Sympathetic Nervous System: Definition, Function, Disorders
The sympathetic nervous system (SNS) drives the body’s rapid “fight-or-flight” response, preparing organs for stress by increasing heart rate, blood pressure, airflow, and energy release. Its structure includes spinal neurons, sympathetic chain ganglia, collateral ganglia, and neurotransmitters like norepinephrine and epinephrine. This guide explains SNS anatomy, physiology, pathways, receptors, organ effects, disorders, diagrams, and NEET-focused MCQs.
This Story also Contains
- What Is the Sympathetic Nervous System (SNS)?
- Functions of the Sympathetic Nervous System
- Anatomy of the Sympathetic Nervous System
- Physiology of the Sympathetic Nervous System
- Role of SNS in Homeostasis
- Disorders of the Sympathetic Nervous System
- Sympathetic Nervous System NEET MCQs (With Answers & Explanations)
- Recommended video on "Sympathetic Nervous System"
What Is the Sympathetic Nervous System (SNS)?
The sympathetic nervous system consists of one of the two main divisions in the autonomic nervous system the other being the parasympathetic nervous system. It prepares the body for responding to stress or emergencies, which one commonly calls the "fight-or-flight" response. This involuntary action is essential in maintaining homeostasis in the body.
Importance SNS
It is important because the SNS can rapidly marshal all the resources of the body during stressful situations to ensure survival. Through its regulation of heart rate, blood pressure, energy mobilisation, and other activities, the SNS allows the body to cope with external challenges while maintaining internal balance.
Functions of the Sympathetic Nervous System
Read about the functions of Sympathetic Nervous system functions:
Fight-or-Flight Effects
Increases blood pressure
Dilates airways
Glucose released from energy stores
Organ-Specific Effects
Cardiovascular System: Increases heart rate and blood pressure
Respiratory System: Bronchodilators
Digestive System: Slows digestion
Metabolic Processes: Glucose metabolism
Anatomy of the Sympathetic Nervous System
The SNS anatomy consists of neurons and ganglia that run from the spinal cord to various organs and systems of the body.
Neurons And Neurotransmitters
The SNS is a system composed of preganglionic neurons originating in the spinal cord and postganglionic neurons extending to target organs.
Principal neurotransmitters include norepinephrine and epinephrine.
Preganglionic vs Postganglionic Neurons
The preganglionic neurons reside within the thoracic and lumbar regions of the spinal cord.
The postganglionic neurons reside within the ganglia near or in target organs.
Sympathetic Chain & Collateral Ganglia
The sympathetic chain refers to the row of ganglia that runs down along the vertebral column parallel to the spinal cord.
The visceral efferent collateral ganglia are more anterior and associated with major abdominal arteries.
Pathways of Sympathetic Fibers
There are specific pathways of sympathetic fibres from the spinal cord to their destination organs in connecting either through the ganglia of the sympathetic chain or bypassing it for the collateral ganglia.
Physiology of the Sympathetic Nervous System
The SNS physiology represents the intricate mechanisms of such quick and effective responses.
Mechanisms of Activation
Activation starts with a stimulus, which causes the hypothalamus to send signals to the spinal cord for the activation of preganglionic neurons.
Neurotransmitters like norepinephrine and epinephrine play a very vital role in transmitting the signal across synapses and in binding with adrenergic receptors on target cells.
Adrenergic Receptors
Alpha receptors generally cause constriction of blood vessels.
Beta receptors increase heart rate and relax airway muscles.
Effects on Different Organs and Systems
Cardiovascular System: Increases heart rate and raises blood pressure.
Respiratory System: Bronchodilation, thus it eases breathing.
Digestive System: Inhibits digestive processes.
Urinary System: Affects bladder control.
Metabolic Effects: Increases glucose metabolism, and mobilizes energy.
Role of SNS in Homeostasis
It is essential in homeostasis because it controls various activities in the body.
Body Temperature Regulation
Maintains body temperature through the control of blood flow to the skin surface and activity of sweat glands.
Stress Adaptation
Stress Response and Adaptation: Help the body adjust to stress by liberating cortisol and other stress hormones.
Interactions with Parasympathetic Nervous System
SNS is responsible for the "fight or flight" response, the parasympathetic nervous system is responsible for the "rest and digest" response.
The autonomic nervous system has two divisions, sympathetic and parasympathetic, that balance each other's effects to maintain homeostasis.
Disorders of the Sympathetic Nervous System
Disorders of the sympathetic nervous system are:
Hypertension: High blood pressure, continued over time, can be influenced by overactivity of the SNS.
Heart Failure: The SNS may result in heart failure because of the excess load on it through stress signals.
Anxiety Disorders: Overactive activity of SNS is associated with anxiety and panic disorders.
Pheochromocytoma: A rare tumour of the adrenal gland that might lead to excess production of adrenaline.
Sympathetic Nervous System NEET MCQs (With Answers & Explanations)
Important questions asked in NEET from this topic are:
Functions of Sympathetic Nervous System
Physiology of Sympathetic Nervous System
Practice Questions for NEET
Q1. Which of the following constitutes cranio-sacral outflow in the nervous system?
Parasympathetic
Cranial
Spinal
Sympathetic
Correct answer: 1) Parasympathetic
Explanation:
Cranio-sacral outflow (cranial nerves) 3, 7, 9, 10, and the sacrum are the sources of the preganglionic nerve fibres. Compared to postganglionic nerve fibres, preganglionic nerve fibres are longer. Cholinergic nerve fibres are found both before and after ganglionics.
Hence, the correct answer is option 1) Parasympathetic.
Q2. Which of the following physiological entities experience increased activity when the parasympathetic system is engaged?
Lacrimal gland, sweat gland, arrector pili
Heart, lacrimal gland, pancreas
Heart, adrenal gland, sweat gland
Gut, urinary bladder, digestive gland
Correct answer: 1) Lacrimal gland, sweat gland, arrector pili
Explanation:
The lacrimal gland, responsible for tear production shows increased activity under parasympathetic stimulation leading to increased tear secretion. Sweat glands which produce sweat to regulate body temperature also experience increased activity under parasympathetic control. The arrector pili muscles which are responsible for causing goosebumps, contract under the parasympathetic influence.
Hence, the correct answer is option 1) The lacrimal gland, sweat gland, arrector pili.
Q3. The organ of corti is a structure present in
External ear
Middle ear
Semi-circular canal
Cochlea
Correct answer: 4) Cochlea
Explanation:
In the parasympathetic nervous system, the primary neurotransmitter released is acetylcholine (ACh). Acetylcholine is released at both the preganglionic and postganglionic synapses. Preganglionic neurons release acetylcholine, which binds to nicotinic receptors in the postganglionic neurons. Subsequently, postganglionic neurons also release acetylcholine, which acts on muscarinic receptors located in the target organs, such as the heart, digestive tract, and glands. This neurotransmitter is responsible for mediating the parasympathetic "rest and digest" responses, such as slowing the heart rate, promoting digestion, and conserving energy.
Hence the correct answer is option 4) Acetylcholine.
Also Read:
Recommended video on "Sympathetic Nervous System"
Frequently Asked Questions (FAQs)
It is an autonomic response for preparing the body for prompt action in stressful situations or emergencies through the fight-or-flight response.
The SNS increases the heart rate and force of contraction, increasing blood supply to the vital organs and muscles during stressful conditions.
Accelerated heartbeat, blood pressure, sweating, anxiety, and high blood sugar are symptoms.
Deep breathing, meditation, yoga, and regular exercise reduce the activity of SNS, thus decreasing the stress in the minds of individuals.
The Sypathetic nervous system (SNS) is a preparation of the body to take action, whereas parasympathetic nervous systems play a role in rest and digestion.