The anatomy of the human brain is as complex as its function. As our understanding increases about how the brain works, the brain is theoretically divided (meaning there are no natural lines or separations) into lobes from front to back based on the relative placement and known function. The brain is further broken down into various regions and subregions that are more specifically, and theoretically, associated with exact cause and effect actions of the nervous system. The distinction between all of these regions is blurred as they are activated by activities and experiences to produce our actions and reactions. Signals overlap across the grey matter as an intricate web of electrical communication that every part of the human anatomy requires to function, both voluntary and involuntary.
Gross Anatomy
The main portion of the brain is called the cerebrum and is contained within the skull.The cerebrum is divided into the right and left hemispheres, which is where the terms “right brain” and “left brain” come from when discussing how certain signals are not equally processed on both sides. The surface of the cerebrum, the cortex, has a folded appearance, increasing surface area to fit more neurons into the cerebral cortex.The folds are called gyri (singular, gyrus).
The underside of the brain is called the cerebellum, which is from the Latin “little brain”. Attached to the cerebellum is the brain stem, which is the lower part of the brain where the spinal cord enters the cerebrum. The cranial nerves and the motor and sensory neurons of the spinal cord converge in the brain stem, making it an extremely vulnerable structure. There are also four cavities in the cerebrum, called ventricles, that produce and circulate cerebrospinal fluid (CSF). CSF is a clear fluid made in the ventricles by the choroid plexus from the arterial blood in order to circulate nutrients to the brain and spinal cord. The CSF also cushions the brain and transports hormones.
Cellular Level
The basic building blocks of the grey matter of the brain are cells called neurons. Each neuron stretches out from its cell body, or nucleus, to connect to other neurons via a synapse. Axons carry signals away from the cell body, whereas dendrites carry them toward the cell body (for more about the structure and function of neurons specifically, see the NCBI bookshelf).
Cerebral Brain Regions
The frontal lobe of the cerebrum is, as the name implies, the front part of the brain. The frontal lobe contains the primary motor cortex, which includes control of the voluntary movements of specific body parts. The temporal lobe is beneath the frontal lobe and above the cerebellum, folding out around the sides of the brain in the temple region and extending posterior to beneath the occipital lobe. The temporal lobe contains the primary auditory cortex. This lobe includes the hippocampus, which is involved in memory formation.
The parietal lobe is the top and posterior portion of the brain folding down along the sides to meet the temporal lobe behind the frontal lobe and above the occipital lobe. This lobe is involved in sensory integration, including hand-eye coordination. The occipital lobe is the smallest lobe and located at the very back of the brain. It is the visual processing center and contains most of the human visual cortex.
Brain Stem Regions
The brain stem is divided into three parts. The medulla oblongata is the lower portion and is involved in autonomic functions. The midbrain, also known as the mesencephalon, is the middle portion of the stem and is closely associated with the motor system pathways. Components of the midbrain include the substantia nigra, cerebral aqueduct, and red nucleus. The pons is the upper part of the brain stem where the cerebellum is attached and relays information between the cerebellum and cerebrum.
