Saturday, August 14, 2010

Betz Cells

Betz cells are pyramidal neurons which are situated in the fifth layer of the primary motor cerebral cortex. They are named after Vladimir Alekseyevich Betz, who described them in his work published in 1874. These neurons are the largest in the central nervous system, sometimes reaching 100 ┬Ám in diameter, and have the longest axons.

Betz cells send their long axons down to the spinal cord where they establish synapses directly with spinal cord anterior horn cells, which in turn synapse directly with their target muscles. While Betz cells have one apical dendrite typical to pyramidal neurons, they have more primary dendritic shafts, and these do not leave the soma only at basal angles but rather branch out from almost any point asymmetrically. These perisomatic and basal dendrites project into all cortical layers, but most of their horizontal arbors populate layers V and VI, some reaching down into the white matter. According to one study, Betz cells represent about 10% of the total pyramidal cell population in layer Vb of the human primary motor cortex.