Parasympathetic drugs

Question 1

Desribe neurotransmission in the parasympathetic system

Answer 1

Impulse carried to a Nicotinic AChR followed by muscarinic AChR ; impulse terminates at target gland

Question 2

Describe the roles of the parasympathetic system

Answer 2

Pupil constriction
Bronchiole constriction and secretion
Decreased HR and BP
Increased GI motility and secretions
Contraction of bladder (micturation)
Exocrine secretions - salivation and lacrimation

Question 3

Describe the different types of mAChRs

Answer 3

All act via metabotropic events and utilise different 2nd messengers via intracellular Ca2+ and protein phosphorylation

3 types ; M₁ (Brain) , M₂ (cardiac) , M₃ (smooth muscle/exocrine)

Question 4

What is the diference between metabotropic and ionotropic receptors?

Answer 4

Ionic ligands bind to ionotropic receptors while non-ionic ligands bind to metabotropic receptors.

Upon binding, metabotropic receptors initiate a cascading reaction or a signal transduction mechanism such as G protein

Question 5

Describe the molecular Mechanism of M₃ receptor activation

Answer 5

G_q protein is activated

release of intracellular Ca2+ = contraction

Question 6

Describe the molecular mechanism of M₂ receptor activation

Answer 6

G_i proteins are activated which inhibit production of cAMP = inhibiton of PKA = inactivation of Ca2+ channels

also K+ channels open = K+ leave = lower V_m = more likely for AP to occur

overall effect is bradycardia

Question 7

What is the use of pilocarpine, a M3 agonist

Answer 7

cause pupil constriction

used to assess smoot muscle function

Question 8

Describe the use of atropine , an M3 antagonist

Answer 8

M₃ antagonist

causes pupil dilatation (mydriasis), treats organophosphate anticholinesterase insecticide poisoning, bradychardia due to surgery/MI/beta-blocker overdose

Question 9

Describe the use of carbachol, a muscarinic agonist

Answer 9

used to treat glaucoma to promote miosis as constriction of circular muscle leads to drainage of aqueous humour , reducing intraocular pressure

Question 10

What is glaucoma

what causes it

Answer 10

Excess aqueous humour leads to increased intraocular pressure , compressing the optic nerve

this leads to tunnel vision and blindness

Question 11

Describe the therapeutic uses of muscarinic receptor antagonists

Answer 11

Bladder control is an autonomic reflex arc but higher control can override it

incontinence is caused when higher control is lost

M₃ antagonist (oxybutynin) can be used to inhibit the reflex arc ; side effects are tachycardia, dry mouth and

Scopolamine is a non-selective antagonist ; longer duration of action

CNS depression = sedation

used to treat travel sickness and bowel colic (cramp)

Question 12

Desribe the uses of indirectly acting parasympathomimetics

Answer 12

Block termination of neurotransmission by inhibiting AChE reversibly, prolonging the action of ACh at receptors

physostigmine increases mitosis in glaucoma treatment, stimulate bladder, treat atropine poisoning

neostigmine acts more effectively at NMJs so is used to treat myasthenia gravies

Question 13

Symptoms of organophosphate anticholinesterase poisoning

Answer 13

Miosis, salivation, sweating, bradychardia

fasciculation (muscle spasms due to spontaneous release of ACh) and paralysis

anxiety, restlessness, dizziness

Question 14

Treatment of anticholinesterase poisoning

Answer 14

Use anti-muscarinic drugs such as atropine to block mAChR

drugs that dephosphorylate AChE to activate them