Agonist induced autophosphorylation, internalization and down regulation is a distinctive feature of: A. G-protein coupled receptors B. Intrinsic ion channel containing receptors C. Tyrosine protein kinase receptors D. Receptors regulating gene expression

Agonist induced autophosphorylation, internalization and down regulation is a distinctive feature of: A. G-protein coupled receptors B. Intrinsic ion channel containing receptors C. Tyrosine protein kinase receptors D. Receptors regulating gene expression
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C. Tyrosine protein kinase receptors
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Agonist induced autophosphorylation, internalization and down regulation is a distinctive feature of: A. G-protein coupled receptors B. Intrinsic ion channel containing receptors C. Tyrosine protein kinase receptors D. Receptors regulating gene expression

Description : Agonist induced autophosphorylation, internalization and down regulation is a distinctive feature of: A. G-protein coupled receptors B. Intrinsic ion channel containing receptors C. Tyrosine protein kinase receptors D. Receptors regulating gene expression

Last Answer : C. Tyrosine protein kinase receptors

The following receptor type has 7 helical membrane spanning amino acid segments with 3 extracellular and 3 intracellular loops: A. Tyrosine protein kinase receptor B. Gene expression regulating receptor C. Intrinsic ion channel containing receptor D. G protein coupled receptor

Description : The following receptor type has 7 helical membrane spanning amino acid segments with 3 extracellular and 3 intracellular loops: A. Tyrosine protein kinase receptor B. Gene expression regulating receptor C. Intrinsic ion channel containing receptor D. G protein coupled receptor

Last Answer : D. G protein coupled receptor

The following receptor type has 7 helical membrane spanning amino acid segments with 3 extracellular and 3 intracellular loops: A. Tyrosine protein kinase receptor B. Gene expression regulating receptor C. Intrinsic ion channel containing receptor D. G protein coupled receptor

Description : Receptors perform the following function/functions: A. Ligand recognition B. Signal transduction C. Both ligand recognition and signal transduction D. Disposal of agonists and antagonists

Last Answer : D. Disposal of agonists and antagonists

The insulin receptor is a: A. Ion channel regulating receptor B. Tyrosine protein kinase receptor C. G-protein coupled receptor D. None of the above

Description : The insulin receptor is a: A. Ion channel regulating receptor B. Tyrosine protein kinase receptor C. G-protein coupled receptor D. None of the above

Last Answer : B. Tyrosine protein kinase receptor

Muscarinic cholinergic receptors: A. Are located only on parasympathetically innervated effector cells B. Mediate responses by opening an intrinsic Na+ ion channel C. Are present on vascular endothelium which has no cholinergic nerve supply D. Predominate in the autonomic ganglia

Description : Muscarinic cholinergic receptors: A. Are located only on parasympathetically innervated effector cells B. Mediate responses by opening an intrinsic Na+ ion channel C. Are present on vascular endothelium which has no cholinergic nerve supply D. Predominate in the autonomic ganglia

Last Answer : C. Are present on vascular endothelium which has no cholinergic nerve supply

The receptor transduction mechanism with the fastest time-course of response effectuation is: A. Adenylyl cyclase-cyclic AMP pathway B. Phospholipase C-IP3: DAG pathway C. Intrinsic ion channel operation D. Protein synthesis modulation

Description : The receptor transduction mechanism with the fastest time-course of response effectuation is: A. Adenylyl cyclase-cyclic AMP pathway B. Phospholipase C-IP3: DAG pathway C. Intrinsic ion channel operation D. Protein synthesis modulation

Last Answer : C. Intrinsic ion channel operation

The following receptor has an intrinsic ion channel: A. Histamine H1 receptor B. Histamine H2 receptor C. Adrenergic alfa receptor D. GABA-benzodiazepine receptor

Description : The following receptor has an intrinsic ion channel: A. Histamine H1 receptor B. Histamine H2 receptor C. Adrenergic alfa receptor D. GABA-benzodiazepine receptor

Last Answer : D. GABA-benzodiazepine receptor

A partial agonist can antagonise the effects of a full agonist because it has: A. High affinity but low intrinsic activity B. Low affinity but high intrinsic activity C. No affinity and low intrinsic activity D. High affinity but no intrinsic activity

Description : A partial agonist can antagonise the effects of a full agonist because it has: A. High affinity but low intrinsic activity B. Low affinity but high intrinsic activity C. No affinity and low intrinsic activity D. High affinity but no intrinsic activity

Last Answer : A. High affinity but low intrinsic activity

A partial agonist can antagonise the effects of a full agonist because it has: A. High affinity but low intrinsic activity B. Low affinity but high intrinsic activity C. No affinity and low intrinsic activity D. High affinity but no intrinsic activity

Description : A partial agonist can antagonise the effects of a full agonist because it has: A. High affinity but low intrinsic activity B. Low affinity but high intrinsic activity C. No affinity and low intrinsic activity D. High affinity but no intrinsic activity

Last Answer : A. High affinity but low intrinsic activity

Which of the following statement(s) is/are true concerning cell membrane receptors? a. The largest family of cell surface receptors are the G-protein-linked receptors b. Activities of the G-protein involve binding and hydrolysis of ATP c. The G protein receptor generates an intracellular messenger commonly through the use adenylate cyclase d. Tyrosine kinase receptors are considered G-protein-linked receptors

Description : Which of the following statement(s) is/are true concerning cell membrane receptors? a. The largest family of cell surface receptors are the G-protein-linked receptors b. Activities of the ... through the use adenylate cyclase d. Tyrosine kinase receptors are considered G-protein-linked receptors

Last Answer : Answer: a, c All water-soluble regulatory molecules bind to the cell surface receptor proteins. Binding of the appropriate ligand evokes an intracellular signal which usually regulates ... are adenylate cyclase, which converts ATP to cAMP, and the polyphosphoinositide-specific phospholipase C

Down regulation of receptors can occur as a consequence of: A. Continuous use of agonists B. Continuous use of antagonists C. Chronic use of CNS depressants D. Denervation

Description : Down regulation of receptors can occur as a consequence of: A. Continuous use of agonists B. Continuous use of antagonists C. Chronic use of CNS depressants D. Denervation

Last Answer : A. Continuous use of agonists

Which of the following is a G protein coupled receptor: A. Muscarinic cholinergic receptor B. Nicotinic cholinergic receptor C. Glucocorticoid receptor D. Insulin receptor

Description : Which of the following is a G protein coupled receptor: A. Muscarinic cholinergic receptor B. Nicotinic cholinergic receptor C. Glucocorticoid receptor D. Insulin receptor

Last Answer : A. Muscarinic cholinergic receptor

Study of drug-receptor interaction has now shown that: A. Maximal response occurs only when all receptors are occupied by the drug B. Drugs exert an ‘all or none’ action on a receptor C. Receptor and drugs acting on it have rigid complementary ‘lock and key’ structural features D. Properties of ‘affinity’ and ‘intrinsic activity’ are independently variable

Description : Study of drug-receptor interaction has now shown that: A. Maximal response occurs only when all receptors are occupied by the drug B. Drugs exert an all or none' action on a ... lock and key' structural features D. Properties of affinity' and intrinsic activity' are independently variable

Last Answer : D. Properties of ‘affinity’ and ‘intrinsic activity’ are independently variable

Study of drug-receptor interaction has now shown that: A. Maximal response occurs only when all receptors are occupied by the drug B. Drugs exert an ‘all or none’ action on a receptor C. Receptor and drugs acting on it have rigid complementary ‘lock and key’ structural features D. Properties of ‘affinity’ and ‘intrinsic activity’ are independently variable

Description : Study of drug-receptor interaction has now shown that: A. Maximal response occurs only when all receptors are occupied by the drug B. Drugs exert an all or none' action on a ... lock and key' structural features D. Properties of affinity' and intrinsic activity' are independently variable

Last Answer : D. Properties of ‘affinity’ and ‘intrinsic activity’ are independently variable

The following is not a feature of competitive antagonists: A. Chemical resemblance with the agonist B. Parallel rightward shift of the agonist log doseresponse curve C. Suppression of maximal agonist response D. Apparent reduction in agonist affinity for the receptor

Description : The following is not a feature of competitive antagonists: A. Chemical resemblance with the agonist B. Parallel rightward shift of the agonist log doseresponse curve C. Suppression of maximal agonist response D. Apparent reduction in agonist affinity for the receptor

Last Answer : C. Suppression of maximal agonist response

The following is not a feature of competitive antagonists: A. Chemical resemblance with the agonist B. Parallel rightward shift of the agonist log doseresponse curve C. Suppression of maximal agonist response D. Apparent reduction in agonist affinity for the receptor

Description : The following is not a feature of competitive antagonists: A. Chemical resemblance with the agonist B. Parallel rightward shift of the agonist log doseresponse curve C. Suppression of maximal agonist response D. Apparent reduction in agonist affinity for the receptor

Last Answer : C. Suppression of maximal agonist response

With regard to membrane receptors for hormones: a. they are often glycoproteins b. they are important for hormones made up of steroid c. those for insulin exhibit an intrinsic protein kinase activity d. glucagon uses calcium as a second messenger

Description : With regard to membrane receptors for hormones: a. they are often glycoproteins b. they are important for hormones made up of steroid c. those for insulin exhibit an intrinsic protein kinase activity d. glucagon uses calcium as a second messenger

Last Answer : they are often glycoproteins

Muscarinic cholinergic receptors: A. Are located only on parasympathetically innervated effector cells B. Mediate responses by opening an intrinsic Na+ ion channel C. Are present on vascular endothelium which has no cholinergic nerve supply D. Predominate in the autonomic ganglia

Description : Muscarinic cholinergic receptors: A. Are located only on parasympathetically innervated effector cells B. Mediate responses by opening an intrinsic Na+ ion channel C. Are present on vascular endothelium which has no cholinergic nerve supply D. Predominate in the autonomic ganglia

Last Answer : C. Are present on vascular endothelium which has no cholinergic nerve supply

Beta adrenergic blockers lower intraocular tension by: A. Down regulating adenylyl cyclase in ciliary body through reduced activation of β2 adrenoceptors B. Constricting ciliary blood vessels C. Blocking adrenergic action on trabecular meshwork D. Reducing aqueous formation unrelated to beta adrenoceptor mediation

Description : Beta adrenergic blockers lower intraocular tension by: A. Down regulating adenylyl cyclase in ciliary body through reduced activation of β2 adrenoceptors B. Constricting ciliary blood vessels ... action on trabecular meshwork D. Reducing aqueous formation unrelated to beta adrenoceptor mediation

Last Answer : A. Down regulating adenylyl cyclase in ciliary body through reduced activation of β2 adrenoceptors

The GABAB receptor: A. Is an intrinsic ion channel containing receptor B. Mediates neuronal depolarization C. Is insensitive to blockade by bicuculline D. Regulates intracellular cAMP

Description : The GABAB receptor: A. Is an intrinsic ion channel containing receptor B. Mediates neuronal depolarization C. Is insensitive to blockade by bicuculline D. Regulates intracellular cAMP

Last Answer : C. Is insensitive to blockade by bicuculline

Tyrosine kinase activity is present in (A) α-Adrenergic receptors (B) β-Adrenergic receptors (C) Cholinergic receptors (D) Insulin receptors

Description : Tyrosine kinase activity is present in (A) α-Adrenergic receptors (B) β-Adrenergic receptors (C) Cholinergic receptors (D) Insulin receptors

Last Answer : Answer : D

A drug which does not produce any action by itself but decreases the slope of the log dose-response curve and suppresses the maximal response to another drug is a: A. Physiological antagonist B. Competitive antagonist C. Noncompetitive antagonist D. Partial agonist

Description : A drug which does not produce any action by itself but decreases the slope of the log dose-response curve and suppresses the maximal response to another drug is a: A. Physiological antagonist B. Competitive antagonist C. Noncompetitive antagonist D. Partial agonist

Last Answer : C. Noncompetitive antagonist

A drug ‘R’ producing no response by itself causes the log dose-response curve of another drug ‘S’ to shift to the right in a parallel manner without decreasing the maximal response: Drug ‘R’ is a: A. Partial agonist B. Inverse agonist C. Competitive antagonist D. Noncompetitive antagonist

Description : A drug ‘R’ producing no response by itself causes the log dose-response curve of another drug ‘S’ to shift to the right in a parallel manner without decreasing the maximal response: Drug ‘R’ is a: A. Partial agonist B. Inverse agonist C. Competitive antagonist D. Noncompetitive antagonist

Last Answer : C. Competitive antagonist

A drug which does not produce any action by itself but decreases the slope of the log dose-response curve and suppresses the maximal response to another drug is a: A. Physiological antagonist B. Competitive antagonist C. Noncompetitive antagonist D. Partial agonist

Description : A drug which does not produce any action by itself but decreases the slope of the log dose-response curve and suppresses the maximal response to another drug is a: A. Physiological antagonist B. Competitive antagonist C. Noncompetitive antagonist D. Partial agonist

Last Answer : C. Noncompetitive antagonist

A drug ‘R’ producing no response by itself causes the log dose-response curve of another drug ‘S’ to shift to the right in a parallel manner without decreasing the maximal response: Drug ‘R’ is a: A. Partial agonist B. Inverse agonist C. Competitive antagonist D. Noncompetitive antagonist

Description : A drug ‘R’ producing no response by itself causes the log dose-response curve of another drug ‘S’ to shift to the right in a parallel manner without decreasing the maximal response: Drug ‘R’ is a: A. Partial agonist B. Inverse agonist C. Competitive antagonist D. Noncompetitive antagonist

Last Answer : C. Competitive antagonist

a1 – receptors are coupled with _______ G protein. (a) Gs (b) Gi (c) Gq (d) Go

Description : a1 – receptors are coupled with _______ G protein. (a) Gs (b) Gi (c) Gq (d) Go

Last Answer : Ans: C

Which one of the following drugs does NOT act through G-Protein coupled receptors? (A) Epinephrine (B) Insulin (C) Dopamine (D) TSH

Description : Which one of the following drugs does NOT act through G-Protein coupled receptors? (A) Epinephrine (B) Insulin (C) Dopamine (D) TSH

Last Answer : (B) Insulin

The following statement about histamine is not correct: A. It is the sole mediator of immediate hypersensitivity reaction B. It plays no role in delayed hypersensitivity reaction C. It serves as a neurotransmitter in the brain D. All types of histamine receptors are G protein coupled receptors

Description : The following statement about histamine is not correct: A. It is the sole mediator of immediate hypersensitivity reaction B. It plays no role in delayed hypersensitivity reaction C. It serves as a neurotransmitter in the brain D. All types of histamine receptors are G protein coupled receptors

Last Answer : A. It is the sole mediator of immediate hypersensitivity reaction

The following statement about histamine is not correct: A. It is the sole mediator of immediate hypersensitivity reaction B. It plays no role in delayed hypersensitivity reaction C. It serves as a neurotransmitter in the brain D. All types of histamine receptors are G protein coupled receptors

Description : The following statement about histamine is not correct: A. It is the sole mediator of immediate hypersensitivity reaction B. It plays no role in delayed hypersensitivity reaction C. It serves as a neurotransmitter in the brain D. All types of histamine receptors are G protein coupled receptors

Last Answer : A. It is the sole mediator of immediate hypersensitivity reaction

Induction of drug metabolizing enzymes involves: A. A conformational change in the enzyme protein to favour binding of substrate molecules B. Expression of enzyme molecules on the surface of hepatocytes C. Enhanced transport of substrate molecules into hepatocytes D. Increased synthesis of enzyme protein

Description : Induction of drug metabolizing enzymes involves: A. A conformational change in the enzyme protein to favour binding of substrate molecules B. Expression of enzyme molecules on the surface of ... C. Enhanced transport of substrate molecules into hepatocytes D. Increased synthesis of enzyme protein

Last Answer : D. Increased synthesis of enzyme protein

Induction of drug metabolizing enzymes involves: A. A conformational change in the enzyme protein to favour binding of substrate molecules B. Expression of enzyme molecules on the surface of hepatocytes C. Enhanced transport of substrate molecules into hepatocytes D. Increased synthesis of enzyme protein

Description : Induction of drug metabolizing enzymes involves: A. A conformational change in the enzyme protein to favour binding of substrate molecules B. Expression of enzyme molecules on the surface of ... C. Enhanced transport of substrate molecules into hepatocytes D. Increased synthesis of enzyme protein

Last Answer : D. Increased synthesis of enzyme protein

.Gene regulation governing lactose operon of E.coli that involves the lac I gene product is (a) negative and repressible because repressor protein prevents transcription (b) feedback inhibition because excess of β-galactosidase can switch off transcription (c) positive and inducible because it can be induced by lactose (d) negative and inducible because repressor protein prevents transcription.

Description : .Gene regulation governing lactose operon of E.coli that involves the lac I gene product is (a) negative and repressible because repressor protein prevents transcription (b) feedback inhibition ... be induced by lactose (d) negative and inducible because repressor protein prevents transcription.

Last Answer : (d) negative and inducible because repressor protein prevents transcription.

Gene regulation governing lactose operon of E.coli that involves the lac I gene product is (a) negative and repressible because repressor protein prevents transcription (b) feedback inhibition because excess of β-galactosidase can switch off transcription (c) positive and inducible because it can be induced by lactose (d) negative and inducible because repressor protein prevents transcription.

Description : Gene regulation governing lactose operon of E.coli that involves the lac I gene product is (a) negative and repressible because repressor protein prevents transcription (b) feedback inhibition ... be induced by lactose (d) negative and inducible because repressor protein prevents transcription.

Last Answer : (d) negative and inducible because repressor protein prevents transcription.

Marked redistribution is a feature of: A. Highly lipid soluble drugs B. Poorly lipid soluble drugs C. Depot preparations D. Highly plasma protein bound drugs

Description : Marked redistribution is a feature of: A. Highly lipid soluble drugs B. Poorly lipid soluble drugs C. Depot preparations D. Highly plasma protein bound drugs

Last Answer : A. Highly lipid soluble drugs

Marked redistribution is a feature of: A. Highly lipid soluble drugs B. Poorly lipid soluble drugs C. Depot preparations D. Highly plasma protein bound drugs

Description : Marked redistribution is a feature of: A. Highly lipid soluble drugs B. Poorly lipid soluble drugs C. Depot preparations D. Highly plasma protein bound drugs

Last Answer : A. Highly lipid soluble drugs

Marked redistribution is a feature of: A. Highly lipid soluble drugs B. Poorly lipid soluble drugs C. Depot preparations D. Highly plasma protein bound drugs

Description : Marked redistribution is a feature of: A. Highly lipid soluble drugs B. Poorly lipid soluble drugs C. Depot preparations D. Highly plasma protein bound drugs

Last Answer : A. Highly lipid soluble drugs

Receptor agonists possess: A. Affinity but no intrinsic activity B. Intrinsic activity but no affinity C. Affinity and intrinsic activity with a + sign D. Affinity and intrinsic activity with a – sign

Description : Receptor agonists possess: A. Affinity but no intrinsic activity B. Intrinsic activity but no affinity C. Affinity and intrinsic activity with a + sign D. Affinity and intrinsic activity with a – sign

Last Answer : C. Affinity and intrinsic activity with a + sign

Receptor agonists possess: A. Affinity but no intrinsic activity B. Intrinsic activity but no affinity C. Affinity and intrinsic activity with a + sign D. Affinity and intrinsic activity with a – sign

Description : Receptor agonists possess: A. Affinity but no intrinsic activity B. Intrinsic activity but no affinity C. Affinity and intrinsic activity with a + sign D. Affinity and intrinsic activity with a – sign

Last Answer : C. Affinity and intrinsic activity with a + sign

Blockade of both dopamine D2 and serotonin 5-HT2A/2C receptors is a distinctive feature of: A. Pimozide B. Haloperidol C. Ketanserin D. Clozapine

Description : Blockade of both dopamine D2 and serotonin 5-HT2A/2C receptors is a distinctive feature of: A. Pimozide B. Haloperidol C. Ketanserin D. Clozapine

Last Answer : D. Clozapine

The protein IRS-1 is phosphorylated by (A) Protein kinase A (B) Protein kinase C (C) Tyrosine kinase activity of insulin receptor (D) Tyrosine kinase activity of IGF-1 receptor

Description : The protein IRS-1 is phosphorylated by (A) Protein kinase A (B) Protein kinase C (C) Tyrosine kinase activity of insulin receptor (D) Tyrosine kinase activity of IGF-1 receptor

Last Answer : Answer : B

All the following statements about epidermal growth factor are true except (A) It is a protein (B) It possess quaternary structure (C) Its receptor is made up of a single polypeptide chain (D) Its receptor possesses tyrosine kinase domain

Description : All the following statements about epidermal growth factor are true except (A) It is a protein (B) It possess quaternary structure (C) Its receptor is made up of a single polypeptide chain (D) Its receptor possesses tyrosine kinase domain

Last Answer : Answer : B

The plasma half life of penicillin-G is longer in the new born because their: A. Plasma protein level is low B. Drug metabolizing enzymes are immature C. Glomerular filtration rate is low D. Tubular transport mechanisms are not well developed

Description : The plasma half life of penicillin-G is longer in the new born because their: A. Plasma protein level is low B. Drug metabolizing enzymes are immature C. Glomerular filtration rate is low D. Tubular transport mechanisms are not well developed

Last Answer : D. Tubular transport mechanisms are not well developed

The antagonism between adrenaline and histamine is called ‘physiological antagonism’ because: A. Both are physiologically present in the body B. They act on physiological receptors C. Both affect many physiological processes D. They have opposite physiological effects

Description : The antagonism between adrenaline and histamine is called ‘physiological antagonism’ because: A. Both are physiologically present in the body B. They act on physiological receptors C. Both affect many physiological processes D. They have opposite physiological effects

Last Answer : D. They have opposite physiological effects

Drugs acting through receptors exhibit the following features except: A. Structural specificity B. High potency C. Competitive antagonism D. Dependence of action on lipophilicity

Description : Drugs acting through receptors exhibit the following features except: A. Structural specificity B. High potency C. Competitive antagonism D. Dependence of action on lipophilicity

Last Answer : D. Dependence of action on lipophilicity

What is true in relation to drug receptors: A. All drugs act through specific receptors B. All drug receptors are located on the surface of the target cells C. Agonists induce a conformational change in the receptor D. Partial agonists have low affinity for the receptor

Description : What is true in relation to drug receptors: A. All drugs act through specific receptors B. All drug receptors are located on the surface of the target cells C. Agonists induce a conformational change in the receptor D. Partial agonists have low affinity for the receptor

Last Answer : C. Agonists induce a conformational change in the receptoR

An 'orphan drug' is: A. A very cheap drug B. A drug which has no therapeutic use C. A drug needed for treatment or prevention of a rare disease D. A drug which acts on Orphanin receptors

Description : An 'orphan drug' is: A. A very cheap drug B. A drug which has no therapeutic use C. A drug needed for treatment or prevention of a rare disease D. A drug which acts on Orphanin receptors

Last Answer : C. A drug needed for treatment or prevention of a rare disease

Agonistic action on which of the following adrenergic receptors located on ciliary epithelial cells reduces aqueous secretion: A. β1 receptor B. β2 receptor C. α1 receptor D. α2 receptor

Description : Agonistic action on which of the following adrenergic receptors located on ciliary epithelial cells reduces aqueous secretion: A. β1 receptor B. β2 receptor C. α1 receptor D. α2 receptor

Last Answer : D. α2 receptor

Pyridostigmine differs from neostigmine in that: A. It is more potent orally B. It is longer acting C. It produces less muscarinic side effects D. It does not have any direct action on NM receptors

Description : Pyridostigmine differs from neostigmine in that: A. It is more potent orally B. It is longer acting C. It produces less muscarinic side effects D. It does not have any direct action on NM receptors

Last Answer : B. It is longer acting

The mechanism by which neostigmine improves contraction of myasthenic muscle involves: A. Repetitive binding of the acetylcholine molecules to the same receptors at the muscle endplate B. Diffusion of acetylcholine released from motor nerve endings to a wider area activating neighbouring receptors C. Activation of motor end-plate receptors by neostigmine molecules themselves D. All of the above

Description : The mechanism by which neostigmine improves contraction of myasthenic muscle involves: A. Repetitive binding of the acetylcholine molecules to the same receptors at the muscle endplate B. Diffusion of ... Activation of motor end-plate receptors by neostigmine molecules themselves D. All of the above

Last Answer : D. All of the above

Neostigmine is preferred over physostigmine for treating myasthenia gravis because: A. It is better absorbed orally B. It has longer duration of action C. It has additional direct agonistic action on nicotinic receptors at the muscle end plate D. It penetrates blood-brain barrier

Description : Neostigmine is preferred over physostigmine for treating myasthenia gravis because: A. It is better absorbed orally B. It has longer duration of action C. It has additional direct agonistic action on nicotinic receptors at the muscle end plate D. It penetrates blood-brain barrier

Last Answer : C. It has additional direct agonistic action on nicotinic receptors at the muscle end plate