Please read chapter 15, The Autonomic Nervous System, complete this study guide, and study this material BEFORE coming to the first class.

Transcription

1 Please read chapter 15,, complete this study guide, and study this material BEFORE coming to the first class. I. Introduction to the autonomic nervous system: Briefly describe the autonomic nervous system. A. It is part of the nervous system. B. It functions involuntarily and automatically. C. It includes peripheral nerve fibers within cranial and spinal nerves that lead to visceral organs. D. Examples of functions E. The autonomic nervous system is mainly MOTOR. 1. Please explain. 2. Does this mean that there are no sensory impulses coming from those visceral effectors that are innervated by the ANS? Explain. F. The ANS is mainly reflex 1. Sensory impulses from visceral organs hypothalamus, brain stem or spinal cord. 2. Motor impulses viscera (visceral effectors) G. What are the basic differences between the somatic efferent and autonomic divisions of the nervous system? *To understand the ANS you may need to go back and review nerve physiology from chapter 12 if you ve forgotten the basic nerve histology, components of a reflex arc, and concepts of neurotransmitters and how they work. Revised Spring

2 II. Somatic Division and Autonomic Division of the Nervous System: Briefly compare the ANS with the SNS (See Fig in Chapter 12, The Nervous System) A. Somatic nervous system (SNS) 1. Consists of efferent neurons that conduct impulses from CNS to skeletal muscles (somatic effectors). 2. Voluntary 3. Does it belong to the PNS or CNS? 4. Is it motor or sensory? B. Autonomic nervous system (ANS) 1. Consists of efferent neurons that convey impulses from the CNS to visceral effectors (smooth muscle, cardiac muscle and glands) 2. Involuntary 3. Does it belong to the PNS or CNS? 4. Is it motor or sensory? C. Neuron Pathways: Outline the somatic neuron pathway and the autonomic neuron pathway. Compare them. (See Fig and Table 15.1) 1. Somatic neuron pathways usually have a single neuron between the CNS and the somatic effector. (Would this be a motor or sensory neuron?) Refer also to 1 st semester notes detail. 2. The autonomic neuron pathways involve two neurons between the CNS and visceral effector. These are referred to as the preganglionic neurons and postganglionic neurons. (Draw this.) a. Preganglionic neuron 1) Cell body in brain or spinal cord (in CNS) 2) Preganglionic fiber (axon) a) Myelinated b. Autonomic ganglion b) Exits as part of a cranial n. or spinal n. Revised Spring

3 c. Postganglionic neuron 1) Postganglionic fiber completely outside the CNS. 2) It is the second efferent neuron in the autonomic pathway. d. Visceral effector III. Divisions of the Autonomic Nervous System: What are the two divisions of the ANS? What is meant by dual inervation? Describe the two divisions of the ANS. (Fig and 15.3 copy this and study this carefully see also Table 15.2) A. Sympathetic division of ANS 1. Thoracolumbar division 2. Preganglionic fibers leave spinal cord with ventral roots of spinal nerves in thoracic and lumbar regions. a. Thoracic and first two lumbar segments. b. This is referred to as the "thoracolumbar outflow." 3. These preganglionic fibers travel with somatic efferent fibers of SNS to the autonomic ganglia. They re relatively short. 4. Autonomic ganglia of sympathetic division of ANS a. Sympathetic trunk (paravertebral ganglia, lateral ganglia) 1) Series of ganglia running parallel on either side of vertebrae. 2) They extend from the cervical region to the sacral region. 3) The fibers of these ganglia may be referred to as the "sympathetic chain" b. Prevertebral (collateral) ganglia 1) Series of ganglia running close to the abdominal arteries that give them their names. a) Inferior mesenteric b) Superior mesenteric c) Celiac (in region of solar plexus)-forms the largest autonomic plexus) NOTE: In certain parts of the body nerve fibers extending from the autonomic ganglia are interlaced into plexuses. The most famous is the "solar plexus" which consists of the fibers that surround the celiac artery and its branches. Thus, the reason for the dramatic effects on heart, lungs, and arteries produced by a hard punch to this region. 5. Postganglionic cell bodies a. 30 or more in each autonomic ganglion b. Preganglionic axons synapse with these postganglionic cell bodies. Revised Spring

4 c. This is an example of divergence. Review last semester notes. What is the significance of divergence? See conclusions below. 6. Postganglionic fibers rejoin spinal nerves; travel with them (briefly); then branch to form the rami communicantes (communicans); and then travel to innervate widely separated organs of the body. 7. Conclusions: a. An impulse beginning with one preganglionic neuron may affect several visceral effectors. b. Most sympathetic responses have a widespread effect on the body. B. Parasympathetic Division of ANS 1. Craniosacral division 2. Preganglionic fibers arise from brain stem and sacral region of spinal cord. a. Cranial outflow 1) Fibers exit from nuclei in brainstem and travel as part of cranial nerves (review last semester notes cranial nerves) a) Oculomotor (III) b) Facial (VII) c) Glossopharyngeal (IX) d) Vagus (X) responsible for 80% of cranio-sacral outflow b. Sacral outflow 1) 2nd-4th sacral nerves 2) Exits from lateral gray horns 3. Autonomic ganglia of parasympathetic division of ANS a. Also called terminal ganglia b. Ganglia located near or within walls of visceral effectors c. Preganglionic fibers relatively very long while the postganglionic fibers are very short d. Preganglionic neurons synapse with only 4-5 postganglionic neurons. 4. Conclusions: a. Preganglionic fibers are long, postganglionic fibers are short b. Ganglia are found near or within the associated organ (visceral effectors) c. Each supplies only one visceral effector. d. Therefore parasympathetic postganglionic fibers don't have a widespread effect as sympathetic outflow we say the effect is more localized. Revised Spring

5 Note: Concerning the cranial outflow, you will see that there are four pairs of ganglia that innervate the head and are located close to the organs they innervate. They are called terminal ganglia. Notice that they are associated with. Specifically, the last neuron of the cranial outflow is associated with which cranial nerve? What organs does this nerve innervate? Can you see how this is a very important nerve? Please refer to text (Table 15.3 and Fig. 15.6) to compare structural features of the sympathetic and parasympathetic divisions. IV. Physiology of the ANS (Refer to supplemental diagram comparing neuron pathways) Describe the physiological aspects of the ANS as outlined below. Note: Study Fig very carefully. Again, study Table A. Chemical Transmission 1. Neuroeffector junction: points of contact between autonomic fibers and visceral effectors. May be either neuromuscular or neuroglandular. 2. Cholinergic fibers (release acetylcholine-ach) a. all sympathetic and parasympathetic preganglionic fibers. b. all parasympathetic postganglionic fibers. c. some (very few) sympathetic postganglionic fibers (eg: most sweat glands, blood vessels of skeletal muscles and external genitalia). d. What are the two types of cholinergic receptors (Fig. 15.6) Compare these and their effects. 1) Nicotinic 2) Muscarinic e. Cholinesterase (AChE) quickly inactivates acetylcholine, therefore the effects are only short term and NOT very widespread. 3. Adrenergic fibers (release the neurotransmitter norepinephrine-ne) (The hormones NE and epinephrine are released from the adrenal medulla of the adrenal gland see Chapter 18) a. most sympathetic postganglionic fibers. b. COMT inactivates norepinephrine very slowly. Revised Spring

6 c. MAO also inactivates norepinephrine very slowly. d. NE and Epinephrine may also diffuse into the bloodstream from the adrenal gland. e. Conclusion: The effect is, therefore, longer lasting and more widespread. f. What are the two main types of adrenergic receptors? Compare these and their effects. 1) alpha receptors 2) beta receptors NOTE: Based on anatomical and physiological characteristics, explain how the sympathetic division has a more widespread and longer lasting effect on the body than does the parasympathetic. B. Effects of the ANS on the Body (Know Figs &15.3 and Tables 15.2&15.3) Think logically It s not as difficult as it seems! 1. Dual innervation: Organs are innervated by branches of both the parasympathetic and sympathetic divisions of ANS. a. One speeds up while the other slows down. b. One stimulates activities while the other inhibits. c. It may be either sympathetic or parasympathetic depending on the organ. 2. Examples of dual innervations and effects a. Sympathetic stimulates the heart while parasympathetic inhibits the heart. b. Sympathetic inhibits digestive processes while the parasympathetic stimulates digestive processes. 3. Parasympathetic, generally speaking, is responsible for the "rest-repose" system during which you store and conserve energy. 4. Sympathetic, generally speaking, is responsible for those activities needing the expenditure of energy, the stress response, the fight-or flight response. 5. When the body is in homeostasis a. The parasympathetic is dominant. Revised Spring

7 b. The sympathetic is activating the body just enough to give us energy to keep us going, to counter the parasympathetic system. V. Fight-or-Flight Response Describe the fight-or-flight response as a stress response and list physiological effects that occur as a result. Complete this on the back of this page. VI. Visceral Autonomic Reflex Arc Outline and describe the visceral autonomic reflex arc and compare it to the somatic reflex arc previously learned. Receptor Afferent (sensory) neuron Association neuron Visceral efferent (motor) preganglionic neuron Visceral efferent (motor) postganglionic neuron Visceral effector VIII. Receptor Agonists and Antagonists Describe how a variety of drugs can selectively activate or block specific cholinergic or adrenergic receptors. How do beta-blockers, e.g. Propanalol (Inderol), work on the heart? Compare B 1 and B 2 How would metaprolol (Lopressor), a selective B 1 blocker, compare? IX. Endocrine Aspects of ANS (Chapter 18) This will be on the final exam as well!!! Outline and study the adrenal gland specifically the adrenal medulla and its hormones epinephrine and norepinephrine Note their relationship to the ANS. What does it mean when the text says they are sympathomimetic? Stress and the General Adaptation Syndrome o E Situations (sympathetic) vs. SLUD (what does this stand for?) and Rest Repose o Stages of the General Adaptation Syndrome The Alarm Reaction The Resistance Reaction Exhaustion Remember this will be on your final exam at the end of this semester as well as on Exam 1. Don t forget it. Hold on to these notes!!! Revised Spring