Biological RhythmsII

8/3/2019 Biological RhythmsII

1/49


2/49


3/49


4/49


5/49


6/49


7/49


8/49


9/49


10/49


11/49


12/49


13/49


14/49


15/49


16/49


17/49

mating


18/49

Variations in physiology


19/49

Types of biological rhythms


20/49

Causes of bio-rhythms

Proximate causes

Endogenous vs. Exogenous clocks

Ultimate causes


21/49

Proximate causes

How can animals achieve bio-rhythms?

Alternative 1: They have an internal clockthat regulate these activities (endogenous

clock) Clock runs independently from environment

Alternative 2: They use environmental

cues to base their behaviors on(exogenous clock) Clock depends on environment


22/49

Mating calls of male crickets


23/49

Terminology

Entrainment :: when an external cue isused to calibrate the endogenous clock

Zeitgeber (time-giver) :: the external cuethat is used in entrainment

Example: cricket entrainsto light; light isthe zeitgeberfor the mating call


24/49

Proximate causes

How can animals achieve bio-rhythms?

Alternative 1: endogenous clock

Alternative 2: exogenous clock

Answer: clock mechanism have both

endogenous and exogenous components!


25/49

Proximate causes

Endogenous / exogenous

Take a deeper look:

Sensory systems

Clock nucleus

Clock mechanism


26/49

Model of internal clock

Zeitgebers


27/49

Types of Zeitgebers ::time-givers

Light

Temperature

Cycles of moon Social cues

Food

Rain And more!


28/49


Non-image formingPhoto-receptors


29/49

Clock-setting: Sensory receptors

Non-image formingphoto-receptor--melanopsin


30/49

Proximate causes

Sensory systems

Non-image forming retinal cells

Rods and cones NOT required for

entrainment

Clock nucleusMelanopsin and the

three blind mice


31/49


Suprachiasmaticnucleus(SCN)


32/49

Clock nucleus


33/49

Clock nucleus: Summary

Destroy SCN arrhythmic patterns inphysiology and behavior (Zucker, 1983)

Implant SCN into arrhythmic hamsterssome regain circadian rhythm (DeCoursey

et al., 1989)

Conclusion: evidence that SCN is themaster clock


34/49


?


35/49

Clock nucleus: SCN output

Criterion:

Time-regulatedproduction in SCN

Receptor proteins attarget tissue

Experimentaladministration disruptsnormal cycle

Subst.: Prokineticin(PK2) (Cheng et al, 1992)

PK2 is produced in a

strongly circadianpattern

SCN-projected regionsproduce receptorproteins

PK2 injections lead todisruptions of normalcycle


36/49

Proximate causes

Sensory systems

Non-image forming retinal cells

Rods and cones NOT required for entrainment

Clock nucleus SCN is the master clock

PK2 as (candidate) SCN output

Clock mechanism

How do SCN cells keep time?

Genetic mechanism


37/49

Clock mechanism: pergene

pergene codes for PER protein

PER protein builds up

Enters nucleus inhibits expression of pergene!

(negative feedback loop) Enzyme casein kinase 1 (CK1) breaks down

PER protein

Slows PER build up

timgene codes for TIM protein PER + TIM = resilient to breakdown

Cycle of gene expression and protein production with negative


38/49

Cycle of gene expression and protein production with negative

feedback on gene expression is the basis of the circadian clock.

Per when conjugated to TIM and CRY can not be broken down

easily. But eventually it is broken down and then a new cycle of

PER production starts.


39/49

Clock mechanism: pergene mutations


40/49

Proximate causes: Summary

Endogenous clock Entrained by exogenous cues (zeitgebers)

Sensory receptors

Rods and cones Non-image forming sensory receptors

Master clock nucleus: SCN

SCN output: chemical messengers

PK2 Genetic components:

PER expression


41/49

Ultimate causes

Environment

Why entrainment?

Preparing for activities Doing things at the right time


42/49

Why endogenous?

Question: Why did we evolve anendogenous clock anyway?

If environmental cues (e.g. day/night) cycle is

so regular, why dont we use exogenous clues


43/49

Why endogenous?

Endogenousclocks that entrain toexogenouscues allows for flexibility Imagine if the sun didnt come up (e.g. Artic circle)

Allows some independence from environment

This system allows for regularity in aoften/(in case) noisy environment


44/49

Preparation for activities

Growl that was what your stomach just made

Most of you eat lunch about this time on aregular basis Growl = body preparing for food

Physiological changes must occur to help withdigestion Redirect flow of blood, increase levels of enzymes,

etc

Body needs to warm up :: just like your car

Preparations help with digestion


45/49

Preparation for activities

Your body prepares for other activities: Sleeping, waking, mating

These activities entail their own

physiological demands/state Energy, body temp, etc.

Body regularlyprepares itself for these

activities so they can occur at the righttime e.g. eat lunch at noon, 5am sleep


46/49

Ultimate causes

Environment Temporal regularity in environment

Why entrainment? Allows for regularity in a noisy environment

Preparing for activities Body prepares you so you can do things at the right

time

How does your body know what the right time

is? Ex: Predator vs. prey Social reasons


47/49

Body knows best

Predator / prey :

Predator :: eat!

Predator eat when prey is most vulnerable (i.e. sleep)

Prey :: dont be eaten! Rat that was asleep when owl was around died out

Social reasons:

Need to mate when others are active

Rats that were asleep when everyone else wasmating didnt pass on their genes

Knowing when to mate : tomorrow


48/49

Summary

Proximate causes

Endogenous clock entrained with exogenouscues

Sensory receptors specifically for time

SCN :: master clock

Controls lots of systems

Clock driven by pergene a gene driving behavior


49/49

Summary

Ultimate causes

Environmental regularity bio-rhythms

Body prepares for activities

Body does activities at the right time

Biological RhythmsII

Documents