🞂 Central Nervous System (CNS)
The CNS consists of your brain and spinal cord. Think of it as the command centre that processes information and sends out instructions.
Nervous System Structure and Function » Central and Peripheral Nervous System
What you'll learn this session
Study time: 30 minutes
- The structure and function of the central nervous system (CNS)
- The structure and function of the peripheral nervous system (PNS)
- How the somatic and autonomic nervous systems work
- The sympathetic and parasympathetic divisions of the autonomic nervous system
- How neurons transmit information through the nervous system
- Real-world applications of nervous system knowledge
Introduction to the Nervous System
Your nervous system is like your body's electrical wiring - it controls everything from your thoughts and movements to your breathing and digestion. It's made up of billions of nerve cells that communicate with each other and the rest of your body through electrical and chemical signals. Let's explore how this amazing network is organised!
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; the basic building block of the nervous system.
- Synapse: The junction between two neurons where signals are passed from one to another.
The Two Main Divisions of the Nervous System
🧠 Peripheral Nervous System (PNS)
The PNS includes all the nerves that branch out from the CNS to the rest of your body. These are like the messengers that carry information to and from the command centre.
The Central Nervous System: Your Body's Control Centre
The Brain
The brain is the most complex organ in your body, weighing about 1.4 kg. It contains around 86 billion neurons and is protected by the skull and three layers of membranes called meninges.
🧠 Cerebrum
The largest part of the brain, responsible for conscious thought, memory, language and voluntary movement.
🎭 Cerebellum
Located at the back of the brain, it coordinates movement, posture and balance.
💪 Brain Stem
Connects the brain to the spinal cord and controls basic life functions like breathing, heart rate and blood pressure.
The Spinal Cord
The spinal cord is a long, thin bundle of nervous tissue that extends from the brain stem down through the spine. It's about 45 cm long in adults and is protected by the vertebral column (backbone).
Functions of the spinal cord include:
- Carrying messages between the brain and the rest of the body
- Controlling reflexes - automatic responses that don't need the brain's input
- Coordinating some movements
Did You Know? 💡
The brain uses about 20% of the body's oxygen and calories, despite making up only 2% of the body's weight. It's like a power-hungry computer that never shuts down!
The Peripheral Nervous System: Your Body's Messenger Network
The PNS consists of all the nerves outside the CNS. These nerves branch throughout your body, connecting your central nervous system to your muscles, organs and sensory receptors.
The PNS is divided into two main parts:
🏃 Somatic Nervous System
Controls voluntary movements and carries sensory information to the CNS. When you decide to kick a football or pick up a pen, your somatic nervous system makes it happen.
💬 Autonomic Nervous System
Controls involuntary functions like heart rate, digestion, breathing and sweating - things that happen without you having to think about them.
The Autonomic Nervous System: Automatic Control
The autonomic nervous system is further divided into two branches that often work in opposition to each other:
⚡ Sympathetic Division
This is your "fight or flight" system. It prepares your body for action and stress by:
- Increasing heart rate and blood pressure
- Dilating pupils
- Increasing breathing rate
- Directing blood to muscles and away from digestion
- Releasing glucose for energy
🏡 Parasympathetic Division
This is your "rest and digest" system. It helps your body relax and conserve energy by:
- Decreasing heart rate and blood pressure
- Constricting pupils
- Stimulating digestion
- Promoting relaxation
- Conserving energy
Case Study Focus: Adrenaline Response
Imagine you're about to take an important exam. Your sympathetic nervous system kicks in, causing your heart to race and your palms to sweat. This is because it's activating your adrenal glands to release adrenaline (epinephrine), preparing you for the "stress" of the exam. After the exam, your parasympathetic system takes over, helping you calm down. This balance between the two systems helps you respond appropriately to different situations.
How Neurons Work: The Communication Network
Neurons are the basic building blocks of your nervous system. They're specialised cells designed to transmit information through electrical and chemical signals.
Structure of a Neuron
A typical neuron has three main parts:
- Cell Body (Soma): Contains the nucleus and maintains the cell
- Dendrites: Branch-like structures that receive signals from other neurons
- Axon: A long fibre that carries signals away from the cell body to other neurons, muscles, or glands
How Neurons Communicate
Neurons communicate through a process called synaptic transmission:
- An electrical impulse travels down the axon of a neuron
- When it reaches the end of the axon (the synapse), it triggers the release of chemicals called neurotransmitters
- These neurotransmitters cross the tiny gap (synaptic cleft) between neurons
- They bind to receptors on the receiving neuron, potentially triggering a new electrical impulse
Amazing Fact! 🌟
Information travels along neurons at speeds of up to 120 metres per second (268 mph)! This is why you can react so quickly when you touch something hot.
Real-World Applications
Understanding the nervous system helps us in many areas:
💊 Medicine
Treatments for conditions like epilepsy, Parkinson's disease and depression often target specific parts of the nervous system.
🏆 Sports
Athletes train their nervous systems to improve reaction times and coordination.
💻 Technology
Brain-computer interfaces and artificial neural networks are inspired by how our nervous system works.
Summary
The nervous system is a complex network divided into the central nervous system (brain and spinal cord) and the peripheral nervous system (all other nerves). The peripheral nervous system includes the somatic system for voluntary control and the autonomic system for involuntary functions. The autonomic system is further divided into sympathetic ("fight or flight") and parasympathetic ("rest and digest") divisions. This intricate system allows your body to respond to its environment, maintain internal balance and perform countless functions every second of every day.
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