The brain is the central organ of the human nervous system—commanding thought, emotion, sensation, and movement. It’s a complex, multilayered structure with billions of neurons and over 100 trillion synapses.
🧠 Major Divisions of the Human Brain
1. Cerebrum
- Largest part (about 80% of brain mass)
- Divided into left and right hemispheres
- Each hemisphere has 4 lobes:
- Frontal lobe: reasoning, planning, motor control, emotions
- Parietal lobe: sensory input, spatial awareness
- Temporal lobe: hearing, memory, language
- Occipital lobe: vision
- Covered by the cerebral cortex (gray matter)
2. Cerebellum
- Located at the back of the brain, under the cerebrum
- Coordinates movement, balance, and posture
- Contains more neurons than the cerebrum but is much smaller
3. Brainstem
- Connects brain to spinal cord
- Controls basic life functions: breathing, heart rate, swallowing
- Divided into:
- Midbrain
- Pons
- Medulla oblongata
4. Diencephalon
- Deep inside the brain, includes:
- Thalamus: relay station for sensory signals
- Hypothalamus: controls hormones, temperature, hunger, circadian rhythms
- Epithalamus: includes the pineal gland (produces melatonin)
🧬 Brain Matter & Cells
- Gray matter: contains neuron cell bodies (processing areas)
- White matter: contains myelinated axons (information highways)
- Glial cells: support neurons (astrocytes, microglia, oligodendrocytes)
🧪 Other Key Structures
| Structure | Function |
|---|---|
| Corpus callosum | Connects the left and right cerebral hemispheres |
| Limbic system | Emotions, memory (includes hippocampus, amygdala) |
| Basal ganglia | Motor control, habit learning |
| Ventricles | Cavities filled with cerebrospinal fluid (CSF) |
| Meninges | 3 protective layers (dura mater, arachnoid, pia mater) |
🩺 Brain Stats
- Weight: ~1.4 kg (3 lbs)
- Energy use: ~20% of body’s total
- Oxygen demand: extremely high—~25% of total oxygen supply
- Neurons: ~86 billion
- Synapses: estimated 100+ trillion
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