RELEASE

From spike to transmitter

1 A spike reaches the terminal and opens voltage-gated calcium channels

2 Calcium (Ca²⁺) flows into the terminal

3 Calcium triggers vesicles to fuse with the membrane, which is called exocytosis

4 The neurotransmitter spills into the cleft and diffuses across

Calcium is the trigger that turns an electrical signal into a chemical one.

WHAT HAPPENS NEXT

Four fates for transmitter

Released molecules do not stay long. They bind a receptor, get pumped back, get broken down, or drift away.

The message ends because the molecules are removed.

THE FATES

What each one means

🔒

Bind

Attach to a receptor and pass on the message

♻️

Reuptake

A transporter protein pumps it back into the terminal or nearby cells

✂️

Breakdown

An enzyme in the cleft chops it into inactive pieces

🌫️

Diffusion

It drifts out of the cleft and is cleared elsewhere

Different transmitters rely on different fates.

EXAMPLES

Each transmitter has a favorite

Dopamine, serotonin Mainly cleared by reuptake through their transporters, DAT and SERT

Acetylcholine Broken down very quickly by the enzyme acetylcholinesterase

Glutamate Taken up mostly by astrocytes using transporters

GABA Taken up by GABA transporters

Cleanup machinery is a common drug target.

WHY CLEANUP MATTERS

It sets how long a message lasts

Fast cleanup keeps each signal short and crisp. Blocking cleanup makes the transmitter linger and strengthens its effect. Cleanup is also why transmitter levels change in milliseconds to seconds, which is a big reason they are so hard to measure.

The off switch is as important as the on switch.

UNIT 4 STUDY COMPLETE

🧹

Ready for the Fab Challenge?

You've followed a neurotransmitter from release to cleanup and seen why cleanup shapes the signal.