The brain is the most complex organ in the human body. It is responsible for what people say, do and think. The brain and its partner, the spinal cord, complete the central nervous system. They work together in sync to keep our processes working, but the brain is the organ in charge. The human brain is located within the structure of the skull and is fully grown in size by age six. An average adult brain weighs approximately three pounds and is heavier than the six year old brain. This is due to the growth of the cells in the brain. The number of cells does not change but the size of those cells do grow as we head toward adulthood.
The brain is composed of three main sections, the fore brain, the mid brain and the hind brain Each section has its own set of duties, some much more complex than others.
The fore brain comprises about 70% of the neurons in the central nervous system and it is further divided into the cerebrum, thalamus and the hypothalamus. The cerebrum is the largest part of a human brain and bears the responsibility for both actions and thoughts. Within the cerebrum are the four lobes of the brain; frontal, parietal, occipital and temporal. The cerebrum is a wrinkled mass of tissue that, if spread out, could be as large as a pillowcase. The ‘folding‘ allows for the expansion of the brain and aids in efficiency. The cerebrum is separated into the left hemisphere and the right hemisphere. Each hemisphere controls the opposite side of the body. Right handed people are considered to be left brain dominant and the left hemisphere is responsible for language, logic and math skills. The reverse is that left handed people are right brain dominant and are more artistically inclined as the right hemisphere is responsible for spatial abilities, music and visual imagery. Studies have shown that when damage occurs to one hemisphere it is sometimes possible for the opposite hemisphere to compensate for some of the loss. The thalamus and hypothalamus are part of the limbic system. According to evolutionary age the limbic system is older than the cerebrum. It is buried deeper in the brains structure and is sometimes referred to as the emotional brain. The hypothalamus is in charge of our survival function, feeding, fighting, fleeing and the need to reproduce.
The mid brain is located between the fore brain and the hind brain The midbrain is the center of motor activity in the brain. Any damage to this portion of the brain is likely to result in some type of motor deficit. The mid brain is also responsible for auditory and visual processes and eye movement. The mid brain houses the reticular formation which controls sleep cycles.
The hindbrain contains the cerebellum, the pons and the medulla and attaches to the spinal cord. The cerebellum helps maintain your sense of equilibrium and coordination. Alcohol affects this portion of the brain first. The pons is, essentially a relay station between the brain and the spinal cord. It is involved in the regulation of respiration. The medulla is responsible for autonomic (involuntary) functions such as breathing and heart rate.
The brain, with all of its parts working in conjunction with each other, is nothing short of amazing. It is our primary organ of life. It is a strong, intelligent and surprisingly resilient organ with a complexity matched by the brain of no other animal.
Is the Limbic System Only Found in the Cerebrum?
The cerebrum, which is the Latin word for “brain,” makes up the largest part of the human brain. It is responsible for a host of functions, including perception, thought, imagination, judgment and decisions. The cerebrum is divided into two cerebral hemispheres. Due to the crossing over of the spinal tracts, the left hemisphere controls the muscles on the right side of the body, while the right hemisphere controls the muscles on the left side of the body. The diencephalon is also located deep within the cerebrum.
The diencephalon has four main structures. The thalamus is specifically involved in sensory perception and regulation of movement. It connects the areas of the cerebral cortex that are involved in sensory perception and movement with other parts of the brain and spinal cord that also have a role in sensation and movement. The lateral geniculate nucleus (LGN) processes signals from the optic nerve and passes them to the visual areas of the cerebral cortex. The hypothalamus is very small but plays a major role in regulating hormones, body temperature, the pituitary gland, the adrenal glands and many other activities, including appetite, levels of pleasure, sexual satisfaction, response to pain, anger and aggressive behavior. The hypothalamus sends instructions to the rest of the body via the autonomic nervous system, which allows the hypothalamus to regulate, for example, blood pressure, heart rate, breathing, digestion and perspiration. The hypothalamus also sends instructions via the fourth structure called the pituitary gland. The posterior lobe of the pituitary gland receives hormones from the hypothalamus and releases them into the blood, a process that is vitally important in regulating growth and metabolism.
The limbic system is a group of brain structures which govern emotions and behavior. The limbic system is responsible for controlling various functions in the body, including interpreting emotional responses, regulating hormones and storing memories. The limbic system is also involved with sensory perception, olfaction (sense of smell) and motor function. The thalamus and hypothalamus are two structures of the cerebrum that are part of the limbic system. The two additional structures that make up the limbic system are the amygdala and the hippocampus. The amygdala and hippocampus play important roles in memory. The amygdala is located on either side of the thalamus and is responsible for determining which memories are stored and where those memories are kept in the brain. The amygdala is also an emotion center, as it sends signals to the hypothalamus and evokes a response. Signals from the olfactory system are regularly sent to the amygdala, which is why specific odors sometimes have a powerful effect on emotions and memories. The hippocampus sends these memories out to the cerebral hemisphere for long-term storage and then retrieves them when necessary. If this area of the brain is damaged, a person may be unable to form new memories.
In addition to the thalamus, hypothalamus, hippocampus and amygdala, there are other structures located near the limbic system that are essential to its functioning. The cingulate gyrus is the part of the cerebrum closest to the limbic system. It provides a path from the thalamus to the hippocampus and is in charge of focusing attention on events with emotional significance and for associating memories to odors and to pain. The ventral tegmental area of the brainstem, located below the thalamus, consists of paths that are responsible for pleasure. Damage to this area leaves people with difficulty in finding pleasure in life, choosing instead to turn to drugs, alcohol or gambling. The basal ganglia are found over and to the sides of the limbic system and are responsible for repetitive behaviors, reward experiences and focusing attention. The prefrontal cortex, which is the part of the brain that lies in front of the motor areas, is also intimately linked with the limbic system. This area is involved in thinking about the future, planning and taking action, and plays an important part in pleasure and addiction as well.