The healthy human brain contains tens of billions of neurons—specialized cells that process and transmit information via electrical and chemical signals. They send messages between different parts of the brain, and from the brain to the muscles and organs of the body. Alzheimer’s disease disrupts this communication among neurons, resulting in loss of function and cell death.
The cell body contains the nucleus, which houses the genetic blueprint that directs and regulates the cell’s activities.
Dendrites are branch-like structures that extend from the cell body and collect information from other neurons.
The axon is a cable-like structure at the end of the cell body opposite the dendrites and transmits messages to other neurons.
The function and survival of neurons depend on several key biological processes:
How Does Alzheimer’s Disease Affect the Brain?
The brain typically shrinks to some degree in healthy aging but, surprisingly, does not lose neurons in large numbers. In Alzheimer’s disease, however, damage is widespread, as many neurons stop functioning, lose connections with other neurons, and die. Alzheimer’s disrupts processes vital to neurons and their networks, including communication, metabolism, and repair.
At first, Alzheimer’s disease typically destroys neurons and their connections in parts of the brain involved in memory, including the entorhinal cortex and hippocampus. It later affects areas in the cerebral cortex responsible for language, reasoning, and social behavior. Eventually, many other areas of the brain are damaged. Over time, a person with Alzheimer’s gradually loses his or her ability to live and function independently. Ultimately, the disease is fatal.a computer generated graphic of the brain with labels pointing to the cerebral cortex, entorhinal cortex, and the hippocampus
What Are the Main Characteristics of the Brain with Alzheimer’s?
Many molecular and cellular changes take place in the brain of a person with Alzheimer’s disease. These changes can be observed in brain tissue under the microscope after death. Investigations are underway to determine which changes may cause Alzheimer’s and which may be a result of the disease.
Communication. Neurons are constantly in touch with neighboring brain cells. When a neuron receives signals from other neurons, it generates an electrical charge that travels down the length of its axon and releases neurotransmitter chemicals across a tiny gap, called a synapse. Like a key fitting into a lock, each neurotransmitter molecule then binds to specific receptor sites on a dendrite of a nearby neuron. This process triggers chemical or electrical signals that either stimulate or inhibit activity in the neuron receiving the signal. Communication often occurs across networks of brain cells.
For More Information About Alzheimer’s Brain Changes
NIA Alzheimer’s and related Dementias Education and Referral (ADEAR) Center
800-438-4380
[email protected]
www.nia.nih.gov/alzheimers
