Endogenous pacemakers and exogenous zeitgebers

Question 1

What is an exogenous Zeitgebers (EZs)

Answer 1

Stuff happens outside - external cues that may affect or entrain our biological rhythms

Question 2

Examples of exogenous Zeitgebers EZs

Answer 2

Social cues and light

Question 3

What is an endogenous pacemakers Eps?

Answer 3

Internal mechanisms - that regulate our biological rhythms

Question 4

EP body example

Answer 4

Internal biological clock (SCN)

Question 5

What is the Suprachiasmatic nucleus (SCN)

Answer 5

Acts as a master clock linking the brain regions that control sleep and arousal

Question 6

Where is the SCN located?

Answer 6

A tiny bunch of nerve cells located in the hypothalamus in each hemisphere of the brain
* One of the primary endogenous pacemakers and is influential in maintaining circadian rhythms such as sleep and wake cycle

Question 7

What resets the circadium rhythms?

Answer 7

However the rhythm is reset by external cues (EZs) so it can respond to environmental changes

Question 8

Where does SCN receive info from?

Answer 8

Light info from the optic nerve

Question 9

What is the pineal gland?

Answer 9

responds to signals from the SCN and releases melatonin (sleep hormone) to increase secretion and night and decrease levels as light increases in the mornings

The pineal gland and the SCN jointly function as endogenous pacemakers in the brain their sensitivity to light and role of melatonin mean their activity must be synchronised with light/ dark rhythm outside

Question 10

How does light affect the circadian rhythms?

Answer 10

Light resets the internal bodily clock keeping on a 24hr cycle

Question 11

What are the social cues as EZs?

Answer 11

Social cues - such as mealtimes and social activities may act as a EZ

Question 12

How do EZs and EPs interact?

Answer 12

• Light enters eye and is processed
• The optic nerve transfers the information about light to the SCN
• The SCN regulates the pineal gland to relase melatonin
• Causes the sleep wake cycle

Question 13

What does melatonin do?

Answer 13

a sleep hormone that produces sleep

Question 14

Morning - interaction of EZs and EPs

Answer 14

Morning → Optic nerve receives light transfers information to SCN → stimulates pineal gland to decrease Melatonin ( sleep hormone)

Question 15

Night EZs and EPs interaction

Answer 15

Optic nerve receives decreased light transfers information to SCN → stimulates pineal gland to increase Melatonin ( sleep hormone)

Question 16

Strengths of EZs and EPS

Answer 16

• Mutant hamsters study
  Genetic breeding of hamsters with a 20 hr rhythm
  SCNs removed and transplanted into normal hamsters - had an impact of gaining a 24hr sleep cycle
  This increases support for existence SCN as the main endogenous pacemaker in the sleep-wake cycle
• Evidence light is EZ
  27 office workers in an experimental group exposed to strong blue light, they shift their cr to match office lighting
  Control group - 27 office workers with normal office lighting rhythms matched shifting time of natural light of dawn
  Strongly suggests light is an EZ and artificial light can disrupt EPs overriding natural light as primary EZ
• Real world application
  Light exposure to avoid jetlag
  Exposure to bright light prior to E-W flight decreased the time needed to readjust to local time on arrival
  This can shift the rhythm up to 2hrs with continuous bright light
  Realworld utility and application of this theory

Question 17

EZs and EPs interactions strengths

Answer 17

Aldcrodt spent 25 days in a lab with no EZs → had to play ‘amazing grace’ on bagpipes at the same time every days → found sleep-wake cycle slipped into the 30-hr period

Question 18

what happens when you have disruption to the rhythms?

Answer 18

• ^ anxiety
• less alert
• less vigilent