Copyright 2010, John Wiley & Sons, Inc. Chapter 11 Autonomic Nervous System (ANS)

Copyright 2010, John Wiley & Sons, Inc. Introduction to the ANS Somatic nervous system (SNS) + ANS  peripheral nervous system (PNS) ANS  Not under conscious control  Is regulated by hypothalamus, brainstem The ANS supplies nerves to viscera  Smooth muscle (stomach, blood vessels)  Cardiac muscle (heart)  Glands (sweat and digestive glands)

Copyright 2010, John Wiley & Sons, Inc. Comparison: SNS vs ANS SNS  Controls skeletal muscle  Conscious, voluntary control  Motor pathway: one neuron from CNS to effector  Does include sensory neurons (from skin, skeletal muscles, and special sense organs)  All release the neurotransmitter ACh ANS  Controls viscera: smooth and cardiac muscle, and glands  Unconscious, involuntary  Motor pathway: series of two neurons from CNS to effector  Does include sensory neurons (monitors viscera)  Two divisions: sympathetic, parasympathetic  Release either ACh or NE

Copyright 2010, John Wiley & Sons, Inc. Somatic Nervous System

Copyright 2010, John Wiley & Sons, Inc. ANS Motor Pathways Autonomic motor pathway includes two motor neurons  Preganglionic neuron from CNS to neuron in autonomic ganglion  Postganglionic neuron from cell body in ganglion to effector

Copyright 2010, John Wiley & Sons, Inc. ANS Motor Pathways

Copyright 2010, John Wiley & Sons, Inc. Divisions of the ANS Sympathetic (S) division + parasympathetic (P) division Most viscera supplied with nerves of both S and P divisions: dual innervation S and P have opposite (antagonistic) effects  Heart rate: S stimulates, P inhibits  Digestive organs: S inhibit, P stimulate S: “flight or flight” P: “rest and digest” Some viscera receive only S (not P) nerves:  Sweat glands, many blood vessels, hair muscles

Copyright 2010, John Wiley & Sons, Inc. Sympathetic (S) Division Sympathetic preganglionic neurons  Have cell bodies located in lateral gray of spinal cord segments T1-T12 + L1-L2 So S division is called “thoracolumbar”  Axons pass through ventral roots of spinal nerves May branch many times May ascend or descend to many levels of S trunk ganglia (from cervical to sacral) Can synapse with 20 or more postganglionic neuron cell bodies Results: widespread S effects (viscera respond “in sympathy with one another”)

Copyright 2010, John Wiley & Sons, Inc. Sympathetic (S) Division Sympathetic postganglionic neurons  S postganglionic neurons cell bodies located In S “trunk ganglia” (2 long chains lateral to vertebrae)  From cervical to sacral regions  widespread S effects  Many axons from these cell bodies pass back into spinal nerves to reach viscera in skin (sweat glands, hair muscles, blood vessels) In S “prevertebral ganglia” anterior to 3 large abdominal arteries  Named celiac, superior and inferior mesenteric ganglia  Supply abdominal viscera: stomach, intestine, kidneys, liver, spleen  Axons pass from ganglia to viscera in S nerves

Copyright 2010, John Wiley & Sons, Inc. Sympathetic (S) Division

Copyright 2010, John Wiley & Sons, Inc. Parasympathetic (P) Division P preganglionic neurons  Cell bodies located in brainstem + in spinal cord segments S2-S4 Therefore P division is called “craniosacral”  Axons in cranial nerves III, VII, IX and X and in pelvic nerves from S2-S4 Vagus nerves (cranial nerves X) carry 80% of all P nerve impulses. Vagus nerves carry both motor and sensory neurons to/from viscera within the thorax and most of the abdominal cavity. P preganglionic axons do not branch or pass though S trunk ganglia but pass directly almost to viscera

Copyright 2010, John Wiley & Sons, Inc. Parasympathetic (P) Division P postganglionic neurons  Cell bodies lie in terminal ganglia Located within or near the innervated organ So P nerves cause precise, localized (not widespread) effects Because of anatomical arrangement, S nerves supply all viscera but P nerves do not reach some viscera. These include sweat glands, arrector pili muscles of hairs in skin, kidneys, spleen, adrenal medullae, and the walls of most blood vessels.  Axons pass from ganglia to viscera in P nerves

Copyright 2010, John Wiley & Sons, Inc. Parasympathetic (P) Division

Copyright 2010, John Wiley & Sons, Inc. ANS Neurotransmitters: Comparison Acetylcholine (ACh) ACh more common; released by:  All S and P preganglionic axons  All P postganglionic axons  Some S postganglionic axons (to sweat glands) ACh destroyed by enzyme ACh-ase so short-lived response Norepinephrine (NE) NE less common; released by:  Almost all S postganglionic axons NE has longer lasting effects enhanced by epinephrine + NE from adrenal medullae

Copyright 2010, John Wiley & Sons, Inc. Sympathetic Effects “Fight-or-flight” activities  Increase heart rate and contraction, and blood pressure (BP)  Dilate pupils  Dilate airways  Dilate vessels to skeletal muscles, heart, liver and adipose tissue  Constrict blood vessels to nonessential organs: skin, GI tract, kidneys  Mobilize nutrients for energy: glucose and fats

Organ/TissueActivityEffect EyePupil dilationincreased HeartHeart rate & forceincreased BloodPressureincreased LungsAirway dilationincreased Kidney Blood vessel diameter; urine production decreased GI tract Blood vessel diameter Sphincter decreased contracted Skeletal muscleBlood vessel diameterincreased Adipose tissue Blood vessel diameter Breakdown of TGs and FAs increased Liver Blood vessel diameter Release of bile acids increased Skinsweat gland activityincreased PancreasGlucagon secretionincreased PancreasInsulin/Digestive enzyme secretiondecreased Pituitary gland (post.)ADH hormone secretionincreased Urinary bladderMuscle wall & diameter of sphincterrelaxation & decrease SkinSmooth muscles of hair folliclescontract ("goose bumps") UterusSmooth muscles of uterine wall contract (pregnant) relax (non-pregnant) Sex organsMuscles for ejaculation of semen (man)contract MouthSalivary gland secretiondecreased Activities of the sympathetic division of the ANS (Generally: "Fight-or-flight responses")

Copyright 2010, John Wiley & Sons, Inc. Parasympathetic Effects Rest-and-digest activities  SLUDD Salivation Lacrimation Urination Digestion Defecation  Decrease heart rate, airway diameter, pupil diameter

Organ/TissueActivityEffect EyeRadial muscle/Pupil dilationn.e. HeartHeart rate & forcedecreased BloodPressuredecreased LungsAirway narrowing (bronchoconstriction)increased Kidney Blood vessel diameter; urine production n.e. GI tract Blood vessel diameter, motility Sphincter increased relaxed Skeletal muscleBlood vessel diametern.e. Adipose tissue Blood vessel diameter TG, FA build-up n.e. Liver Blood vessel diameter Storage of bile decreased increased Skinsweat gland activityn.e. PancreasSecretion of digestive enzymes & insulinincreased Pituitary gland (post.)ADH hormone secretionn.e. Urinary bladderMuscle wall & diameter of sphinctercontraction & increase SkinSmooth muscles of hair folliclesn.e. UterusSmooth muscles of uterine wallminimal effect Sex organsErection of penis and clitorisincreased MouthSalivary gland secretionincreased Activities of the parasympathetic division of the ANS (Generally: "SLUDD responses")

ANS & Human Health Understand the important aspect of mind-body harmony and control means, such as music, yoga, tai-chi, forms of meditation (e.g. prayers), hiking, gardening to sustain human health These activities are able to stimulate/activate the parasympathetic division of the ANS to restore PNS homeostasis and feelings of relaxation and “happiness” Copyright 2010, John Wiley & Sons, Inc.

Pathology – Disease & disorders connected with ANS Horner's syndrome Loss of sympathetic stimulation of muscles of one side of the face due to inherited mutation, an injury or a disease that affects the sympathetic outflow through the cervical ganglion. Symptoms include drooping of the upper eyelid, constricted pupil and loss of sweating. Autonomic dysreflexia Exaggerated sympathetic ANS response which occurs in 85% of individuals with spinal cord injury above the T6 level. Mass stimulation of sympathetic nerves below the level of injury due to ascending sensory nerve impulses from the lower body. Symptoms include: pounding head ache, severe high blood pressure, pale cold skin below injury level; warm, flushed sweating skin above injury level; Can lead to stroke, seizures and heart attacks if untreated!

Copyright 2010, John Wiley & Sons, Inc. Raynaud's syndrome (RS) Human skin microcirculation disorder caused by hyperactivation of the sympathetic system causing extreme vaso- constriction of peripheral blood vessel & episodic skin ischemia. Disorder is manifested by pallor, cyanosis and erythema of the fingers in response to different forms of stress, e.g. cold or emotional. Exact pathophysiology of RS is currently not known, but it has been hypothetized that it may be caused by an autonomic alteration in the sympathetic innervation of the blood vessels of the skin. RS can progress into a systemic autoimmune disease mainly due to progressive systemic sclerosis (= hardening) of the blood vessels.

Copyright 2010, John Wiley & Sons, Inc. Parasympathicomimetics (Part-1) Generally drugs which elicit the same effects as the post-synaptic nerves of the parasympathetic division of the ANS. Have acetyl choline-like effects on the effectors; many are used for treatment of high blood pressure. Prominent examples are: 1. Acetyl choline - very short-lived within the body therefore not very useful for therapy or treatment 2. Carbachol - stimulates smooth muscles of intestines and bladder;

Copyright 2010, John Wiley & Sons, Inc. Parasympathicomimetics (Part 2) 3. Muscarin - molecule of the poisonous mushroom Amanita muscaria; - leads to very strong Vagus nerve stimulation with typical intoxication syndromes, which include: - increased salivation, excessive sweat production, diarrhea, vomiting, cardiovascular collapse 4. Pilocarpin - toxic component of the South American plant Pilocarpus jaborandi; toxic effects on the human include: - excessive sweat production, strong bronchial mucus secretion, increased motility of GI tract; vomiting, - often used in low doses to treat Glaucoma;