• Transduce chemical signals into electrical signals
• Allow for rapid response
• Important for electrically excitable cells such as nerves or muscles

Function

1. Channel protein in closed conformation so ions cannot pass
2. Ligand binds to ligand binding site
3. Channel protein changes to open conformation so ions can now pass and cause a cellular response
4. Ligand leaves
5. Channel changes back to closed conformation and ions can no longer pass

Role of Ligand-gated Ion Channel in Synaptic Transmission

1. Action potential travels down presynaptic axon
2. Cargo vesicle fuses with presynaptic plasma membrane and releases neurotransmitters
3. Neurotransmitters (ligands) bind to ligand-gated ion channel in postsynaptic cell membrane opening the channel
4. When enough ions pass into the postsynaptic cell, voltage-gated ion channels open
5. More ions pass through these channels, further changing the membrane voltage and opening voltage-gated channels further along the membrane
6. This depolarization (action potential) travels along the membrane to the next synapse continuing the signal transmission

Types of Ligand-gated Ion Channels

Excitatory

• Na+ channels – allow positive ions into the cell depolarizing the membrane and driving it closer to firing an action potential

Inhibitory

• Cl- channels – allow negative ions into the cell making it harder for the membrane to depolarize
• K+ channels – allow positive ions out of the cell making it harder for the membrane to depolarize