What does sympathetic mean

What is the Sympathetic Nervous System?

The sympathetic nervous system (SNS) is a major division of the autonomic nervous system (ANS), which itself is a part of the peripheral nervous system. The autonomic nervous system controls involuntary bodily functions – those that happen automatically without conscious thought, such as breathing, heart rate, digestion, and pupil dilation. The ANS is further divided into the sympathetic and parasympathetic nervous systems, which generally have opposing effects on the body, working together to maintain homeostasis (a stable internal environment).

The 'Fight-or-Flight' Response

The primary role of the sympathetic nervous system is to orchestrate the body's response to stress, danger, or excitement – commonly known as the 'fight-or-flight' response. When your brain perceives a threat, whether it's a physical danger (like encountering a predator) or a psychological stressor (like a looming deadline or a public speaking engagement), the SNS kicks into high gear. This response is an ancient evolutionary mechanism designed to prepare you to either confront the threat directly (fight) or escape from it quickly (flight).

Physiological Effects of Sympathetic Activation

Activation of the sympathetic nervous system leads to a cascade of physiological changes throughout the body, all aimed at maximizing your chances of survival or successful performance in a stressful situation. These changes include:

• Increased Heart Rate and Blood Pressure: The heart beats faster and more forcefully, and blood vessels constrict, raising blood pressure. This ensures that oxygenated blood is pumped more rapidly to vital organs and muscles.
• Increased Respiration Rate: Breathing becomes quicker and shallower to take in more oxygen.
• Pupil Dilation: The pupils widen to allow more light to enter the eyes, improving vision, especially in low-light conditions, and enhancing your ability to scan your surroundings for threats or escape routes.
• Redirection of Blood Flow: Blood is diverted away from non-essential functions, like digestion, and directed towards skeletal muscles, the heart, and the brain, preparing them for intense activity.
• Glucose Release: The liver releases stored glucose (sugar) into the bloodstream, providing a readily available source of energy for muscles and the brain.
• Increased Sweating: Sweat glands become more active to help cool the body, which can generate heat during intense physical exertion.
• Slowed Digestion: Digestive processes slow down or stop altogether, as energy is prioritized for immediate survival needs.
• Release of Hormones: The adrenal glands, stimulated by the SNS, release hormones like adrenaline (epinephrine) and noradrenaline (norepinephrine) into the bloodstream. These hormones prolong and amplify the effects of the sympathetic nervous system.

Neural Pathways

The sympathetic nervous system uses a specific neural pathway involving two main types of neurons: preganglionic and postganglionic neurons. Preganglionic neurons originate in the thoracic and lumbar regions of the spinal cord. They synapse (connect) with postganglionic neurons in sympathetic ganglia, which are clusters of nerve cell bodies located near the spinal cord (forming the sympathetic chain) or further away. These postganglionic neurons then travel to their target organs (like the heart, lungs, or blood vessels) to exert their effects.

Neurotransmitters Involved

The primary neurotransmitters used by the sympathetic nervous system are noradrenaline (norepinephrine), released by most postganglionic sympathetic neurons directly onto their target organs, and acetylcholine, released by preganglionic neurons onto postganglionic neurons. As mentioned, the adrenal medulla, stimulated by sympathetic preganglionic fibers, releases adrenaline (epinephrine) and noradrenaline into the bloodstream, acting as hormones that circulate and affect various tissues throughout the body.

Sympathetic vs. Parasympathetic

It's crucial to understand the sympathetic system in contrast to its counterpart, the parasympathetic nervous system. While the sympathetic system mobilizes the body for action, the parasympathetic system promotes 'rest and digest' functions. It conserves energy, slows heart rate, lowers blood pressure, stimulates digestion, and promotes relaxation. Together, these two systems maintain a dynamic balance, ensuring the body functions optimally under varying conditions. For example, after the 'fight-or-flight' response subsides, the parasympathetic system becomes dominant, helping the body return to its normal resting state.

When Does Sympathetic Activation Occur?

Sympathetic activation isn't limited to life-threatening situations. It can be triggered by a wide range of stimuli, including:

• Physical exertion or exercise
• Excitement or anticipation
• Fear or anxiety
• Sudden loud noises
• Cold temperatures
• Pain
• Social stressors

Chronic activation of the sympathetic nervous system, often due to prolonged stress, can have detrimental effects on health, contributing to conditions like hypertension, heart disease, anxiety disorders, and weakened immune function.

In Summary

The sympathetic nervous system is a vital component of our survival mechanism, preparing us to face challenges by initiating the 'fight-or-flight' response. It orchestrates a complex series of bodily adjustments designed to enhance physical capacity and alertness when needed, while the parasympathetic system ensures we can recover and rest afterwards.