Cholinergic receptor

There are no Renshaw cells at the neuromuscular junction. Renshaw cells inhibit motor neurons in the anterior gray horn of the spinal cord. Action potentials on the alpha motor neuron release acetylcholine (ACh) from the axon terminal. The ACh diffuses across the synaptic cleft and stimulates nicotinic receptors on the muscle endplate, generating an action potential that causes contraction of the muscle fiber. Cholinergic receptors on the muscle endplate are cation channels.

Ans. is ‘b’ i.e., Nicotinic receptor proteins

o Myasthenia gravis is an autoimmune disorder due to development of antibodies against Nm type of nicotinic receptors.

Ans. is ‘a’ i.e., Bronchial smooth muscle

• Smooth muscles have muscarinic receptors (M₃ type).

Ans. is ‘b’ i.e., Carbachol

o Amongst the given options carbachol has maximum nicotinic actions. It has nicotinic as well as muscarinic action.

Ans is ‘c’ i.e. Contract radial muscles of iris

• Radial muscles are innervated by sympathetic systems not by parasympathetic (muscarinic) system

Iris muscles that control the size of pupil

 There are two types of muscles in iris that control the size of pupil:

1. The iris sphincter or constrictor pupillae (circular muscles): These muscles are innervated by the parasym­pathetic system and cause constriction of pupil (miosis).
2. The iris dilator or dilator pupillae (radial muscles): These muscles are innervated by sympathetic (a, adren­ergic) system and cause dilatation of pupil (mydriasis)

• So, pupil size may be altered by following mechanisms by different ANS drugs:

A. Mydriasis (dilatation of pupil)

• Sympathomimetic drugs (a, agonists): By contraction of radial muscles (dilator).
• Antimuscarinic drugs: By blocking the action of circular muscles (pupillary sphincter).

B. Miosis (constriction of pupil)

1. Parasympathomimetic (muscarinic) drgus: By stimulating the contraction of circular muscles (pupillary sphincter).
2. Sympatholytic drugs (a, antagonists): By blocking the action of radial muscles (iris dilator) About other options

• Muscarinic antagonists (antimuscarinic drugs) decrease both gastric and respiratory (bronchial) secretions o Antimuscarinic drugs facilitate AV conduction (see previous explanations).

Ans. is ‘c’ i.e., Muscarinic receptor inhibition

Oxybutnin

o Oxybutynin is an anticholinergic drug.

o It is relatively selective for M₃ receptors, so it has selective action on urinary bladder.

• Because of its vesicoselective action it is used for detrusor instability and urinary incontinence.

Ans. is ‘a’ i.e., Inhibiting nicotinic receptors at myoneural junction

o D-tubocurarine is a skeletal muscle relaxant that acts by competitive inhibition of N_M receptors at neuron-muscular junction.

Ans. is ‘a’ i.e., Muscarinic acetylcholine receptors

“Blurred vision, dry mouth, urinary hesitancy or retention, and constipation represent the most common antimuscarinic complaints”.

Ans. C: Bronchial Smooth Muscle

The nicotinic cholinergic receptors are found in the neuromuscular junctions of somatic muscles; stimulation of these receptors causes muscular contraction. They are also found in the autonomic ganglia of autonomic nervous system and

central nervous system

Muscarinic receptors are found in:

M 1-brain M 2-heart

M 3-smooth muscle

M 4-smooth muscle, pancreatic acinar and islet tissue

Myasthenia gravis

• It is an autoimmune neuromuscular disease leading to fluctuating muscle weakness and fatigue.
• It is an autoimmune disorder, in which weakness is caused by circulating antibodies that block acetylcholine receptors at the postsynaptic neuromuscular junction, inhibiting the excitatory effects of the neurotransmitter acetylcholine on nicotinic receptors throughout neuromuscular junctions.
• Myasthenia is treated medically with acetylcholinesterase inhibitors or immunosuppressants, and, in selected cases,thymectomy.

Ans. D: Nicotinic receptor antagonist

Bupropion/amfebutamone is an atypical antidepressant and smoking cessation aid.

It acts as a norepinephrine and dopamine reuptake inhibitor (NDRI), as well as alpha3 beta4-nicotinic receptor antagonist.

Bupropion belongs to the chemical class of aminoketones and is similar in structure to stimulants cathinone and diethylpropion, and to phenethylamines in general.

Bupropion is an effective antidepressant on its own but it is particularly popular as an add-on medication in the cases of incomplete response to the first-line selective serotonin reuptake inhibitor (SSRI) antidepressant.

Since it does not inhibit serotonin reuptake at all (or very insignificantly), bupropion does not cause weight gain or sexual dysfunction like the SSRI group of antidepressants.

It precipitates seizures

Ans. Neostigmine

Ans. Contraction of skeletal muscle

Ans. is ‘c’ i.e., Nicotinic cholinergic receptors

Ans. is ‘a’ i.e., Partial nicotine receptor agonist

Varenicline

• It is partial agonist at the nicotine receptor.
• It is used in nicotine addicts.

• The commonest cardiovascular effect of tricyclic antidepressant overdose is sinus tachycardia, which is attributable
• to the inhibition of norepincphrine reuptake and the anticholinergic action.
• However, the most important toxic effect of tricyclics is the slowing of depolarisation of the cardiac action potential by inhibition of the sodium current and this delays propagation of depolarisation through both myocardium and conducting tissue.
• This results in prolongation of the QRS complex and the PR/QT intervals with a predisposition to cardiac arrhythmias.
• This inhibition of sodium flux into myocardial cells can occur to such an extent that depressed contractility can result and this, coupled with the reduction in peripheral resistance, contributes to hypotension.

Ans. is ‘c’ i.e., Neuromuscular junction 

Cholinergic receptors

• There are two types of cholinergic receptors :
• Muscarinic → Found at – All postaganglionic parasympathetic sites, Few postaganglionic sympathetic sites (sweat gland & blood vessels), CNS.
• Nicotinic —4 Found at – Ganglia (both sympathetic and parasympathetic), Skeletal muscles, Adrenal medulla, CNS