Information Processing Within Neurons

Once information has been received by a neuron, the neuron needs to integrate its 10,000 inputs and make a binary decision: go or no go?

If the neuron needs to send information over a long distance, then the decision point is the axon hillock, where the nerve cell body gives rise to an axon. There, voltage-gated sodium and potassium channels are present, and if the electrical potential of the neuron at that point is at or above the threshold for triggering an action potential, then an action potential travels from the axon hillock to the axon terminals, where neurotransmitter release occurs.

If the neuron is only sending information locally, then an action potential may not be required. In this case, the decision point is each individual presynaptic contact. If the electrical potential at that point is sufficient to trigger enough voltage-gated calcium channels, then calcium enters the active zone cytoplasm, vesicles fuse with the presynaptic membrane, and neurotransmitter is released.

Objectives for this Part include:

1. Describe the salient features of signal transduction at the synapse.
2. Give examples of signal transduction by ionotropic receptors (ligand-gated ion channels).
3. Give examples of signal transduction by metabotropic receptors (G protein-coupled receptors).
4. Explain retrograde modulation of synaptic activity in presynaptic neurons.
5. Illustrate the properties of electrical synapses.
6. Summarize cable properties of neurons.
7. Describe how the events on the postsynaptic side of the synapse result in postsynaptic potentials.
8. State the principles underlying spatial and temporal summation of graded potentials.
9. Predict the function of a neuron from your knowledge of neuronal shape and information processing properties.