Answer: Betz cells in the primary motor cortex are the largest cells in the brain, with a cell soma area of about 1 mm.
Betz cells are a unique population of neurons that exist in layer 5b of the primary motor cortex (M1). About 10% of all cells in layer 5b are Betz cells. They are excitatory neurons, and synthesize and release the neurotransmitter glutamate. Betz cells receive inputs from area 6, the somatosensory cortex and the thalamus.
As pyramidal cells in M1, Betz cells are the cells that represent the output of this gray matter. They are upper motor neurons, and they send their axonal projections down the corticospinal tract to the appropriate level of the spinal cord. In addition to being some of largest somata among neurons, they also have very long axons
Betz cells were first described in 1874 by the Ukranian scientist Vladimir Betz.