Sympathetic Nervous System: Definition, Function, Disorders

The sympathetic nervous system is part of the autonomic nervous system and is involved in the body's involuntary "fight or flight" response. The structure of the sympathetic nervous system consists of neurons of the spinal cord connected to organs through ganglia. Its function allows for rapid adjustments, such as increased heart rate and blood flow when one experiences stress. Disorders may interrupt these responses and disturb the cardiovascular and metabolic balance. This is one of the important topics from the Neural Control and Coordination chapter of Biology.

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This Story also Contains

1. Sympathetic Nervous System (SNS)
2. Sympathetic Nervous System Functions
3. Anatomy of the Sympathetic Nervous System
4. Physiology of the Sympathetic Nervous System
5. Sympathetic Nervous System and Homeostasis
6. Common Disorders and Diseases

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.

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.

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Sympathetic Nervous System Functions

Read about the functions of Sympathetic Nervous system functions:

Fight-or-Flight Response:

• Increases blood pressure

• Dilates airways

• Glucose released from energy stores

Effects on Other Organs and Systems:

• 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 Involved:

• 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 And 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 And 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 Action

• Activation starts with a stimulus, which causes the hypothalamus to send signals to the spinal cord for the activation of preganglionic neurons.

• Neurotransmitters: Norepinephrine and Epinephrine these neurotransmitters play a very vital role in transmitting the signal across synapses and in binding with adrenergic receptors on target cells.

• Receptor Types: Adrenergic Receptors (Alpha and Beta Receptors): Alpha receptors generally cause constriction of blood vessels, while 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.

Sympathetic Nervous System and Homeostasis

It is essential in homeostasis because it controls various activities in the body.

Role in Homeostatic Regulation

• Body Temperature: Maintains body temperature through the control of blood flow to the skin surface and activity of sweat glands.

• Stress Response and Adaptation: Help the body adjust to stress by liberating cortisol and other stress hormones.

Interactions with the 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.

Common Disorders and Diseases

• 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.

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