Fossils of isolated land plant spores (Heckman et al, 2001) suggest land plants may have been around as long as 475 million years ago; Fossils of land plant spores within plant fragments (Wellman et al., 2003) date back to 425 million years ago ( these were found in Oman and appear to be liverwort-like, although elaters are noticeably absent!)
The noun PUPILLARY REFLEX has 1 sense: 1. reflex contraction of the sphincter muscle of the iris in response to a bright light (or certain drugs) causing the pupil to become smaller. Familiarity information: PUPILLARY REFLEX used as a noun is very rare. Dictionary entry details.
A withdrawal reflex, also known as a flexor reflex, is a polysynaptic reflex arc. Sensory and motor neurons are part of this reflex, as are association neurons. Pain is the most obvious stimuli that initiates the flexor reflex, as painful stimuli sets the whole reflex into action. reflex arc is in fact the simplest and most primitive nerve pathway in the human body. A reflex arc is designed to administer unconscious automatic actions which are determined to be protective in nature to keep a body in homeostasis.