Database results:
examBoard: AQA
examType: GCSE
lessonTitle: Synaptic Transmission
Your brain contains around 86 billion neurons that form a complex network allowing you to think, feel and interact with the world. These neurons communicate through a fascinating process called synaptic transmission. Let's explore how these amazing cells work!
Key Definitions:
Neurons have a unique structure that helps them transmit information quickly and efficiently. Each part plays a vital role in how messages travel through your nervous system.
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.
Myelin sheath: A fatty layer that insulates the axon and speeds up transmission.
Nodes of Ranvier: Gaps in the myelin sheath where the signal jumps, speeding up transmission.
Axon terminals: The end branches of the axon that release neurotransmitters.
Sensory neurons: Carry information from your senses to your brain.
Motor neurons: Carry commands from your brain to your muscles.
Interneurons: Connect neurons to each other within the brain and spinal cord.
Different neurons have different shapes depending on their function. Some have very long axons (up to a metre!), while others have complex branching dendrites to receive lots of signals.
Neurons don't actually touch each other. Instead, they communicate across tiny gaps called synapses. This process is called synaptic transmission and is the foundation of all brain activity.
When neurons communicate, they send electrical signals that trigger chemical messages. This happens in a specific sequence:
An electrical signal (action potential) travels down the axon of the presynaptic neuron. This works like an electrical current moving along a wire.
When the signal reaches the axon terminal, it triggers calcium channels to open. Calcium enters the cell, causing vesicles (tiny sacs) containing neurotransmitters to fuse with the cell membrane and release their contents into the synapse.
Neurotransmitters cross the synaptic cleft (the gap) and bind to specific receptors on the postsynaptic neuron, like a key fitting into a lock.
When neurotransmitters bind to receptors, they can either excite the neuron (make it more likely to fire) or inhibit it (make it less likely to fire).
To stop the signal, neurotransmitters are either reabsorbed back into the presynaptic neuron (reuptake) or broken down by enzymes in the synapse.
If enough excitatory signals are received, the postsynaptic neuron will generate its own action potential, continuing the message. If inhibitory signals dominate, the message stops.
Neurotransmitters are the chemical messengers that carry signals across synapses. Different neurotransmitters have different effects on the body and brain.
These make it more likely that the receiving neuron will fire an action potential:
These make it less likely that the receiving neuron will fire an action potential:
Parkinson's disease shows what happens when specific neurotransmitter systems malfunction. In Parkinson's, the neurons that produce dopamine (a neurotransmitter involved in movement control) gradually die off. This leads to symptoms like tremors, stiffness and difficulty with movement.
Treatment often involves medications that increase dopamine levels in the brain or mimic dopamine's effects. This case study demonstrates how crucial proper synaptic transmission is for normal brain function and how specific neurotransmitters control different aspects of our behaviour.
Many drugs work by altering synaptic transmission. Understanding this helps us understand both medical treatments and the effects of recreational drugs.
Antidepressants: Many work by preventing the reuptake of serotonin, keeping it in the synapse longer (SSRIs).
Anti-anxiety medications: Often enhance the effects of GABA, increasing inhibition in the brain.
ADHD medications: Often affect dopamine and noradrenaline levels to improve attention and focus.
Stimulants (e.g., caffeine): Block adenosine receptors, reducing the brain's natural "slow down" signals.
Alcohol: Enhances GABA's inhibitory effects and blocks glutamate's excitatory effects.
Nicotine: Mimics acetylcholine at certain receptors, creating a temporary boost in attention and mood.
Synaptic transmission is at the heart of everything your brain does. It allows for:
Understanding synaptic transmission helps scientists develop treatments for conditions like depression, anxiety, epilepsy and neurodegenerative diseases. It's also key to understanding how our experiences shape our brains through a process called neuroplasticity - the brain's ability to reorganize itself by forming new neural connections.
Your brain contains approximately 100 trillion synapses - that's about 1,000 times the number of stars in our galaxy! Each neuron can form connections with up to 10,000 other neurons, creating an incredibly complex network that makes you who you are.
The speed of neural transmission varies. In unmyelinated neurons, signals travel at about 0.5-2 metres per second. In myelinated neurons, signals can zoom along at up to 120 metres per second - that's about 430 km/h!
Log in to track your progress and mark lessons as complete!
Login NowDon't have an account? Sign up here.