Mossy Fiber

2022-09-25:

Mossy Fiber #

• At least in the hippocampus, mossy fibers are axons projecting from Dentate Gyrus Granule Cells that terminate on the CA3.
• There are also mossy fibers that terminate in the cerebellum, which originate from the cerebral cortex, spinal cord, and some other areas.
• Unmyelinated.
  • So I’m gonna guess they have a high degree of ephatic coupling ( Ephaptic coupling in cortical neurons (epthatic: adjacent fibers exchanging ions))
    • On Rhythms of the Brain: Jhanas, Local Field Potentials, and Electromagnetic Theories of Consciousness
      • Consciousness Is a Thing, Not a Process (Pockett, 2017)
        • In this she specifically talks about neocortical Pyramidal Cells
        • Feed-back produces relatively large LFPs, while feed-forward activity doesn’t.
        • 
          • (I really barely have any idea what I’m looking at here)
          • Figure 1. Genesis of local field potentials (LFPs). (A): LFPs are basically population excitatory postsynaptic potentials (EPSPs) that are generated by synaptic action on the apical dendritic tufts of pyramidal cells. When presynaptic terminals (not shown) release neurotransmitter at site B, positive ions enter the postsynaptic dendrite, leaving a transient negative ‘hole’ in the extracellular fluid. To ‘complete the circuit’ an equal number of positive ions exit the postsynaptic cell nearer the cell body. This process can be modelled as a large equivalent dipole. (B): Cartoon showing how the negative poles of the smaller dipoles representing entry of positive ions to the postsynaptic dendrites of many synapses can summate to produce the large extracellular voltage transients seen as LFPs (green area). This summation only happens when two conditions are met: (1) many synapses are active synchronously, and (2) the postsynaptic dendrites are anatomically aligned, so that the negative poles of the small dipoles overlap spatially. This explains why large LFPs are not produced during feedforward synaptic activity. Feedforward activity goes mostly through the stellate cells in Layer 4, which do not have anatomically aligned dendrites. Large LFPs are generated only during synchronous feedback synaptic activity, as illustrated in (B).