The Brain and the Effects of Alzheimer's Disease

Neurons

It has been estimated that the brain has over 100 billion brain cells, a large proportion of which are nerve cells, called neurons. The functions of neurons are to process, send and receive information. A neuron is made up of a cell body (with its nucleus) dendrites (which receive messages from other neurons) and an axon (which sends messages to other neurons). Neurons are highly interconnected, forming the message pathways we need to think and function.




The Brain

The brain is composed of many different structures that work independently and together to supervise the rest of the body. If we think of the body as a large company, the brain is the board of directors.


The Brain Stem

The brain stem is located at the point where the brain and spinal cord are connected. It is important among the brain structures involved in basic physical survival, and participates in the regulation of consciousness. It also signals other brain areas to "get ready" for incoming information. In people with Alzheimer's disease, the brain stem continues to function normally at least until the advanced stages of the disease.

The Cerebellum

The Cerebellum is a large structure attached to the back of the brain stem. It helps maintain and adjust posture and balance, as well as coordinate and refine movement. The cerebellum is not highly affected by Alzheimer's disease.

The Cerebrum

The Cerebrum makes up about 85% of the weight of the human brain. Within the cerebrum are many structures that play a acritical role in normal living.

Cerebral Hemispheres: The brain is divided into two halves called hemispheres. Each hemisphere controls the opposite side of the body. while each hemisphere has some uniquely special features, they normally work together, constantly sending messages back-and-forth. Alzheimer's disease effects both hemispheres.

The Cerebral Cortex: The cerebral hemispheres are covered with an intricately folded layer of nerve cells called the cortex. The cortex is about an eighth to a quarter of and inch thick. Among other functions, the cortex makes possible all our higher mental abilities, such as thinking, speaking, and remembering. If the brain is considered the board of directors of our body, the cortex is the chairman of the board. The cortex is one of the brain structures that is greatly affected by Alzheimer's disease.

Lobes of the Cerebrum: Each cerebral hemisphere is divided into four parts: the frontal lobe the parietal lobe, the temporal lobe and the occipital lobe.

The Frontal lobes: The frontal lobe of each hemisphere is located behind the forehead. The frontal lobes oversee much of what the rest of the brain is doing and are important in our ability to plan, make judgments, and carry out purposeful behavior. The frontal lobes are connected with other brain systems which control alertness and emotion.

Alzheimer's disease causes damage to the frontal lobes that results in distinct changes in behavior.

1. Inability to plan or carry out complex action or comprehend a complex idea.
For example, the completion of a sequence of steps may be difficult or impossible for a person with of Alzheimer's disease, even though the individual may be capable of performing each step by itself.

2. Inability to change behavior. Damage to the frontal lobes may also cause an individual to be less able to change a current behavior when a new one is required. He may make more mistakes and may be harder to get along with when placed in a new situation.

3. Inability to focus attention. When the frontal lobes are damaged, individuals may lose the ability to focus their attention, becoming easily distracted and drifting from one task to another without completing any of them.

4. Emotional aspects of frontal lobe damage. Because the frontal lobes are highly interconnected to other brain areas which are important in the control of emotion, people with Alzheimer's disease experience many emotional problems. Apathy, irritibility and suspiciousness are all common features of the disease. Also people with frontal lobe damage may be unable to inhibit or control the expression of urges that are socially inappropriate, such as sexual urges, anger, and hostility. They may also laugh or cry inappropriately.

The Temporal Lobes: The temporal lobes, located behind the temples, interpret the sounds from the environment, both language and non-language. Alzheimer's disease also causes significant damage to these lobes.

Left Temporal Lobe: The left temporal lobe is especially important to communication. Damage to the left temporal lobe may cause loss of ability to understand language in written or oral form. It can also cause difficulty in understanding and remembering lists of words, sentences or complex verbal material. The ability to acquire new verbal learning may be dramatically diminished. Finally, damage to the left temporal lobe may leave the individual unable to perform simple addition and subtraction.

Right Temporal Lobe: The right temporal lobe is specialized for recognition and interpretation of non-language sounds, including environmental sounds, music and rhythm. When the right temporal lobe is damaged, individuals may not be able to recognize what a sound is or what it means.

The right temporal lobe is also important for organizing what we see into meaningful patterns and for remembering things that we see. Individuals with right temporal damage are likely to have spatial disorientation and difficulty recognizing complex visual stimuli. They may also have problems making fine visual discrimination, such as being able to detect the edges of a place mat on a table cloth.

Summary: The temporal lobes are prominently affected by Alzheimer's disease, which is a primary reason communication, memory, and visual-perceptual problems occur.

The Parietal Lobes: The parietal lobes are located above the temporal lobes and behind the frontal lobes. It is in the parietal lobes that sensory information for the enviroment is analyzed. The parietal lobes help us keep track of the placement of our bodies, and how we are positioned in space.

1. Constructional disorders: When damage occurs to the parietal lobes, constructional disorders may occur. Constuctional disorders include difficulty drawing a picture of a clock or assembling a coffee pot correctly.

2. Association cortex: The function of the temporal and parietal lobes includes an area that is called the association cortex, which is significantly affected by Alzheimer's disease. Damage to the association cortex is primarily responsible for impairment of conceptual knowledge and the ability to make inferences.

The Occipital Lobes: The occipital lobes are situated at the back of each hemisphere and are primarily involved in visual perception and association. Of the four lobes, this one is least affected by Alzheimer's disease.

Hippocampus

The hippocampus plays a major role in emotion, behavior, the ability to reason, and the selective storage and retrieval of information. It is responsible for transferring new information to long term memory. A principal basis for problems with reasoning and memory in Alzheimer's disease is damage to the hippocampus.