Pharmacology

Question 1

Why does atropine produce initial bradycardia?

Answer 1

Auto-inibition; Atropine blocks M1 receptors of presynaptic neurons so Ach can’t bind. Vagus nerve then releases more Ach into the synapse. Ach slows heart rate, thus initial bradycardia

Question 2

Why does atropine cause prolonged tachycardia?

Answer 2

Atropine blocks M2 receptors on SA (sinoatrial node) of the heart

Question 3

Conditions contra-indicated by atropine

Answer 3

Glaucoma, prostatic hypertrophy, urinary retention

Question 4

Why is there an initial slight decrease in systolic pressure and then an increase in diastolic pressure?

Answer 4

Atropine doesn’t have a direct effect on BP since PNS doesn’t innervate blood vessels.
Initial slight decrease in systolic pressure:
Decreased cardiac output associated with bradycardia (CO= stroke volume x HR)
Slightly but significantly prolonged increase in diastolic pressure:
atropine induced tachycardia

Question 5

Cholinergic system

Answer 5

• entire parasympathetic nervous system
• pre-ganglionic neurons of sympathetic nervous system, including adrenal medulla (only 1 neuron)
• post-ganglionic sympathetic nervous system innervating sweat glands
• somatic motor neurons
• CNS