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examBoard: AQA
examType: GCSE
lessonTitle: Excitation and Inhibition
Your brain contains roughly 86 billion neurons that communicate through a complex system of electrical and chemical signals. These signals can either excite or inhibit other neurons, creating the basis for all your thoughts, feelings and actions. Let's explore how this fascinating process works!
Key Definitions:
Before we dive into excitation and inhibition, let's understand the structure of a neuron. Think of neurons as the messaging system of your body - they receive, process and send information constantly.
A typical neuron consists of:
Neurons communicate in a specific direction:
Excitation is like pressing the accelerator in a car - it increases the likelihood that a neuron will fire an action potential. When a neuron is excited, it's more likely to pass on information to the next neuron.
When excitatory neurotransmitters bind to receptors on a neuron, they cause positive ions (like sodium, Na+) to flow into the cell. This makes the inside of the neuron less negative (more positive), a process called depolarisation. If enough excitatory signals arrive at once, the neuron reaches its threshold potential, triggering an action potential that travels down the axon.
Glutamate is the main excitatory neurotransmitter in the brain. It's vital for learning and memory. Too much glutamate can cause excitotoxicity, damaging neurons.
An action potential is an "all-or-nothing" event. Once threshold is reached (about -55mV), a full action potential occurs. It can't be half-triggered or partially fired.
An EPSP is a small depolarisation in the receiving neuron. Multiple EPSPs can add up (summation) to reach threshold and trigger an action potential.
Inhibition is like pressing the brake in a car - it decreases the likelihood that a neuron will fire. Inhibition is just as important as excitation for normal brain function, as it helps control and fine-tune neural activity.
When inhibitory neurotransmitters bind to receptors, they typically cause negative ions (like chloride, Cl-) to flow into the cell, or positive ions (like potassium, K+) to flow out. This makes the inside of the neuron more negative, a process called hyperpolarisation. This moves the neuron further from its threshold, making it less likely to fire.
GABA (gamma-aminobutyric acid) is the main inhibitory neurotransmitter. It helps reduce anxiety and is the target of anti-anxiety medications like benzodiazepines.
Inhibition is crucial for preventing excessive neural activity. Without it, neurons would constantly fire, potentially leading to seizures.
An IPSP is a small hyperpolarisation in the receiving neuron, making it harder for that neuron to reach threshold and fire.
Your brain functions properly when there's a balance between excitation and inhibition. Think of it like a seesaw - too much in either direction can cause problems.
A neuron typically receives thousands of inputs - some excitatory, some inhibitory. The neuron acts as an integrator, summing up all these signals. If excitatory inputs outweigh inhibitory ones enough to reach threshold, the neuron fires.
This balance is crucial for:
Neurons integrate signals through two types of summation:
Both types can contribute to reaching threshold potential and triggering an action potential, or they can prevent firing if inhibitory signals dominate.
Epilepsy is a neurological disorder characterised by seizures, which are periods of abnormal brain activity. Research shows that many forms of epilepsy result from an imbalance between excitation and inhibition in the brain.
In epilepsy, there is often:
Anti-epileptic medications often work by either reducing excitation or enhancing inhibition. For example, drugs like sodium valproate block sodium channels to reduce excitation, while benzodiazepines enhance the effects of GABA to increase inhibition.
This real-world application shows how understanding neural excitation and inhibition can lead to effective treatments for neurological disorders.
Understanding excitation and inhibition helps explain many aspects of brain function and dysfunction:
Many medications target excitation or inhibition:
Excitation and inhibition underlie many mental processes:
Neurons communicate through a complex interplay of excitatory and inhibitory signals. Excitation increases the likelihood of a neuron firing by depolarising the membrane, while inhibition decreases this likelihood through hyperpolarisation. The balance between these processes is crucial for normal brain function and imbalances can lead to various neurological and psychiatric disorders.
Remember these key points:
Understanding these processes helps explain how your brain works and how various treatments for neurological and psychiatric conditions affect neural function.
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