Neurophysiology and Information Christopher Fiorillo BiS 527, Spring 2010 042 350 4326,
[email protected] Part 4: Synaptic Transmission Reading: Bear, Connors, and Paradiso Chapter 5 Or any other neuroscience textbook. A Single Neuron with Synapses in Yellow Synapses Are Physical Contacts between Neurons that Enable Fast Transmission of Information • Types of Synaptic Contacts – Axodendritic: Axon to dendrite – Axosomatic: Axon to cell body – Axoaxonic: Axon to axon – Dendrodendritic: Dendrite to dendrite Two Types of Synaptic Transmission • Chemical Transmission – 1921- Otto Loewi • Electrical Transmission – 1959- Furshpan and Potter • There was a long-lasting debate about whether transmission was chemical or electrical. Both occur, but chemical transmission is much more common. Direction of Information Flow • Information usually flows in one direction – First neuron = Presynaptic neuron – Target cell = Postsynaptic neuron Postsynaptic neuron Presynaptic neuron Electrical Synapses Are Composed of Gap Junctions • Gap junction are large channels – Large enough (1-2 nm) to allow all ions plus other small molecules to pass – A Connexon spans the membrane - formed by six connexin proteins • Cells are said to be “electrically coupled” – Flow of ions from cytoplasm to cytoplasm Electrical Synapses • Very fast transmission – Chemical transmission has a delay • Postsynaptic potentials (PSPs) have the same form as the presynaptic potential, but are smaller • Most electrical synapses are bidirectional, but some are unidirectional A Chemical Synapse