Neuroscience: Neurons and Neurotransmitters

Neuroscience and the Brain

• Neuroscience is the study of the nervous system, including the brain, spinal cord, and peripheral nerves.

Neurons

• A neuron is a nerve cell that sends information via electrical and chemical signals.
• The three main parts of a neuron are dendrites (receive signals), cell body/soma (contains the nucleus), and axon (sends signals).
• The myelin sheath is a fatty layer around the axon that insulates it and speeds up neural impulses.
• An action potential is an electrical impulse that travels along the axon, releasing neurotransmitters at the synapse.
• At the synapse, neurotransmitters cross the gap between neurons and bind to receptor sites on the receiving neuron.

Neurotransmitters

• Acetylcholine is involved in muscle movement and memory.
• Dopamine is linked to reward, motivation, and motor control.
• Serotonin affects mood, appetite, and sleep.
• GABA serves as the main inhibitory neurotransmitter.
• Glutamate is the main excitatory neurotransmitter.
• Endorphins provide natural pain relief and euphoria.

Central Nervous System (CNS) and Cerebral Cortex

• The central nervous system (CNS) includes the brain and spinal cord, serving as the body's control center.
• The four lobes of the cerebral cortex are the frontal, parietal, occipital, and temporal lobes.
• The Occipital lobe is primarily responsible for vision.

Limbic System

• The limbic system involves emotion, motivation, and memory and includes the amygdala, hippocampus, and hypothalamus.

Brain Lateralization

• Lateralization of function refers to the specialization of each brain hemisphere (left or right) for certain tasks, such as language (left) and spatial tasks (right).

Brain Plasticity

• Neuroplasticity is the brain's ability to reorganize and make new neural connections for adaptation and learning.
• The corpus callosum that connects the left and right hemispheres is severed in split-brain surgery.
• The hypothalamus regulates bodily functions like hunger, thirst, temperature, and controls the pituitary gland.

Sensation and Perception

• Sensation is detecting raw sensory input, while perception involves interpreting and organizing that input.
• An absolute threshold is the minimum stimulation needed to detect a stimulus 50% of the time.
• Signal detection theory explains how stimuli are detected based on sensory and psychological factors, including attention and expectations.

Vision

• Rods and cones are contained in the retina (the layer at the back of the eyeball).
• Rods function in low light and do not detect colors.
• Cones enable color vision and detailed vision in bright light.
• The trichromatic theory of color vision suggests that three types of cones (red, green, blue) combine for the full spectrum of colors.
• Monocular depth cues include linear perspective, relative size, interposition, and texture gradient.

Illusions

• An illusion is a perception that deviates from reality, demonstrating top-down processing and the brain's interpretive role.

Transduction

• Transduction is the process by which physical energy (light, sound, chemicals) is converted into neural signals.

Hearing

• Place theory posits that pitch depends on where the basilar membrane is stimulated.
• Frequency theory suggests that pitch depends on how fast the membrane vibrates.

Taste, Smell, and Pain

• Humans detect sweet, sour, salty, bitter, and umami (savory) taste qualities.
• The olfactory bulb processes smell signals after olfactory receptor neurons detect airborne molecules.
• Fast nerve fibers carry quick, sharp pain signals.
• Slow fibers carry dull, aching pain signals.

Top-Down Processing etc

• Top-down processing occurs when knowledge, expectations, or experiences shape the interpretation of sensory input.
• Selective attention is the brain's ability to focus on one stimulus while filtering out others.

Sleep and Consciousness

• Circadian rhythm is the body's ~24-hour biological cycle, which regulates sleep/wake patterns and other bodily functions.
• The sleep stages are N1 (light sleep), N2 (sleep spindles), N3 (deep/slow-wave sleep), and REM (rapid eye movement).
• REM sleep is called paradoxical sleep, the brain is active (like wakefulness), but the body is largely paralyzed.
• Examples of sleep disorders include insomnia (trouble falling or staying asleep), sleep apnea (stop breathing), and narcolepsy (sudden sleep attacks).
• REM rebound is an increase in REM sleep following REM deprivation.
• Nightmares are vivid bad dreams in REM sleep (usually remembered).
• Night terrors are intense fear experiences in N3, often not remembered.
• Microsleeps are brief, unintended episodes of sleep (seconds long) in a person who is severely sleep-deprived.
• The restorative theory explains that sleep is necessary for the body and brain to repair, grow, and consolidate memories.

Hallucinations and the Hypothalamus

• Hypnagogic hallucinations are vivid, dream-like experiences that occur just as one is falling asleep, common in narcolepsy.
• The suprachiasmatic nucleus (SCN) acts as the "master clock" in the hypothalamus and regulates circadian rhythms.

Psychoactive Substances

• Psychoactive drugs are substances that alter mood, perception, thought, or behavior by affecting brain chemistry.
• Hallucinogens cause hallucinations or sensory distortions (e.g., LSD, psilocybin).
• Alcohol ranks second in dependence/abuse in the US, following nicotine.
• Examples of depressants include alcohol, barbiturates, and benzodiazepines (e.g., Valium).
• Opioids mimic endorphins, the body's natural painkillers.
• Stimulants increase CNS (central nervous system) activity (e.g., caffeine, cocaine), while depressants slow CNS activity (e.g., alcohol).
• Hallucinogens distort or intensify sensory experiences and can lead to hallucinations.
• Addiction is considered a brain disease. It involves changes in brain chemistry and pathways that underlie craving and control loss.