Nervous System Structure and Function » Somatic and Autonomic Systems

What you'll learn this session

Study time: 30 minutes

The structure and function of the nervous system
The difference between the somatic and autonomic nervous systems
How the sympathetic and parasympathetic divisions work
Real-world applications of nervous system knowledge
Common disorders related to nervous system dysfunction

Introduction to the Nervous System

Your nervous system is like your body's electrical wiring - it helps you sense the world around you and respond to it. It's made up of billions of nerve cells (neurons) that send messages around your body at lightning speed!

Key Definitions:

Nervous System: The network of nerve cells and fibres that transmits signals between different parts of the body.
Neuron: A specialised cell that transmits nerve impulses.
Central Nervous System (CNS): The brain and spinal cord.
Peripheral Nervous System (PNS): All the nerves outside the CNS that connect it to the rest of the body.

📖 Basic Structure

The nervous system has two main parts:

Central Nervous System (CNS): Your brain and spinal cord - the command centre!
Peripheral Nervous System (PNS): All the nerves that branch out from your CNS to the rest of your body.

💡 Basic Function

Your nervous system has three main jobs:

Sensory: Collecting information from your environment
Integration: Processing and making sense of that information
Motor: Telling your body how to respond

The Peripheral Nervous System: Somatic vs Autonomic

The PNS is further divided into two major systems that have very different jobs:

🏃 Somatic Nervous System

What it does: Controls voluntary movements and carries sensory information to the CNS.

Key features:

You have conscious control over it
Controls skeletal muscles (the ones you can move on purpose)
Helps you interact with the outside world
Example: Moving your hand away from a hot surface

💪 Autonomic Nervous System

What it does: Controls involuntary bodily functions.

Key features:

Works automatically without conscious thought
Controls smooth muscles, cardiac muscles and glands
Regulates internal environment
Example: Heart rate, digestion, breathing

The Autonomic Nervous System: Two Opposing Forces

The autonomic nervous system has two divisions that often work in opposition to maintain balance in your body:

⚡ Sympathetic Division

The "Fight or Flight" System

Activates during stress or emergencies to prepare your body for action.

Effects include:

Increases heart rate
Dilates pupils
Increases breathing rate
Diverts blood to muscles
Decreases digestion
Releases adrenaline

🏡 Parasympathetic Division

The "Rest and Digest" System

Dominates during calm, relaxed states to conserve energy and maintain normal body functions.

Effects include:

Decreases heart rate
Constricts pupils
Slows breathing
Increases digestion
Stimulates salivation
Promotes relaxation

How the Autonomic Nervous System Works

The autonomic nervous system uses a two-neuron chain to send signals from the CNS to target organs:

📊 Preganglionic Neuron

First neuron in the chain that starts in the CNS and extends to a ganglion (a cluster of nerve cells).

📋 Ganglion

A relay station where the signal transfers from the first neuron to the second.

📌 Postganglionic Neuron

Second neuron that carries the signal from the ganglion to the target organ.

Case Study Focus: The Polyvagal Theory

Developed by Dr. Stephen Porges, this theory expands our understanding of the autonomic nervous system. It suggests that the parasympathetic nervous system has two different circuits:

Ventral vagal circuit: Promotes social connection and calm states
Dorsal vagal circuit: Triggers immobilisation or "freeze" responses in extreme danger

This theory helps explain why some people "freeze" during traumatic events rather than fighting or fleeing and has important implications for treating trauma and anxiety disorders.

Real-World Applications

🏥 Medical Applications

Understanding the nervous system helps doctors:

Diagnose neurological disorders
Develop treatments for conditions like epilepsy
Create medications that target specific parts of the nervous system
Understand how anaesthetics work

🧠 Psychological Applications

Knowledge of the nervous system helps psychologists:

Understand anxiety and stress responses
Develop relaxation techniques that activate the parasympathetic system
Treat phobias by addressing the fight-or-flight response
Explain the physical symptoms of psychological disorders

Common Disorders of the Nervous System

When parts of the nervous system don't work properly, various disorders can result:

👀 Autonomic Disorders

Dysautonomia: A condition where the autonomic nervous system doesn't work properly, causing issues with heart rate, blood pressure, digestion and temperature regulation.

💫 Somatic Disorders

Multiple Sclerosis: A condition where the immune system attacks the protective covering of nerves, disrupting communication between the brain and body.

💦 Stress-Related

Chronic Stress: Long-term activation of the sympathetic nervous system can lead to health problems including high blood pressure, weakened immune system and digestive issues.

Bringing It All Together

Your nervous system is an incredible network that keeps you alive and helps you interact with the world. The somatic system lets you move voluntarily and sense your environment, while the autonomic system keeps your internal processes running smoothly.

The balance between the sympathetic ("fight or flight") and parasympathetic ("rest and digest") divisions of your autonomic nervous system is crucial for your health and wellbeing. When this balance is disrupted, various physical and psychological problems can occur.

Understanding how these systems work together gives us valuable insights into human behaviour, health and disease - making it a fascinating area of study in psychology!

Fun Fact: The Speed of Thought

Nerve impulses can travel at speeds of up to 120 metres per second (268 miles per hour)! Different types of neurons conduct signals at different speeds, with the fastest being those with a fatty covering called myelin.

This is why reflex actions are so quick - the signal travels along your nerves at incredible speeds to protect you from danger!

🧠 Test Your Knowledge!