How does an electrical impulse travel from one neuron to the next (IB-SL 6.5)?
- The arrival of an action potential at the synaptic knob opens calcium ion channels in the pre-synaptic membrane and Ca++ flow in from the synaptic cleft 2. Ca++ cause vesicles of neurotransmitters to fuse with the pre-synaptic membrane and release transmitter substance into the synaptic cleft by exocytosis 3. Neurotransmitter diffuses across the synaptic cleft and binds with receptor proteins. In the post-synaptic membrane there are specific receptors for each neurotransmitter. They also act as channels for ions to pass. The attachment of a neurotransmitter to the receptor opens the ion channel. As the sodium ions rush into the cytoplasm of the post-synaptic neuron depolarisation of the post-synaptic membrane occurs (until threshold level is reached, facilitation). An action potential is generated along the post-synaptic neuron. 4. The neurotransmitter is inactivated by enzyme complex and resting potential is re-established 5. The inactivated products from the transmitter re-enter the pre-synaptic knob are resynthesized into neurotransmitters and packages for reuse.
