13) Rhythmic Behaviors and Sleep

Question 1

What are the 4 measurements for neural timing systems that affect biological processes or behaviors?

What cues influence our biorhythms? (2)

Answer 1

1. Ultradian -Feeding cycles
2. Circadian - daily, day-night rhythms
   
   • sleeping cycles
   • blood pressure, body temp., metabolic rate, cortisol levels
3. Infradian - >day rhythms
   
   • female menstrual cycles
4. Circannual - yearly rhythms
   
   • Migratory cycles
   • hibernation

Our biorhythms are influenced by both internal cues - biological clocks on free-running rhythms and external cues - Zeitgebers (such as light)

Question 2

Internal cues:

Define free-running rhythms ​

External cues:

Define Zeitgeber

What are zeitgebers disturbed by and what can this lead to?

Answer 2

Free-running rhythms - body’s own rhythm in the absence of all external cues

Zeitgeber - environmental cue to entrain a biological rhythm

• Ex: Light

Our zeitgebers can be disturbed by:

• Light pollution
• Long distance travel
• graveyard shift workers

These can lead to fatigue, jet lag, obesity, diabetes, stress, emotional distress

Question 3

What is our master biological clock? What structure in our brain is regulating our biological cycles?

How did we find out this was the structure?

Answer 3

Superchiasmatic Nucleus (SCN) - located in the Hypothalamus

• Lesioning the SCN = animals still eat, drink, exercise and sleep BUT at random times.
• Neurons here are more active during the light cycle
• Rhythmic pattern is an intrinsic property
• SCN Rhythm is genetic

Question 4

SCN rhythm is entrained usually by…?

Specialized …. hyperpolarize or depolarize to light?

What photopigment do these specialized cells have?

Also entrained by…?

Answer 4

SCN rhythm is usually entrained by light

• Specialized photosensitive RGCs (pRGCs) depolarize to light
• Contain the photopigment melanopsin
• Make up 1-3% of all RGCs spread across retina

Also entrained by exercise, feeding, arousal, etc. from other inputs into the SCN

Question 5

How do SCN pacemakers drive slave oscillators? (Directly and Indirectly but how)

Example?

Answer 5

1. Directly - axonal connections to other brain regions
2. Indirectly - hormonal release from SCN themselves or by controlling hormonal release from other areas (pituitary or pineal gland)

EXAMPLE: Pineal gland release of melatonin during dark phase

• Promotes sleep and rest
• Supports parasympathetic system “rest and digest”
• inhibits hamster’s gonads and they shrink (circannual)

Question 6

Why do we sleep?

How do we measure sleep?

Answer 6

We sleep to:

• Conserve energy - reduce metabolism and temp.
• Helps with memory consolidation

Sleep is a distributed process throughout brain

An EEG electroencephalogram is used

• Electrodes pasted onto standard locations of the skull record brain-wave activity

Question 7

What are the stages of sleep?

What is the sleep-wake cycle largely controlled by?

Answer 7

1. Awake
2. Non-REM sleep
   
   • 4 stages with decreasing frequency and increasing amplitude
   • Stage 1 = shallow; Stage 4 = deep sleep (slow wave sleep)
3. REM sleep - EEG looks like you are awake

The sleep wake cycle is largely controlled by the brainstem sending signals to the rest of the brain

Question 8

Cycle through stages of sleep every … min?

Characteristics of Non-REM and REM sleep?

Answer 8

Cycle through stages of sleep every 90 min.

Non-REM

• Body temp. and blood flow decreases
• Heart Rate and respiration decreases
• Some muscle tone
• Tossing/turning, talking, sleepwalking
• little dreaming

REM

• Body temp. regulation stops = start to drift towards room temp.
• Heart rate and respiration increases
• Atonia - No large muscle tone
  
  • Descending brainstem projections inhibit motor neurons
• Dreaming

Question 9

Does racking up sleep debt have effects? Short term, long term? What are they?

Answer 9

No long term effects of occasional sleep deprivation

Chronic sleep deprivation

• Impaired regulation of homeostatic processes
• Impairment in immune function

Question 10

What are the 4 systems that promote wakefulness and their corresponding neurochemicals?

What nuclei modulate these systems and how? Where are they located?

Answer 10

1. Cholinergic nuclei
   
   • ACh
2. Raphe nuclei
   
   • 5-HT or Serotonin
3. Tuberomamillary nucleus of hypothalamus
   
   • Histamine
4. Locus coerculeus
   
   • NE

Nuclei that modulate all these above systems: Lateral hypothalamic area (orexin neurons) and Ventrolateral preoptic nucleus (VLPO)

These nuclei regulate sleep-wake by modulating thalamocortical projections

• VLPO is inhibitory
• Orexin (hypocretin) neurons are excitatory

Located above SCN

Question 11

What is narcolepsy? How much of the population does it affect?

What structure is altered in narcoleptic type 1 people?

Differences between narcolepsy type 1 and type 2

Answer 11

Narcolepsy is the onset of irresistible attacks of sleep at any time. Fragmented sleep with increased REM (pink in image).

90% of Orexin neurons are lost in people with narcolepsy I

Narcolepsy type 1

• Cataplexy = sudden limb paralysis often triggered by strong emotions
  
  • Brainstem nuclei inhibit motor neurons during REM
    
    • But Amygdala can drive this inhibition without orexin
• CSF orexin concentration low
• 0.014% of population

Narcolepsy type 2

• No cataplexy
• CSF orexin concentration is normal
• 0.064% of population