Which statement about cerebrospinal fluid (CSF) is correct?

1. CSF is a by-product of nerve cell activity.
2. CSF production is sped up during a seizure.
3. CSF flows from the lateral ventricles toward the fourth ventricle.
4. CSF is produced within the venous sinuses.
5. CSF is produced in the fourth ventricle and flows toward the fifth ventricle.