15.4 Drugs that Affect the Autonomic System
3 min read•june 18, 2024
The autonomic nervous system controls involuntary functions in our body. Drugs can affect this system, either boosting or blocking its effects. These drugs work by interacting with specific receptors, mimicking or inhibiting natural chemicals in our body.
Understanding how these drugs work is crucial for treating various conditions. Some drugs speed up our heart rate and increase blood pressure, while others do the opposite. It's like having a remote control for our body's automatic functions.
Drugs Affecting the Autonomic Nervous System
Drug classes in autonomic system
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- drugs act on receptors
- Acetylcholine receptor agonists mimic the effects of acetylcholine ()
- Acetylcholinesterase inhibitors prevent the breakdown of acetylcholine, increasing its concentration ()
- block the effects of acetylcholine
- Muscarinic receptor antagonists block the effects of acetylcholine on ()
- Adrenergic drugs act on (alpha and beta)
- Sympathomimetic drugs mimic or enhance the effects of the sympathetic nervous system
- Direct-acting drugs directly stimulate adrenergic receptors ()
- Indirect-acting drugs increase the release or prevent the reuptake of ()
- Mixed-acting drugs have both direct and indirect effects ()
- Sympatholytic drugs block or reduce the effects of the sympathetic nervous system
- Alpha-adrenergic receptor antagonists block the effects of on alpha receptors ()
- Beta-adrenergic receptor antagonists block the effects of norepinephrine on beta receptors ()
- Sympathomimetic drugs mimic or enhance the effects of the sympathetic nervous system
Cholinergic vs adrenergic compounds
- Cholinergic compounds act on acetylcholine receptors and produce parasympathetic effects
- Decreased heart rate and contractility reduce cardiac output (acetylcholine)
- Increased gastrointestinal motility and secretion promote digestion (bethanechol)
- Constriction of pupils causes ()
- Increased bronchial secretion and constriction can lead to bronchoconstriction ()
- Adrenergic compounds act on adrenergic receptors and produce sympathetic effects
- Increased heart rate and contractility increase cardiac output (norepinephrine)
- Decreased gastrointestinal motility and secretion reduce digestion (epinephrine)
- Dilation of pupils causes (phenylephrine)
- improves airflow in the lungs ()
- Increased blood pressure results from and increased cardiac output ()
Sympathomimetic vs sympatholytic drugs
- Sympathomimetic drugs mimic or enhance the effects of the sympathetic nervous system
- Stimulate adrenergic receptors directly or indirectly increasing heart rate, blood pressure, and causing (epinephrine, )
- Used to treat conditions such as , , and
- Sympatholytic drugs block or reduce the effects of the sympathetic nervous system by antagonizing adrenergic receptors
- Alpha-adrenergic receptor antagonists decrease blood pressure by reducing peripheral resistance ()
- Beta-adrenergic receptor antagonists decrease heart rate, contractility and reduce blood pressure ()
- Used to treat hypertension, , and
Nicotine's impact on cardiovascular control
- Nicotine stimulates in the and releasing
- Acute effects of nicotine increase heart rate, blood pressure, cause and increase cardiac output and oxygen demand
- Chronic effects of nicotine lead to desensitization of nicotinic receptors and increased risk of cardiovascular diseases
- narrows and hardens arteries reducing blood flow
- reduces blood flow to the heart muscle
- occurs when blood flow to the heart is blocked causing damage to heart tissue
- Stroke happens when blood flow to the brain is disrupted leading to brain damage
- Withdrawal effects of nicotine include decreased heart rate, blood pressure and increased activity
Neurotransmission in the Autonomic Nervous System
- are chemical messengers that transmit signals across synapses
- The autonomic nervous system uses primarily acetylcholine and norepinephrine as neurotransmitters
- Adrenergic receptors are targets for norepinephrine and epinephrine in the sympathetic nervous system
- is an enzyme that breaks down acetylcholine, terminating its effects
- The limits the entry of many autonomic drugs into the central nervous system
- are involuntary responses mediated by the autonomic nervous system, regulating various bodily functions
Key Terms to Review (62)
Acetylcholine: Acetylcholine is a neurotransmitter that plays a crucial role in the communication between neurons, the activation of muscle fibers, and the regulation of various physiological processes in the body. It is a key player in the functioning of the nervous system, muscle tissues, and the autonomic nervous system.
Acetylcholine (ACh): Acetylcholine is a neurotransmitter in the nervous system that plays a crucial role in stimulating muscle contractions and is involved in various brain functions including memory and learning. In the context of skeletal muscle, it is essential for transmitting nerve signals to muscle cells, leading to muscle movement.
Adrenal medulla: The adrenal medulla is the inner part of the adrenal glands, which are located above each kidney. It secretes important hormones such as adrenaline (epinephrine) and noradrenaline (norepinephrine) in response to stress.
Adrenal Medulla: The adrenal medulla is the inner portion of the adrenal gland, responsible for the production and secretion of the hormones epinephrine (adrenaline) and norepinephrine (noradrenaline). These hormones play a crucial role in the body's response to stress and in the regulation of various physiological processes.
Adrenergic Receptors: Adrenergic receptors are a class of G protein-coupled receptors that bind to the neurotransmitters epinephrine (adrenaline) and norepinephrine (noradrenaline). These receptors play a crucial role in the regulation of the autonomic nervous system, mediating the physiological effects of the sympathetic nervous system.
Agonist: In the context of anatomy and physiology, an agonist is a muscle that causes or facilitates movement when it contracts, working as the primary mover. It plays a crucial role in the muscular system by interacting with skeletal muscles to produce specific movements.
Agonist: An agonist is a substance that binds to and activates a receptor, eliciting a physiological response. Agonists are crucial in the context of skeletal muscle interactions, muscle naming, and the autonomic nervous system.
Albuterol: Albuterol is a short-acting beta-2 adrenergic agonist medication primarily used to treat and prevent symptoms of asthma, chronic obstructive pulmonary disease (COPD), and other respiratory conditions by relaxing and opening the airways.
Amphetamine: Amphetamine is a powerful central nervous system stimulant that increases the release of neurotransmitters such as dopamine and norepinephrine in the brain. This class of drugs is often used to treat attention deficit hyperactivity disorder (ADHD) and narcolepsy, but it also has a history of recreational use due to its euphoric effects. Understanding amphetamines is crucial when discussing their impact on the autonomic system and how they can alter physiological responses.
Angina Pectoris: Angina pectoris is a type of chest pain or discomfort that occurs when the heart muscle does not get enough oxygen-rich blood. It is a symptom of an underlying heart condition, typically coronary artery disease, and is often associated with physical exertion or emotional stress.
Antagonist: In the muscular system, an antagonist muscle acts in opposition to the action of a specific agonist muscle, relaxing and yielding while the agonist contracts. This coordinated action allows for smooth and controlled movements.
Antagonist: An antagonist is a muscle or muscle group that acts in opposition to the action of another muscle or muscle group. It is responsible for producing a movement that is the reverse or opposite of the action produced by the agonist muscle.
Anticholinergic drugs: Anticholinergic drugs are medications that block the action of acetylcholine, a neurotransmitter involved in transmitting messages in the nervous system, particularly within the autonomic nervous system. These drugs are used to treat a variety of conditions by inhibiting parasympathetic nerve impulses.
Anticholinergics: Anticholinergics are a class of drugs that block the action of the neurotransmitter acetylcholine, which is responsible for various functions in the body, including muscle contractions, glandular secretions, and cognitive processes. These drugs are used to treat a variety of conditions, such as overactive bladder, Parkinson's disease, and certain types of movement disorders.
Atenolol: Atenolol is a beta-blocker medication primarily used to treat high blood pressure, angina, and certain types of irregular heart rhythms. It works by blocking the effects of the hormone epinephrine (adrenaline) to reduce the workload on the heart, thereby lowering blood pressure and heart rate.
Atherosclerosis: Atherosclerosis is a chronic, inflammatory condition characterized by the buildup of plaque within the arteries, leading to narrowing and hardening of the blood vessels. This condition is a major contributor to cardiovascular disease and can have significant implications for the central nervous system, autonomic system, cardiac cycle, and vascular homeostasis.
Atropine: Atropine is a naturally occurring tropane alkaloid compound that acts as an anticholinergic agent, blocking the action of the neurotransmitter acetylcholine in the parasympathetic nervous system. It is primarily used in the context of drugs that affect the autonomic system.
Autonomic Ganglia: Autonomic ganglia are clusters of nerve cell bodies located outside the central nervous system that serve as relay stations for the autonomic nervous system. They play a crucial role in the regulation and coordination of involuntary bodily functions, such as heart rate, blood pressure, digestion, and respiration, by transmitting signals between the central nervous system and the target organs.
Autonomic Reflexes: Autonomic reflexes are involuntary physiological responses controlled by the autonomic nervous system. They regulate vital functions such as heart rate, breathing, digestion, and other unconscious bodily processes without conscious control. These reflexes play a crucial role in maintaining homeostasis and are particularly relevant in the context of drugs that affect the autonomic system.
Beta-1 Receptors: Beta-1 receptors are a type of adrenergic receptor that are primarily found in the heart and kidney. They are responsible for mediating the effects of the neurotransmitter norepinephrine, which is released by the sympathetic nervous system. The activation of beta-1 receptors plays a crucial role in regulating cardiovascular function and various physiological processes within the body.
Bethanechol: Bethanechol is a cholinergic agonist, a type of drug that stimulates the parasympathetic nervous system by directly activating muscarinic acetylcholine receptors. It is primarily used to treat urinary retention and certain gastrointestinal disorders by increasing the tone and contractility of smooth muscle tissues.
Blood-Brain Barrier: The blood-brain barrier is a highly selective semipermeable membrane that separates the circulating blood from the brain and extracellular fluid in the central nervous system (CNS). It acts as a gatekeeper, controlling the movement of substances between the bloodstream and the brain to maintain the optimal environment for neuronal function and protection.
Blood-brain barrier (BBB): The blood-brain barrier is a selective permeability barrier that separates the circulating blood from the brain and extracellular fluid in the central nervous system (CNS). It protects the brain from foreign substances in the blood that may injure the brain, regulates transport of nutrients and waste, and maintains a stable environment for the brain.
Bradycardia: Bradycardia is a condition characterized by an abnormally slow heart rate, typically less than 60 beats per minute. This term is particularly relevant in the context of understanding drugs that affect the autonomic system and the metabolic states of the body.
Bronchodilation: Bronchodilation is the expansion of the bronchial air passages in the lungs. It occurs when the muscles surrounding these passages relax, allowing for increased airflow to and from the lungs.
Bronchodilation: Bronchodilation refers to the dilation or widening of the bronchial tubes, the passageways that carry air in and out of the lungs. This process helps to increase airflow and reduce airway resistance, making it easier to breathe. Bronchodilation is an important mechanism in the context of the autonomic nervous system and drugs that affect the autonomic system.
Bronchospasm: Bronchospasm is a sudden and involuntary constriction of the smooth muscles lining the bronchi and bronchioles, leading to narrowing of the airways. This phenomenon is a key feature in various respiratory conditions and is closely tied to the functioning of the autonomic nervous system.
Catecholamines: Catecholamines are a group of chemical messengers produced by the adrenal glands and certain neurons in the brain. They play a crucial role in the regulation of the autonomic nervous system, the endocrine system, and various physiological processes throughout the body's development and aging.
Cholinergic: Cholinergic refers to the action of neurotransmitters and drugs that mimic or enhance the effects of acetylcholine, the primary neurotransmitter of the parasympathetic nervous system. These substances play a crucial role in regulating various bodily functions, including heart rate, digestion, and muscle contraction.
Cholinesterase: Cholinesterase is an enzyme responsible for breaking down acetylcholine, a neurotransmitter crucial for communication between nerve cells and muscle activation. This enzyme plays a significant role in the autonomic nervous system by regulating the duration and intensity of the signal transmitted by acetylcholine, ensuring that muscle contractions are properly controlled and preventing excessive stimulation.
Coronary artery disease: Coronary artery disease (CAD) is a condition characterized by the narrowing or blockage of the coronary arteries, which supply blood to the heart muscle. This occurs due to the buildup of plaque, composed of fat, cholesterol, and other substances, leading to reduced blood flow and oxygen supply to the heart. CAD is a major cause of heart attacks and can be influenced by various risk factors, including high blood pressure, smoking, and diabetes.
Dopamine: Dopamine is a neurotransmitter that plays a crucial role in the nervous system, influencing perception, motor function, motivation, reward, and various other physiological processes. It is a key component in understanding the function of nervous tissue, the central nervous system, and the autonomic system, as well as the effects of certain drugs on the body.
Endogenous chemical: An endogenous chemical is a substance produced naturally within the body that plays a role in various bodily functions, including those regulated by the autonomic nervous system. These chemicals include hormones, neurotransmitters, and other cellular signaling molecules.
Ephedrine: Ephedrine is a sympathomimetic amine that acts as a bronchodilator and stimulant, primarily affecting the sympathetic nervous system. It is derived from the plant Ephedra and is used medically to treat conditions like asthma and hypotension, while also being known for its potential as a performance-enhancing drug due to its stimulating effects.
Exogenous chemical: An exogenous chemical is a substance that originates outside the body and can affect the autonomic nervous system when introduced into the body. These chemicals include drugs, toxins, or pharmacological agents that can either mimic or block natural neurotransmitters within the autonomic nervous system.
Hypotension: Hypotension is defined as abnormally low blood pressure, which can result in symptoms like dizziness, fainting, or shock. This condition is significant as it can be influenced by various factors such as medications, hormonal regulation, and heart function, affecting overall body perfusion and health.
Methacholine: Methacholine is a cholinergic agonist, meaning it binds to and activates acetylcholine receptors in the body. This action mimics the effects of the neurotransmitter acetylcholine, which is responsible for various autonomic functions regulated by the parasympathetic nervous system.
Miosis: Miosis is the process of pupillary constriction, or the narrowing of the pupil, which is controlled by the parasympathetic division of the autonomic nervous system. This physiological response is important in regulating the amount of light entering the eye and maintaining optimal visual acuity.
Muscarinic Receptors: Muscarinic receptors are a class of G protein-coupled receptors that are activated by the neurotransmitter acetylcholine. These receptors play a crucial role in the parasympathetic division of the autonomic nervous system, regulating various physiological processes throughout the body.
Mydriasis: Mydriasis is the dilation or widening of the pupils, which can occur due to exposure to certain drugs, diseases, or trauma. It is a response that can either be part of normal physiology or indicate an underlying condition when it occurs abnormally.
Mydriasis: Mydriasis is the dilation or widening of the pupil of the eye, which can occur as a result of certain drugs or medical conditions. This term is particularly relevant in the context of 15.4 Drugs that Affect the Autonomic System, as some drugs can directly influence the pupillary response.
Myocardial infarction: Myocardial infarction, commonly known as a heart attack, occurs when blood flow to a part of the heart is blocked for an extended period, causing damage or death to the heart muscle. This condition is often related to coronary artery disease, where the arteries supplying blood to the heart become narrowed or blocked due to plaque buildup. Understanding this term helps in recognizing how various factors, including autonomic nervous system drugs and cardiac physiology, play crucial roles in the heart's functioning and recovery processes.
Neostigmine: Neostigmine is a cholinesterase inhibitor drug that works by blocking the enzyme acetylcholinesterase, which is responsible for breaking down the neurotransmitter acetylcholine. This results in increased levels of acetylcholine at the synaptic cleft, leading to enhanced neurotransmission in the autonomic nervous system.
Neurotransmitters: Neurotransmitters are chemical messengers that transmit signals between neurons, or nerve cells, in the body. They play a crucial role in the communication and function of the nervous system, including the brain, spinal cord, and peripheral nerves.
Nicotinic Acetylcholine Receptors: Nicotinic acetylcholine receptors are a type of ionotropic receptor that responds to the neurotransmitter acetylcholine, playing a crucial role in muscle contraction and neurotransmission in the nervous system. These receptors are found at the neuromuscular junction, where they mediate communication between motor neurons and muscle fibers, leading to muscle activation. Additionally, they are also present in the central and peripheral nervous systems, affecting various physiological processes, including the autonomic nervous system.
Norepinephrine: Norepinephrine is a neurotransmitter and hormone produced by the adrenal glands that plays a key role in the body's fight or flight response, increasing heart rate, blood pressure, and blood sugar levels. It also helps to regulate sleep cycles, attention, and memory functions.
Norepinephrine: Norepinephrine, also known as noradrenaline, is a neurotransmitter and hormone produced by the adrenal glands. It plays a crucial role in the body's sympathetic nervous system, triggering physiological responses to stress and preparing the body for 'fight-or-flight' situations.
Parasympathetic Nervous System: The parasympathetic nervous system is one of the two divisions of the autonomic nervous system, responsible for the body's resting, digesting, and restorative functions. It works in opposition to the sympathetic nervous system, promoting relaxation and conserving energy.
Parasympathomimetic drugs: Parasympathomimetic drugs are a class of medications that mimic the effects of the neurotransmitter acetylcholine, stimulating the parasympathetic nervous system. These drugs promote rest-and-digest activities by decreasing heart rate, increasing glandular secretions, and relaxing muscles in the gastrointestinal tract.
Phentolamine: Phentolamine is a non-selective alpha-adrenergic antagonist that blocks the effects of epinephrine and norepinephrine on alpha-1 and alpha-2 adrenergic receptors in the autonomic nervous system.
Phenylephrine: Phenylephrine is a sympathomimetic drug that acts as an alpha-1 adrenergic receptor agonist, primarily affecting the autonomic nervous system. It is commonly used as a decongestant, vasoconstrictor, and mydriatic agent in various medical applications.
Pilocarpine: Pilocarpine is a cholinergic drug that mimics the action of the neurotransmitter acetylcholine, primarily stimulating the muscarinic receptors in the autonomic nervous system. It is commonly used in the treatment of glaucoma by promoting fluid drainage from the eye and reducing intraocular pressure, demonstrating its role in influencing autonomic functions.
Postganglionic neurons: Postganglionic neurons are the second-order neurons in the autonomic nervous system that transmit signals from the autonomic ganglia to the target organs. They serve as the final relay in the autonomic pathways, responsible for the efferent control of various physiological functions.
Prazosin: Prazosin is an alpha-1 adrenergic receptor antagonist that is primarily used to treat hypertension, benign prostatic hyperplasia, and post-traumatic stress disorder. It works by blocking the action of norepinephrine, a neurotransmitter that normally stimulates alpha-1 receptors, leading to vasodilation and reduced blood pressure.
Propranolol: Propranolol is a beta-blocker medication primarily used to treat high blood pressure, angina, and certain heart rhythm disorders. It works by blocking the effects of the hormone epinephrine (adrenaline), which can help reduce the workload on the heart and lower blood pressure.
Pseudoephedrine: Pseudoephedrine is a sympathomimetic drug that acts as a decongestant by stimulating the alpha-adrenergic receptors in the nasal mucosa, leading to vasoconstriction and reduced nasal congestion. It is commonly used to treat the symptoms of allergies, colds, and sinus infections.
Sympatholytic drug: A sympatholytic drug is a type of medication that inhibits the postganglionic functioning of the sympathetic nervous system. It can lower blood pressure, reduce heart rate, and decrease stress responses by blocking or dampening the effects of sympathetic neurotransmitters.
Sympathomimetic drug: A sympathomimetic drug is a type of medication that mimics or enhances the effects of the sympathetic nervous system, leading to increased heart rate, widened airways, and other responses typically associated with "fight or flight" reactions. These drugs can be used in treatments for conditions like asthma, cardiac arrest, and nasal congestion.
Sympathomimetics: Sympathomimetics are a class of drugs that mimic the effects of the sympathetic nervous system by stimulating adrenergic receptors. These drugs can produce effects similar to the body's natural fight-or-flight response, such as increased heart rate, blood pressure, and respiratory rate.
Tachycardia: Tachycardia is a medical term that refers to a rapid heart rate, typically defined as a heart rate exceeding 100 beats per minute in adults. This condition is particularly relevant in the context of drugs that affect the autonomic nervous system, as certain medications can directly or indirectly influence the heart's rhythm and rate of contraction.
Vasoconstriction: Vasoconstriction is the narrowing of the blood vessels due to the contraction of the muscular walls of the vessels, primarily in small arteries and arterioles. This process decreases blood flow and increases blood pressure within the vessel.
Vasoconstriction: Vasoconstriction is the physiological process by which blood vessels, specifically arteries and arterioles, narrow or constrict in response to various stimuli. This reduction in the diameter of the blood vessels results in decreased blood flow to the affected area, which can have significant implications for the body's overall function and homeostasis.