Synapse

 

This is the study of synapses. Synapses are junctions between neurons where they exchange neurotransmitters and also impulse traffic.

A synapse consist of the following

  • Presynaptic membrane
  • Synaptic grid
  • Synaptic cleft
  • Post-synaptic membrane
  • Presynaptic membrane

Contains the synaptosomes which are vesicles containing the secretory granules that carry neurotransmitters. The neurotransmitters are in different categories.

  • Acetylcholine:

  • Neuropetides: These include motilin, bombesin, insulin, calcitonin etc. Some are more of neuromodulators rather than neurotransmitters- eg insulin

  • Amine: These include catecolamines such epinephrine and norepinephrine, serotonin, histamine etc

  • Amino Acids: GABA- gamma amino butyric acid, glycine

  • Putative neurotransmitters. These include purinergic transmitters such as ATP

Nerves are also classified in relation to their contained neurotransmitters-

  • Cholinergic nerves
  • Purinergic
  • Gabaergic
  • Aminergic
  • Adrenergic etc

But what most neuroscientists may not be aware of is the fact all secretory granules of neurons contain at least one of the above substances. This include- calcium, ATP, a biogenic amine, a neuropeptide, lipid, which are packaged by the Golgi apparatus into one granule. Hence it may not necessarily hold to classify a nerve on the basis of only one of the component neurotransmitter unless it is clear that the neurotransmitter is the main component released from the synaptosome.

Synaptosomes are released directly into the synaptic cleft after they have passed the synaptic grid. They then pass through the synaptic cleft in order to impinge on the postsynaptic membrane, which they then depolarize. This then generates impulse traffic, which continues the transmission to the next axon.

The synaptic apparatus is placed at the bouton terminaux.

Synapse can occur at any part of the neuron. The commonest synapse is the axodendritic synapse, which is between the axon forming the presynaptic membrane and the dendrite forming the postsynaptic membrane.

Others are

1.                  Axo-axonal synapse

2.                  Axosomatal

3.                  Somatosomatal

4.                  Somato-axonal

5.                  Somato-dendritic.

 

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