I haven’t heard of a clocking mechanism in brains, but signals propagate much slower and a walnut / crow brain is much larger than a cpu die.
Brain waves (partially). They aren't exactly like a cpu clock, but they do coordinate activity of cells in space and time.
There are different frequencies that are involved in different types of activity. Lower frequencies synchronize across larger areas (can be entire brain) and higher frequencies across smaller local areas.
There is coupling between different types of waves (i.e. slow wave phase coupled to fast waves amplitude) and some researchers (Miller) thinks the slow wave is managing memory access and the fast wave is managing cognition/computation (utilizing the retrieved memory).
Nerve signals are both chemical reactions and electrical impulses like metal wire. Electrical impulses are sent along the fat layer by ions Potassium , Calcium, Sodium etc.
Twitch responses are actually done in spinal cord. The signals are short circuited all along the spine and return back to muscle without touching the brain ever.