There are five stages of sleep that cycle throughout the sleep process (Gerrig and Zimbardo pp.162-165) stage one, stage two, stage three, stage four, and non-REM sleep. Occasionally a sixth step is identified as waking. (The Sleep Channel, sleepdisorderchannel.com/stages.) The waking stage begins the sleep cycle. It is often referred to as relaxed wakefulness and is the period where the body prepares to sleep. As the body relaxes from the tense awake state, muscles relax, a feeling of sleepiness overtakes the person, and eye movement slows. At this relaxed state, stage one sleep begins. (The Sleep Channel.)
During stage one, sleep brain waves are emitted at 3 to 7 cps. (Gerrig and Zimbardo pp.162-165) There is a 50% reduction in body and brain activity seen in wakefulness and stage one of the sleep cycle. Eyes are also closed during this phase of sleep but if a person is awoken during this phase they will not feel as if they have slept. (The Sleep Channel.)
Sleep spindles, mild bursts of electrical activity or 12 to 16 cps, characterize stage two sleep. (Gerrig and Zimbardo pp.162-165). Stage two is also characterized with light sleep where stillness of the body is disrupted by periodic muscle twitches. Physical symptoms during this stage include slowed heart rate, and body temperature drop. This is a transitory period from light sleep to deep sleep. (The Sleeping Channel.)
Stage three and four sleep, are considered deep sleep. Brain waves slow to 1 to 2 cps, and a person’s’ breathing and heart rate decrease. (Gerrig and Zimbardo pp.162-165) These phases of deep sleep are also known as slow-wave or delta sleep. During these stages electromyogram printouts show waves of high amplitude. This indicates a steady pattern of deep sleep and “rhythmic continuity.” (The Sleep Channel.) The final stage of sleep is where electrical activity of the brain increases. EEG looks similar to stages one and two, but here is where REM sleep occurs, and dreaming initiates. (Gerrig and Zimbardo pp.162-165) During this phase there is a remarkable change in the person’s physiological state. Rapid eye movement, increase in heart rate and respiration, and twitching of the face, fingers, and legs all characterize this phase of sleep. However partial paralysis also occurs during this phase that immobilized the major voluntary muscle groups including those in the chin and neck. (The Sleeping Channel.)
There are a number of sleeping disorders that range from mild to life-threatening. Bruxism, or teeth gnashing, occurs with an involuntary grinding of the teeth during sleep. This causes rapid wearing down of the teeth and jaw pain. Although a specific cause is not known, it is thought to be linked to stress, trauma to the face, a malfunction in the nervous system, a poor diet, or because of allergies. (The National Sleep Foundation, http://www.sleepfoundation.ord/disorder.cfm.) Insomnia is perhaps the most familiar of the sleep disorders and is characterized by the chronic inability to sleep normally. The symptoms that are characteristic of this disorder are difficulty falling asleep, frequent waking, inability to return to sleep, and early morning awakening. (Gerrig and Zimbardo pp.162-165) Insomnia is not classified as a disease, per se, more as a complex web of symptoms that indicate an underlying problem or psychosis. (The National Sleep Foundation.)
Narcolepsy is a disorder where a person has an irresistible compulsion to sleep during the daytime. (Gerrig and Zimbardo pp.162-165) Stimulants and antidepressants are commonly used to treat this disorder. Science has yet to pin down a culprit for the cause, it is thought to be linked to blood pressure management and depression. (The National Sleep Foundation.)
Sleep apnea is a disorder that affects the upper respiratory system that causes the person to stop breathing while they are asleep. (Gerrig and Zimbardo pp.162-165.) Again the exact cause is still unknown to science, but the site of obstruction for victims of Sleep Apnea seems to be the soft palate (the soft palate is the area at the base of the tongue.)
Because there isn’t a rigid structure to support this structure the airway in patients with OSA have a tendency to collapse once the muscles are relaxed during sleep. Once the muscles relax the airway collapses and the patient is unable to breath. In order to regain an airway, the patient needs to awake to tense the muscles and open the airway. (The National Sleep Foundation.)
Gerrig and Zimbardo. Psychology and Life. 16th edition. Boston. 2002.
Hampton, Stephanie. The Human Sexual Response Cycle. Retrieved 05/17/04 from http://www.umkc.edu/sits/hsw/Sexresponse/.
Lecture 9: Language Acquisition. Retrieved 05/17/04 from http://avru1.derby.ac.uk/~steve/devpsy/docs/lecture9.html.
The National Sleep Foundation. Sleep Disorders. Retrieved 05/17/04 from http://www.sleepfoundation.ord/disorder.cfm.
The Sleep Channel. The Stages of Sleep. Retrieved 05/17/04 from http://sleepdisorderchannel.com/stages/