Neurobiology: Acetylcholine Synthesis & Action

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Questions and Answers

What type of receptors do muscarinic antagonists primarily affect?

Beta-adrenergic receptors

Muscarinic receptors (correct)

Alpha-adrenergic receptors

Nicotinic receptors

Which substance is known to regenerate acetylcholinesterase?

Curare

Pralidoxime chloride (2-PAM) (correct)

Atropine sulphate

Muscarine

What lethal effect can occur from sufficient doses of curare?

Cardiac arrest

Respiratory hyperventilation

Asphyxiation due to diaphragm paralysis (correct)

Severe cardiac arrhythmia

What is the primary component necessary for the synthesis of epinephrine?

Norepinephrine Signup and view all the answers

What type of molecules primarily bind to cell surface receptors?

Lipid-insoluble molecules Signup and view all the answers

What effect does atropine sulphate generate when administered?

Sympathetic effects Signup and view all the answers

What occurs as a result of receptor activation?

Alterations in electrical state or permeability of the plasma membrane Signup and view all the answers

Which of the following describes the role of nicotinic receptors?

Mediate skeletal muscle contraction Signup and view all the answers

Which mechanism is NOT a type of signal transduction pathway?

Inhibition of gene transcription Signup and view all the answers

How do steroid hormones typically reach their receptors in a cell?

By passing through the plasma membrane Signup and view all the answers

Curare has been historically used for which medical purpose?

Treatment of tetanus and strychnine poisoning Signup and view all the answers

What is a primary function of receptors located in the plasma membrane?

Eliciting cellular responses upon ligand binding Signup and view all the answers

What is the primary action of cholinergic blockers?

Inhibit acetylcholine at receptors Signup and view all the answers

What kind of cellular responses can be triggered by receptor activation?

Changes in contractile activities Signup and view all the answers

Which of the following is a feature of receptor specificity?

Receptors show selectivity for specific ligands Signup and view all the answers

What are the components required for the synthesis of Acetylcholine (ACh)?

Choline and Acetylcoenzyme-A Signup and view all the answers

Which option describes the role of JAK kinases in signal transduction?

Act as a signaling mediator in the cytoplasm Signup and view all the answers

Which enzyme is responsible for hydrolyzing Acetylcholine in the synaptic cleft?

Acetylcholinesterase Signup and view all the answers

What happens to choline after Acetylcholine is hydrolyzed?

It is reused for the synthesis of new ACh Signup and view all the answers

Which of the following substances can inhibit the action of acetylcholinesterase?

Parathion Signup and view all the answers

What is the primary function of Acetylcholine once it is secreted into the tissue?

To elicit a nerve signal transmitter function Signup and view all the answers

How is choline transported back into the presynaptic cell after the hydrolysis of Acetylcholine?

By a high affinity choline uptake (HACU) system Signup and view all the answers

What is the role of Pralidoxime chloride (2-PAM) in relation to acetylcholinesterase?

It regenerates the enzyme after organophosphate poisoning Signup and view all the answers

What is the immediate effect of cholinergic nerve ending secretions of Acetylcholine in the tissue?

It causes a temporary increase in signal transmission Signup and view all the answers

What role do first messengers play in cell signaling?

They bind to receptors and initiate the signaling process. Signup and view all the answers

What primarily occurs after a receptor is activated by a first messenger?

The receptor activates primary effectors inside the cell. Signup and view all the answers

Which of the following describes the function of secondary effectors in a signaling pathway?

They receive signals from second messengers and carry out the cellular response. Signup and view all the answers

What is the first step in the signal transduction process?

Binding of first messengers to receptors. Signup and view all the answers

Which type of receptor is Clonidine classified as?

α2 agonist Signup and view all the answers

What distinguishes second messengers from primary effectors?

Primary effectors are always proteins, while second messengers can be small molecules. Signup and view all the answers

Which of the following is NOT a component of the signaling pathway?

Signal terminators Signup and view all the answers

What is the main purpose of the signal transduction pathway?

To transmit signals and create specific responses inside the cell. Signup and view all the answers

What is the role of acetylcholinesterase in cholinergic synapses?

To hydrolyze acetylcholine into acetyl CoA and choline Signup and view all the answers

Which of the following substances inhibits acetylcholinesterase?

Parathion Signup and view all the answers

Cholinergic blockers are divided into two main groups based on their receptor affinities. What is the classification of drugs that selectively block muscarinic receptors?

Muscarinic antagonists Signup and view all the answers

What characteristic effect do muscarinic antagonists have on the body?

Parasympatholytic effect Signup and view all the answers

Which substance is derived from toadstools and has a similar effect to atropine?

Muscarine Signup and view all the answers

What is the primary mechanism of action of curare in muscle relaxation?

Blockade of autonomic ganglia and NMJ Signup and view all the answers

What happens to choline after it is released during neurotransmission?

It is transported back to the presynaptic cell by HACU Signup and view all the answers

Which type of drug is the first paralytic used in anesthesia that produces flaccidity in skeletal muscle?

Curare Signup and view all the answers

Study Notes

Synthesis of Acetylcholine (ACh)

ACh is synthesized in the cytoplasm of the nerve terminal from choline and acetyl coenzyme-A (Acetyl-CoA) in the presence of the enzyme choline acetyltransferase.
ACh is released into the synaptic cleft by exocytosis.

Termination of Action of Acetylcholine

ACh is broken down into acetate and choline by acetylcholinesterase, an enzyme bound with collagen and glycosaminoglycans.
Choline is transported back into the terminal nerve ending to be used for the synthesis of new ACh.
Acetate diffuses into the surrounding medium.
Parathion inhibits acetylcholinesterase, leading to the accumulation of ACh in the synaptic cleft.

Cholinergic Blockers (Antagonists)

Cholinergic blockers are divided into two groups based on their receptor affinities:
- Muscarinic antagonists: Selectively block the muscarinic postganglionic synapses of the parasympathetic nerves.
- Nicotinic antagonists: Block autonomic ganglia and the neuromuscular junction (NMJ) in skeletal muscle.

Cholinergic Blockers and Acetylcholinesterase Regenerator

Atropine sulphate is a cholinergic blocker that produces sympathetic effects.
Pralidoxime chloride (2-PAM) is a cholinesterase regenerator used to treat organophosphate poisoning.

Muscarine and Curare

Muscarine, found in certain mushrooms, acts on muscarinic receptors.
Curare, a poison derived from plants, acts on nicotinic receptors.

Synthesis of Norepinephrine and Epinephrine

Norepinephrine (NE) is synthesized in the axoplasm of adrenergic nerve fiber endings but is completed inside the secretory vesicles.
Epinephrine is synthesized from NE within the adrenal medulla.

Receptors and Signal Transduction in the ANS

Signal transduction: The process of transmitting a chemical or physical signal through a cell by a series of molecular events, typically protein phosphorylation.
Signal transduction pathway: The sequence of events from receptor activation to cellular response.
Components:
- Ligands (first messengers): Initiate the signal transduction pathway.
- Receptors: Signal transducers that bind to ligands and activate primary effectors.
- Primary effectors: Proteins that activate second messengers.
- Second messengers: Small molecules that spread and intensify the signal.
- Secondary effectors: Proteins that carry out the cell's response.

Action of Water-Soluble Messengers (First Messengers or Ligands) - Receptor Activation

Receptors are proteins or glycoproteins located in the plasma membrane or inside the cell.
Binding of ligands to receptors triggers events inside the cell, causing a conformational change in the receptor (receptor activation).
Receptor activation can change:
- Permeability, transport properties, or electrical state of the plasma membrane
- Metabolism
- Secretory activity
- Proliferation and differentiation rate
- Contractile activities

Types of Signal Transduction

Ion channel-linked receptors: The receptor acts as an ion channel.
Enzyme-linked receptors: The receptor functions as an enzyme, usually a tyrosine kinase.
Cytokine receptors: The receptor activates a Janus Kinase (JAK) in the cytoplasm.
G-protein-coupled receptors: The receptor is coupled to a G protein.

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Description

This quiz covers the synthesis, termination, and action of acetylcholine (ACh) in the nervous system. It explores the processes involved in ACh production, release, and breakdown, as well as the implications of cholinergic blockers. Test your knowledge on this essential neurotransmitter!