Complex sentence: Many types of neurons emit action potentials constantly at rates of up to 10--100 per second; some types, however, are much quieter, and may go for minutes or longer without emitting any action potentials.
Split into simpler sentences: Many types of neurons emit action potentials constantly at rates of up to 10--100 per second. However, some types are much quieter, and may go for minutes or longer without emitting any action potentials.