Brain and Nervous System

As people age, the number of nerve cells in the brain decreases only slightly. Several things help compensate for this decline. As cells are lost, new connections are made between the remaining nerve cells. New nerve cells may form in some areas of the brain, even during old age. In addition, the brain has more cells than it needs to perform most activities—a characteristic called redundancy.

The substances and structures involved in sending messages in the brain change. The levels of some chemical messengers (neurotransmitters) and enzymes decrease, and others increase. The number of some types of receptors on nerve cells decreases, and the number of others increases. (Receptors are structures on the nerve cells that neurotransmitters attach to, causing a specific action in the cells.)

Because of these changes, the brain may function slightly less well. Older people may react and do tasks somewhat more slowly. Some mental functions may be subtly reduced. They include vocabulary, short-term memory, the ability to learn new material, and the ability to recall words.

After about age 60, the number of cells in the spinal cord begins to decrease. As a result, older people may notice a decrease in sensation.

As people age, nerves may conduct signals more slowly. Usually, this change is so minimal that people do not notice it. Also, the nervous system's response to injury is reduced. Nerves may repair themselves more slowly and incompletely in older people than in younger people. Therefore, older people are more vulnerable to injury and disorders.