Exam 2 Biopsychology: Lecture 8 Biological Rhythms

Circadian rhythms

Once a day rhythms

What physiological or cognitive processes do circadian rhythms influence?

Temperature, alertness, blood pressure, and hormone levels.

What does the circadian rhythm control and run on?

Runs on an approximate 24-hour cycle and controls sleep-wake cycles.

Nocturnal

Active most during dark

Diurnal

Active most during day

Crepuscular

Active at twilight

Matutinal

Active at dawn

The hamster running on its wheel where we measure how much it runs across the day. What would happen if we took away any signal

to the hamster that it was light or dark?

Under constant light (/dark) the hamster still runs at a set time of day suggests something is determining the rhythm

Biological clock

An internal timer in living organisms that regulates daily cycles

Free running

It happens without any cues for time where it happens a little later each day.

Free running period

Lets us measure the animal's natural biological controlled rhythm

Zeitgebers

Cues in the environment (meal time, light, changes in regular input) that prompt rhythm synchronization

When does melatonin begin to surge?

Prior to dark

When does cortisol begin to surge?

Before light/awakening

When does the growth hormone exhibit a peak?

Shortly after dark onset

Phase shift

When something prompts out rhythms to change (time zone)

Who was Richter (1967)?

Lesioned or removed various endocrine glands but no impact was found. Started looking at brain bases for rhythm.

Hypothalamus

Set of many brain nuclei that are essential for homeostasis.

What findings did Richter (1967) find about the brain?

Found that when he lesioned the hypothalamus it disrupted the circadian rhythm.

Who was Zucker and colleagues (1970s)?

Made the connection that destroying the suprachiasmatic nucleus (SCN) affects the circadian rhythm.

What happens if you harm the SCN?

Lesioning the SCN in the brain disrupts circadian and hormonal rhythms, but does not get rid of them.

Mutation tau

Drastically shortens the animal's internal circadian (body clock) rhythm through an inherited gene.

Retinohypothalamic pathway

Light information from the eyes directly reaches the SCN through this pathway

Pineal gland

In birds and amphibians, light is sensed here in the brain near a thin piece of skull.

Which specific type of neuron forms the retinohypothalamic tract, and what makes them unique compared to typical cells of their class?

ipRGCs are sensitive to light without needing input from rods or cones.

The axons of light-sensitive retinal ganglion cells project via the retinohypothalamic tract to which specific structure in the brain?

The suprachiasmatic nucleus (SCN) of the hypothalamyus (which regulates circadian rhythms).

What protein cells do ipRGCs express?

Melanopsin

What are the retinal inputs to the SCN?

ipRGCs

What light frequencies are ipRGCs most sensitive to?

Blue range

Clock and Cycle (Bmal1)

Two proteins that bind together and make a dimer, then can interact with DNA

What happens after the Clock and Cycle bind?

After binding to DNA the two genes are synthesized into proteins called Per and Cryptochrome (Cry)

What happens when Per and Cry proteins dimerize?

Inhibit the activity of Clock/Cycle turning off Per and Cry production.

Negative feedback

A system regulates its activity by its product suppressing its output

Why does light entrainment occur?

ipRGCs signal light detection by releasing glutamate which stimulates SCN neurons to increase Per production

Night owls

Greater risk for obesity and depression, need to overcome their natural rhythm to adapt

A cell's molecular clock

Always all in sync as long as the SCN is intact and functional, SCN is the master pacemaker