Question

Sympathetic nervous system induces

(a) secretion of digestive juices

(b) heart beat

(c) secretion of saliva

(d) all of these.

Answer 1

Answer is option b. Heart Beat

Explanation:

Let us learn about the sympathetic and parasympathetic nervous system to decide about the other options given in the question and conclude how they are not related to the sympathetic nervous system

The autonomic part of the nervous system controls various functions of the body automatically which are initiated in the brain below the level of cerebrum. The nervous system includes following components:

Differences between Sympathetic and Parasympathetic Nervous system:

Parameter	Sympathetic	Parasympathetic
Neurotransmitter	Noradrenaline, Adrenaline	Acetylcholine
Function	Flight or Fight; Stress or emergency An organism can survive without Sympathetic nervous system when maintained stress free	Assimilation and conservation of energy An organism cannot survive without Parasympathetic nervous system
Synonym	Dorsolumbar system	Craniosacral system
Distribution	Wide	Limited to the neck trunk

Functions of Sympathetic nervous system:

Sympathetic nervous system exerts its actions via alpha and beta receptors present in various organs as mentioned below and the functions of sympathetic nervous system are quite antagonistic to parasympathetic system.

Eye: Dilator pupillae contain alpha 1 receptors and ciliary muscles contain alpha 1 and alpha 2 receptors which are responsible for mydriasis without cycloplegia, decreased aqueous humor production

Heart: The Sinoatrial node (SA node) contains Beta 1 receptors which results in increased force of contraction that ultimately results in positive ionotropy and increased blood pressure

Blood vessels: Beta2 stimulation causes vasodilation whereas Alpha 1,2 stimulation causes vasoconstriction

Lungs: Bronchioles are innervated by Beta 2 receptors whose stimulation by sympathetic nervous system(SNS) results in bronchodilation

Metabolism: Stimulation by SNS results in glycogenolysis and lipolysis mediated through Beta 2 and Beta 3 respectively

Uterus(Has Beta2 receptors): SNS agonistic action produces relaxation of uterine muscles

Other functions: SNS stimulation results in urinary retention, vas deferens contraction, aggregation of platelets, decreases the contraction of skeletal muscles.

As we can see in the above functions sympathetic nervous system induces heart beat. So option b is correct answer.

Why not other options?

Option a: Secretion of Digestive juices:

Gastrointestinal tract is innervated by M3(Muscarinic subtype 3) receptors of Parasympathetic nervous system whose stimulation will result in increased secretions of digestive juices. Thus, secretion of digestive juices is attributed to the parasympathetic nervous system but not the sympathetic nervous system. Hence option a is wrong

Option c: Secretion of Saliva

As mentioned above for option a, Gastrointestinal tract is innervated by M3 receptors of parasympathetic nervous system, whose stimulation in the respective organ result in the increased secretion of respective fluid. So salivary secretion is also governed by the parasympathetic system but not the sympathetic system. Hence Option c is also false.

Option d. Since option a, c are false, option d all of these cannot be true. From this we can fairly conclude that option b is the correct answer for the given question