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What is the primary role of G-proteins in neurotransmitter receptor activation?
What is the primary role of G-proteins in neurotransmitter receptor activation?
What is the primary mechanism by which local anesthetics inhibit neuronal conduction of pain signals?
What is the primary mechanism by which local anesthetics inhibit neuronal conduction of pain signals?
What is auto-phosphorylation in the context of kinase receptors?
What is auto-phosphorylation in the context of kinase receptors?
Which of the following best describes the action of phospholipase A2 activated by G-proteins?
Which of the following best describes the action of phospholipase A2 activated by G-proteins?
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Which local anesthetic is often used for nasal surgery due to its vasoconstrictive properties?
Which local anesthetic is often used for nasal surgery due to its vasoconstrictive properties?
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Which receptors are associated with sympathetic and parasympathetic divisions of the autonomic nervous system?
Which receptors are associated with sympathetic and parasympathetic divisions of the autonomic nervous system?
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What is a common unwanted effect of high systemic doses of local anesthetics?
What is a common unwanted effect of high systemic doses of local anesthetics?
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Which type of local anesthetics tends to produce the metabolite PABA, associated with allergic reactions?
Which type of local anesthetics tends to produce the metabolite PABA, associated with allergic reactions?
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What triggers the dissociation of G-protein subunits during receptor activation?
What triggers the dissociation of G-protein subunits during receptor activation?
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What is the effect of G-protein coupled receptors on intracellular signaling?
What is the effect of G-protein coupled receptors on intracellular signaling?
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How does succinylcholine achieve muscle relaxation during general anesthesia?
How does succinylcholine achieve muscle relaxation during general anesthesia?
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What outcome is associated with the activation of the insulin receptor via auto-phosphorylation?
What outcome is associated with the activation of the insulin receptor via auto-phosphorylation?
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Which of the following amide local anesthetics has a longer duration of action?
Which of the following amide local anesthetics has a longer duration of action?
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What is a key difference between the action of acetylcholine and succinylcholine at nicotinic receptors?
What is a key difference between the action of acetylcholine and succinylcholine at nicotinic receptors?
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Which of the following describes G-proteins most accurately?
Which of the following describes G-proteins most accurately?
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What is the effect of high doses of local anesthetics that cross the blood-brain barrier?
What is the effect of high doses of local anesthetics that cross the blood-brain barrier?
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What role do voltage-gated Ca2+ channels play in neurotransmitter release?
What role do voltage-gated Ca2+ channels play in neurotransmitter release?
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What is the 'active zone' in the context of presynaptic nerve terminals?
What is the 'active zone' in the context of presynaptic nerve terminals?
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What happens during exocytosis of synaptic vesicles?
What happens during exocytosis of synaptic vesicles?
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What is referred to as a 'quantum' in the context of neurotransmitter release?
What is referred to as a 'quantum' in the context of neurotransmitter release?
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What triggers the fusion of synaptic vesicles with the presynaptic membrane?
What triggers the fusion of synaptic vesicles with the presynaptic membrane?
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Which statement is true regarding the presence of Na+ and K+ channels in the presynaptic nerve terminal?
Which statement is true regarding the presence of Na+ and K+ channels in the presynaptic nerve terminal?
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How does calcium concentration affect neurotransmission?
How does calcium concentration affect neurotransmission?
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What aspect of synaptic vesicles is affected by certain medications?
What aspect of synaptic vesicles is affected by certain medications?
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What is the primary function of acetylcholinesterase in the synapse?
What is the primary function of acetylcholinesterase in the synapse?
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Which of the following drugs is classified as an acetylcholinesterase inhibitor approved for dementia?
Which of the following drugs is classified as an acetylcholinesterase inhibitor approved for dementia?
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How do acetylcholinesterase inhibitors affect acetylcholine levels in the central nervous system?
How do acetylcholinesterase inhibitors affect acetylcholine levels in the central nervous system?
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What role does acetylcholine play in REM sleep?
What role does acetylcholine play in REM sleep?
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Which psychiatric health issue has been suggested to be influenced by acetylcholine levels?
Which psychiatric health issue has been suggested to be influenced by acetylcholine levels?
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What is the initial effect of succinylcholine on muscle activity?
What is the initial effect of succinylcholine on muscle activity?
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Which drug directly acts to prevent calcium release during malignant hyperthermia?
Which drug directly acts to prevent calcium release during malignant hyperthermia?
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Which of the following drugs is classified as a non-depolarizing muscle relaxant?
Which of the following drugs is classified as a non-depolarizing muscle relaxant?
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What is a major side effect common to both nicotinic antagonists and succinylcholine?
What is a major side effect common to both nicotinic antagonists and succinylcholine?
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In patients with pseudocholinesterase deficiency, succinylcholine can lead to which condition?
In patients with pseudocholinesterase deficiency, succinylcholine can lead to which condition?
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Which of the following is a characteristic of malignant hyperthermia?
Which of the following is a characteristic of malignant hyperthermia?
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Which drug potentiates GABA-A channel activity and is used as a spasmolytic?
Which drug potentiates GABA-A channel activity and is used as a spasmolytic?
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What type of muscle relaxant is vecuronium classified as?
What type of muscle relaxant is vecuronium classified as?
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Study Notes
Presynaptic Nerve Terminal
- Presynaptic vesicles contain proteins that sense Ca2+ concentration, hold the vesicle in place for release, and are involved in docking, release, and uptake of the vesicle within the presynaptic nerve terminal.
- Voltage-gated Na+ and K+ channels are present in the axon but not in the presynaptic nerve terminal membrane.
- Depolarization of the presynaptic terminal activates voltage-gated Ca2+ channels (VGCC) located in the presynaptic terminal membrane.
- Ca2+ influx raises intra-cytoplasmic Ca2+ concentrations.
- Many synaptic vesicles are located in the active zone, close to the presynaptic terminal membrane.
- Increased Ca2+ levels bind to Ca2+ sensing proteins on synaptic vesicles in the active zone, triggering fusion with the presynaptic nerve terminal membrane.
- This fusion releases neurotransmitter into the synaptic cleft through exocytosis, a rapid process requiring a few hundred microseconds.
- A single synaptic vesicle contains a quantum of neurotransmitter molecules.
- Fusion of individual vesicles results in quantal release of neurotransmitter.
- Medications can alter neurotransmission by influencing Ca2+ levels or inhibiting vesicle release.
G-Proteins as Transducers of Receptor Activation
- Receptors linked to intracellular proteins and enzymes act through G-proteins.
- G-proteins bind GTP.
- Receptor activation by a neurotransmitter stimulates GTP binding and dissociation of the G-protein into subunits.
- Free subunits affect adenylate cyclases, phospholipase C, Phospholipase A2, various kinases, and indirectly ion channels.
- G-protein coupled receptors are found throughout the nervous system, including the autonomic nervous system (ANS).
Kinase Receptors as Transducers of Receptor Activation
- Kinase receptors undergo autophosphorylation, leading to a cascade of phosphorylation of intracellular proteins.
- The insulin receptor is an example of a kinase receptor.
- Insulin binding to the receptor triggers dimerization and autophosphorylation, ultimately leading to glucose uptake and storage.
Local Anesthetics
- Local anesthetics block neuronal action potentials by blocking voltage-gated sodium channels, inhibiting neuronal conduction of pain signals.
- Local anesthetics are reversible and vary in duration of action.
- Common examples include lidocaine, mepivacaine, bupivacaine, tetracaine, benzocaine, procaine (Novocain), and cocaine.
- Cocaine also blocks reuptake of catecholamines.
- Side effects include:
- High systemic doses can lead to death due to blockade of neurons responsible for respiration and cardiovascular problems.
- Depression of skeletal and smooth muscle contraction.
- Seizures at high doses that cross the blood brain barrier.
- Ester analogs produce PABA, which can cause allergic reactions (Amides do not cause this).
Neuromuscular Blockers
- Used during general anesthesia to prevent muscle reflex responses and achieve flaccid paralysis.
- Two methods:
- Competitive inhibition of acetylcholine at nicotinic channels (skeletal muscle nicotinic receptor antagonists).
- Depolarization blockade with succinylcholine.
- Succinylcholine is an agonist at the nicotinic receptor, causing muscle contraction.
- Succinylcholine is not degraded by acetylcholinesterase and persists on nicotinic receptors, inhibiting endogenous acetylcholine interaction and blocking muscle contraction.
- This leads to channel desensitization and muscle paralysis.
- Succinylcholine initially causes muscle contraction (Phase I) followed by rapid desensitization and flaccid paralysis (Phase II).
- Drugs:
- Tubocurarine, atracurium, mivacurium, vecuronium, pancuronium, rocuronium (nicotinic antagonists).
- Succinylcholine (depolarizing block).
- Side effects include:
- Ganglionic blockade, causing decreased blood pressure and tachycardia.
- Histamine release.
- Respiratory paralysis.
- Malignant hyperthermia and death at high doses.
- Prolonged muscle relaxation and severe apnea in individuals with pseudocholinesterase deficiency.
Spasmolytics (Muscle Relaxants)
- Used to block muscle contraction during surgery and manage malignant hyperthermia.
- Malignant hyperthermia is a genetic defect triggered by inhalant anesthesia, leading to excessive calcium release from the sarcoplasmic reticulum, causing muscle contraction, oxygen depletion, and hyperthermia.
- Dantrolene (Dantrium) blocks calcium release, preventing malignant hyperthermia, but is hepatotoxic.
- Other spasmolytics include:
- Diazepam (Valium).
- Carisoprodol (Soma).
- Baclofen.
Acetylcholinesterase Inhibitors
- Acetylcholinesterase degrades acetylcholine in the synapse.
- Acetylcholinesterase inhibitors used for dementia include donepezil (Aricept) and rivastigmine (Excelon).
- These inhibitors cross the blood brain barrier.
- Acetylcholine levels are implicated in autism and REM sleep.
Neurotransmitters and Psychiatric Disorders
- The discussed neurotransmitters, while important, are not the only ones involved in the CNS or psychiatric disorders.
- These neurotransmitters contribute to the basal level or “tone” of the CNS.
- Changes in these neurotransmitters are linked to various psychiatric disorders and are targeted by medications that modulate them.
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Description
Explore the mechanisms involved in the presynaptic nerve terminal, including the role of voltage-gated calcium channels and synaptic vesicles in neurotransmitter release. This quiz covers key processes such as vesicle docking, depolarization, and exocytosis. Test your understanding of how calcium influx influences synaptic transmission.