The autonomic nervous system controls the functions of the internal organs via t
ID: 3505247 • Letter: T
Question
The autonomic nervous system controls the functions of the internal organs via the release of neurotransmitters (NT) that bind to specific receptors on the effector cells (smooth muscle, cardiac muscle, glands). Each cell type will have a specific response to a NT – a NT activates some effector cells while it inhibits others, and can produce totally different actions in different effectors. Understanding the control of the ANS on effectors has largely come about by studying pharmacological agents that mimic or block the effects of the NTs released by the autonomic nerve terminals.
a. The ANS branches (parasympathetic and sympathetic) are generally tonically active – what does this mean?
b. Agonist and antagonist drugs have been used to elucidate the control of the ANS on effectors. Define what agonist and antagonist agents are and how they work?
c. Given knowledge of the ANS control on heart rate and knowledge that neural input from the ANS to the SA node of the heart is tonically active, fill in the table below with your predictions for the effects (use: increase in heart rate, decrease in heart rate, no effect on heart rate) of the ANS agonist drugs on heart rate. Assume you are comparing the drug effect relative to a resting heart rate prior to drug administration.
Agonist drug
Heart rate changes following administration
(Effector tissue is the SA Node)
Alpha-adrenergic
Beta-adrenergic
Muscarinic
d. Explain your answer to the effect of the muscarinic agonist on heart rate.
e. Given knowledge of the ANS control on heart rate and knowledge that neural input from the ANS to the SA node of the heart is tonically active, fill in the table below with your predictions of heart rate changes (use: increase in heart rate, decrease in heart rate, no effect on heart rate) in response to the administration of the antagonist drug. Assume you are comparing the drug effect relative to a resting heart rate prior to drug administration.
Antagonist drug
Heart rate changes following administration
(Effector tissue is the SA Node)
Alpha-adrenergic
Beta-adrenergic
Muscarinic
Nicotinic*
* Think about where these receptors in the ANS are located and what the intrinsic rate of the SA node is
f. Explain your answer to the effect of the nicotinic antagonist on heart rate.
Agonist drug
Heart rate changes following administration
(Effector tissue is the SA Node)
Alpha-adrenergic
Beta-adrenergic
Muscarinic
Explanation / Answer
A- The sympathetic and parasympathetic system physiologically are always active(having a minimal amount of release of neurotransmitters) in the body, making a balance between the effect of both. This is known as they are tonically active.
B- Agonists are those drugs which when bind to receptors gives the response same as an endogenous substrate.
Antagonists are drugs which when bound to receptors, have no effect on the receptor. Thus, they act as a blocking agent which doesn't allow any other molecule to bind as well.
Drugs can act by 4 mechanisms-
C- Alpha adrenergic- No effect on heart rate
Beta- adrenergic- Increase in heart rate
Muscarinic- Decrease in heart rate
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