After studying this chapter, the student should be able to:
State the physiologic characteristics of sleep stages and what constitutes normal sleep.
Describe the neural mechanisms underlying sleep–wake regulation in the brain.
Display an understanding of the diagnosis and classification of common sleep disorders.
Describe the effects on sleep and the mechanisms of action of commonly prescribed medications for sleep and sleep disorders, as well as commonly used nonprescription agents.
Sleep can be defined as a physiologic state characterized by behavioral quiescence and reduced awareness of sensory inputs that can be reversed by a stimulus of sufficient magnitude. For centuries, sleep was thought of as a passive state, the absence of wakefulness, when your mind and body turned off until it was time to start another day. Modern medicine, however, has given us great insight into the fact that sleep is a very active process, with distinct stages regulated by the complex interaction of a myriad of neurologic, metabolic, and behavioral factors. Like food and water, sleep is an essential physiologic process that is regulated by a homeostatic drive—if you get too little of it for a period of time, you want more of it in the future. This chapter discusses the complexity of the state of sleep, building on the introduction in Chapter 23, and introduces various pathologic and nonpathologic conditions associated with sleep.
The breakthroughs in neurophysiology necessary to examine sleep occurred relatively recently. In 1934, Hans Berger first described the potentials that can be observed by comparing 2 points on the scalp above the brain, waves we commonly refer to as the electroencephalogram (EEG). In 1936, Frederic Bremer noticed that transection of the brain at the level of the rostral midbrain in experimental animals produced a slow, rhythmic pattern on the EEG, whereas transection lower in the caudal membrane allowed the brain to maintain the EEG typically seen in wake. Building on this work, in 1946, Giuseppe Moruzzi and Horace Magoun first described an area in the midbrain-pontine junction they called the reticular activating system, which is necessary for keeping an animal awake. The first published description of a substate during sleep associated with the highest amount of dream recall, termed rapid eye movement (REM) sleep due to the characteristic saccadic movements seen, was by William Dement and Nathaniel Kleitman in 1956. Since that time, there have been a great many discoveries identifying what brain areas are responsible for the control of these processes.
The sleep disorders discussed in this chapter range from very common to very rare. Obstructive sleep apnea (OSA) is believed to affect approximately 25% of adults between the ages of 30 and 70 years. Because of the role that obesity plays in the pathophysiology of this disorder, the incidence of OSA has been steadily increasing over the past several decades. Restless legs syndrome (RLS) has an estimated ...