Psychology Chapter on Consciousness and Sleep

Consciousness, Wakefulness, and Sleep

• Consciousness is awareness of internal and external stimuli (perceptions, feelings, thoughts).
• Specific neuron populations in the brainstem, hypothalamus, and basal forebrain regulate consciousness.
• These neurons project to the cerebral cortex to determine the consciousness state.
• Consciousness levels fluctuate throughout the day, from alertness to drowsiness.
• Sensory perception and consciousness are regulated by interacting neural pathways.
• Sensory stimuli influence consciousness levels. Excessive stimuli cause wakefulness; lack of stimuli leads to drowsiness/sleep. Conversely, consciousness levels affect sensory cortex sensitivity. Wakefulness increases sensitivity, while sleep/coma decreases it.

Reticular Activating System (RAS) and Wakefulness

• The RAS, located in the upper brainstem, is a network of nuclei regulating wakefulness, sleep & consciousness.
• RAS receives projections from somatosensory, visual, and auditory pathways.
• RAS neurons are multimodal, responding to diverse stimuli (unlike unimodal sensory neurons).
• RAS is a non-specific neural pathway.
• RAS includes nuclei like locus coeruleus (LC), pedunculopontine (PPT), laterodorsal tegmental (LDT) nuclei, raphe nuclei, substantia nigra (SNc), and ventral tegmental area (VTA), each with specific neurotransmitters (e.g., noradrenaline in LC).
• Activity of these nuclei varies across consciousness states (e.g., noradrenaline peaks in wakefulness).
• Increased RAS activity correlates with wakefulness.
• Other brain regions involved in wakefulness regulation include the hypothalamus (TMN, LHA) and basal forebrain, which are more active during wakefulness.
• The Ascending Reticular Activating System (ARAS) promotes wakefulness by projecting from the RAS, hypothalamus, and basal forebrain to the cerebral cortex.
• ARAS has two pathways: dorsal (through thalamic nuclei) and ventral (direct to cortex).
• Damage to the RAS/ARAS causes loss of consciousness (coma).
• General anesthetics and CNS depressants inhibit RAS/ARAS activity.
• CNS stimulants enhance RAS/ARAS activity.

Circadian Rhythms

• Circadian rhythms are natural 24-hour fluctuations in physical, mental, and behavioral processes.
• These rhythms influence sleep-wake cycles, activity, melatonin, body temperature, hormone secretion, blood pressure, and heart rate.
• Light is a key factor affecting circadian rhythms.
• The suprachiasmatic nucleus (SCN) in the hypothalamus is the biological clock.
• Retinal ganglion cells containing melanopsin (sensitive to blue light) transmit light information to the SCN via the retinohypothalamic pathway.
• The SCN regulates melatonin secretion from the pineal gland.
• Light input inhibits melatonin secretion, increasing levels in darkness.
• Melatonin typically rises between 9 PM and 10 PM, peaking during sleep.
• Melatonin receptors are throughout the brain and body, influencing circadian rhythms like sleep-wake.

Electroencephalography (EEG) and Sleep Stages

• EEG records brain electrical activity using scalp electrodes.
• EEG is used to diagnose neurological disorders, especially epilepsy.
• The EEG signal represents the sum of postsynaptic potentials (EPSPs and IPSPs) from pyramidal neurons in the cerebral cortex.
• Synchronized activity of pyramidal neurons produces EEG patterns.

This quiz covers key concepts related to consciousness, wakefulness, and sleep. Explore how the brain regulates different states of consciousness and the role of the Reticular Activating System in maintaining wakefulness. Test your understanding of neural pathways and sensory perception's impact on these states.