The cerebrum is the largest part of the human brain, made up of two hemispheres and four of the main parts of the brain. When envisioning a human brain, it is generally the cerebrum that comes to mind. Everything not controlled by the brain stem and the cerebellum is controlled by the cerebrum. Without this part of the brain, sight, smells, movement, muscle control, and even the ability to make a complicated choice would be impossible.
The cerebral cortex is the characteristic wrinkled surface of the brain, full of tightly compacted neurons with all sorts of complex jobs. This area of the cerebrum does not only serve as the main surface of the brain, but also controls function such as vision and motor response. The cortex has four areas, or “lobes,” known as the frontal, parietal, occipital, and temporal. These lobes determine how a person perceives and reacts to sensory data, emotional responses, orientation, memory, and speech abilities.
The limbic system handles more handles emotions more specifically than the cortex, and consists of the thalamus, amygdala, hippocampus, and hypothalamus. The hypothalamus processes feelings like hunger and thirst and controls the pituitary gland, which is responsible for growth. The amygdala regulates feelings such as fear or anxiety. The hippocampus handles the ability to turn short-term learning into long-term memory, while the thalamus primarily relays sensory data to the cerebral cortex.
Unlike the sensation and data from touch, taste, hearing, or sight, smells are routed through a part of the brain known as the olfactory bulb. It is this tiny system that allows humans to tell strong scents from weak ones, distinguish smells from one another, and blot out general scents to focus on specific, important ones. A malfunctioning olfactory bulb can be responsible for a diminished sense of smell, since it is the system that relays information from the nose to the brain.
The basal ganglia are located deep within the structures of the cerebrum. Really a collection of nuclei that surround the thalamus and limbic system, the basal ganglia are responsible for quite a lot, despite their tiny size. Voluntary movement, learning, and motor behavior are managed by the basal ganglia. One interesting function of this part of the cerebrum is action selection which is what allows a person to make a choice given several options. Mental disorders such as obsessive compulsive disorder and attention deficit hyperactivity disorder are associated with a malfunctioning basal ganglia, as are motor control conditions such as Parkinson's disease.