Circadian rhythm
physiological processes that vary around the 24 hour day include activity, alertness, gene expression, organ physiology, and hormone secretion
Characteristics of Circadian rhythms
- Cyclic
- Self-sustaining
- Entrainable
The free-running rhythm
In the absence of zeitgebers, activity patterns cycle with an endogenous pattern
Phase-shift
Drift out of phase with 12 hour day/light cycle
suprachiasmatic nucleus (SCN)
The master pace-maker located in the hypothalamus. SCN generates internal circadian rhythms in gene expression, electrophysiology, and hormone secretion.
photosensitive retinal ganglion cells
projections from RGCs transfers information about light and dark to SCN which synchrnoizes a phase of SCN rhythms with the external enviornment
SCN outputs
hypothalamus, hippocampus, cortex, and brain stem
Clock genes
- Clock and BMAL1
- CRY and PER
- REV and ROR
- CCG
The Circadian gene process
- BMAL1-Clock complex activates the transcritpion of CRY and PER which inhibit BMAL1-Clock
- REV negatively regulates the expression of BMAL1 while ROR positively regulates it
- BMAL1-Clock regulates the expression of CCG which modulates essential physiological processes
Sleep
Readily reversible state of reduced responsiveness and interaction with the environment
Why do we sleep?
Restoration and adaptation
Non-REM
an idling brain in a movable body
REM
an active, hallucinating body in a paralyzed body
SWS
stage 3 and 4
Stage 1
Low amplitude high freq
Stage 2
sleep spindles of high amplitude and high frequency that last for a few seconds
REM Sleep properties
Increased:
1. eye movement
2. heart rate
3. respiratory rate
4. penile erection
Decreased: muscle tone
Wakefulness neuronal activity
acethylcholine, noreprinephrine, serotonin, histamine, and orexin active
REM Sleep neuronal activity
Neurons releasing noreprinephrine and serotonin are inactive. Neurons releasing acethycholine are active
Slow Wave Sleep activity
Neurons releasing noreprinephrine, serotonin, and acethycholine decrease activity
Neural mechanisms of dreaming
- Increased neuronal activity in brain stem (midbrain and pons), limbic system (amygdala and hippocampus), thalamus, and visual cortex
- Decreased neuronal activity in the PFC
- Neural activity in the brain stem activated the thalamus and visual cortex to generate info
- dopaminergic neurons in VTA activate the limbic system and induce strong emotions
The two process model of sleep
Process S - Build up of homeostatic sleep drive
Process C - Circadian signaling
Adenosine
- Builds up in brain during wakefulness due to energy consumption
- Increase throughout the day
- Blocked by caffine
Melatonin
- Hormone secreted by pineal gland in brain
- Helps maintain daily schedule of waking up and sleeping
- Inhibited by daylight
