BIOL 335
Rhode Island College
Jerome A. Montvilo, Ph.D.
Autonomic Nervous System

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I. Introduction

II. Action

     A. Activity

          1. Involuntary

     B. Effectors

          1. Visceral (smooth) muscles,
               cardiac muscles, glands

     C. “Fight-or-Flight” / “Rest-and-Relax”
               Responses (More Later)

III. Divisions

     A. Sympathetic Nervous System

          1. Increases energy use

     B. Parasympathetic Nervous System

          1. Decreases energy use

     C. Dual Innervation

IV. Neurons

     A. Double Neuron System (Usually)

          1. Autonomic Ganglia

               a. Adrenal Medulla

                    i. No second neuron

          2. Preganglionic Fibers
               [Preganglionic Neurons]

          3. Postganglionic Fibers
               [Postganglionic Neurons]

     B. Neurotransmitters

          1. Parasympathetic

               a. Preganglionic

                    i. Acetylcholine [ACh]

               b. Postganglionic

                    i. Acetylcholine [ACh]

          2. Sympathetic

               a. Preganglionic

                    i. Acetylcholine [ACh]

               b. Postganglionic

                    i. Post-ganglion

                         a) Norepinephrine [NE]

                    ii. Post-medulla

                         a) Sympathomimetic Hormones

                              i) Norepinephrine [NE]

                              ii) Epinephrine [E]

V. Receptors

     A. Cholinergic Fibers

          1. Parasympathetic and sympathetic
               preganglionic neurons; parasympathetic
               postganglionic neurons

          2. Neurotransmitter

               a. Acetylcholine [ACh]

          3. Often the opposite effect of adrenergic
               fibers (below)

               a. Decrease heart rate; contract bronchial
                    muscle; increase digestive peristalsis;

     B. Cholinergic Receptors

          1. Nicotinic Receptors

               a. On autonomic ganglia neurons
                    (parasympathetic and sympathetic
                    postganglionic fibers)

               b. Respond to parasympathetic and
                    sympathetic ACh from preganglionic

          2. Muscarinic Receptors

               a. On visceral (smooth) muscle,
                    cardiac muscle, glands

               b. Respond to parasympathetic ACh
                    from postganglionic fibers

     C. Adrenergic Fibers

          1. Sympathetic postganglionic neurons

          2. Neurotransmitters

               a. Norepinephrine [NE] [Noradrenaline]

          3. Often the opposite effect of cholinergic
               fibers (above)

               a. Increase heart rate; relax bronchial
                    muscle; decrease digestive peristalsis

     D. Adrenergic Receptors

          1. Alpha [] Receptors

               a. Alpha1 [1] Receptors

                    i. Excitatory: contracts iris, decreases lung
                         secretions; contracts arterioles and veins

               b. Alpha2 [2] Receptors

                    i. Inhibitory: inhibits salivary glands; allows

          2. Beta [] Receptors

               a. Beta1 [1] Receptors

                    i. On visceral (smooth) muscle,
                         cardiac muscle, glands

                    ii. Usually excitatory

                         a) Increase rate and force of heart

               b. Beta2 [2] Receptors

                    i. On visceral (smooth) muscle,
                         cardiac muscle, glands

                    ii. Usually inhibitory

                         a) Relax smooth muscles (to
                              dilate bronchioles)

               (c. Beta3 [3] Receptors)

                    i. Usually excitatory

                    ii. On adipose tissue; causes fat

VI. “Fight-or-Flight” / “Rest-and-Relax [Repose]”

     A. Dual Innervation of Effectors

     B. Excitatory and/or Inhibitory Receptors

     C. “Fight-or-Flight” Response

          1. Sympathetic System

          2. Response to Emergency Situations

               a. Epinephrine [Adrenaline] released
                    from adrenal glands

               b. Bronchiole diameter increases

               c. Heart rate increases 

               d. Blood pressure increases

               e. Muscle blood vessels diameters increase

               f. Digestive peristalsis decreases

     D. “Rest-and-Relax [Repose]” Response

          1. Parasympathetic System

          2. Returns systems to normal after
               emergency situations

               a. Epinephrine [Adrenaline] release
                    from adrenal glands stopped

               b. Bronchiole diameter decreases

               c. Heart rate decreases 

               d. Blood pressure decreases

               e. Muscle blood vessel diameters decrease

               f. Digestive peristalsis increases

VII. Summary

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Page obtained from link at URL: Prepared by Jerome A. Montvilo, Ph.D. for the use of his students. Copyright © by Jerome A. Montvilo. All rights reserved. Please send questions, comments, or suggestions to Last updated 4 September, 2007