Sympathetic Vs Parasympathetic Nervous System Explained

Nervous systems are remarkable creations, particularly the one that keeps our heart beating, lungs breathing, and digestion churning on autopilot.

This is the autonomic nervous system and it’s made up of two parts: the sympathetic and parasympathetic nervous systems. Both are important, and both have an essential role to play in our overall health and well-being…

In this post, we take a fascinating journey along your neural pathways, explaining the sympathetic vs parasympathetic nervous system, and their role in the autonomic nervous system. What they do, why they’re important, and how they differ from each other.

The Autonomic Nervous System

The mammalian nervous system is a complex network. It controls almost everything that goes on in our body. We can broadly split it into 2 main systems.

  1. The brain and spinal cord make up the central nervous system. This is the command centre of the body, where all the decisions are made.
  2. Everything outside the spinal cord is the peripheral nervous system. This system relays information from all the various body systems and organs back to the brain via the spinal cord.

The peripheral nervous system in turn is split into a series of systems, each with its own specific role to play in the overall scheme of nerve networks.

The autonomic nervous system (ANS) is one of these networks, albeit a vitally important one. Functioning like an autopilot, it’s responsible for regulating all those things we do automatically (heartbeat, breathing, digestion, immune response).

What Are the Sympathetic and Parasympathetic Nervous Systems?

The autonomic nervous system, in turn, has 2 ‘sub networks’ – the sympathetic and parasympathetic nervous systems. You can probably think of them as the ‘go’ and ‘slow’ settings of the autonomic nervous system.

Between them, they maintain a balance between our fight-or-flight, and rest-and-digest, functions. Not only is this balance important for our overall health (think stress vs relaxation), it’s also important for maintaining homeostasis within our body.

Maintaining Homeostasis

Homeostasis is a self-regulatory process that allows organisms, including the human body, to remain stable whilst at the same time adjusting to external changes.

Probably the most common example of this, and one we’re most familiar with, is our ability to maintain a consistent body temperature even in temperature extremes.

To explain:

As we know, our body temperature fluctuates within what is considered a normal range for our species based on our gender, age, health, and so on. This is our ‘normothermia’ range. However, it doesn’t go much below or above this range (or it shouldn’t if we’re healthy!).

When the autonomic nervous system senses there is a danger that it might, we start sweating (too hot) or shivering (too cold). These automatic reactions cool us down or heat us up, and keep our temperature stable. They are triggered by the sympathetic and parasympathetic nervous systems respectively.

Keeping Us Warm

When body temperature drops, the sympathetic nervous system goes into action. It triggers the release of hormones (i.e. adrenaline) that constrict blood vessels in the skin.

This reduces the amount of blood flowing close to the skin’s surface, helping conserve body heat. At the same time, it may set off a shivering response that helps generate heat.

Cooling Us Down

When body temperature rises, the parasympathetic system takes over. It dilates blood vessels in the skin to increase blood flow close to the surface and dissipate heat. It may also trigger a sweating response to allow excess heat to escape via sweat evaporation on your skin.

This is an obvious example but the hormone responses triggered by these 2 nervous systems to help maintain body temperature ALSO have other functions.

For example, when we exercise or are faced with perceived danger, the sympathetic system kicks in to boost our performance. When we finish exercising, or the danger goes away, the parasympathetic system steps in to help with recovery.

Explaining The Difference Between The Sympathetic and Parasympathetic Nervous Systems?

The sympathetic nervous system is responsible for the ‘go’ activities regulated by the autonomic nervous system. It primarily uses norepinephrine neurotransmitters to:

  • Activate our fight-or-flight response.
  • Prepare our body to respond to apparent threats.
  • Increase heart rate, speed up respiration, dilate pupils, redirect blood flow to muscles, and slow down digestion.

When the sympathetic nervous system gets going, you know you’re pumped and primed for action. Once upon a time, we relied on it for survival. Today not so much, although it is important for homeostasis as we explained above.

In direct contrast, the parasympathetic nervous system controls the ‘slow’ setting. This much more relaxed system uses acetylcholine neurotransmitters to:

  • Promote rest-and-digest activities.
  • Help the body to relax, recuperate, and conserve energy.
  • Slow down heart rate and breathing, stimulate digestion, and encourage repair and growth.

But why do we need both of these seemingly opposing systems?

It all comes back to maintaining homeostasis, or a balanced state of being.

We likely wouldn’t be here as a species if we were forever in slow mode; predators would have made short work of us a long time ago.

However, it’s also not healthy to be perpetually in go mode either. The hormones released by the sympathetic nervous system directly contribute to stress and anxiety with all the health problems associated with those.

Conclusion: Sympathetic Vs Parasympathetic Nervous System Explained

Chiropractic care can play a vital role in supporting this delicate balance. Spinal misalignments can interfere with nerve communication, potentially affecting the autonomic nervous system.

Regular chiropractic adjustments can help restore proper spinal alignment, potentially promoting optimal nervous system function and supporting a healthy balance between the “go” and “slow” responses.

Clare Cullen
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