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The Neuron
Dendrites: Branch-like structures that receive messages from other neurons.
Soma (Cell Body): The neuron's life-support center, containing the nucleus.
Nucleus: Houses the cell's genetic material and decides whether the neuron should fire.
Axon: The long, thin fiber that carries electrical messages away from the cell body.
Myelin Sheath: A fatty layer that insulates the axon and speeds up the electrical signal.
Nodes of Ranvier: Gaps in the myelin sheath that allow the signal to jump, further increasing speed.
Schwann Cells: Special cells that form the myelin sheath in the peripheral nervous system.
Axon Terminal: The end of the axon where it connects with other neurons or muscles.
Terminal Buttons: Located at the axon terminal, these store and release neurotransmitters.
Reuptake: The process where excess neurotransmitters are reabsorbed by the sending neuron to be used again.
Think of It Like This:
Imagine a neuron as a tiny messenger:
Dendrites receive a message like a mailbox.
The soma (cell body) reads the message.
The axon is like a delivery truck, carrying the message along a highway (myelin sheath).
The terminal buttons deliver the message to another neuron (or muscle) like a package.
Reuptake is like returning the delivery truck to the depot to pick up more packages.
Neural Communication
The Action Potential: The Neuron's "Message"
Resting Potential (-70mV): The neuron is at rest, like a battery charged and ready.
Inside: Mostly potassium ions (K+)
Outside: Mostly sodium ions (Na+)
Threshold (-55mV): The trigger point – if enough stimulation reaches the neuron, it fires.
Action Potential: A brief electrical charge that travels down the axon, like a wave.
Depolarization: Sodium gates open, and Na+ ions rush in, making the inside of the neuron positive.
Repolarization: Potassium gates open, and K+ ions rush out, restoring the negative charge inside.
Refractory Period: A short "recharge" time where the neuron cannot fire again.
Key Points About Neural Firing
All-or-None Principle: A neuron either fires completely or not at all. There are no partial fires.
Semi-Permeable Membrane: The axon's membrane has gates that control the flow of ions (Na+ and K+).
Neurotransmitters: Chemical Messengers
Synapse: The tiny gap between neurons.
Receptor Sites: Specialized places on the receiving neuron's dendrites where neurotransmitters fit like keys in locks.
Excitatory Neurotransmitters: Increase the chance the next neuron will fire.
Inhibitory Neurotransmitters: Decrease the chance the next neuron will fire.
Important Neurotransmitters
Acetylcholine (ACh):
Functions: Muscle movement, learning, memory, attention.
Too Much: Muscle spasms
Too Little: Alzheimer's disease
Dopamine:
Functions: Mood, emotion, reward, arousal.
Too Much: Schizophrenia, addiction
Too Little: Parkinson's disease
Norepinephrine (Noradrenaline):
Functions: Alertness, arousal, "fight-or-flight" response, mood.
Too Much: Anxiety
Too Little: Depression
GABA (Gamma-Aminobutyric Acid):
Functions: Main inhibitory neurotransmitter, calming the brain, regulating sleep.
Too Much: Sleep and eating disorders
Too Little: Anxiety, epilepsy, insomnia
Glutamate:
Functions: Main excitatory neurotransmitter, learning, memory.
Too Much: Overstimulation, migraines, seizures
Endorphins:
Functions: Pain relief, pleasure, stress reduction.
Too Much: Artificial highs, reduced pain sensitivity
Too Little: Possible link to addiction
Serotonin:
Functions: Mood regulation, appetite, sleep.
Too Much: Hallucinations
Too Little: Depression
Agonists vs. Antagonists: How Drugs Affect Neurotransmitters
Agonists: Mimic neurotransmitters, enhancing their effects.
Antagonists: Block neurotransmitters, inhibiting their effects.
The Nervous System
Central Nervous System (CNS):
Brain: The control center, responsible for thoughts, emotions, and actions.
Spinal Cord: The information highway, transmitting messages between the brain and the rest of the body.
Peripheral Nervous System (PNS): The nerves that branch out from the CNS to the rest of the body.
Autonomic Nervous System (ANS): Controls involuntary bodily functions (heartbeat, digestion, etc.)
Sympathetic Nervous System: Activates the "fight-or-flight" response in stressful situations, increasing heart rate, breathing, and releasing adrenaline.
Parasympathetic Nervous System: Calms the body down after stress, promoting rest and digestion (homeostasis).
Somatic Nervous System: Controls voluntary muscle movement and carries messages from the sense organs.
Types of Neurons
Sensory Neurons (Afferent): Carry messages from the senses to the central nervous system (CNS).
Interneurons: Found only in the CNS, act as messengers between sensory and motor neurons.
Motor Neurons (Efferent): Carry messages from the CNS to muscles and glands.
The Endocrine System
Key Features:
A slow-acting but longer-lasting communication system.
Works with the nervous system to maintain balance (homeostasis).
Supports the "fight-or-flight" response during stress.
Major Glands and Hormones:
Pituitary Gland: The "master gland," controls other glands and releases growth hormone.
Thyroid Gland: Produces thyroxine, which regulates metabolism (how your body uses energy).
Pineal Gland: Secretes melatonin, which influences sleep-wake cycles.
Adrenal Glands: Located on top of the kidneys, these release:
Adrenaline (epinephrine): For quick bursts of energy in stressful situations.
Corticosteroids (cortisol): For longer-term stress responses and blood sugar regulation.
Gonads (testes/ovaries): Produce sex hormones that influence development and reproduction.
Studying the Brain
Protection: The brain and spinal cord are cushioned by cerebrospinal fluid and encased in meninges (protective membranes).
Lesions and Ablation: Intentionally damaging or removing brain tissue to study the effects on behavior. This is done in research and sometimes to treat certain medical conditions.
Brain Imaging Techniques
Electroencephalogram (EEG): Records electrical activity on the brain's surface using electrodes placed on the scalp. Useful for studying brain waves and identifying problems.
Magnetic Resonance Imaging (MRI): Creates detailed images of brain tissue using magnetic fields and radio waves. Helpful for detecting tumors and injuries.
Functional Magnetic Resonance Imaging (fMRI): Measures brain activity by tracking changes in blood flow. Shows which brain areas are active during tasks.
Positron Emission Tomography (PET): Uses a radioactive tracer (like glucose) to reveal brain activity and metabolism.
Computerized Tomography (CT): Creates cross-sectional images of the brain (and body) using X-rays. Good for seeing bone structures.
Brain Stimulation Therapies
Deep Brain Stimulation (DBS): An electrode implanted in the brain delivers electrical impulses to specific areas, used to treat conditions like Parkinson's disease.
Transcranial Magnetic Stimulation (TMS): A noninvasive method using magnetic fields to stimulate or inhibit nerve cells in the brain, used to treat depression and other disorders.
The Cerebral Cortex: The Brain's Outer Layer
Wrinkled surface with grooves (sulci) and ridges (gyri) to maximize surface area.
Divided into two hemispheres (left and right) connected by the corpus callosum, a bundle of nerve fibers that enables communication between them.
Contains association areas responsible for complex mental processes like thinking, memory, planning, and language.
The Four Lobes and Their Functions:
Frontal Lobe:
Executive Functions: Decision-making, problem-solving, reasoning, planning.
Personality: Influences traits like impulsivity and social behavior.
Motor Cortex: Controls voluntary muscle movements.
Parietal Lobe:
Sensory Processing: Receives and interprets touch, pressure, temperature, and pain signals from the body.
Somatosensory Cortex: The main area for processing touch sensations.
Occipital Lobe:
Visual Processing: Responsible for vision.
Primary Visual Cortex: Processes basic visual information from the eyes.
Visual Association Cortex: Interprets visual information to recognize objects and understand the visual world.
Temporal Lobe:
Auditory Processing: Responsible for hearing.
Wernicke's Area: Crucial for understanding language (located in the left temporal lobe).
Right Temporal Lobe: Processes music and tonal changes.
Lower Temporal Lobe: Involved in some visual processing, like recognizing patterns.
Agnosia: A condition where damage to the temporal lobe makes familiar objects unrecognizable.
The Brainstem
Function: Controls essential life-supporting functions.
Key Structures:
Medulla: Regulates heart rate, breathing, digestion, swallowing, and sneezing. Think of it as the brain's autopilot.
Pons: A bridge that relays information between the brainstem and higher brain regions (cerebellum and cortex).
Reticular Formation: A network of nerves involved in:
Arousal: The state of being awake, alert, and attentive.
Pain Modulation: Helps control the intensity of pain signals.
Reticular Activating System (RAS): A part of the reticular formation that regulates the sleep-wake cycle and filters sensory input.
The Cerebellum and Limbic System
Cerebellum:
Function: Coordinates fine motor movements, balance, and posture. Think of it like the brain's athlete.
Important Note: The spinal cord controls reflexes, which are automatic responses to stimuli that don't require conscious thought.
Limbic System: Often called the "emotional brain," it plays a key role in memory, emotions, and drives.
Thalamus: The brain's sensory switchboard. All sensory information (except smell) passes through the thalamus before being sent to other areas for processing.
Hippocampus: Essential for forming and retrieving long-term memories, as well as spatial navigation (knowing where you are).
Amygdala: The emotional center, especially involved in fear, aggression, and emotional memories.
Hypothalamus: Regulates the body's internal state (homeostasis) by controlling:
Hunger and thirst
Body temperature
Sleep-wake cycles
The endocrine system (hormone release)
Lateral Hypothalamus: Triggers feelings of hunger.
Ventromedial Hypothalamus: Signals fullness or satiety.
More Brain Structures and Functions
Basal Ganglia:
Functions: Motor control, cognition (pleasure, motivation, learning, reward).
Dopamine Connection: The basal ganglia are involved in releasing dopamine, a neurotransmitter associated with pleasure and reward.
Language Areas (Left Hemisphere):
Wernicke's Area: Understanding language (spoken and written).
Broca's Area: Producing speech.
Hemispheric Specialization:
Left Hemisphere: Language, logic, analysis.
Right Hemisphere: Spatial reasoning, creativity, facial recognition.
Brain Plasticity (Neuroplasticity): The brain's ability to change and adapt throughout life. If one area is damaged, another area may take over its function.
Key Figures in Brain Research
Carl Wernicke: Discovered the area of the brain responsible for language comprehension.
Michael Gazzaniga & Roger Sperry: Pioneered research on split-brain patients, revealing differences in function between the two hemispheres.
Phineas Gage: A railroad worker whose personality changed dramatically after a brain injury, providing early insights into the localization of brain functions.
Sleep and the Brain
Circadian Rhythm: Our 24-hour biological clock, regulated by the hypothalamus. It controls sleep-wake cycles, body temperature, and other bodily functions.
Sleep Cycle: Each cycle lasts about 90 minutes and includes different stages of sleep, including REM (rapid eye movement) sleep when most dreaming occurs.
Sleep and the Brain
Measuring Sleep: EEG and Brain Waves
Electroencephalogram (EEG): Records brain waves using electrodes placed on the scalp. Different sleep stages have distinct brain wave patterns:
Awake/Alert: Beta waves
Relaxed: Alpha waves
NREM-1 (Light Sleep): Theta waves
NREM-2 (Sleep Spindles): Brief bursts of brain activity
NREM-3 (Deep Sleep): Delta waves
Stages of Sleep
NREM-1 (Hypnagogic State): Transitional stage, relaxed but not fully asleep. May experience hallucinations.
NREM-2: Deeper sleep with sleep spindles (bursts of brain activity).
NREM-3 (Deep Sleep): Slow-wave sleep, essential for physical restoration and growth hormone release.
REM (Rapid Eye Movement): Brain activity increases, vivid dreams occur, muscles are paralyzed.
Sleep Deprivation: The Consequences
Lack of sleep can lead to:
Difficulty concentrating and reduced productivity
Weakened immune system
Increased risk of accidents
Mood problems (irritability, anxiety)
Hallucinations (in extreme cases)
Why Do We Sleep? Theories
Protection: Sleep kept our ancestors safe from predators at night.
Restoration: Sleep allows the body and brain to repair and rebuild.
Memory Consolidation: Sleep helps strengthen and organize memories.
Growth: The pituitary gland releases growth hormone during sleep, particularly in deep sleep.
Sleep Disorders
Insomnia: Difficulty falling asleep or staying asleep.
Narcolepsy: Sudden, uncontrollable sleep attacks, sometimes entering REM sleep directly.
Night Terrors: Abrupt awakenings with intense fear and panic, usually occurring during deep sleep (NREM-3).
Sleep Apnea: Repeatedly stopping and starting breathing while asleep.
Sleepwalking (Somnambulism): Walking or performing complex behaviors while asleep.
REM Behavior Disorder: Acting out dreams due to a lack of muscle paralysis during REM sleep.
Theories of Dreaming
Sigmund Freud's Wish Fulfillment: Dreams are a safe way for the unconscious mind to express hidden desires and conflicts.
Manifest Content: The remembered storyline of a dream.
Latent Content: The hidden, symbolic meaning of a dream.
Information Processing: Dreams help us sort through and consolidate memories from the day.
Physiological Function: Dreams may help maintain and develop neural pathways in the brain.
Activation-Synthesis Theory: Dreams are the brain's attempt to make sense of random neural activity during sleep.
Cognitive Theory: Dreams reflect our knowledge, understanding, and thoughts.
Psychoactive Drugs and Their Effects
Psychoactive Drugs: Chemicals that change perceptions, moods, and consciousness.
Tolerance: The diminishing effect of a drug with regular use, requiring larger doses to achieve the same effect.
Withdrawal: Unpleasant physical and psychological symptoms experienced when stopping or reducing drug use.
Dependence (Addiction): A compulsive craving for and use of a drug despite negative consequences.
Types of Psychoactive Drugs
Depressants: Slow down brain activity and bodily functions.
Alcohol: Reduces inhibitions, impairs judgment and memory, slows reaction time.
Barbiturates: Sedatives or tranquilizers that can be highly addictive and dangerous.
Opiates (e.g., heroin, morphine): Painkillers that are highly addictive and can cause overdose.
Stimulants: Increase brain activity and bodily functions.
Caffeine: Boosts alertness and energy.
Nicotine: Highly addictive, found in tobacco products.
Amphetamines: Suppress appetite, increase energy, but can lead to anxiety and dependence.
Methamphetamine: A powerful, illegal stimulant with severe side effects and high risk of addiction.
Stimulants and Hallucinogens
Cocaine:
Effect: Intense euphoria and energy by blocking dopamine reuptake.
Risks: Highly addictive, heart problems, paranoia.
Ecstasy (MDMA):
Effects: Increased empathy, euphoria, energy.
Risks: Dehydration, overheating, high blood pressure, long-term damage to serotonin neurons.
Hallucinogens (Psychedelics): Alter perceptions, causing hallucinations.
LSD: Powerful hallucinogen with unpredictable effects, can cause intense emotions and "bad trips."
Marijuana (THC):
Effects: Relaxation, altered perception, impaired coordination and memory.
Risks: Potential for addiction, impaired cognitive function, lung damage (if smoked).
Why People Use Drugs
Biological Factors: Genetic predisposition, changes in the brain's reward system.
Psychological Factors: Stress, trauma, mental health disorders.
Social-Cultural Factors: Peer pressure, cultural norms, media influence.
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