Lecture 4 - Circadian Rhythms and Sleep Flashcards
How is the endogenous molecular pacemaker called that drives daily rhythms affecting physiology, biochemistry, behaviour and other functions?
The circadian clock.
What are oscillations?
Oscillations are activity patterns.
Can single cells hold the complete network forming cell-autonomous clocks?
Yes.
Flies aren’t active with bright light and dark, but they are active in dusk and dawn. The fly anticipates the lights going on and off by rising and falling activity level.
What does this tell us?
This tells us that there’s a clock telling the fly what to do.
What’s the difference between ‘free run’ and ‘entrainment’?
Free run = a biological rhythm exists without any external input or cues.
Entrainment = a biological rhythm is synchronised to an external (e.g. light/dark) oscillation.
Entrainment allows organism to adapt.
What are some external oscillations for entrainment?
Light is the strongest entrainment.
Also, social-cues: different light-dark periods will cause flies to perform the cycle of their group.
Circadian systems are organised into three main parts: The core clock Input pathways Output pathways What do these parts do?
The core clock - keeps time.
Input pathways - synchronises the clock to the environment.
Output pathways - transmits information to temporally organise behaviour and physiology.
Negative feedback loop -
Day: per gets formed by … and degraded by … , but PP2A helps some of the per survive.
Night: per and … are formed, … prevents degradation of per by coming together as heterodimer. With help from … per-tim-Dbt enter nucleus and inhibit … .
Dawn: light activates … and degrades tim (after being ubiquinated by F-box protein Jet). There’s no protection for … without tim, so it gets degraded by Dbt. The inhibition of … is lifted.
Day: per gets formed by Clk/Cyc and degraded by Dbt, but PP2A helps some of the per survive.
Night: per and tim are formed, tim prevents degradation of per by coming together as heterodimer. With help from CK2 per-tim-Dbt enter nucleus and inhibit their own transcription.
Dawn: light activates cryptochrome (Cry) and degrades tim (tafter being ubiquinated by F-box protein Jet). There’s no protection for per without tim, so it gets degraded by Dbt. The inhibition of Clk/Cyc is lifted.
What role does Shaggy (Sgg) play in the negative feedback loop?
Shaggy binds to Cry and this way prevents Tim from degradation by light.
Adaptation to environment:
The rising and the setting of the sun is not the same every day. Several input factors (zeitgebers) harmonise the clock neurons to the environment.
Name a few Zeitgebers.
Light, temperature, social-cues, magnetism, etc.
How does light (most important zeitgeber) reach the clock neurons?
Via photoreceptive organs containing rhodopsins –> eyes, ocelli, and Hofbauer-Buchner eyelets (HB-eyelets).
The role of pigment dispersing factor (PDF) neurons:
An … of the clock.
Coordination and synchronisation of … of the clock neurons when external … are absent (an internal …).
Phase the … of the clock neurons and the … to the right time of the day under light/dark.
A … and arousal factor of the clock.
An output transmitter of the clock.
Coordination and synchronisation of oscillations of the clock neurons when external signals are absent (an internal Zeitgeber).
Phase the oscillations of the clock neurons and the activity peaks to the right time of the day under light/dark.
A light-input and arousal factor of the clock.
What is one word to describe the function of PDF neurons?
Instructive.
Name a few morning-cells and describe their role.
PDF-expressing neurons: sLNv and lLNv.
They promote arousal/behaviour during the light period.
They are necessary for morning anticipation
What happens when M-cells are activated at night?
What happens when M-cells are completely removed?
Activation of M-cells (e.g. lLNv) disrupts night-time sleep.
Removal of M-cells increases sleep and causes a substantial reduction in morning anticipation.
