Definitions

Question 1

Zeitgeber

Answer 1

A rhythmic signal capable of entraining circadian clocks.

Question 2

Free-running period

Answer 2

Behaviour of internal clocks under Zeitgeber‐free conditions. When free‐running, circadian rhythms cycle with their endogenous period which usually deviates from 24 hours.

Question 3

Entrainment

Answer 3

The coordination of a self‐sustained oscillator via rhythmic signals from a pacemaking oscillator (i.e. a zeitgeber)

Question 4

Phase angle

Answer 4

Phase angle of entrainment is defined as the relationship between the timing of the biological clock and the timing of an external time cue (i.e., zeitgeber)

There can be a difference between the entraining cycle and the entrained rhythm. This difference can be measured by selecting a point in the entraining cycle (e.g. light on), and a phase reference point in the resulting rhythm (e.g. the onset of a particular activity/e.g. waking up). The difference between these two points is known as the phase angle.

Question 5

Chronotype

Answer 5

the internal circadian rhythm or body clock of an individual that influences the cycle of sleep and activity in a 24-hour period

Question 6

Negative Feeback

Answer 6

Negative feedback is achieved by PER:CRY heterodimers that translocate back to the nucleus to repress their own transcription by inhibiting the activity of the CLOCK:BMAL1 complexes.

Question 7

Phase Response Curve

Answer 7

The curve illustrates the shift in circadian rhythm (phase shift) in response to a stimulus, e.g. light exposure.

Question 8

Temperature compensation

Answer 8

Circadian clocks have a remarkable capacity for temperature compensation, which renders clock output largely insensitive to environmental temperature fluctuations (i.e., providing for constant periodicity in the face of the wide swings of temperature that most organisms experience daily and seasonally).