BIOL273 Lecture Notes - Neuroglia, Myelin, Axoplasmic Transport

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3 Feb 2013
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1e The Chemical synapse
How are signals transmitted between cells?
- neurons join to other neurons by gap junctions( set of holes through the membranes that allow
electrical signals to pass through from one cell to the other) = electrical synapses
- most neurons communicate with other cells CHEMICALLY through CHEMICAL synapses
- illustration in notebook
- synapse: presynaptic axon terminal, synaptic cleft, postsynaptic dendrite
- presynaptic cell: cell that releases the NT
- postsynaptic cell: binds the NT
- space between the two = synaptic cleft (interstitial fluid)
- when NT binds to receptor , it can initiate graded potentials (either depolarizing 'excitatory
postsynaptic potential EPSP' or hyper-polarizing 'inhibitory postsynaptic potential IPSP') >
receptor is ligand-gated channel
Neurotransmitters and Receptors
- amount of NT bound to receptors is in equilibrium with the amount that is free in the synaptic cleft
- any factor that decreases the amount of free NT reduces the no. of NT-bound receptors:
1) diffusion out of synaptic cleft (NT)
2) degradation by enzymes in the cleft
3) uptake by glial cells or re-uptake by the presynaptic cell (recycle)
- only one kind of NT releases and one kind of receptor
- in any synapse there's only one kind of GP(signal) to be produced(transmitted) : either excitatory
postsynaptic potential or inhibitory postsynaptic potential (not both)
- a single neuron can have up to 10,000 synapses !!! ^
- a single axon can have multi branches (axon terminals), a single AP can bring about the release
of diff NTs at diff chemical synapses
- pre synaptic inhibition vs. pre synaptic facilitation
- recently discovered that postsynaptic cell can signal the presynaptic. Allows a bidirectional
exchange of information:
- presynaptic cell axon terminal is converting electrical signals into chemical signals
because the more action potentials it receives the faster it arrives the more NT is
released
- postsynaptic membrane does the opposite, incoming chemical signals (NT) are
converted to electrical signals (GP)
- the more NT the greater the amplitude of those electrical signals that are
generated at the post-synaptic membrane
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