Limitless Biology: Synapse Structure
14.1.4 • The Gap Between Neurones
The Synaptic Gap: Neurones That Don't Touch
🔬 The Big Reveal
Under a microscope, two neurones might look like they're touching. But when you zoom in closer, you discover a tiny gap between them.
Key Term: This gap is called the Synaptic Cleft (approximately 20 nanometers wide).
⚡ Why No Direct Contact?
The electrical impulse cannot jump this gap. Instead, the signal must be converted into a chemical message.
This is why synapses only work in ONE direction (pre → post).
🧩 The Three Key Components
1. Pre-synaptic Neurone (The Sender)
- Vesicles: Tiny sacs filled with neurotransmitter molecules
- Many Mitochondria: Provide energy (ATP) for recycling neurotransmitters
2. Synaptic Cleft (The Gap)
The 20nm space where neurotransmitters diffuse from pre-synaptic to post-synaptic membrane.
3. Post-synaptic Neurone (The Receiver)
- Receptor Proteins: Specifically shaped to bind with the neurotransmitter (lock-and-key fit)
🎯 Examiner Trap
Students often write "neurones are connected at synapses." WRONG! They are NOT connected — there is always a gap (the synaptic cleft).
🎯 Exam Success Summary
Key Terms to Remember:
- • Pre-synaptic neurone
- • Post-synaptic neurone
- • Synaptic cleft
- • Vesicles
- • Receptor proteins
Critical Facts:
- • Neurones do NOT touch
- • Gap is ~20nm wide
- • Vesicles contain neurotransmitter
- • Receptors are complementary shaped
Examiner Traps:
- • Don't say neurones are "connected"
- • Vesicles are PRE-synaptic only
- • Receptors are POST-synaptic only
- • Signal goes ONE direction only
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