The Human Brain : From Neurone to Nervous System

SYNAPSES


  1. A Synapse is a close functional contact between the membranes of an axon terminal and another nerve cell, and a site of cellular communication.

  2. There are some similarities between central synapses and the neuromuscular junction (NMJ) - the motor end plate - particularly in the mechanisms by which transmitters are released. At most central synapses there may be some thickening but no repeated folding of the post-synaptic membrane comparable to that at the NMJ.

  3. The commonest transmitters in the CNS are glutamate (excitatory) and GABA (Gamma-Amino-Butyric Acid, inhibitory), and a single afferent impulse arriving at a synapse usually produces only subthreshold changes in the post-synaptic membrane potential. Excitatory transmitters depolarise and inhibitory transmitters hyperpolarise the membrane.

  4. The generation of action potentials depends on the algebraic sum of sub-threshold depolarisations and hyperpolarisations; when the axon hillock reaches threshold, and only then does the axon fire action potentials.

  5. Key Words: Glutamate, excitation (EPSP); GABA, inhibition (IPSP); summation of subthreshold events





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