The central nervous system includes the brain and spinal cord. The peripheral nervous system consists of nerves connecting our limbs to the spinal cord through ganglions and controls movement and regulates autonomous functions, such as heart beat, digestion, bowel movement and breathing. A good example of a peripheral nerve is the sciatic nerve, the largest nerve in the human body, that connects the leg and foot muscles and skin to the spinal cord.
The human brain is a miracle. It is the ultimate center of all thought, creativity and life.
The brain weighs approximately 3 pounds and makes up 2% of the total body weight, but uses 22% to 25% of all energy consumed by our body.
Looking at the brain we see it divided right in the middle into two symmetrical halves, or hemispheres. There is a right and a left hemisphere, both looking identical but with distinct functions.
Right brain functions
Left brain functions
|Creativity and Imagination||Reasoning|
|Intuition||Science and math/numbers skills|
|Music awareness and appreciation||Logic|
|Left-hand control||Right-hand control|
In general, the right side of the brain controls the left side of our body, whereas the left side controls the right side.
Both hemispheres are not isolated but connected through a structure called the corpus callosum. The corpus callosum is like an enormous bundle of over 200 million cables, called fibers, that interconnect the two hemispheres.
The wrinkly surface of the human brain is called the cortex or cerebral cortex. The cortex consists of tightly packed neurons, the basic functional building blocks of the nervous system
Also called nerve cells, neurons are special type of cells responsible for most of the brains actions, such as movement, thoughts and memory and are essential for our senses, such as vision, hearing, taste and smelling. As cells, they have several similarities with other cells in our body, such as a membrane, cell body and a nucleus. However, neurons are specialized cells responsible for communication of information between different neurons in the nervous system.
Neurons communicate through specialized connections called synapses, using electrical and chemical signals. The chemical signals used are also called neurotransmitters. Well known and important neurotransmitters are acetylcholine, glutamate, adrenaline, noradrenaline, and glycine. Without neurotransmitters, neurons are unable to communicate with each other, disabling many brain functions. Therefore, a healthy level of neurotransmitters is imperative for the proper function of the brain.
The cortex of each hemisphere is divided into four sections, or lobes:
- FRONTAL LOBE
- TEMPORAL LOBE
- PARIETAL LOBE
- OCCIPITAL LOBE
The lobe closest to our forehead is called the frontal lobe. The frontal lobe is responsible for decision making, planning, thinking and social adaptation. It is responsible for forming our personality by determining our social behavior. The frontal lobe also enables us to speak fluently and in a meaningful manner.
The importance of the frontal lobe for forming our personality is best illustrated by an accident Phineas Gage, a railroad worker, experienced. A large pole was driven into his head and damaged his frontal lobe. He survived the accident, but his personality dramatically changed. Once a mild-mannered man with splendid work ethics, the damage to his frontal lobes changed his personality to an extremely rude, lazy and socially offensive person.
On top of the brain, the upper portion of the brain located behind the frontal lobes is called the parietal lobes.
The parietal lobes are responsible for self-awareness of the body and processes sensory information, such as taste, temperature, touch, vision and hearing. The parietal lobes integrate sensory information and provide decision making facts to the rest of the brain. For example, hot temperatures on a surface are sensed by our hand and this information is processed in the parietal lobes. As a result of processing the high-temperature sensation, the parietal lobes “order” the immediate removal of the hand from the hot surface to avoid a severe burn.
Parietal lobe injuries are most common in football players and accident survivors suffering from traumatic brain injuries. Sustained injuries are permanent and are likely to cause difficulties in recognizing people and objects, having an awareness of the persons own body and extremities in space and impairment in mathematical skills. Additionally, the capabilities for multitasking, focus and perception, coping with stress and human relations are greatly impacted or disabled.
Behind the parietal lobes, towards the back of our head, are the occipital lobes.
This lobe is responsible for visual perception and processing of information we gather through our eyes. The results of this processing enable us to react to visual information, such as reading, driving a vehicle and watching movies, but also avoiding dangerous situations, such as avoiding car accidents and running away from danger. Visual information processed in our occipital lobe and further computed in the parietal lobe enables us to recognize loved ones, a nice painting and our environment in general.
Damages to the occipital lobe usually result in loss of vision. Severe damage to this lobe may cause total blindness, whereas partial damage can result in partial loss of vision, inability to recognize objects, colors and 3-D coordinates of the body in space.
The temporal lobes are located under the frontal, parietal and occipital lobes, and close to the upper tip of our ear lobes.
Temporal lobes are involved in processing sensory input and are crucial for short and long-term memory, storage and retrieval. Our hearing and auditory perception is processed by the auditory cortex of the left temporal lobe. This lobe is also responsible for recognition of objects, scenes and faces by processing visual stimuli. The temporal cortex is responsible for creation, processing, storage and retrieval of short term and long-term memories. In addition, it processes visual stimuli with sensory input and attaches qualities to newly generated memories. For example, the sight of a red rose and its beautiful scent are perceived by the temporal lobe as two distinct stimuli. The temporal lobe associates the visual information with olfactory sensation of the scent and stores the information as a memory of a “red rose with beautiful scent”. Patients with damage to the temporal lobe have difficulties recalling visual memories, processing new visual stimuli into memories, recognizing faces and familiar objects, and facial expressions. Moreover, their hearing is impaired or absent, and speech formulation and continuity negatively affected.