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examBoard: Pearson Edexcel
examType: IGCSE
lessonTitle: Electrical Impulses
Our bodies are constantly responding to changes in our environment. When you touch something hot, you pull your hand away. When you see a football coming towards you, you catch it or duck. These responses happen because your nervous system detects stimuli and coordinates your body's reactions through electrical impulses.
Key Definitions:
The nervous system is divided into two main parts:
The nervous system helps us respond to our environment by:
Electrical impulses are the body's way of sending messages quickly. They can travel at speeds of up to 120 metres per second! This speed is essential for:
Without electrical impulses, our reactions would be too slow to avoid danger or function effectively.
Neurons are specialised cells designed to carry electrical impulses. They have a unique structure that allows them to transmit signals efficiently.
A typical neuron consists of:
Contains the nucleus and most of the cell's organelles. It's the control centre of the neuron.
Short branched extensions that receive signals from other neurons and carry them towards the cell body.
A long extension that carries impulses away from the cell body to other neurons, muscles, or glands.
Some axons are covered by a fatty substance called myelin. This forms the myelin sheath, which insulates the axon and speeds up the transmission of electrical impulses. The gaps in the myelin sheath are called nodes of Ranvier and they help the impulse jump from node to node, making transmission even faster.
Electrical impulses are created by the movement of charged particles (ions) across the neuron's membrane. This process involves several steps:
When a neuron is not sending a signal, it's in a 'resting state':
When a neuron is stimulated:
In the 1940s, scientists Alan Hodgkin and Andrew Huxley studied how electrical impulses work using the giant axon of a squid. These axons can be up to 1mm in diameter (huge compared to human neurons), making them easier to study. By inserting tiny electrodes into the axon, they could measure the electrical changes during an impulse. Their work was so important it won them a Nobel Prize in 1963 and formed the basis of our understanding of how neurons communicate.
Electrical impulses follow what's called the "all-or-nothing principle". This means:
This is like turning on a light switch - it's either on or off, with no in-between state.
Neurons don't physically touch each other. Instead, they communicate across tiny gaps called synapses. This is how one neuron passes its message to the next.
The process of synaptic transmission involves:
An electrical impulse reaches the end of the axon (presynaptic terminal).
This triggers the release of chemical messengers called neurotransmitters into the synaptic cleft (gap).
Neurotransmitters bind to receptors on the next neuron, potentially triggering a new electrical impulse.
Common neurotransmitters include acetylcholine, dopamine and serotonin. After transmitting the signal, neurotransmitters are either broken down by enzymes or reabsorbed by the presynaptic neuron (a process called reuptake).
Many drugs work by affecting synapses. For example, caffeine blocks the receptors for adenosine (a neurotransmitter that makes you feel tired), keeping you alert. Antidepressants often work by preventing the reuptake of serotonin, leaving more of this "feel-good" neurotransmitter in the synapse. Understanding how synapses work has been crucial for developing medications for mental health conditions and neurological disorders.
Some responses need to happen extremely quickly to protect us from harm. These are called reflex actions and they involve a special neural pathway called a reflex arc.
A reflex arc works like this:
What makes reflex actions special is that they don't need to travel all the way to the brain for processing. This makes them much faster - crucial when you need to remove your hand from a hot surface before serious damage occurs!
Understanding how electrical impulses work helps us:
Electrical impulses are fundamental to human coordination. They allow us to:
Without the rapid transmission of electrical impulses through our nervous system, even simple tasks would be impossible. Our ability to generate and transmit these signals is what allows us to interact with the world around us in a coordinated way.
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