstriction ▪ Gastrointestinal: ↑ motility, ↑ secretions ▪ Genitourinary: ↑ bladder’s detrusor muscle activity, erection ▪ Metabolic: ↓ glycogenesis ▪ Glands: ↑ salivation ▪ Pupils: miosis Figure 51.3 Neurons originating in the hypothalamus synapse with parasympathetic preganglionic cells bodies in brainstem, spinal cord at levels S2, S3, and S4. Pre-ganglionic neurons synapse in cranial ganglia and near/in target organ. OSMOSIS.ORG 447
Figure 51.4 Summary of parasympathetic components of cranial nerves III (oculomotor), VII (facial), and IX (glossopharyngeal). Figure 51.5 Parasympathetic preganglionic neurons release acetylcholine, which binds to nicotinic receptors on the post-ganglionic neuron. The post-ganglionic neuron also releases acetylcholine, which binds to muscarinic (G-protein coupled) receptors on target organs. 448 OSMOSIS.ORG
Chapter 51 Neurology: Autonomic Nervous System OSMOSIS.ORG 449
ADRENERGIC RECEPTORS osms.it/adrenergic-receptors ▪ Metabotropic receptors: respond to catecholamines (norepinephrine, epinephrine) ▪ Located on sympathetic effector organs → stimulated → sympathetic/ sympathomimetic response ▪ Types ▫ ɑ, β adrenergic receptors: ɑ1, ɑ2, β1, β2, β3 ɑ1 Adrenergic receptors (stimulatory effect) ▪ Gastrointestinal tract blood vessels, skin blood vessels → vasoconstriction ▪ Bladder, gastrointestinal (GI) tract sphincters → contraction ▪ Radial (dilator) muscle of iris → contraction ▪ Pancreas → ↓ secretion ▪ Liver → ↑ glycogenolysis ɑ2 Adrenergic receptors (inhibitory effect) ▪ Presynaptic nerve terminals (autoreceptors) → presynaptic inhibition of neurotransmitter release ▪ Postganglionic parasympathetic nerve terminals in GI tract (heteroreceptors) → ↓ insulin secretion ▪ ↓ platelet aggregation β1 Adrenergic receptors (stimulatory effect) ▪ Heart ▫ Sinoatrial (SA) node → ↑ heart rate (positive chronotropic effect) ▫ Atrioventricular (AV) node → ↑ conduction (positive dromotropic effect) ▫ Ventricular muscle → ↑ contractility (positive inotropic effect) ▪ Salivary glands → ↓ salivation ▪ Adipose tissue → lipolysis ▪ Kidney → ↑ renin secretion 450 OSMOSIS.ORG β2 adrenergic receptors (stimulatory effect) ▪ Skeletal muscle blood vessels → vasodilation ▪ Bronchioles → relaxation ▪ Pancreas → ↑ secretion ▪ Liver → ↑ glycogenolysis, ↑ gluconeogenesis β3 adrenergic receptors (stimulatory effects) ▪ Adipose tissue → lipolysis, thermogenesis ▪ Detrusor muscle → relaxation Adrenergic receptor mechanism ▪ Catecholamines binding → Gq (stimulatory) or Gi (inhibitory) protein activation → second messenger cascade → ↑ phospholipase C or ↓ adenylate cyclase → effect ▪ ɑ1 adrenergic receptors ▫ Gq protein activation → second messenger cascade → ↑ phospholipase C → ↑ IP3, DAG, Ca2+ → stimulatory effect ▪ ɑ2 adrenergic receptors ▫ Gi protein activation → ↓ adenylate cyclase → ↓ cAMP → inhibitory effect ▪ β1 adrenergic receptors ▫ Gs protein activation → ↑ adenylate cyclase → ↑ cAMP → stimulatory effect ▪ β1 adrenergic receptors ▫ Gs protein activation → ↑ adenylate cyclase → ↑ cAMP → stimulatory effect CATECHOLAMINES ▪ Neurotransmitters synthesized, released by adrenergic neurons ▪ Include epinephrine (adrenaline), norepinephrine (noradrenaline), dopamine
Chapter 51 Neurology: Autonomic Nervous System Synthesis ▪ Tyrosine → L-dopa; catalyzed by tyrosine hydroxylase ▪ L-dopa → dopamine; catalyzed by dopa decarboxylase ▪ Dopamine → norepinephrine; catalyzed by β hydroxylase ▪ Norepinephrine → epinephrine; catalyzed by phenylethanolamine-Nmethyltransferase (PNMT); only in adrenal medulla Degradation ▪ All catecholamines can be degraded by deamination by monoamine oxidase (MAO)/methylation by catechol-Omethyltransferase (COMT)/both ▪ Norepinephrine ▫ MAO: dihydroxymandelic acid ▫ COMT: normetanephrine ▫ Both: 3-methoxy-4-hydroxymandelic acid (VMA) ▪ Epinephrine ▫ MAO: dihydroxymandelic acid ▫ COMT: metanephrine ▫ Both: 3-methoxy-4-hydroxymandelic acid (VMA) ▪ Dopamine ▫ MAO: dihydroxyphenylacetic acid ▫ COMT: 3-methoxytyramine ▫ Both: homovanillic acid (HVA) Adrenergic transmission ▪ Present in ▫ Most postganglionic sympathetic neurons (norepinephrine) ▫ Adrenal medulla’s chromaffin cells (epinephrine) ▫ Ventral tegmental area, substantia nigra (dopamine) Figure 51.6 Types of adrenergic receptors, the G-proteins with which they can be coupled, and the catecholamines that bind with them. OSMOSIS.ORG 451
CHOLINERGIC RECEPTORS osms.it/cholinergic-receptors ▪ Receptors respond to neurotransmitter acetylcholine ▪ Located on parasympathetic effector organs, CNS → stimulated → parasympathetic/parasympathomimetic response Nicotinic receptors ▪ Ionotropic receptors ▪ Type: location ▫ Nm: neuromuscular junction (non autonomic) ▫ Nn: autonomic ganglia and adrenal medulla ▪ Mechanism ▫ Acetylcholine binding → Na+, K+ diffusion → depolarization → voltage Na+ channel activation → action potential → stimulatory effect Muscarinic receptors ▪ Metabotropic receptors (G-protein coupled receptors) ▪ Located in CNS, all parasympathetic effector organs, some sympathetic effector organs ▪ Type: location ▫ M1: autonomic ganglia, exocrine glands, CNS ▫ M2: heart, sweat glands, CNS ▫ M3: smooth muscle (blood vessels, lungs), glands, eyes, CNS ▫ M4: CNS, sweat glands ▫ M5: CNS 452 OSMOSIS.ORG ▪ Mechanism ▫ Acetylcholine binding → Gq (stimulatory) or Gi (inhibitory) protein activation → second messenger cascade → ↑ phospholipase C/↓ adenylate cyclase → stimulatory/inhibitory effect ▫ M1, M3, M5 → Gq protein activation → ↑ phospholipase C → ↑ IP3, DAG, Ca2+ → stimulatory effect ▫ M4 → Gi protein activation → ↓ adenylate cyclase → ↓ cAMP → inhibitory effect ▫ M2 → Gi protein activation → K+ channel activation → inhibitory effect ACETYLCHOLINE (ACh) ▪ Neurotransmitter synthesized, released by cholinergic neurons ▪ Synthesis ▫ Acetyl CoA + choline → acetylcholine; catalyzed by choline acetyltransferase ▪ Degradation ▫ Acetylcholine → acetylcholine CoA + choline; catalyzed by cholinesterase ▪ Cholinergic transmission is present in ▫ Basal ganglia, hippocampus, cerebral cortex ▫ All neuromuscular junctions ▫ All preganglionic neurons (both parasympathetic, sympathetic neurons) ▫ All postganglionic parasympathetic neurons ▫ Some postganglionic sympathetic neurons (sweat glands)
Chapter 51 Neurology: Autonomic Nervous System Figure 51.7 Types of muscarinic receptors and the G-proteins with which they can be coupled. Figure 51.8 Mechanism of action of receptors coupled with Gq protein. The type of adrenergic receptor that couples with Gq protein is the alpha 1 receptor. The types of cholinergic muscarinic receptors that couple with Gq protein are the M1, M3, and M5 receptors. OSMOSIS.ORG 453
Figure 51.9 Mechanism of action of receptors coupled with Gs protein. The type of adrenergic receptor that couples with Gs protein is the beta receptor. The type of cholinergic muscarinic receptor that couples with Gs protein is the M3 receptor. Figure 51.10 Mechanism of action of receptors coupled with Gi protein. The type of adrenergic receptor that couples with Gi protein is the alpha 2 receptor. The types of cholinergic muscarinic receptors that couple with Gi protein are the M2 and M4 receptors. 454 OSMOSIS.ORG

Osmosis High-Yield Notes

This Osmosis High-Yield Note provides an overview of Autonomic Nervous System essentials. All Osmosis Notes are clearly laid-out and contain striking images, tables, and diagrams to help visual learners understand complex topics quickly and efficiently. Find more information about Autonomic Nervous System:

Sympathetic nervous system

Parasympathetic nervous system

Adrenergic receptors

Cholinergic receptors