Tuesday, 7 May 2013

Neuroanatomy - Neurons and Glia



Neurons and glia 

Neuron -
  • electrical signalling,
  • large,
  • round cell body (soma, perikaryon),
  • axons,
  • dendrites,

Axon transport:
Axoplasmic flow:
  • slow transport of enzymes and cytoskeletal components,
  • filaments,
  • microtubules. 1-5 mm/day.

    Fast axonal transport:
·        transport of membrane bound organelles (neurosecretory vesicles).
·        uses microtubule network and molecular motors (e.g. kinesin).
·        400 mm/day

Myelin (axons) - Schwann cells in PNS, Oligodendrocytes in CNS
In PNS each internode approx 1mm. One schwann cell = one internode
In CNS each oligodendrocyte can myelinate up to 50 axons (20 average). Demyelination => Multiple sclerosis


Neurones:
Multipolar (large with long dendrites) -
  • motor neurons,
  • Purkinje cells

Unipseudopolar -
  • sensory neurons,
  • no true dendrites, - dorsal root ganglion neurons

Bipolar -
  • short process (axons and dendrites equal) -
  • certain interneurons,
  • retinal bipolar cells

Glia:
  • smaller than neurons.

Macroglia:
·        schwann cell,
·        oligodendrocyte,
·        astrocyte,
·        ependymal cells.

Microglia (macrophages)

Oligodendrocytes = small cell body. intrafascicular oligodendrocytes, satellite oligodendrocytes (non-myelinating)

Astrocytes =
  • star shaped,
  • large number of highly branched long and short processes,
  • found in grey and white matter.
  • Forms interspersed meshwork surrounding all other elements (gap junctions, glial limitans, blood brain barrier).
  • Functions: removal of neurotransmitter from extracellular space around synapse, regulation of extracellular K+ , scaffold for migrating neuroblasts. disease => gliosis, glioma

Ependymal cells =
  • glia which line the ventricles and central canal,
  • cuboidal morphology,
  • ciliated