According to New Scientist, the human brain contains about 100 billion neurons and weighs about 3 lbs. The brain is protected by the skull and a series of membranes surrounding this important organ. A healthy diet, mental exercise and physical exercise can keep the brain functioning at its best.
Gross Structure
The left and right cerebral hemispheres make up the largest part of brain mass, which is called the cerebrum. They are connected by a dense network of fibers called the corpus callosum. Each cerebral hemisphere is made up of four lobes, which each control different aspects of brain activity. Below the cerebral hemispheres lies the occipital lobe, then the cerebellum and finally the brain stem. Deep inside the brain, surrounded by the cerebral hemispheres, is the lymbic system, which contains smaller structures such as the amygdala, hypothalamus, thalamus and hippocampus within it.
Cellular Structure
All of the structures of the brain are made up of two types of cells, neurons and glial cells. Neurons send electrical and chemical signals to each other and out to other organs and systems of the body. The cell body of a neuron controls the activity of the cell, while axons and dendrites send information out and take information in respectively. Glial cells function as amplifiers and modulators in the brain, increasing or decreasing the signals sent out by neurons. They also surround and protect neurons.
Function
The brain controls all activity, voluntary and involuntary, in the body and takes in all of the sensory input a person experiences. The cerebrum of the brain is also responsible for memory, decision making and emotion. In the limbic system, urges such as hunger, emotions such as fear and the storage of new memories are controlled. The cerebellum handles repetitive movements and habits while the brainstem handles unconscious body activity, including heartbeat and breathing.
Diseases
Aging has a strong effect on the brain, shrinking and losing some neural connections as time passes. Some specific diseases of the aging brain include Alzheimer's disease and Parkinson's disease. Other brain diseases can strike at any age, including epilepsy, stroke and brain cancer. Damage to the brain may also come in the form of traumatic injury, birth defects or infection.
Plasticity
Perhaps the most important aspect of the brain and the one that makes it able to carry out all of its different functions is plasticity, which refers to the brain's ability to change and alter itself to adapt to different circumstances or information. The brain does this by creating new connections between neurons and pruning away connections that become unnecessary or redundant. Without plasticity, no new memories would form, learning could not occur and consciousness could not exist.
