Neurotransmitters are important chemical messengers that help neurons (nerve cells) talk to each other at a space called the synapse. This process involves moving across a tiny gap around 20-40 nanometers wide during what we call synaptic transmission.

How Synaptic Transmission Works

1. Release of Neurotransmitters:

   • When an electrical signal (called an action potential) reaches the end of a neuron, special gates (voltage-gated calcium channels) open up.
   • Calcium ions enter the neuron, causing tiny packets (called synaptic vesicles) to join with the neuron's membrane.
   • About 100-200 of these packets can release neurotransmitters because of one single action potential. This causes a big increase in the amount of neurotransmitter in the area.

2. Diffusion Across the Synaptic Cleft:

   • After being released, neurotransmitters like glutamate, GABA, and dopamine move quickly across the synaptic cleft.
   • This movement happens very fast—usually in just a few microseconds—so the neurons can communicate quickly.
   • The difference in concentration helps with this movement. For example, the amount of neurotransmitter in the sending neuron can be thousands of times higher than in the gap at first.

3. Binding to Postsynaptic Receptors:

   • When these neurotransmitters reach the next neuron, they attach to special spots called receptors on the neuron's surface.
   • Depending on the type of receptor, the process that happens next can be different. There are two main types:
     • Ionotropic receptors: These allow signals to pass through quickly.
     • Metabotropic receptors: These make changes that last longer.
   • There are about 1,000 different types of neurotransmitter receptors in the human brain.

Sending the Signal

4. Generation of Postsynaptic Potentials:

   • When neurotransmitters bind to receptors, they can create either excitatory postsynaptic potentials (EPSPs) or inhibitory postsynaptic potentials (IPSPs).
   • For example, when glutamate activates a specific receptor (called an NMDA receptor), it can create an EPSP of about 1-5 mV. If enough of these EPSPs combine and reach a certain level (around -55 mV), they can trigger an action potential in the next neuron.

5. Ending the Signal:

   • The signal from neurotransmitters doesn’t last forever. There are a few ways it gets turned off:
     • Reuptake: The sending neuron can take back up to 90% of the neurotransmitter.
     • Enzymatic degradation: Some neurotransmitters can be broken down by special enzymes (like acetylcholine by acetylcholinesterase).
     • Diffusion: Some of the neurotransmitters can just float away from the synapse.
   • Clearing neurotransmitters effectively is really important. If they don't get cleared, it could cause continuous signaling, which might be dangerous for the brain.

In short, neurotransmitters move quickly across the synaptic cleft through a process of release, movement, binding to receptors, and sending signals. Understanding how this all works is key to learning how our brains communicate and how it affects our thoughts and actions.