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Pyramidal cells, or pyramidal neurons, are a type of multipolar neuron found in areas of the brain including the cerebral cortex, the hippocampus, and the amygdala. Pyramidal cells are the primary excitation units of the mammalian prefrontal cortex and the corticospinal tract .
There is also a distinct pathway from layer 3 of the EC directly to CA1, often referred to as the temporoammonic or TA-CA1 pathway. Granule cells of the DG send their axons (called "mossy fibers") to CA3. Pyramidal cells of CA3 send their axons to CA1. Pyramidal cells of CA1 send their axons to the subiculum and deep layers of the EC.
The pyramidal tracts include both the corticobulbar tract and the corticospinal tract.These are aggregations of efferent nerve fibers from the upper motor neurons that travel from the cerebral cortex and terminate either in the brainstem (corticobulbar) or spinal cord (corticospinal) and are involved in the control of motor functions of the body.
These are the corticobulbar and corticospinal fibers that make up the pyramidal tracts. About 90% of these fibers leave the pyramids in successive bundles and decussate (cross over) in the anterior median fissure of the medulla oblongata as the pyramidal decussation or motor decussation.
The pyramidal cells in CA3 have a unique type of dendritic spine called a thorny excrescence or thorn, only found in CA3 pyramidal cells and hilar mossy cells. The thorn has a thin single spine with a number of heads. Clusters of thorns sit on a dendrite on a broad stem.
It is the tract of the mossy fiber projections, both inhibitory and excitatory from the granule cells of the dentate gyrus. One mossy fiber may make up to 37 connections to a single pyramidal cell, and innervate around 12 pyramidal cells on top of that. Any given pyramidal cell in the stratum lucidum may get input from as many as 50 granule cells.
Betz cells are not the sole source of direct connections to those neurons because most of the direct corticomotorneuronal cells are medium or small neurons. [3] While Betz cells have one apical dendrite typical of pyramidal neurons, they have more primary dendritic shafts, which can branch out at almost any point from the soma (cell body). [4]
An apical dendrite is a dendrite that emerges from the apex of a pyramidal cell. [1] Apical dendrites are one of two primary categories of dendrites, and they distinguish the pyramidal cells from spiny stellate cells in the cortices.