L6 - Drugs Affecting the Autonomic Nervous System (Part I) Flashcards
What is the role of the autonomic nervous system (ANS)?
- The ANS conveys outputs from the central nervous system (CNS) to the rest of the body, except for skeletal muscle contraction.
Is the autonomic nervous system voluntary or involuntary?
- The autonomic nervous system is largely involved in involuntary control.
What are the functions regulated by the autonomic nervous system?
- It regulates contraction and relaxation of smooth muscle, exocrine and endocrine secretions, heartbeat, and energy metabolism.
What are the key components of a neuron?
- A neuron consists of a cell body, an axon, and a nerve terminal.
What is the role of the nerve terminal in a neuron?
- The nerve terminal releases neurotransmitters that can act on other neurons, muscles, or glands.
What is a ganglion?
- A ganglion is a collection of neuron cell bodies outside the CNS with innervating nerve terminals.
How many divisions does the autonomic nervous system have, and what are they?
- The autonomic nervous system has three divisions: sympathetic, parasympathetic, and enteric.
Which divisions of the autonomic nervous system are primarily focused on in the lecture?
- The focus is on the sympathetic and parasympathetic divisions.
What is the general anatomical pattern of the autonomic nervous system?
- Both sympathetic and parasympathetic divisions follow a two-neuron pattern with preganglionic and postganglionic neurons.
Where are the parasympathetic ganglia located?
- Parasympathetic ganglia usually lie close to or within the target organ.
Where are the sympathetic ganglia located?
- Sympathetic ganglia are found as paravertebral chains and midline ganglia.
What are the main activities of the sympathetic and parasympathetic systems?
- Sympathetic activity increases during stress, while parasympathetic activity predominates during satiation and repose (rest and digest).
How do sympathetic and parasympathetic systems affect organs?
- They can produce either opposing or similar effects on organs.
How is information relayed from the CNS to target organs?
- An impulse from the CNS travels down a preganglionic neuron, releasing a chemical that excites the postganglionic neuron, which in turn releases chemicals that bind to receptors on the target organ.
How do drugs affect autonomic neurotransmission?
- Drugs can bind to receptors at various points in the pathway, affecting neurotransmission in the autonomic nervous system.
What are the two main chemicals in the autonomic nervous system?
- The two main chemicals are acetylcholine and noradrenaline.
What neurotransmitter is released by neurons leaving the CNS?
- All neurons leaving the CNS release acetylcholine, which acts on nicotinic acetylcholine receptors.
What neurotransmitter is released by parasympathetic postganglionic neurons?
- Parasympathetic postganglionic neurons release acetylcholine, which acts on muscarinic acetylcholine receptors.
What neurotransmitter is released by sympathetic postganglionic neurons?
- Sympathetic postganglionic neurons release noradrenaline, which may act on α- or β-adrenoceptors, with an exception for the sweat glands.
What are nicotinic acetylcholine receptors?
- Nicotinic acetylcholine receptors are ligand-gated ion channels that allow increased Na+ permeability, sending action potentials and exciting cells.
Where are muscle-type nicotinic receptors located?
- Muscle-type nicotinic receptors are found at the skeletal neuromuscular junction.
What role do ganglionic nicotinic receptors play?
- Ganglionic nicotinic receptors are responsible for transmission in both the sympathetic and parasympathetic systems.
What are CNS-type nicotinic receptors, and where are they found?
- CNS-type nicotinic receptors are widespread in the brain and are excitatory.
What is the effect of drugs that act as agonists of ganglionic nicotinic receptors?
- These drugs activate nicotinic ACh receptors in ganglia, stimulating transmission in the autonomic nervous system and affecting various tissues and organs.
Why are ganglionic nicotinic receptor agonists of limited therapeutic use?
- Because they affect almost all autonomic functions, leading to complex and widespread effects.
What are some examples of ganglionic nicotinic receptor agonists?
- Examples include nicotine and dimethylphenylpiperazinium (DMPP).
What are the effects of ganglionic nicotinic receptor agonists on the body?
- Effects include tachycardia, increased blood pressure, variable gastrointestinal motility, and increased secretions from glands such as bronchial and salivary glands.
What are examples of ganglionic nicotinic receptor antagonists (blockers)?
- Examples include hexamethonium, trimetaphan, and tubocurarine.
What are the effects of blocking ganglionic nicotinic receptors?
- Effects include hypotension, loss of cardiovascular reflexes, inhibition of secretions, gastrointestinal paralysis, and impaired urination.
What is the current clinical use of ganglionic nicotinic receptor antagonists?
- These drugs are clinically obsolete, except for the occasional use of trimetaphan in anesthesia to produce controlled hypotension.
What are muscarinic acetylcholine receptors (mAChRs)?
- Muscarinic acetylcholine receptors are G-protein-coupled receptors (GPCRs) found on tissues such as the heart, smooth muscle, and glands.
What are the main types of muscarinic acetylcholine receptors?
- The two main types are M2 and M3 receptors.
What is the role of M2 muscarinic acetylcholine receptors?
- M2 receptors are found on the heart and have mainly inhibitory effects, reducing cardiac rate and force of contraction.
What is the role of M3 muscarinic acetylcholine receptors?
- M3 receptors are found on glands and smooth muscle, causing secretion and contraction.
How do M2 muscarinic acetylcholine receptors inhibit the heart?
- They inhibit the heart by activating K+ channels, causing hyperpolarization, and inhibiting adenylate cyclase, reducing cAMP levels and Ca2+ conductance.
How do M3 muscarinic receptors stimulate smooth muscle and glands?
- M3 receptors increase intracellular Ca2+ levels by activating IP3, leading to smooth muscle contraction and glandular secretion.
What are examples of muscarinic acetylcholine receptor agonists?
- Examples include acetylcholine, muscarine, pilocarpine (used for glaucoma), and bethanechol (stimulates bladder and gastrointestinal smooth muscle).
What are examples of muscarinic acetylcholine receptor antagonists?
- Examples include atropine (blocks all mAChRs and has various effects) and ipratropium (M3 antagonist used for asthma).
How does botulinum toxin affect acetylcholine release?
- Botulinum toxin cleaves proteins involved in vesicle release, thereby preventing acetylcholine release.
What is the role of acetylcholinesterase (AChE)?
- Acetylcholinesterase (AChE) breaks down acetylcholine into acetate and choline, regulating free acetylcholine levels.
What drug inhibits acetylcholinesterase, and what is its use?
- Ecothiopate inhibits acetylcholinesterase and is used as eye drops to treat glaucoma.
