Autonomic Nervous System-3 PDF

# Autonomic Nervous System - 3 ## Intended Learning Outcomes 1. Discuss the mode of actions of sympathetic and parasympathetic nervous systems. 2. Recognize sympathetic and parasympathetic tones. 3. Discuss the causes and clinical pictures of Horner syndrome, Pheochromocytoma, Paralytic ileus and...

# Autonomic Nervous System - 3 ## Intended Learning Outcomes 1. Discuss the mode of actions of sympathetic and parasympathetic nervous systems. 2. Recognize sympathetic and parasympathetic tones. 3. Discuss the causes and clinical pictures of Horner syndrome, Pheochromocytoma, Paralytic ileus and Organophosphates: Pesticides Poisoning and Nerve Gases. ## Mode of Action of Sympathetic and Parasympathetic Nervous System **What is the advantage of dual innervation of many organs by both branches of autonomic nervous system?** * It enables precise control over an organ's activity, like having both an accelerator and a brake to control the speed of a car. * The heart rate is increased by sympathetic and decreased by parasympathetic supply to the heart according to the body condition. * The two divisions of the autonomic nervous system are usually reciprocally controlled; increased activity in one division is accompanied by a corresponding decrease in the other. ### 1. Sympathetic Nervous System #### A. Generalized action (Mass Discharge) * It often responds by mass discharge. * Fight, fear or severe pain activate the hypothalamus. * This results in widespread discharge of almost all portions of the sympathetic nervous system throughout the body called the alarm or stress response. * Mass discharge increases in many ways the ability of the body to perform strong muscle activity. ### 2. Parasympathetic System #### A. Localized action * It usually causes specific localized responses. * Parasympathetic cardiovascular reflexes usually act only on the heart to decrease its rate of beating. * Likewise, other parasympathetic reflexes cause secretion mainly by the mouth glands, or in other instances secretion is mainly by the stomach glands. #### B. Generalized action * Sometimes parasympathetic nervous system dominates in quiet, relaxed situations such as digestion. * The parasympathetic system promotes these "rest - and - digest" types of bodily functions while slowing down those activities that are enhanced by the sympathetic system. * There is no need, for example, to have the heart beating rapidly and forcefully when the person is in a tranquil setting. ### 3. Sympathetic and parasympathetic "Tone" * Normally, the sympathetic and parasympathetic systems are continually active, and the basal rates of activity are known, respectively, as sympathetic tone and parasympathetic tone. #### Sympathetic Tone 1. Smooth muscles of arterioles: Sympathetic tone normally keeps almost all the systemic arterioles constricted to maintain arterial blood pressure. 2. Adrenal medulla: Sympathetic tone normally produces basal secretion of Epinephrine and Norepinephrine which help to maintain the blood pressure and blood glucose levels. #### Parasympathetic tone 1. Gastrointestinal tract: It produces basal level of smooth muscle contraction (prevent distention) and small amount of digestive juice. 2. Sino - atrial node (SAN): Decreasing the high intrinsic activity. Normally, vagus nerve (10th cranial nerve) has a tone on SA node decreasing its rate from 100 beat per minute to nearly 70 beat per minute. This is called vagal tone. ## The Different Forms of Interaction of Sympathetic and Parasympathetic Activities * Most organs are innervated with both divisions of ANS. Dual innervation can be: 1. Antagonistic 2. Cooperative 3. Complementary ### Dual antagonistic effects: * Many organs receive dual innervation with antagonistic effects, including the digestive tract airways heart and urinary bladder. For example: * Stimulation of sympathetic nerves increases heart rate; stimulation of parasympathetic nerves decreases heart rate. * Stimulation of sympathetic nerves decreases digestive tract motility and secretion; stimulation of parasympathetic nerves increases both. * Stimulation of sympathetic nerves induces bronchdilatation; stimulation of parasympathetic nerves induces bronchoconstriction. ### Organs that are innervated by only one division of the ANS: #### Sympathetic nervous system only: 1. Adrenal medulla 2. Most blood vessels 3. Cutaneous blood vessels 4. The pilomotor muscles in the skin (hair follicles) 5. Sweat glands 6. Ventricles 7. Dilator pupillae muscle #### Parasympathetic nervous system only: * Constrictor pupillae and oesophagus ### Dual complementary effect: * The effects of sympathetic and parasympathetic activation can be considered complementary. * An example is the innervation of salivary glands, where both are excitatory and stimulate secretion of saliva. * Parasympathetic activation causes release of watery saliva, while sympathetic activation causes the production of thick, viscous saliva. ### Dual cooperative effect: * Activation of parasympathetic nerves to the penis increases blood flow and leads to erection while activation of sympathetic nerves to the penis causes ejaculation. ## Autonomic Disorders ### Myasthenia gravis * It is a disease characterised by extreme muscular weakness (myasthenia means "muscular weakness"; gravis means "severe"). **Cause:** * It is an autoimmune disease caused by antibodies to nicotinic receptors at neuromuscular junction. * This causes nicotinic receptors destruction reducing receptors available for interaction with acetyl choline. * Thus, not all the released acetyl choline molecules can find a functioning receptor with which to bind. * As a result, acetylcholinesterase destroys much of the acetyl choline before it interacts with a receptor **Manifestations:** 1. Muscle weakness especially after physical activity (repeated stimulation of the nerve to skeletal muscle results in reduction of the acetyl choline vesicles increasing weakness and fatigability of body muscles). 2. Rapid fatigability 3. Ptosis and double vision (due to weakness of the extra-occular eye muscles) 4. Difficult swallowing (dysphagia) 5. Weakness of the respiratory muscles may lead to death **Treatment:** Neostigmine * It inhibits acetylcholinestrase temporarily and prolongs the action of acetyl choline at the neuromuscular junction. ### Horner syndrome * It is an interruption of sympathetic innervation to face. **Causes:** 1. Nerve injury, injury to the carotid artery 2. Tumor in the lung. **Manifestations:** * In most cases the problem is unilateral, with symptoms occurring only on the side of the damage. 1. Anhidrosis (reduced sweating) 2. Ptosis (drooping eyelid) 3. Miosis (constricted pupil) 4. Enophthalmos (sunken eyeball) 5. Vasodilation of skin blood vessels suppling the face. ### Raynaud's phenomenon * It is a spasm of arteries causes attacks of reduced blood flow to fingers and toes during exposure to cold or during stressful condition. * Smoking increases the severity of the symptoms **Causes:** 1. Idiopathic 2. Secondary to lupus erythramatosis or rheumatoid arthritis. **Manifestations:** * The symptoms often include a triphasic change in color of the skin of the digits. 1. Pallor, coldness, and numbness. 2. Cyanosis (skin turns blue or even purple), and intense pain. 3. Deep red, swelling, and tingling. **Treatment:** 1. α - adrenoceptor antagonists (e.g., prazosin) 2. Surgical sympathectomy ### Pheochromocytoma * It is a tumor of adrenal medulla, characterized by excessive secretion of epinephrine and norepinephrine in blood generalized sympathetic stimulation. **Manifestations:** 1. ↑ heart rate (tachycardia), and palpitation. 2. Vasoconstriction of blood vessels ↑ arterial blood pressure and headache. 3. ↑ alertness, anxiety and fear. 4. ↑ glycogen break down → ↑ blood glucose level. 5. Excessive sweating **Treatment:** 1. Surgical removal of tumor 2. Drugs to decrease blood pressure and heart rate. ### Paralytic Ileus (Paralysis of the Intestine) * It is a decrease in the intestinal motility sufficient to inhibit the passage of food through the intestine and lead to intestinal blockage. **Cause:** * It is due to increased sympathetic activity. * It occurs after abdominal surgery * Certain drugs (e.g., anaesthesia, opioids) * Electrolyte disturbance derivative **Manifestations:** 1. Abdominal pain 2. Abdominal distension 3. No bowel movement 4. Vomiting 5. Constipation **Treatment:** * Acetyl choline derivative ### Organophosphates: Pesticides Poisoning and Nerve Gases * Organophosphate (pesticides) and nerve gases (used in war) inhibit acetylcholinesterase and prolong the actions of acetylcholine → Excessive stimulation of nicotinic and muscarinic receptors. **Manifestations:** 1. Diarrhea and vomiting 2. Urination 3. Miosis 4. Bradycardia (↓ heart rate) 5. Bronchial constriction 6. Excitation of skeletal muscle 7. Lacrimation 8. Salivation 9. Sweating **Treatment:** * The muscarinic cholinergic receptor antagonist e.g. atropine **Organophosphate Poisoning Symptoms** * D: Diarrhea * U: Urination * M: Miosis * B: Bradycardia * B: Bronchospasm * E: Excitation of skeletal muscle and CNS * L: Lacrimation * S: Salivation * S: Sweating ## Student Activity **True and False** * All body organs receive dual innervation of sympathetic and parasympathetic nerves. **F** * Myasthenia gravis is an autoimmune disease. **T** * Horner's syndrome is associated with exophthalmos. **F** ## References 1. Barrett KE, Barman SM, Brooks HL, and Yuan JX. (2019). Ganong's Review of Medical Physiology. 26th ed. ebook by McGraw-Hill Education. 2. Hall JE, and Hall ME. (2021). Guyton and Hall Textbook of Medical Physiology. 14th ed. eBook by Elsevier, Inc. 3. Sherwood L, (2016). Human Physiology From Cells to Systems. 9th ed. eBook by Nelson Education, Ltd. ## Image Description The last image is a photograph of students walking and sitting in a courtyard of a university building.