Biological Rhythms - Exam #1


Biological Rhythms (1)

Rhythms with two defining characteristics: 1) they recur at regular intervals and 2) they are generated by a biological organism. They are grouped according to their period and named after their frequency. (1)


A rhythm with a period less than 24 hours


A rhythm with a period approximately 24 hours


A rhythm with a period greater than 24 hours


In the 1729, a French geophysicist/
astronomer named Jean-Jacques d'Ortous
de Mairan became interested in the leaf
movements of the ________ plant - leaves
open during the day and close at night (first evidence that biological rhythms are endogenous)


a reccurent event. can be characterized by its period, frequency, amplitude, and phase


the length of time required to complete one cycle of the rhythm (the amount of time from peak to peak or trough to trough)


the number of completed cycles per unit of time


the amount of change above and below the average value


represents a point on the rhythm relative to some reference time point during the cycle

phase relation

where you are in relation to another rhythm, which can be a biological or environmental rhythm


claims resistance to change, maintenance of "set points", bounce back after unpredictable events

Biological Rhythms (2)

claims programmed changes, ensures variability, and allows preparation for predictable events (2)


Input from environment --> Clock (internal time keeping machine) --> Output to rest of body


a rhythm in an animal when exogenous cues have been removed


if a rhythm is not generated by an endogenous clock or it has not been tested, we use a more ______ term like daily rhythm, seasonal rhythm, etc.


the environment matches the endogenous rhythm to the external environment in a process called __________


stimuli that entrain biological rhythms (time-givers)

generate, entrain, communicate time information

endogenous clocks ________ the rhythm, environmental cues ______ the rhythm of the clock to the environmental cycle, and the output systems ___________ ______ _________ from the clock to the body.

light-light, dark-dark, light-dark

LL, DD, LD (three terms separated by commas)

Period (tau)

the length of time required to complete one cycle of the rhythm


Greek letter meaning active phase


Greek letter meaning inactive phase

subjective day

the daytime portion of the organism's endogenous rhythm

subjective night

the nighttime portion of the organism's endogenous rhythm

double plotted actogram

a graphical representation of an animal's sleep-wake cycle in which the data has been plotted side by side with every other day repeating so the graph is easier to read


the time in which cycles are out of phase when an oscillator is entraining


any endogenous system capable to generating a self-sustaining rhythm in the absence pf rhythmic input


an oscillator capable of setting the period and phase of an overt rhythm

Circadian Rhythm(s)

Three Properties of ______________ ___________
1) self sustaining oscillators persist in constant conditions
2) oscillators take several cycles to entrain
3) oscillators can only entrain to cycle lengths close to their endogenous period.


(True/False) You can decide whether a certain rhythm is the result of an endogenous circadian oscillator by making sure it aligns with the Three Properties of Circadian Rhythms.

positive masking

induction of overt behavior without influencing the underlying clock is called _______ _________
ex. sounding a buzzer at the same time everyday

negative masking

suppression of overt behavior without influencing the underlying clock is called ________ _________
ex. placing an animal under anesthesia


(true/false) oscillators can manage rhythm of pacemakers, but pacemakers can only influence rhythm-less tissue


(true/false) entrainment adjusts period and phase

parametric entrainment

light acts through continuous modulation to entrain the circadian clock

non-parametric entrainment

light acts at discrete phases (dawn/dusk) to entrain the circadian clock through instantaneous phase shifts each day

Phase Response Curve (PRC)

a graph created by using the mean adjustment in period by giving a burst of light during different parts of a cycle depicting an animals limits of entrainment. it allows you to predict the behavior of an animal in response to light, whether it is a single

dead zone

Light pulses during the animal's subjective day fall in the ____ ____

phase delay

light pulses during an animal's early subjective night results in a ______ _______

phase advance

light pulses during an animal's late subjective night results in a ______ _________

period, phase

Light entrainment determines ______ and _______ (alphabetical, separated by commas)


(true/false) Entrainment on the positive slope of a PRC is not used because it would function as a positive feedback loop. if light hits the PRC shallower on positive slope, cycle would continue to delay

Aschoff's Rule (The Circadian Rule)

The rule that states that, in nocturnal animals, increases in light intensity increase tau (period) and decrease alpha (active phase). In diurnal animals, increases in light intensity decrease tau and increase alpha.

Activity, Arousal, Novelty

Three characteristics of novel wheel that might be critical for its zeitgeber effects: (alphabetical, separated by commas)


(true/false) exogenous melatonin can entrain animals if given in the early subjective day

food entrained

Evidence for an endogenous ________ ____________ oscillator:
1) pattern persists after removal of periodic feeding in constant conditions (food deprivation)
2) has limits of entrainment - feeding schedules between 22-31 hour cycles
3) exhibits transients

Partitioning, Synchronization

Two main categories of social influence on daily rhythms are temporal _________ and temporal __________ (alphabetical, separated by commas)

Circadian Pacemaker(s)

an endogenous self-sustained oscillator that imposes its period on, and dictates the phase of, other (subordinate) oscillators and/or non-oscillatory structures. The ____________ ___________ must also be connected to the external environment such that zei

b-mal, clock

The positive core clock genes are _________, __________, and rev-erb(alpha) (alphabetical, separated by commas)

cryptochrome, period

the negative core clock genes are ___________ and ____________. (alphabetical, separated by commas)