Brain Structure

During human embryonic development, the brain forms from the walls of the neural tube. The human proto-brain is divided into four sections: the forebrain, the midbrain, the hindbrain, and the spinal cord. The forebrain is the largest section and forms two distinct structures, the telencephalon and the diencephalon. The telencephalon is the largest of the two and goes on to form the cortex that wraps around the diencephalon and midbrain sections in the fully developed brain. The diencephalon goes on to form the group of structures commonly known as the brain stem, composed of the thalamus, the hypothalamus, and the basal telencephalon. In addition to these grey matter structures, the developing brain forms the inner capsule. The inner capsule is a group of white matter - myelinated axon bundles - continuous with the cortical white matter that connects the thalamus to the cortex. Another important white matter structure is a commissure known as the corpus callosum that is an important link between the two hemispheres of the brain. The midbrain is made of the tectum and the tegmentum, which are responsible for a lot of auditory and visual reflexes. Through it runs the cerebrospinal aqueduct that transports cerebrospinal fluid (CSF) between the brain and spinal cord. As for the forebrain, the hindbrain can be split into two sections. The rostral-most section contains the cerebellum, our motor control centre, and the pons, which serves as a relay centre between the forebrain and the cerebellum. The caudal-most section contains the medulla, which switches signals between the body and the brain from ipsilateral to contralateral. Lastly, the spinal cord is composed of the dorsal horn, the intermediate zone, and the ventral horn. These grey matter structures are all involved in the relay of signals between the body and the brain. The dorsal horn is involved in signal reception, the intermediate zone is largely composed of interneurons and serves as a relay point, and the ventral horn is the location of efferent neurons that carry information to effector organs in the body such as muscles.