1.1. Summarise the physiology of the nervous system

This guide will help you answer 1.1. Summarise the physiology of the nervous system.

The nervous system is one of the most critical systems in the human body. It is responsible for controlling and coordinating activities and ensuring the body works in harmony. It achieves this by sending, receiving, and processing information. This guide covers how the nervous system is structured and functions, along with its main components and processes.

Overview of the Nervous System

The nervous system is a highly organised network of cells. It is divided into two major parts:

• Central Nervous System (CNS) – Includes the brain and spinal cord.
• Peripheral Nervous System (PNS) – Consists of nerves outside the brain and spinal cord that link the CNS to the rest of the body.

This system enables the body to respond to internal and external stimuli. It works by transmitting electrochemical signals known as nerve impulses. These signals travel through specialised cells called neurons.

What are Neurons?

Neurons are specialised cells that transmit nerve impulses. They are the core units of the nervous system and are designed to rapidly communicate information. Each neuron has three main parts:

1. Cell Body (Soma) – Contains the nucleus and manages the cell’s functions.
2. Dendrites – Short, branch-like structures that receive signals from other neurons.
3. Axons – Long fibres that carry nerve impulses away from the cell body to other neurons, muscles, or glands.

Neurons interact at junctions called synapses. At the synapse, one neuron passes chemical or electrical signals to another.

Types of Neurons

There are three primary types of neurons, depending on their function:

• Sensory Neurons – Transmit information from the senses (like touch, sight, and sound) to the CNS.
• Motor Neurons – Carry signals from the CNS to muscles or glands to trigger a response.
• Interneurons – Found in the CNS, they connect sensory and motor neurons and integrate information.

What is Central Nervous System (CNS)?

The CNS is the control centre of the body. It processes information and issues instructions. The brain and spinal cord are its components.

The Brain

The brain is the most complex organ, controlling thought, memory, emotions, and more. It is divided into several areas:

• Cerebrum – Responsible for voluntary actions, thinking, learning, and memory.
• Cerebellum – Coordinates movement, posture, and balance.
• Brainstem – Manages essential functions like breathing, heart rate, and sleep.

The brain is protected by the skull and three layers of membranes called meninges. It is also cushioned by cerebrospinal fluid, which provides nutrients and removes waste.

The Spinal Cord

The spinal cord is a long bundle of nerve tissue running from the brainstem down the spine. It acts as a pathway for messages between the brain and the body. It is also responsible for reflexes, which are rapid, automatic responses to stimuli.

What is the Peripheral Nervous System (PNS)?

The PNS connects the CNS to the limbs and organs. It includes nerves and ganglia (clusters of neurons). The PNS is further divided into two systems:

1. Somatic Nervous System – Controls voluntary movements and sensory information (e.g., moving an arm).
2. Autonomic Nervous System (ANS) – Regulates involuntary processes like heart rate, digestion, and temperature control.

The ANS has two branches:

• Sympathetic Nervous System – Prepares the body for the ‘fight or flight’ response during stress.
• Parasympathetic Nervous System – Promotes the ‘rest and digest’ state when the body is relaxed.

Communication and Nerve Impulses

The nervous system relies on communication between neurons, tissues, and organs. Signals are transmitted as electrical impulses along the axon of a neuron. When the impulse reaches the end of the axon, it triggers the release of chemical messengers called neurotransmitters.

Neurotransmitters cross the synapse and attach to receptors on the next neuron, muscle, or gland, causing a response. Common neurotransmitters include:

• Dopamine – Associated with pleasure and motivation.
• Serotonin – Regulates mood, sleep, and appetite.
• Acetylcholine – Plays a role in muscle movement and learning.

The speed and efficiency of signal transmission depend on the myelin sheath, a fatty layer that insulates some axons and allows impulses to travel faster.

Sensory Input and Motor Output

The nervous system works in two main directions:

• Sensory Input – Sensory neurons detect changes in the environment, such as light, heat, or pressure. These signals are sent to the CNS for processing.
• Motor Output – After processing, the CNS sends instructions to muscles or glands through motor neurons. This triggers actions or adjustments.

For instance, if you touch something hot, sensory neurons send a message to the spinal cord. The spinal cord reacts instantly, pulling your hand away (a reflex).

Homeostasis and the Nervous System

The nervous system plays a central role in maintaining homeostasis – the balance of internal conditions, such as body temperature, hydration, and pH levels. The hypothalamus, a small part of the brain, monitors and controls these internal processes.

It works closely with the endocrine system, which releases hormones to complement nervous responses. For example, the hypothalamus can signal the adrenal glands to release adrenaline during stress.

Ageing and the Nervous System

As people age, the nervous system undergoes changes. These include:

• Slower nerve signal transmission.
• Reduced brain size and weight.
• Weaker memory and reflexes.

However, mental exercises and a healthy lifestyle can help preserve brain function.

Common Disorders of the Nervous System

Various conditions can affect the nervous system. Some common examples include:

• Stroke – Blood supply to the brain is interrupted, causing cell damage.
• Multiple Sclerosis (MS) – An autoimmune disease where the immune system attacks the myelin sheath, affecting signal transmission.
• Epilepsy – A condition causing recurring seizures due to abnormal electrical activity in the brain.
• Parkinson’s Disease – A disorder characterised by the loss of dopamine-producing neurons, affecting movement.

Treatment for these disorders may involve medication, therapy, or surgery. Early intervention is often important in managing these conditions.

Protecting Nervous System Health

To support a healthy nervous system, it is important to:

• Maintain a balanced diet rich in nutrients.
• Exercise regularly to improve blood flow.
• Avoid smoking and excessive alcohol consumption.
• Manage stress through relaxation techniques.
• Get enough sleep to allow the nervous system to recover.

Maintaining nervous system health is vital for overall well-being and quality of life.