Arousal & Sleep Study Notes

Definition of Arousal: Arousal is the physiological and psychological state of being awoken or the stimulation of sensory organs leading to perception.
- Involves activation of:
- Ascending reticular activating system (RAS) which regulates wakefulness.
- Autonomic nervous system (ANS).
- Endocrine system.
Physiological Effects: Results in increased heart rate, blood pressure, and readiness to respond.
Regulatory Importance:
- Critical for consciousness, attention, immigration processing, and motivating behaviors such as:
- Mobility, pursuit of nutrition, fight-or-flight response, and sexual activity (Ref: Masters and Johnson's cycle).
- Included in emotion theories (e.g., James-Lange theory of emotion).
Personality Implications: Variations in baseline arousal can influence whether someone is an extravert or introvert.

Regulatory Mechanisms:
- Multiple neurotransmitters & neuromodulators are produced from specific cell body groups in the brainstem.
- These nuclei have projections throughout the CNS and PNS to modulate arousal.
Key Neurotransmitters Involved in Arousal:
- Norepinephrine
- Serotonin
- Histamine
- Orexin
- Dopamine
- Acetylcholine

Neurotransmitter:
- Defined as a messenger released from a neuron at a specialized junction that diffuses across a cleft.
- Affects one or sometimes two postsynaptic neurons, muscular cells, or other effectors.
Neuromodulator:
- Released from neurons and affects groups of neurons rather than single postsynaptic effects.
- Can act through second messengers and has long-lasting effects.
- May be localized or widespread, overlapping in function with neurohormones.
Neurohormone: A messenger released into the bloodstream, affecting distant peripheral targets.

Presence in Presynaptic Neuron: The substance must exist within the neuron signaling it.
Release Mechanism: The neurotransmitter must be released in response to presynaptic depolarization and require Ca2+ for release.
Presence of Specific Receptors: Specific receptors must be present on the postsynaptic cell to respond to the neurotransmitter.

Classification of Small-Molecule and Peptide Neurotransmitters:
- Small-molecule neurotransmitters include:
- Acetylcholine
- Amino acids (e.g. glutamate)
- Biogenic amines (e.g. serotonin, catecholamines—norepinephrine and dopamine).
Histamine: A unique monoamine that doesn’t belong to the catecholamine group.

Definition: Acetylcholine is found in nerve synapses and its action includes:
- Activation of skeletal muscle contraction and glandular functions in endocrine systems.
Analogy: Acetylcholine likened to a mailperson delivering messages to ensure muscle contraction.
Functions: Role in the peripheral nervous system includes muscle activation. In the central nervous system, it moderates cholinergic system activation.
Significance: Involved in various processes: muscle movement, pain sensation, memory, and REM sleep regulation.

Location: Below the striatum, housing nuclei essential for acetylcholine production.
Components: Nucleus accumbens, nucleus basalis, diagonal band of Broca, and medial septal nuclei are key areas.

Nicotinic Receptors (nAChRs):
- Ionotropic receptors prominent in muscle for nerve-muscle communication and sympathetic/parasympathetic systems.
Muscarinic Receptors (mAChRs):
- G-protein-coupled receptors influential in parasympathetic responses.
Myasthenia Gravis: Autoimmune condition affecting muscle strength through targeting of nicotinic receptors, often treated with acetylcholinesterase inhibitors.

Role:
- Integral in the brain’s reward system; assists in movement and unlearning fearful associations.
Associations: Low dopamine levels linked to Parkinson’s disease, schizophrenia, and attention deficit disorder.
Catecholamines: Catecholamines (dopamine, epinephrine, norepinephrine) released during stress affect physiological functions and the fight-or-flight response.

Location: Midbrain, characterized mainly by dopaminergic neurons projecting to various brain areas.
Functions: Involved in motivation, reward, and addiction.

Chemical Nature: Both act as neurotransmitters and hormones, classified as catecholamines.
Comparison:
- Epinephrine reacts with alpha and beta receptors; norepinephrine interacts with alpha receptors.
Functions: Key roles in arousal, stress response, and modulation of cardiovascular functions.

Definition: The primary site of norepinephrine production; involved in arousal, vigilance, and attention.
Impact of Aging: Decline in LC neurons linked to neurodegenerative disorders such as Alzheimer’s and Parkinson’s diseases.

Definition: Sleep is a recurring state characterized by altered consciousness, inhibited sensory activity, reduced muscle activity, and changes in brain patterns.
Types of Sleep: Alternates between REM and non-REM sleep stages, each contributing to different physiological and psychological processes.
Key Research Contributions: Identified distinct stages of sleep (NREM & REM), underscoring the complexity of sleep beyond passive restorative functions.

Definition: Daily physical, mental, and behavioral changes responsive primarily to light and darkness.
Master Clock: Suprachiasmatic nucleus (SCN) regulates biological clocks across tissues, synchronizing them via input from light.
Health Implications: Disruption of circadian rhythms linked to various health disorders.

Brain Function Maintenance: Sleep is essential for cognitive function, memory consolidation, and overall metabolic processes.
Consequences of Sleep Deprivation: Implications include increased caloric intake, risk of accidents, unattractiveness, immune system weakness, and increased chronic disease risks.
Long-term Impacts: Continued deprivation can lead to cognitive decline and increased mortality risk.