The Human Brain : From Neurone to Nervous System

DENDRITIC SPINE SYNAPSES : STRUCTURAL AND FUNCTIONAL PLASTICITY


  1. The effectiveness of some synapses depends on the the previous level of activity. If the synapse has previously been active, the size of the EPSP is increased : this is called long-term potentiation (LTP). If the synapse has previously been inactive for a time, the size of the EPSP is decreased : this is long-term depression (LTD).

  2. LTP and LTD have been described in various sites including (a) the dorsal horn of the spinal cord and (b) the cerebral cortex, where they appear to be involved in (a) modulation of nociceptive transmission and (b) in memory. In both sites, specialised synaptic structures are present: synaptic glomeruli in the sperficial dorsal horn, and dendritic spine synapses in the cortex, striatum and cerebellum.

  3. The dendrites of neurones in the cerebral cortex, the cerebellar cortex and the basal ganglia have specialised structures called dendritic spines, which are the site of synapses which can modify their synaptic strength. They appear to be involved in learning and memory.

  4. Many of these synapses are glutamatergic, and the changes in their effectiveness are attributable to pre-and post-synaptic mechanisms.

  5. Dendritic spines are small protrusions of cell membrane and cytoplasm from the dendrites of neurones and are commonly found in pyramidal cells of the cerebral cortex, Purkinje cells of the cerebellum, medium spiny neurones of the corpus striatum.

  6. The dendrites of these neurones are covered with spines, each of which is the site of a synaptic contact with an afferent neurone.

  7. Their synaptic strength can adapt to repeated inputs, a process known as long-term potentiation (LTP), and the adaptation is believed to be a mechanism for information storage.

  8. The superficial layers of the dorsal horn contain specialised synapses called glomeruli that are involved in modulation of nociceptive messages.





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