Sleep triggers:
Metabolic activity in the brain → ↑ adenosine → ↓ inhibition on the VPLO; !NB caffeine blocks adenosine receptors → maintain the inhibition on the VPLO → prolongation of the awake state;
Hypocretinergic neurons in the lateral hypothalamus secret orexin (ORX); influenced by motivation to remain awake; ↑ ORX → shifts the balance toward the awake state;
Definition:
A period of rest for the body and mind, during which volition and consciousness are in partial or complete abeyance and the bodily functions partially suspended.
Sleep has also been described as a behavioral state marked by a characteristic immobile posture and diminished but readily reversible sensitivity to external stimuli.
The sleep/wake cycles consists of:
Awake state
Sleep State - Each sleep cycle lasts approximately 90-120 min .
Sleep functions
Sleep adjusts & reorganizes emotions & memory;
accumulation of randomly learned memories in limbic structures → imbalance & disorganized → emotional behavior;
Sleep stabilizes synapses e.g. 1 hour sleep stabilizes synapses for about 4 hours;
Sleep activates synapses that are used infrequently during awake state;
Sleep stabilizes ANS functions.
Neuronal mechanisms of sleep
Flip-flop model - two states that are stable but inhibit one another by two components:
The reticular activating system response for the awake state.
The ventrolateral preoptic nucleus/area (VPLO) - sleep promoting area.
The ventrolateral preoptic nucleus (VLPO) inhibits (GABA neurotransmitter) the main components of the ascending arousal system → Thus VLPO activity promotes