Neurotransmission in the ANS

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Questions and Answers

What role does the vesicle-associated transporter (VAT) play in the transport of ACh?

It transports ACh from the vesicle to the cytoplasm.

It facilitates the uptake of ACh from the cytoplasm into vesicles. (correct)

It converts ACh into inactive metabolites.

It synthesizes ACh from its precursors.

Which enzyme is responsible for converting Dopa into Dopamine?

Dopamine-β-hydroxylase

Dopa decarboxylase (correct)

Tyrosine hydroxylase

Catechol-O-methyltransferase

What triggers the exocytosis of vesicles containing ACh at the nerve terminal?

The binding of ACh to post-synaptic receptors

The influx of Ca²⁺ through voltage-gated Ca²⁺ channels (correct)

The inflow of Na⁺ through sodium channels

The activation of G-proteins in the presynaptic terminal

What is the process by which Noradrenaline (NA) is synthesized within the vesicle?

Dopamine is converted to NA by dopamine-β-hydroxylase. Signup and view all the answers

What type of carrier is involved in the transport of Tyrosine into the presynaptic nerve terminal?

A Na⁺ dependent carrier Signup and view all the answers

What is the primary enzyme responsible for the synthesis of acetylcholine in the nerve terminal?

Choline acetyltransferase (ChAT) Signup and view all the answers

Which of the following best describes how neurotransmitter action is terminated in the synapse?

Metabolism or neuronal reuptake Signup and view all the answers

During cholinergic transmission, what is the role of the choline transporter (CHT)?

To transport choline into the nerve terminal Signup and view all the answers

Which neurotransmitter is primarily associated with non-adrenergic, non-cholinergic (NANC) signaling in the autonomic nervous system?

Substance P Signup and view all the answers

Acetylcholine is synthesized from which two main components?

Choline and acetyl-CoA Signup and view all the answers

What step in neurotransmission refers to the process of neurotransmitter release from vesicles into the synapse?

Exocytosis Signup and view all the answers

Which of the following NANC neurotransmitters is known for playing a role in vasodilation?

Nitric oxide Signup and view all the answers

Which step in neurotransmission would a drug most likely target to inhibit the release of neurotransmitters?

Release Signup and view all the answers

Which mechanism inhibits the breakdown of norepinephrine (NE)?

Inhibition of MAO Signup and view all the answers

Which classes of drugs can prevent the re-uptake of norepinephrine back into presynaptic neurons?

Tricyclic antidepressants and cocaine Signup and view all the answers

What best describes a common non-adrenergic, non-cholinergic (NANC) neurotransmitter's role in the autonomic nervous system?

Contributing to both excitatory and inhibitory responses Signup and view all the answers

Which of the following statements about COMT inhibitors is correct?

They inhibit the action of catechol-O-methyltransferase. Signup and view all the answers

What is the primary action of tricyclic antidepressants in relation to norepinephrine?

They inhibit its re-uptake into presynaptic neurons. Signup and view all the answers

Which of the following neurotransmitters is classified as a non-adrenergic non-cholinergic mediator in the parasympathetic nervous system?

Vasoactive Intestinal Peptide (VIP) Signup and view all the answers

What is the primary effect of hemicholinium on cholinergic neurotransmission?

Blocks the choline transporter Signup and view all the answers

Which drug is responsible for blocking the vesicle-associated transporter that affects cholinergic neurotransmission?

Vesamicol Signup and view all the answers

Which of the following is NOT a step where drugs can interfere with neurotransmission?

Modification of genetic material Signup and view all the answers

Which of the following neurotransmitters is specifically mentioned as a co-transmitter in the peripheral nervous system?

Adenosine triphosphate (ATP) Signup and view all the answers

Which neurotransmitter functions primarily in the sympathetic nervous system as a NANC mediator?

Nitric Oxide Signup and view all the answers

What is the function of monoamine oxidase (MAO) in neurotransmitter action?

Termination of neurotransmitter action Signup and view all the answers

Which of the following is a characteristic of non-adrenergic non-cholinergic (NANC) neurotransmitters?

They include mediators like serotonin and GABA Signup and view all the answers

What is the rate-limiting step in the synthesis of catecholamines?

Conversion of Tyrosine to Dopa Signup and view all the answers

Which enzyme is responsible for the conversion of Dopa to Dopamine?

Dopa decarboxylase Signup and view all the answers

Which statement about the metabolism of catecholamines is correct?

The oxidative branch of metabolism predominates, yielding vanillylmandelic acid (VMA). Signup and view all the answers

Which metabolite is produced in larger quantities from the oxidative branch of noradrenaline metabolism?

Vanillylmandelic acid (VMA) Signup and view all the answers

Which enzyme is NOT involved in the metabolism of catecholamines?

Aldose reductase (AR) Signup and view all the answers

Which substance can inhibit the rate-limiting step in catecholamine synthesis?

Metyrosine (α-methyltyrosine) Signup and view all the answers

What does MHPG sulfate excretion reflect?

Noradrenaline release in the brain Signup and view all the answers

Which catecholamine is formed after the enzymatic conversion of noradrenaline?

Adrenaline Signup and view all the answers

What is the role of the vesicular monoamine transporter (VMAT) in the transmission of adrenergic signals?

To store Noradrenaline (NA) in the vesicle for release Signup and view all the answers

Which enzyme is directly involved in the conversion of Dopamine to Noradrenaline (NA)?

Dopamine-β-hydroxylase Signup and view all the answers

Which transport mechanism employs a Na⁺ dependent carrier during adrenergic transmission?

Transport of Tyrosine into the presynaptic nerve terminal Signup and view all the answers

What is the role of choline acetyltransferase (ChAT) in cholinergic transmission?

It catalyzes the synthesis of acetylcholine. Signup and view all the answers

In cholinergic transmission, what triggers the release of acetylcholine (ACh) into the synapse?

Influx of Ca²⁺ ions Signup and view all the answers

Which of the following components is essential for synthesizing acetylcholine in nerve terminals?

Acetyl-CoA Signup and view all the answers

What is produced when Dopa is converted in the process preceding the formation of Noradrenaline?

Dopamine Signup and view all the answers

How is neurotransmitter action primarily terminated in the synapse?

By enzyme degradation or reuptake Signup and view all the answers

Which of the following neurotransmitters is classified under non-adrenergic, non-cholinergic (NANC) signaling?

Substance P Signup and view all the answers

What is the synthesis process of most neurotransmitters in the peripheral nervous system?

Synthesis occurs in nerve terminals from precursor molecules. Signup and view all the answers

Which component is directly involved in neurotransmitter release in response to nerve stimulation?

Calcium channels Signup and view all the answers

Which statement best reflects the primary mechanism through which drugs exert their effects on neurotransmission?

By interfering with specific steps in neurotransmitter synthesis, storage, release, or reuptake. Signup and view all the answers

Which of the following is the correct sequence of neurotransmitter action from synthesis to termination?

Synthesis → Storage → Release → Termination Signup and view all the answers

Which mechanism specifically inhibits the re-uptake of norepinephrine into the presynaptic neuron?

Tricyclic antidepressants Signup and view all the answers

What is the primary function of COMT inhibitors in the context of neurotransmitter activity?

Inhibit breakdown of norepinephrine Signup and view all the answers

Which of the following substances is classified as a non-adrenergic, non-cholinergic (NANC) neurotransmitter?

Substance P Signup and view all the answers

Which neurotransmitter's action is most likely affected by the use of MAO inhibitors?

Norepinephrine Signup and view all the answers

Which step in neurotransmission would MOST likely be influenced by the use of cocaine?

Re-uptake of neurotransmitters Signup and view all the answers

Which catecholamine is synthesized immediately after dopamine?

Noradrenaline Signup and view all the answers

What is the main urinary metabolite produced from the oxidative metabolism of noradrenaline?

Vanillylmandelic acid (VMA) Signup and view all the answers

Which enzyme is responsible for the production of adrenaline from noradrenaline?

Phenylethanolamine-N-methyltransferase Signup and view all the answers

What effect does metyrosine (α-methyltyrosine) have in the synthesis of catecholamines?

Inhibits the conversion of Tyrosine to Dopa Signup and view all the answers

Which of the following enzymes primarily contributes to the metabolism of catecholamines through oxidative reactions?

Aldehyde dehydrogenase (ADH) Signup and view all the answers

Which metabolite is associated with the reductive metabolism of noradrenaline?

3-methoxy-4-hydroxyphenylglycol (MHPG) Signup and view all the answers

What overall effect would increased levels of monoamine oxidase (MAO) have on catecholamines?

Decrease the levels of catecholamines in the body Signup and view all the answers

Which metabolite's excretion reflects the release of noradrenaline in the brain?

3-methoxy-4-hydroxyphenylglycol (MHPG) Signup and view all the answers

Which neurotransmitter is primarily categorized as a NANC mediator in the sympathetic nervous system?

Neuropeptide Y Signup and view all the answers

What mechanism is primarily targeted when a drug blocks the choline transporter in cholinergic neurotransmission?

Synthesis of acetylcholine Signup and view all the answers

Which of the following is NOT considered a major NANC mediator in the autonomic nervous system?

Acetylcholine Signup and view all the answers

What effect does vesamicol have on cholinergic neurotransmission?

Inhibits the storage of acetylcholine in vesicles Signup and view all the answers

Which of the following neurotransmitters is involved in vasodilation as a NANC mediator?

Nitric oxide Signup and view all the answers

Which step in neurotransmission is directly affected by monoamine oxidase (MAO)?

Termination of neurotransmitter action Signup and view all the answers

Which of the following substances can be considered a co-transmitter in the peripheral nervous system?

All of the above Signup and view all the answers

In what way can drugs interfere with the storage of neurotransmitters?

By inhibiting the transporter for moving neurotransmitters into vesicles Signup and view all the answers

What enzyme is responsible for converting Dopamine to Noradrenaline (NA) inside the vesicle?

Dopamine-β-hydroxylase Signup and view all the answers

Which component is essential for the transport of Tyrosine into the presynaptic nerve terminal?

Na⁺ dependent carrier Signup and view all the answers

What function does the vesicular monoamine transporter (VMAT) serve in adrenergic transmission?

Transports Dopamine into the vesicle Signup and view all the answers

Which two components are produced sequentially during the conversion process of Tyrosine?

Dopamine and Dopa Signup and view all the answers

Which of the following steps is directly influenced by an influx of Ca²⁺ at the nerve terminal?

Exocytosis of vesicles containing neurotransmitters Signup and view all the answers

What is the main precursor for the synthesis of acetylcholine (ACh) in the nerve terminal?

Choline Signup and view all the answers

Which statement best describes the process of neurotransmitter release in the autonomic nervous system?

Neurotransmitters are stored in vesicles and released upon nerve stimulation. Signup and view all the answers

What mechanism primarily terminates the action of neurotransmitters in the synapse?

Enzymatic breakdown and neuronal reuptake Signup and view all the answers

Which neurotransmitter is synthesized from acetyl-CoA and choline in cholinergic transmission?

Acetylcholine Signup and view all the answers

Which NANC neurotransmitter is known for its role in vasodilation?

Nitric oxide Signup and view all the answers

What is the function of the choline acetyltransferase (ChAT) enzyme in cholinergic transmission?

Converting acetyl-CoA into ACh Signup and view all the answers

What is the role of neuronal reuptake in neurotransmission?

To terminate the action of neurotransmitters in the synapse Signup and view all the answers

Which drug class is primarily used to inhibit the re-uptake of norepinephrine back into the presynaptic neuron?

Tricyclic antidepressants Signup and view all the answers

Which describes the storage of neurotransmitters within nerve terminals?

Stored in membrane-bound vesicles Signup and view all the answers

What role do COMT inhibitors play in neurotransmitter activity?

They inhibit the breakdown of norepinephrine. Signup and view all the answers

Which mechanism is involved in terminating the action of norepinephrine in the synaptic cleft?

Re-uptake into presynaptic neurons Signup and view all the answers

Which of the following best describes the role of MAO inhibitors in neurotransmission?

They inhibit the degradation of norepinephrine. Signup and view all the answers

What is the primary effect of using cocaine in the context of norepinephrine?

It inhibits the re-uptake of norepinephrine. Signup and view all the answers

Which neurotransmitter is primarily associated with vasodilation in the parasympathetic nervous system?

Nitric oxide Signup and view all the answers

What step of neurotransmission would be primarily affected by drugs that block vesicle-associated transporters (VAT)?

Storage of neurotransmitters in vesicles Signup and view all the answers

Which neurotransmitter acts as a co-transmitter in the sympathetic nervous system?

Neuropeptide Y Signup and view all the answers

Which drug specifically blocks the choline transporter, affecting acetylcholine synthesis?

Hemicholinium Signup and view all the answers

How do nitrogen oxide neurons primarily differ from cholinergic neurons in their signaling?

Nitric oxide is released into the bloodstream for systemic effects Signup and view all the answers

Which of the following mediators would most likely be categorized as a non-adrenergic, non-cholinergic (NANC) neurotransmitter involved in mood regulation?

Serotonin Signup and view all the answers

Which process involves the dissolution of neurotransmitters in the synapse, leading to their eventual breakdown?

Termination of action Signup and view all the answers

What is the major effect of monoamine oxidase (MAO) in the context of neurotransmitter action?

Degrading neurotransmitters in the synapse Signup and view all the answers

What is the function of the enzyme catechol-O-methyltransferase (COMT) in the metabolism of catecholamines?

It degrades catecholamines by methylation. Signup and view all the answers

Which of the following statements correctly describes the metabolic pathway of noradrenaline?

The oxidative branch mainly results in the formation of VMA as a metabolite. Signup and view all the answers

Which enzyme is involved in the conversion of Dopa to Dopamine?

Dopa decarboxylase Signup and view all the answers

What effect does metyrosine have on catecholamine synthesis?

Inhibits the conversion of tyrosine to dopa. Signup and view all the answers

Which of the following metabolites indicates the release of noradrenaline from the brain?

3-methoxy-4-hydroxyphenylglycol (MHPG) sulfate Signup and view all the answers

Which step in catecholamine metabolism is catalyzed by monoamine oxidase (MAO)?

Oxidation of catecholamines to their corresponding aldehydes. Signup and view all the answers

Which metabolite is primarily produced by the reductive branch of noradrenaline metabolism?

3-methoxy-4-hydroxyphenylglycol (MHPG) Signup and view all the answers

What is the outcome of the activity of phenylethanolamine-N-methyltransferase in catecholamine synthesis?

It catalyzes the methylation of noradrenaline to form adrenaline. Signup and view all the answers

Study Notes

Neurotransmission in the Autonomic Nervous System (ANS)

The ANS is responsible for regulating involuntary bodily functions, including heart rate, digestion, and breathing.
Neurotransmission in the ANS involves the synthesis, storage, release, and termination of neurotransmitters.
Most neurotransmitters are synthesized in nerve terminals, stored in membrane-bound vesicles, and released into the synapse in response to nerve stimulation.
Neurotransmitter action is terminated by metabolism or neuronal reuptake.

Cholinergic Transmission

Acetylcholine (ACh) is the primary neurotransmitter in the parasympathetic nervous system.
Choline, the precursor for ACh, is transported into the nerve terminal by the choline transporter (CHT).
ACh is synthesized from acetyl-CoA and choline by the enzyme choline acetyltransferase (ChAT).
ACh is transported from the cytoplasm into vesicles by a vesicle-associated transporter (VAT).
Action potentials cause an influx of Ca²⁺ through voltage-gated Ca²⁺ channels, leading to exocytosis of vesicles and release of ACh into the synapse.

Adrenergic Transmission

Norepinephrine (NA) is the primary neurotransmitter in the sympathetic nervous system.
Tyrosine is transported into the presynaptic nerve terminal by a Na⁺ dependent carrier.
Tyrosine is converted to Dopa by the enzyme tyrosine hydroxylase.
Dopa is converted to Dopamine by the enzyme dopa decarboxylase.
Dopamine is transported into the vesicle by the vesicular monoamine transporter (VMAT).
Inside the vesicle, Dopamine is converted to Noradrenaline (NA) by the enzyme dopamine-β-hydroxylase.

Non-Adrenergic Non-Cholinergic (NANC) Mediators

NANCs include neurotransmitters other than NA and ACh.
Major NANC mediators in the ANS include:
- Nitric oxide and vasoactive intestinal peptide (VIP) in the parasympathetic NS.
- ATP and neuropeptide Y in the sympathetic NS.
- Others, such as 5-hydroxytryptamine (serotonin), GABA, and dopamine.

Effects of Drugs on Neurotransmission

Drugs can interfere with neurotransmission at various steps:
- Synthesis of NT
- Storage of NT in vesicles
- Release of NT into the synapse
- Interaction of the NT with post-synaptic receptors
- Termination of NT action

Drug Effects on Cholinergic Neurotransmission

Hemicholinium blocks the choline transporter, preventing ACh synthesis.
Vesamicol blocks the vesicle-associated transporter, preventing ACh from entering vesicles.

Drug Effects on Adrenergic Neurotransmission

Metyrosine inhibits the rate-limiting step of catecholamine synthesis, preventing the conversion of tyrosine to Dopa.
Reserpine inhibits the vesicular monoamine transporter, blocking NA from accumulating in vesicles.
Guanethidine prevents the release of NA from the presynaptic neuron.
COMT-inhibitors (e.g.entacapone) or MAO inhibitors (e.g.selegeline) inhibit the breakdown of NA.
Tricyclic antidepressants and cocaine can inhibit the reuptake of NA back into the presynaptic neuron.

Neurotransmission in the Autonomic Nervous System

Neurotransmitters are synthesized in nerve terminals and stored in membrane-bound vesicles.
Neurotransmitters are released into the synapse in response to nerve stimulation.
Termination of neurotransmitter action occurs through metabolism or neuronal reuptake.
Drugs can influence specific steps in neurotransmission.

Cholinergic Transmission

Choline is transported into the nerve terminal using the choline transporter (CHT).
Acetylcholine (ACh) is synthesized from acetyl-CoA and choline via the enzyme, choline acetyltransferase(ChAT).
ACh is transported into vesicles using a vesicle-associated transporter (VAT).
Influx of Ca²⁺ through voltage-gated Ca²⁺ channels triggers exocytosis of ACh into the synapse.

Adrenergic Transmission

Tyrosine is transported into the presynaptic nerve terminal using a Na⁺ dependent carrier.
Tyrosine is converted to Dopa by the enzyme tyrosine hydroxylase.
Dopa is converted to Dopamine by the enzyme dopa decarboxylase.
Dopamine is transported into vesicles via the vesicular monoamine transporter (VMAT).
Inside the vesicle, Dopamine is converted to Noradrenaline (NA) by the enzyme dopamine-β-hydroxylase.

Synthesis of Catecholamines

Catecholamines are synthesized through a series of enzymatic steps starting with Tyrosine.
The rate-limiting step in catecholamine synthesis is the conversion of Tyrosine to Dopa, and can be inhibited by metyrosine (α-methyltyrosine).

Metabolism of Catecholamines

Catecholamines are primarily metabolized by two enzymes: catechol-O-methyltransferase (COMT) and monoamine oxidase (MAO).

Non-Adrenergic Non-Cholinergic (NANC) Mediators

NANC neurotransmitters are those that are not noradrenaline (NA) or acetylcholine (ACh).
Major NANC mediators:
- Nitric oxide and vasoactive intestinal peptide (VIP) in the parasympathetic nervous system (PNS).
- ATP and neuropeptide Y in the sympathetic nervous system (SNS).
Other NANC's include:
- 5-hydroxytryptamine (serotonin)
- GABA
- Dopamine.

Drug Effects on Neurotransmission

Drugs can interfere with neurotransmission at various steps:
- Synthesis of neurotransmitter
- Storage of neurotransmitter in vesicles
- Release of neurotransmitter into the synapse
- Interaction of the neurotransmitter with post-synaptic receptors
- Termination of neurotransmitter action

Drug Effects on Cholinergic Neurotransmission

Hemicholinium blocks the choline transporter, preventing ACh synthesis.
Vesamicol blocks the vesicle-associated transporter (VAT), preventing ACh transport into vesicles.

Drug Effects on Adrenergic Neurotransmission

Cocaine and tricyclic antidepressants inhibit the re-uptake of NA back into the presynaptic neuron.
COMT inhibitors (e.g., entacapone) or MAO inhibitors (e.g., selegeline) can inhibit NA breakdown.

Neurotransmission in the Autonomic Nervous System

The autonomic nervous system uses neurotransmitters to communicate between neurons.
Neurotransmitters are synthesized in nerve terminals, stored in vesicles, released into the synapse, and then removed from the synapse.
Drugs can affect each step in neurotransmission.

Cholinergic Transmission

Choline: Precursor for acetylcholine (ACh) transported into the nerve terminal by the choline transporter (CHT).
Acetylcholine: Synthesized from acetyl-CoA and choline by the enzyme choline acetyltransferase (ChAT).
Vesicle-Associated Transporter (VAT): Transports ACh from the cytoplasm into vesicles.
Nerve stimulation triggers calcium influx, leading to exocytosis of vesicles and ACh release into the synapse.

Adrenergic Transmission

Tyrosine: Transported into the nerve terminal by a sodium-dependent carrier.
Tyrosine Hydroxylase: Converts tyrosine to dopa.
Dopa Decarboxylase: Converts dopa to dopamine.
Vesicular Monoamine Transporter (VMAT): Transports dopamine into the vesicle.
Dopamine β-Hydroxylase: Converts dopamine to noradrenaline (NA) within the vesicle.

Catecholamine Synthesis

Tyrosine is the precursor for catecholamines.
The rate-limiting step in catecholamine synthesis is the conversion of tyrosine to dopa, which can be inhibited by metyrosine.
Catecholamines: Dopamine, noradrenaline, adrenaline

Catecholamine Metabolism

Catechol-O-methyltransferase (COMT) and monoamine oxidase (MAO) are the main enzymes that metabolize catecholamines.
The primary urinary metabolite of noradrenaline is vanillylmandelic acid (VMA).

Non-Adrenergic Non-Cholinergic (NANC) Mediators:

NANC neurotransmitters are those other than noradrenaline and acetylcholine.
NANC mediators in the peripheral nervous system include:
- Parasympathetic: Nitric oxide, vasoactive intestinal peptide (VIP)
- Sympathetic: ATP, neuropeptide Y
- Others: 5-hydroxytryptamine (serotonin), GABA, dopamine

Effects of Drugs on Neurotransmission

Drugs can interfere with neurotransmission by affecting:
- Neurotransmitter synthesis
- Storage of neurotransmitters in vesicles
- Release of neurotransmitters into the synapse
- Interaction of neurotransmitters with post-synaptic receptors
- Termination of neurotransmitter action

Drug Effects on Cholinergic Neurotransmission

Hemicholinium: Inhibits choline transport, preventing ACh synthesis.
Vesamicol: Blocks the VAT, preventing ACh transport into vesicles.

Drug Effects on Adrenergic Neurotransmission

α-Methyltyrosine (Metyrosine): Inhibits tyrosine hydroxylase, reducing catecholamine synthesis.
Reserpine: Depletes noradrenaline stores in vesicles.
Guanethidine: Displaces noradrenaline from vesicles and inhibits release.
COMT Inhibitors: Inhibit the breakdown of noradrenaline, prolonging its action.
MAO Inhibitors: Inhibit the breakdown of noradrenaline, prolonging its action.
Tricyclic Antidepressants, Cocaine: Inhibit the re-uptake of noradrenaline into the presynaptic neuron, prolonging its action.

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Description

Explore the intricate processes of neurotransmission within the autonomic nervous system. This quiz covers the roles of neurotransmitters, focusing on acetylcholine and its synthesis, storage, and action. Test your understanding of how the ANS regulates involuntary bodily functions.