An Introduction to Neurotransmission William Wisden Dept of Clinical Neurobiology INF 364
Fundamental Neuroscience - second edition Squire, Bloom, McConnell, Roberts, Spitzer, Zigmond Academic Press, Explore the Brain and Spinal Cord The Neuron
A neuron
The action potential
Hodgkin & Huxley, 1939
Rate of action potential firing is information
The dendrite
Differences between axons and dendrites AxonsDendrites Take information away from the cell body Bring information to the cell body Smooth Surface Rough Surface (dendritic spines) Generally only 1 axon per cell Usually many dendrites per cell No ribosomes Have ribosomes Can have myelin No myelin insulation Branch further from the cell bodyBranch near the cell body
Dendrites constitute a kind of neural microchip for complex computations
Rate of action potential firing is information Frequency code of impulses within the axons Place/topological code depending on which axons are active
Chemical synapse Axon-dendriteAxo-axonicAxon-soma
Passing information between neurons Gap junctions -electrical transmission fast both directions Chemical transmission slower - unidirectional integrative amplifies and regenerates the signal
The synapse
IN OUT Calcium entry is excitatory Calcium is a second messenger which binds to target proteins e.g. Calmodulin
Axon Terminal Spine Dendrite Action potential Ca2+ Diffusion of Neurotransmitters Across the Synaptic Cleft Neurotransmitter Mobilization and Release Electrical Trigger for Neurotransmission
Ca2+ Action potential Depolarization
Electrical properties
How is the action potential generated?
EXCITATORY + INHIBITORY - IN OUT
Look at the animation!
Neurotransmitters
Excitatory Inhibitory Excitatory
Simple transmitters: -aminobutyric acid (GABA) glutamic acid (glutamate) acetylcholine (Ach)
OUT IN Acetylcholine receptor Cl - GABA A receptor GABAGABA Inhibition Na + Glutamate/AMPA receptor G lu Excitation Na + AChACh
Neurons and glial cells
The process of chemical neurotransmission can be divided into five steps 1. Synthesis of the neurotransmitter in the presynaptic neuron 2. Storage of the neurotransmitter and/or its precursor in the presynaptic nerve terminal 3. Release of the neurotransmitter into the synaptic cleft 4. Binding and recognition of the neurotransmitter by target receptors 5. Termination of the action of the released transmitter
Life cycle of a neurotransmitter
An excitatory (glutamatergic) synapse
A synapse using -aminobutyric acid (GABA)
A synapse that uses acetylcholine (ACh)
Simple circuits
Feed-forward inhibition
Negative feedback Feedback inhibition
Neocortex Interneuron - uses GABA Pyramidal neuron - uses glutamate
Ionotropic and metabotropic receptors Fast Ion flow in/out milliseconds Slow Second messenger cascades seconds
Ionotropic Metabotropic
OUT IN Cl - Na + GABA A receptorGlutamate/AMPA receptor GABAGABA G lu Inhibition Excitation
Neuromodulators Slow synaptic transmission