We all take advantage of sleep and think of it, at times, as a luxury more than a physiological and psychological necessity. Edwards, O’Dreiscoll, et al, in their paper over Aging and Sleep: Physiology and Pathophysiology, simply defined sleep as a natural state characterized by a reduction in voluntary motor activity (skeletal muscle movement) but not involuntary activity (heart, lungs, organs, etc.), and a decreased response to stimulation and stereotypic posture that is both reversible and self-regulating (makes the warning labels on sleep aids like Ambien make more sense). Although the exact concentrations of specific hormones or neurotransmitters needed for sleep is not known, some play a specific and important role in both sleep and in being awake. We can differentiate between the different stages of sleep utilizing measurement tools such as the electroencephalogram (EEG), electrooculography (EOG), and electromyography (EMG). The EEG measures the electrical activity of the brain, the EOG measures eye movement, and the EMG measures the electrical activity in skeletal muscle. Let us first differentiate the different sleep stages of the sleep cycle.
…show more content…
We can divide sleep into two main categories: REM (rapid eye movement) and non-REM sleep. We can then divide non-REM further into 3 stages. Let us begin with non-REM. Sleep is considered a cycle because it cycles through REM and the non-REM stages. The first stage involves between 5-10% of each cycle. It is characterized by closed eyes with semiconsiousness (closer to unconsciousness). The EEG shows what is called theta waves measured to be 4-7 Hz. In contrast, subjects that are awake exhibit alpha waves characterized by 8-14 Hz waves. The second stage is characterized by light sleep and accounts for 45-55% of the cycle. The heart rate starts to slow and body temperature drops. The third, and last, stage of non-REM sleep is also known as deep sleep and accounts for 15-25% of the cycle. The body secretes bursts of growth hormone and prolactin in order to perform repairs in tissues, build bone and muscle, and strengthen the immune system. It is initiated in the preoptic area. Through the EEG it is characterized by delta waves measured to be 5-2 Hz. REM sleep typically starts 90 minutes after sleep initiation and typically lasts for 10 minutes through the first cycle then progressively lengthens as cycles pass. REM sleep is characterized by rapid eye movement and muscle paralysis. Heart rate, breathing, and temperature become unregulated. This stems the term paradoxical sleeping because vitals indicate the sleeper is awake and the brain uses more oxygen than it does when the sleeper is awake. The body determines whether it is supposed to be awake or asleep through a natural timer in the body called the circadian timing system (CTS) located in the anterior hypothalamus, specifically in the suprachiasmatic nucleus. The CTS provides temporal organization for most neurobehavioral physiological, and biochemical variables. For example, prior to waking, body temperature, sympathetic autonomic tone, and plasma cortisol rise in anticipation of increased energetic demands. Changes in the hormones melatonin, prolactin, cortisol and the neurotransmitters acetylcholine and dopamine are noticeable. Cortisol is a hormonal response to stress; it lowers the immune systems effectiveness, and is responsible for keeping us awake. Melatonin is responsible for initiating drowsiness and sleep. The circadian pacemaker located in the suprachiasmatic nucleus has a direct neural connection to the pineal gland with melatonin hormone release. Melatonin is at its highest concentration during the night, but declines significantly throughout the day to eventually reaching an almost undetectable amount. Melatonin secretion is regulated by norepinephrine in the pineal gland. Similar, but opposite, cortisol is recorded to be low at night, but high early in the morning. As sleep progresses through its cycle prolactin is secreted from the pituitary gland and acetylcholine becomes less available in the brain. Prolactin is responsible for water and salt concentration regulation, immune system regulation, and it is important in cellular growth and hematopoiesis. Acetylcholine is a neurotransmitter in the autonomic nervous system that has inhibitory effects in cardiac muscle but excitory effects in skeletal muscle. It is the only neurotransmitter used in the motor division of the somatic nervous system. Eventually the sleep cycles have to stop. As the circadian timing system gets closer to switching to a wake state, dopamine interacts with norepinephrine receptors and inhibits effects of norepinephrine which in
We can divide sleep into two main categories: REM (rapid eye movement) and non-REM sleep. We can then divide non-REM further into 3 stages. Let us begin with non-REM. Sleep is considered a cycle because it cycles through REM and the non-REM stages. The first stage involves between 5-10% of each cycle. It is characterized by closed eyes with semiconsiousness (closer to unconsciousness). The EEG shows what is called theta waves measured to be 4-7 Hz. In contrast, subjects that are awake exhibit alpha waves characterized by 8-14 Hz waves. The second stage is characterized by light sleep and accounts for 45-55% of the cycle. The heart rate starts to slow and body temperature drops. The third, and last, stage of non-REM sleep is also known as deep sleep and accounts for 15-25% of the cycle. The body secretes bursts of growth hormone and prolactin in order to perform repairs in tissues, build bone and muscle, and strengthen the immune system. It is initiated in the preoptic area. Through the EEG it is characterized by delta waves measured to be 5-2 Hz. REM sleep typically starts 90 minutes after sleep initiation and typically lasts for 10 minutes through the first cycle then progressively lengthens as cycles pass. REM sleep is characterized by rapid eye movement and muscle paralysis. Heart rate, breathing, and temperature become unregulated. This stems the term paradoxical sleeping because vitals indicate the sleeper is awake and the brain uses more oxygen than it does when the sleeper is awake. The body determines whether it is supposed to be awake or asleep through a natural timer in the body called the circadian timing system (CTS) located in the anterior hypothalamus, specifically in the suprachiasmatic nucleus. The CTS provides temporal organization for most neurobehavioral physiological, and biochemical variables. For example, prior to waking, body temperature, sympathetic autonomic tone, and plasma cortisol rise in anticipation of increased energetic demands. Changes in the hormones melatonin, prolactin, cortisol and the neurotransmitters acetylcholine and dopamine are noticeable. Cortisol is a hormonal response to stress; it lowers the immune systems effectiveness, and is responsible for keeping us awake. Melatonin is responsible for initiating drowsiness and sleep. The circadian pacemaker located in the suprachiasmatic nucleus has a direct neural connection to the pineal gland with melatonin hormone release. Melatonin is at its highest concentration during the night, but declines significantly throughout the day to eventually reaching an almost undetectable amount. Melatonin secretion is regulated by norepinephrine in the pineal gland. Similar, but opposite, cortisol is recorded to be low at night, but high early in the morning. As sleep progresses through its cycle prolactin is secreted from the pituitary gland and acetylcholine becomes less available in the brain. Prolactin is responsible for water and salt concentration regulation, immune system regulation, and it is important in cellular growth and hematopoiesis. Acetylcholine is a neurotransmitter in the autonomic nervous system that has inhibitory effects in cardiac muscle but excitory effects in skeletal muscle. It is the only neurotransmitter used in the motor division of the somatic nervous system. Eventually the sleep cycles have to stop. As the circadian timing system gets closer to switching to a wake state, dopamine interacts with norepinephrine receptors and inhibits effects of norepinephrine which in