Final answer:
Betz cells are a type of neuron in the primary motor cortex and contribute to the corticospinal tract. They are a small fraction of the total fibers and are significant for their role in motor functions, not their quantity.
Step-by-step explanation:
Betz cells, also known as Betz pyramidal cells, are a type of neuron found in the primary motor cortex of the brain. They are particularly well-known as they are among the largest cells in the central nervous system and play a critical role in motor functions by sending signals that initiate muscle movement. Quantifying the exact percentage of fibers composed of Betz cells is complex and requires nuanced understanding of neuroanatomy. Typically, Betz cells contribute to the corticospinal tract, which is responsible for voluntary motor control. Although they are quite large and significant in function, in terms of sheer numbers, they represent only a small fraction of the total fibers in the motor system.
There isn't a widely recognized exact percentage of total fibers that Betz cells make up, as the total number of fibers in the brain is immense and varies from person to person. Moreover, the function and prominence of Betz cells are more characteristically defined by their role and size rather than their quantity relative to other cells. Therefore, it is more pertinent to understand the functional implications of Betz cells in motor control rather than focusing solely on their numerical proportion in the fiber system.