Why does a mouse fall asleep? - briefly
Mice sleep to conserve energy and allow the brain to consolidate sensory and motor experiences acquired while active. Their circadian cycle schedules rest mainly during daylight hours when predation risk is lower.
Why does a mouse fall asleep? - in detail
Mice exhibit a regular sleep–wake cycle driven primarily by an internal circadian oscillator located in the suprachiasmatic nucleus. Light cues synchronize this oscillator, producing periods of heightened sleep propensity during the dark phase for nocturnal species. When the circadian drive aligns with an accumulating homeostatic sleep pressure, the animal transitions from wakefulness to sleep.
Homeostatic pressure builds as adenosine concentrations rise in the brain during prolonged activity. Elevated adenosine activates A1 receptors, inhibiting arousal‑promoting neurons and facilitating the onset of non‑rapid eye movement (NREM) sleep. Concurrently, reduced orexin signaling diminishes excitatory input to wake‑promoting circuits, further supporting sleep initiation.
Energy conservation constitutes a physiological motive for sleep. During rest, metabolic rate declines, allowing reallocation of glucose and fatty acids to processes such as synaptic remodeling and protein synthesis. Core temperature drops modestly, reducing heat loss and conserving caloric resources.
External factors modulate sleep timing. Ambient temperature below the thermoneutral zone promotes deeper NREM bouts, whereas elevated temperatures shorten sleep episodes. Predator presence or sudden noises trigger rapid arousal via the locus coeruleus, interrupting ongoing sleep.
Electroencephalographic recordings reveal alternating NREM and rapid eye movement (REM) phases. NREM is characterized by high‑amplitude, low‑frequency waves, while REM displays low‑amplitude, high‑frequency activity and muscle atonia. Both phases are essential for memory consolidation and neural plasticity.
Collectively, circadian entrainment, homeostatic drive, neurochemical modulation, metabolic considerations, and environmental conditions converge to regulate the sleep behavior observed in laboratory and wild mice.