The Human Brain

The brain is protected by 3 membranous coverings called meninges (meninx: membrane) which continue backwards on the spinal cord.

Inflammation of the meninges is called meningitis.

• Brain weighs ~1.35 kg (2% body weight, 80% water), protected in cranium, uses over 25% of body oxygen.
• Meninges & CSF — Three membranes: Dura mater → Arachnoid → Pia mater. CSF between them cushions the brain and fills the ventricles and the spinal canal.
• Forebrain — Cerebrum (85% brain mass; 2 hemispheres; 4 lobes — frontal, parietal, temporal, occipital); Diencephalon (contains thalamus and hypothalamus — regulates homeostasis).
• Midbrain — Has corpora quadrigemina (superior colliculi = visual; inferior colliculi = auditory reflexes) and red nucleus (controls posture and motor coordination).
• Hindbrain — Pons (connects brain parts); Cerebellum (balance, posture, muscle tone); Medulla Oblongata (controls heartbeat, respiration, and reflex actions like coughing, sneezing).