Summary
Highlights
The brain starts as a hollow neural tube at three weeks gestation. By five weeks, this tube develops into five vesicles: the telencephalon, diencephalon, mesencephalon, metencephalon, and myelencephalon. Each vesicle develops into distinct parts of the adult brain.
The telencephalon, meaning 'end brain,' develops into the cerebrum, the largest part of the brain. The cerebrum is divided into two hemispheres by the longitudinal fissure. The left hemisphere controls the right side of the body, and the right hemisphere controls the left. Functions can be lateralized, like language predominantly in the left hemisphere. The outer layer of the cerebrum, the cerebral cortex (1-5mm thick), is responsible for consciousness. It's divided into lobes: frontal (motor cortex, higher-order reasoning), parietal (somatosensory cortex, touch, pain, temperature), occipital (vision), and temporal (hearing), and the insula (taste). Deeper within the cerebrum are parts of the basal ganglia (initiates and smooths out motor movement) and the limbic system (emotion).
The diencephalon, meaning 'between brain,' develops into the thalamus and hypothalamus. The thalamus acts as the brain's 'post office' or relay center, sorting sensory information and sending it to the appropriate cortical areas. The hypothalamus is the 'master regulator' of the endocrine system (hormones) and the autonomic nervous system (fight or flight, rest and digest).
The mesencephalon, meaning 'middle brain,' develops into the midbrain, which is the most superior part of the brainstem. Its specific functions are discussed later with the rest of the brainstem.
The metencephalon, meaning 'behind brain,' develops into the pons and the cerebellum. The cerebellum is crucial for fine-tuning motor activity, including muscle tone, balance, and coordination, by interacting with signals from the motor cortex.
The myelencephalon, or 'marrow brain,' forms the medulla oblongata, often simply called the medulla. This is the deepest part of the brain and the lowest aspect of the brainstem.
The brainstem, comprised of the midbrain, pons, and medulla, is vital for basic bodily functions. It regulates heart rate, breathing, blood pressure, and certain head and neck reflexes (like cough and corneal reflexes). It also houses the nuclei of the 12 cranial nerves, which control sensation and motor movement of the head and neck, and acts as a conduit for information flow between the brain and the body.