Neurons, Synapses, Neurotransmitters, and Brain Systems – Comprehensive Study Notes

Neurons transmit information electrochemically: electrical impulse (action potential) travels along the neuron, becoming positive, then returning to negative.
At the axon terminal, neurotransmitters are released from vesicles into the synapse (a 1 \times 10^{-6}\text{ inches} gap).
Neurotransmitters bind to receptors on neighboring neurons, potentially triggering a new impulse.
After release, most neurotransmitters are recycled via reuptake or destroyed.

Neurotransmitters are released, cross the synapse, bind to receptors, and are then cleared (reuptake or destruction).
Drugs can act as antagonists (block activity), agonists (enhance activity), or reuptake inhibitors (prolong activity).

Excitatory neurotransmitters encourage firing; inhibitory neurotransmitters dampen activity.
Acetylcholine (ACH): Movement, attention, memory. Low ACH links to Alzheimer's.
Serotonin: Mood, sleep, appetite, arousal. Low levels linked to some depression; SSRIs increase serotonin in the synapse.
GABA: Main inhibitory neurotransmitter; reduces excitability, linked to arousal regulation and sleep.
Dopamine: Movement, attention, learning, motivation, reward. Excess linked to schizophrenia; low levels in Parkinson's.

Agonists: Increase neurotransmitter activity (e.g., nicotine for ACH, Adderall for dopamine).
Antagonists: Block or slow neurotransmitter activity (e.g., Thorazine for dopamine, some venoms for ACH).
Reuptake inhibitors: Block reuptake, increasing neurotransmitter presence in the synapse (e.g., SSRIs for serotonin).

Central Nervous System (CNS): Brain and spinal cord.
Peripheral Nervous System (PNS): Nerves outside CNS, connects to body.
- Somatic: Voluntary control (skeletal muscles).
- Autonomic: Involuntary control (glands, smooth muscle, heart).
  - Sympathetic: "Fight or flight."
  - Parasympathetic: "Rest and digest."
Spinal cord: Carries brain signals, governs reflexes (e.g., hot stove, patellar reflex).
- Hot stove reflex: sensory, interneuron, motor neuron (3 neurons, 2 synapses).
- Patellar reflex: sensory, motor neuron (2 neurons, 1 synapse).

Glands release hormones into the bloodstream (slower, diffuse effects).
Hypothalamus: Brain region controlling the pituitary gland.
Pituitary gland: "Boss gland," regulates other glands and bodily functions.
Thyroid: Regulates metabolism and growth.
Gonadal hormones: Testosterone (males), estrogen (females) influence sexual characteristics and behaviors.

Brain stem (basement): Basic life support.
- Medulla: Heartbeat, respiration.
- Reticular formation: Arousal, wakefulness.
- Cerebellum: Movement, balance, coordination.
Limbic system (first floor): Emotions, drives.
- Amygdala: Fear, anger, emotional processing.
- Hippocampus: Memory consolidation.
- Hypothalamus: Homeostasis (hunger, thirst, temperature), endocrine control.
- Thalamus: Sensory relay for most senses (except smell).
Cerebral cortex (penthouse): Higher-order thinking.
- Frontal lobe: Decision making, planning, personality.
- Parietal lobe: Sensory processing, spatial orientation.
- Temporal lobe: Auditory processing, language, memory.
- Occipital lobe: Visual processing.
Lateralization: Hemispheres specialize in some functions (e.g., split-brain research).