Sleep in sheep

Abstract

While there is no exact definition of sleep acceptable by all authorities, it is generally accepted that ordinary sleep is characterised by a loss of critical reactivity to events in the environment, an increased threshold of general sensibility and reflex irritability, and the ability of being aroused or brought back to a state of wakefulness (Kleitman, 1929). There are many physiological changes in sleep such as fall in blood pressure, decrease in heart rate, reduction in pH of the blood, reduction in urine secretion, decrease in metabolic rate, slow and regular breathing, muscular relaxation and the disappearance of deep reflex actions, but almost any of these physiological changes may be absent in a sleep which is normal in all other respects. It is therefore more accurate to refer to the physiological accompaniments than to the physiology of sleep (Gillespie, 1929).