Lecture: Postgraduate Psychiatry Intensive Course Date: 9 August 2018

1. Functions of hypothalamus and
circadian rhythms
Rahimah Zakaria
Physiology USM

2. Lecture Outline
• Hypothalamus
• Regions and functions
• Body rhythms
• Circadian rhythms
• Physiology of sleep
• Definitions
• Sleep regulation, theory of sleep
• Sleep stages & cycles and EEG
• Sleep patterns and its developmental aspects
• Functions of sleep
• Factors affecting sleep
• Neurotransmitters associated with sleep

3. Hypothalamus

4. Hypothalamus
• Located inferior to the thalamus
• Represents the ventral region of the midbrain
• Major functions:
I. Homeostatic control includes regulating
hunger, thirst, sex drive, sleep-wake cycles,
body temperature, blood glucose
II. Endocrine control via regulating the release
of pituitary hormones
III. Autonomic control via descending pathways
to sympathetic and parasympathetic
preganglionic neurons
IV. Limbic function via connections to limbic
system regulating emotional behavior

6. Regions of Hypothalamus

7. Functions of Selected Regions of Hypothalamus

8. Body rhythms

9. Body rhythms
Circadian rhythms (circa= approx & diem =day) operate over 24 hrs
e.g. sleep-wake cycle, body temp, plasma
cortisol levels
Ultradian rhythms (less than one day) e.g. stages of sleep (REM=
Rapid Eye Movement, NREM = Non Rapid Eye
Movement Sleep patterns)
Infradian rhythms (more than one day) e.g. female menstrual cycle
Circannial rhythms (yearly) e.g. hibernation patterns
Biological processes that show cyclical variation over time, range from hours to
years, reflect the influence of the earth’s rotation upon us

10. Circadian rhythms
• By definition, circadian rhythms are endogenous and are ‘of
self-sustaining’ in nature and will generate their rhythm and
persist in an absence of any external input (Aschoff 1965)

11. Role of suprachiasmatic nucleus
• The suprachiasmatic nucleus
(SCN) works like an internal clock,
signalling other brain areas when to
be awake and when to sleep
• Light is a powerful zeitgeber (trigger
change in circadian rhythms)
Retino-hypothalamic pathway
(above the optic chiasm)

12. Circadian rhythms in action: sleep
• ‘Free running’ sleep rhythm about 25 hrs
• Entrainment to light dark cycle maintains a 24 hr
periodicity
• Mediated through SCN activity
• Jet-lag
• Rapid shifts in light dark cycle
• Takes a few days for endogenous rhythm to re-
entrain

13. Circadian rhythms in mammals

14. Physiology of Sleep

15. Definitions
• Sleep refers to a state of altered consciousness during which an
individual experiences minimal physical activity and a general slowing
of the body’s physiological processes. The individual can be aroused by
appropriate stimuli
(Coma: a state of unconsciousness from which an individual cannot be
aroused)

16. Sleep Regulation

17. (a) When the flip-flop is in the ‘wake’
state, the arousal systems (lateral
hypothalamus) are active and the
ventrolateral preoptic area is inhibited
and the animal is awake
(b) When the flip-flop is in the ‘sleep’
state, the ventrolateral preoptic area
is active and the arousal system are
inhibited, and the animal is asleep
Theory of sleep

19. Sleep stages

20. Hypnogram

21. Sleep cycle
• 90-110 minutes per cycle
• Switches between NREM and REM
sleep appear to be controlled by
reciprocal inhibition between
monoaminergic neurons and a specific
subset of cholinergic neurons within the
brainstem
• e.g. when REM sleep is triggered, REM-
on cholinergic neurons become
maximally inhibited, while
noradrenergic and serotonergic neurons
become virtually silent (not inhibited)

22. Sleep Stages in EEG

25. Sleep pattern

26. Developmental aspects of sleep
Daily sleep rhythms begin ~ 16 wks.
Total sleep time, REM and SWS
decreases with age.
Elderly frequently experience
insomnia.
WASO: wake after sleep onset; REM: rapid eye movement; SWS: slow wave sleep

27. Functions of sleep
• Restorative Functions
– growth and repair (increases anabolic
hormones, decreases catabolic
hormones)
• Adaptive Functions
– energy conservation (decreases in
metabolic rate and body temperature)
– predator avoidance
• Cognitive Functions
- learning, unlearning, reorganization
• Keep mind alert and enhances mood

28. Factors affecting sleep
• Anxiety
• Cultural norms
• Degree of comfort
• Diet - e.g. caffeine, heavy meal (indigestion)
• Drug or other substances – alcohol, nicotine
• Environment factors – e.g. lighting, temperature, odours, noise
• Lifestyle
• Life span consideration – need for sleep changes with age

29. Neurotransmitters in wakefulness and sleep
Sleep is regulated by neurotransmitters that promote wakefulness and sleep
Wakefulness
• Dopamine (DA)
• Norepinephrine
• Serotonin (5-HT)
• Acetylcholine
• Histamine
• Orexin/hypocretin
Sleep
• Adenosine
• GABA
• Melatonin
• Galanin