Psych 261 - Module 8.1

Front 1

What is endogenous circannual rhythm?

Back 1

Internal rhythm that animals create that prepare them for seasonal changes.

Endogenous - generated from within

Circannual - about year

Front 2

What is endogenous circadian rhythms?

Back 2

Internal rhythm that last about a day. Controls sleep and wake cycle.

Front 3

What evidence indicates that humans have an internal biological clock?

Back 3

People who have lived in an environment with a light–dark schedule much different from 24 hours fail to follow that schedule and instead become wakeful and sleepy on about a 24-hour basis.

Front 4

What resets our circadian rhythm? What would happen if we didnt have something to reset our circadian rhythms?

Back 4

Stimulus that resets our circadian rhythm is called zeitgeber (german for time-giver). Without something to reset it, it would gradually drift away from the correct time.

Front 5

What is the dominant zeitgeber for land animals? Marine animals?

Back 5

Land animals - light. Marine animals - tides.

Front 6

Other than light, what are some zeitgebers?

Back 6

Exercise, arousal of any kind, meals, temperature of the environment. Without light, these zeitgebers are weak on their own.

Front 7

Is it easier to adjust to crossing time zones when travelling east or west? Why?

Back 7

Going west, because we stay awake later at night and then awaken late the next morning, already partly adjusted to the new schedule (phase-delaying circadian rhythm). Going east is more difficult because we phase-advance to sleep earlier and awaken earlier. It's harder to go to sleep before body's usual time and harder to wake up early the next day.

Front 8

What kind of light is better at resetting cirdian rhythms?

Back 8

Short-wavelength light (bluish light)

Front 9

What organ is the main mechanism behind generating circadian rhythms?

Back 9

The suprachiasmatic nucleus (SCN), a part of the hypothalamus. It gets its name from being just above (supra) the optic chiasm.

Front 10

What evidence strongly indicates that the SCN produces the circadian rhythm itself?

Back 10

SCN cells produce a circadian rhythm of activity, even if the cells are isolated and kept in a tissue culture.

Front 11

How does light reset the circadian rhythm?

Back 11

There are special ganglion cells in the retina that contain a photopigment called melanopsin. These cells respond directly to light. Light information reaches the SCN through the retinohypothalamic path (a branch of the optic nerve). The SCN is able to gauge the time of day because these ganglion cells respond slowly to light and turn off slowly when light ceases - therefore they respond to the overall average amount of light, not to instantaneous light.

Front 12

Someone who is blind because of cortical damage can still synchronize his/her circadium rhythm to the local pattern of day and night. Why?

Back 12

If the retina is still intact, the melopsin-containing ganglion cells can still send messages to the SCN, resetting its rhythm.

Front 13

1. What are two genes responsible for circadian rhythm (in fruit flies)?

2. How do they do it?

3. Why do we care about fruit flies?

Back 13

1. Period (produce PER protein) and timeless (produce TIM protein).

2. A higher concentration of the proteins that these genes produce promote sleep. Early in the morning the mRNA that produce the proteins are low and increase throughout the day. The high concentrations synthesize the sleepy proteins, but it takes time so the increase in sleepy proteins begins hours later, when sleep begins. The higher concentration of PER and TIM proteins inhibits production of their mRNA counterparts. So, by the morning, PER and TIM levels are low, so the fruit flies wake up, and the cycle begins again.

3. Mammals have similar proteins to fruit flies' PER and TIM proteins (3 versions of PER protein, and several closely related to TIM)

Front 14

What gland is controlled by the SCN to regulate waking and sleeping? How?

Back 14

The pineal gland, which is an endocrine gland located just posterior to the thalamus. It releases the hormone melatonin, mostly at night, making us sleepy. Melatonin secretion starts to increase around 2-3 hours before bedtime.