Neuron Structure and Function » Review and Practice - Neurons

What you'll learn this session

Study time: 30 minutes

The structure of neurons and their key components
Different types of neurons and their specific functions
How neurons communicate through synaptic transmission
The role of neurotransmitters in neural communication
How to apply this knowledge to exam questions

Structure of Neurons

Neurons are the basic building blocks of the nervous system. These specialised cells are responsible for transmitting electrical and chemical signals throughout the body, allowing us to think, feel, move and respond to our environment.

Key Definitions:

Neuron: A specialised cell that transmits nerve impulses throughout the body.
Synapse: The junction between two neurons where signals are passed.
Neurotransmitter: Chemical messengers that transmit signals across synapses.

📖 Parts of a Neuron

Every neuron consists of three main parts:

Cell body (Soma): Contains the nucleus and maintains the cell's health
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

Additional structures include:

Myelin sheath: Fatty insulation that speeds up signal transmission
Nodes of Ranvier: Gaps in the myelin sheath where the signal jumps
Axon terminals: End points that release neurotransmitters

Types of Neurons

There are three main types of neurons, each with a specific function in the nervous system:

👉 Sensory Neurons

Carry information from sensory receptors (like those in your skin, eyes and ears) to the central nervous system (brain and spinal cord).

Structure: Long dendrites, short axon

🧠 Relay/Interneurons

Connect neurons to each other within the central nervous system, helping to process and integrate information.

Structure: Short dendrites and axons

💪 Motor Neurons

Carry commands from the central nervous system to muscles and glands, causing movement or secretion.

Structure: Short dendrites, very long axon

Neural Communication

Neurons communicate through a combination of electrical and chemical signals. This process is essential for all brain functions, from basic reflexes to complex thoughts.

The Action Potential

An action potential is an electrical impulse that travels along the neuron's axon. Here's how it works:

Resting state: The neuron has a negative charge inside (-70mV) compared to outside
Stimulus: When stimulated, ion channels open, allowing positive sodium ions to flow in
Depolarisation: The cell becomes more positive inside
Threshold: If the charge reaches about -55mV, an action potential is triggered
All-or-nothing response: Once triggered, the action potential always has the same strength
Repolarisation: Potassium ions flow out, restoring the negative charge
Refractory period: A brief time when the neuron cannot fire again

Case Study Focus: Multiple Sclerosis

Multiple Sclerosis (MS) is a condition where the immune system attacks the myelin sheath around neurons. Without proper myelin, signals travel more slowly or get blocked completely. This demonstrates the critical importance of myelin in neural function.

Symptoms include vision problems, muscle weakness and coordination difficulties, directly related to disrupted neural communication.

Synaptic Transmission

Neurons don't physically touch each other. Instead, they communicate across tiny gaps called synapses through a process called synaptic transmission:

🔗 How Synapses Work

An action potential reaches the end of the axon (presynaptic terminal)
This triggers calcium ions to enter the terminal
Calcium causes vesicles containing neurotransmitters to fuse with the cell membrane
Neurotransmitters are released into the synaptic cleft (gap)
Neurotransmitters bind to receptors on the receiving neuron (postsynaptic neuron)
This may excite or inhibit the receiving neuron
Neurotransmitters are then either broken down or reabsorbed (reuptake)

Neurotransmitters

Neurotransmitters are chemical messengers that carry signals across synapses. Different neurotransmitters have different effects on the body and mind.

😃 Dopamine

Associated with reward, pleasure and movement. Low levels are linked to Parkinson's disease, while abnormal levels are associated with schizophrenia.

😴 Serotonin

Regulates mood, appetite and sleep. Low levels are linked to depression and anxiety disorders.

⚠ Adrenaline

Triggers the "fight or flight" response during stress or danger. Increases heart rate and prepares the body for action.

Applying Your Knowledge

Understanding neurons is crucial for explaining many psychological processes and disorders. Here are some ways this knowledge is applied:

Understanding mental health: Many mental health conditions involve neurotransmitter imbalances
Drug effects: Many drugs work by affecting neurotransmitter systems
Brain injuries: Damage to specific neurons can explain particular symptoms
Learning and memory: Neural connections strengthen with repeated use (neuroplasticity)

Exam Tip: Describing vs Explaining

In your GCSE Psychology exam, you may be asked to:

Describe the structure of a neuron (list and identify parts)
Explain how neurons communicate (detail the process and its purpose)

Make sure you understand the difference between these command words!

Review Activity

Test your understanding by labelling a neuron. On a piece of paper, draw a basic neuron and label:

Cell body
Dendrites
Axon
Myelin sheath
Nodes of Ranvier
Axon terminals

Then, trace the path of a signal from when it's received by dendrites to when it's passed to another neuron.

Summary

Neurons are specialised cells that form the foundation of our nervous system. They have a distinct structure with dendrites, a cell body and an axon, which allows them to receive, process and transmit signals. The three main types sensory, relay and motor neurons work together to help us perceive and respond to our environment. Neural communication happens through electrical signals (action potentials) within neurons and chemical signals (neurotransmitters) between neurons at synapses. Understanding this process helps explain both normal brain function and various psychological disorders.

🧠 Test Your Knowledge!