Brain Functions and Development

• The brain's functions include essential life-sustaining activities and complex neural functions.
• It controls heart rate, respiratory rate, blood pressure, and maintains the internal environment through the autonomic and endocrine systems.
• The brain innervates the head, neck, and thoracic and abdominal viscera through cranial nerves.
• It performs high-level tasks, including those associated with intelligence, consciousness, memory, sensory-motor integration, emotion, behavior, and socialization.

Embryonic Development of the Brain

• The brain develops from the rostral part of the neural tube in the fourth week.
• The neural tube expands, forming three primary brain vesicles.
• The three primary vesicles are the prosencephalon (forebrain), mesencephalon (midbrain), and rhombencephalon (hindbrain).
• The caudal portion of the neural tube becomes the spinal cord.
• In week 5, the three primary vesicles divide into five secondary brain vesicles.
• The prosencephalon divides into the telencephalon and diencephalon.
• The mesencephalon remains undivided.
• The rhombencephalon divides into the metencephalon and myelencephalon.
• The brain develops two major bends, or flexures: a midbrain flexure and a cervical flexure.
• Each secondary brain vesicle develops rapidly to produce the major structures of the adult brain.
• The telencephalon develops into the cerebral hemispheres, collectively called the cerebrum.
• The diencephalon develops into the thalamus, hypothalamus, and epithalamus.
• The mesencephalon forms the midbrain.
• The metencephalon becomes the pons (ventrally) and the cerebellum (dorsally).
• The myelencephalon forms the medulla oblongata.
• The midbrain, pons, and medulla constitute the brain stem.
• The central cavity of the neural tube enlarges to form the ventricles of the brain.
• During the late embryonic and fetal periods, the brain grows rapidly, and the cerebral hemispheres envelop the diencephalon and midbrain.
• Each cerebral hemisphere bends into a horseshoe shape.
• By week 26, the cerebral hemispheres' surfaces crease and fold.
• At birth, the hemispheres are wrinkled, allowing more neurons to fit in the limited space.