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Questions and Answers
What is the effect of Phenytoin on the sodium channel?
What is the effect of Phenytoin on the sodium channel?
- It causes repolarization and opens the channel
- It blocks the channel and prevents sodium flow (correct)
- It causes depolarization and closes the channel
- It activates the channel and allows potassium flow
What happens to the sodium channel when Phenytoin is present?
What happens to the sodium channel when Phenytoin is present?
- The gate remains open, allowing sodium to flow
- The gate becomes stuck, causing uncontrolled sodium flow
- The gate closes, preventing sodium from flowing (correct)
- The gate becomes partially open, allowing some sodium to flow
What is the effect of Phenytoin on the resting state of the sodium channel?
What is the effect of Phenytoin on the resting state of the sodium channel?
- It causes the channel to fluctuate between open and closed states
- It causes the channel to open and allow sodium flow
- It has no effect on the resting state of the channel
- It causes the channel to close and prevent sodium flow (correct)
What is the mechanism of action of Phenytoin?
What is the mechanism of action of Phenytoin?
What is the result of Phenytoin's action on the sodium channel?
What is the result of Phenytoin's action on the sodium channel?
What happens to the action potential when Phenytoin is present?
What happens to the action potential when Phenytoin is present?
What is the effect of Phenytoin on depolarization?
What is the effect of Phenytoin on depolarization?
What is the net result of Phenytoin's action on the cell?
What is the net result of Phenytoin's action on the cell?
What is the effect of barbiturates on the GABAA receptor?
What is the effect of barbiturates on the GABAA receptor?
What type of currents are activated at weak depolarization potentials?
What type of currents are activated at weak depolarization potentials?
Which type of blockers do T-type currents resist?
Which type of blockers do T-type currents resist?
What is the effect of GABA on muscle and endocrine cells?
What is the effect of GABA on muscle and endocrine cells?
What is a characteristic of T-type currents?
What is a characteristic of T-type currents?
What is the relationship between barbiturates and the GABAA receptor?
What is the relationship between barbiturates and the GABAA receptor?
What is the mechanism of action of carbamazepine?
What is the mechanism of action of carbamazepine?
What is the indication of carbamazepine?
What is the indication of carbamazepine?
What is the adverse effect of carbamazepine?
What is the adverse effect of carbamazepine?
What is the characteristic of L-type calcium channels?
What is the characteristic of L-type calcium channels?
What is the mechanism of action of phenobarbital?
What is the mechanism of action of phenobarbital?
What is the mechanism of action of ethosuximide?
What is the mechanism of action of ethosuximide?
What is the refractory state of Na+ channels?
What is the refractory state of Na+ channels?
What is the mechanism of action of hydantoin?
What is the mechanism of action of hydantoin?
Which antiepileptic drug is most useful in treating partial and generalized tonic-clonic seizures?
Which antiepileptic drug is most useful in treating partial and generalized tonic-clonic seizures?
Which of the following mechanisms of action is shared by benzodiazepines and barbiturates?
Which of the following mechanisms of action is shared by benzodiazepines and barbiturates?
What is the primary function of GABA in the brain?
What is the primary function of GABA in the brain?
What is the effect of benzodiazepines on the chloride channel?
What is the effect of benzodiazepines on the chloride channel?
Which type of cell types are involved in the shaping of action potentials and controlling patterns of repetitive firing?
Which type of cell types are involved in the shaping of action potentials and controlling patterns of repetitive firing?
Which of the following antiepileptic drugs has a dual mechanism of action?
Which of the following antiepileptic drugs has a dual mechanism of action?
What is the effect of Phenobarbital on the GABAergic system?
What is the effect of Phenobarbital on the GABAergic system?
What is the mechanism of action of tiagabine?
What is the mechanism of action of tiagabine?
What is the primary use of Phenobarbital?
What is the primary use of Phenobarbital?
What is the mechanism of action of Phenobarbital?
What is the mechanism of action of Phenobarbital?
Which of the following antiepileptic drugs is a GABA-T inhibitor?
Which of the following antiepileptic drugs is a GABA-T inhibitor?
What is the effect of GABA on neuronal firing?
What is the effect of GABA on neuronal firing?
What is the result of GABA's action on the brain?
What is the result of GABA's action on the brain?
What type of barbiturate is Phenobarbital?
What type of barbiturate is Phenobarbital?
Which of the following antiepileptic drugs is effective in treating partial and generalized seizures, and has a dual mechanism of action?
Which of the following antiepileptic drugs is effective in treating partial and generalized seizures, and has a dual mechanism of action?
What is the mechanism of action of valproic acid?
What is the mechanism of action of valproic acid?
What is the effect of Phenobarbital on seizure threshold?
What is the effect of Phenobarbital on seizure threshold?
Which of the following antiepileptic drugs is a GABAA receptor agonist?
Which of the following antiepileptic drugs is a GABAA receptor agonist?
What is the primary advantage of using Phenobarbital as an anticonvulsant?
What is the primary advantage of using Phenobarbital as an anticonvulsant?
What is the effect of GABA on neuronal activity?
What is the effect of GABA on neuronal activity?
Study Notes
Phenytoin (PTN)
- Mechanism of action: Blocks Na+ channel, stabilizes membrane by blocking Na+ and Ca2+ influx into neuronal axon, and inhibits release of excitatory amino acids via Ca2+ influx blockade
- Action on Na+ channel: Resting state, arrival of action potential, activation, and refractory state
Carbamazepine
- Mechanism of action: Similar to phenytoin
- Indications: Partial seizures, generalized tonic-clonic seizures (but worsens absence seizures)
- Adverse effects: Bone marrow depression (neutropenia, thrombocytopenia, aplastic anemia)
Ethosuximide
- Mechanism of action: Ca2+ channel blocker
- Characteristics of Ca++ channel: L-type currents require strong depolarization, are long-lasting, and are blocked by organic calcium antagonists
Phenobarbital (Luminal)
- Mechanism of action: Enhances the inhibitory effect of GABA, elevates seizure threshold, and prevents spread of electrical seizure activity
- Increases inhibitory neurotransmitters (e.g., GABA) and decreases excitatory transmission
- Uses: Effective anticonvulsant, primarily used as an alternative when single, non-sedating anti-convulsants are unsuccessful in controlling seizures
- Most useful in treating partial and generalized tonic-clonic seizures
GABA (Gamma-AminoButyric Acid)
- Function: Like the brakes in a car, slows down brain activity, helps us relax and maintain a sense of calmness
- AEDs that interfere with GABA transmission: GABAA receptor agonists, GABA-T inhibitors, GABA reuptake inhibitors
GABA-T Inhibitors
- Examples: Valproic acid, Vigabatrin
GABA Reuptake Inhibitors
- Examples: Tiagabine
Benzodiazepines (BZD)
- Mechanism of action: Enhance GABA effect, bound to Cl- channels
- Effects: Sedative, hypnotic, anticonvulsant, muscle-relaxant
Topiramate
- Mechanism of action: Dual or multiple mechanisms of action
- AED with dual or more mechanisms of action: Gabapentin, Lamotrigine, Zonisamide, Valproic acid, Felbamate
Zonisamide
- Mechanism of action: Unclear, but may involve blockade of sodium channels and enhancement of GABA-mediated inhibition
Valproic Acid (Sodium Valproate)
- Mechanism of action: Unclear, but may involve multiple mechanisms, including GABA-T inhibition, K+ channel opening, and Na+ channel blockade
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Description
This quiz covers the mechanism and action of Phenytoin on sodium channels, including its effects in the resting state.
