The Autonomic Nervous System and Sleep
After a hectic day it can be so easy to get into bed and quickly drift to sleep. A couple of hours later you may find yourself awake and not recalling anything that happened during your shut eye. On a different day you may get into bed and toss and turn until you hear the morning birds chirping. Clearly, sleep, which is seemingly a no-brainer, takes more than just closing your eyes and intending to open them after a while.
Does the sleeping brain think?
Sleep has been a fascinating subject for scientists for many years. The existence of paradoxical sleep which is associated with high brain activity has poked a hole in the theory of the inactive sleeping brain.
This is where the autonomic nervous system comes in
The autonomic nervous system (ANS) regulates most of the unconscious homeostatic events in the human body such as sleep.
Cells involved in regulating autonomic function and sleep use similar neurotransmitters such as norepinephrine and acetylcholine that promote wakefulness. Hypocretin (orexin) neurons send signals to both sleep and autonomic nuclei. Orexin has also been implicated in autonomic changes that are prominent in narcolepsy patients.
When drifting from a state of wakefulness to drowsiness and finally plunging into deep sleep two changes occur in the CNS; the parasympathetic vagal tone increases while the sympathetic tone decreases. There is a gradual increase in parasympathetic activity as sleep progresses from non-REM to deeper levels of non-Rem sleep. The reduction in BP is estimated to be between 10%- 20% and this is commonly referred to as dipping. This causes a simultaneous reduction in heart rate and blood pressure. At the same time, sympathetic activity decreases resulting in a state of regular respiration. Consequently, the non-REM phase of sleep is dominated by parasympathetic activity which is associated with autonomic stability and metabolic recovery.
The reverse happens during phasic REM sleep which is associated with rapid eye movements and vivid dreams. Sympathetic activity peaks and heart rate and blood pressure may fluctuate dramatically.
This panel will shed light on the link between the autonomic nervous system and sleep and the ramifications in autonomic and sleep disorders