Circadian Rhythms

What are the four different types of biological rhythms?

Ultradian: repeat multiple times in 24 hours

Circadian: repeat every 24 hours

Infradian: repeat over the course of days - weeks

Circannual: repeat around once per year

What is a circadian rhythm?

An endogenously generated biological rhythm that occurs approx. every 24 hours without external cues, but which can be entrained in response to external cues.

What is an actogram and how do you interpret it

A graph to visualize an aniaml’s rhythmic activity over time

At the top it will show when it is light (white) and when it is dark (black)

Lack of bars show periods of rest while activity is in frequent black histogram bars.

“Free-running” definition

Refers to when an animal is maintaining a rhythm a behavior in the absence of external

What genes make up the core molecular clock

Period and clock are two examples

How do proteins PER and CRY regulate circadian rhythms

• CLOCK BMAL 1 are transcription factors that can bind together and enter the nucleus to promote the expression of the genes PER and CRY

• The genes PER and CRY are transcribed into mRNA and then mRNA exits the nucleus

• the mRNA is then translated (by ribosomes) into proteins (PER and CRY) that are located in the cytoplasm

• PER and CRY can dimerize and enter the nucleus at night nucleus at night where they interact with CLOCK and BMAL 1 to suppress their own transcription = negative feedback loop

• PER and CRY proteins degrade which allows CLOCK/BMAL 1 to start the cycle over again

What is the suprachiasmatic nucleus (SCN)? What role does it play in circadian rhythms?

• Part of the anterior hypothalamus

• Serves as the central pacemaker for the body

How does the SCN receive light information?

• retinal ganglion cells that contain the photopigment melanopsin and are separate from retinal ganglion cells that receive information ultimately from rods and cones that are important for vision