Exogenous zietgebers

Question 1

These are external environmental stimuli such as

Answer 1

Light and social cues (seasons work etc) that work with endogenous pacemakers
They help to synchronise the internal body clock with the outside world (entrainment)

Question 2

The SCN is reset every morning by light onset

Visual receptors in the retina part of the eye receive the light signal and active the retinohypothalamic tract pathway

Answer 2

This pathway alerts the SCN and pineal glamd effecting melatonin production
Daylight inhibits the release of melatonin and darkness leas to gradual increases