Brain : Alzheimer’s Association

Your brain is your most powerful organ, yet weighs only about three pounds. It has a texture similar to firm jelly.

It has three main parts:

  1. The cerebrum fills up most of your skull. It is involved in remembering, problem solving, thinking, and feeling. It also controls movement.
  2. The cerebellum sits at the back of your head, under the cerebrum. It controls coordination and balance.
  3. The brain stem sits beneath your cerebrum in front of your cerebellum. It connects the brain to the spinal cord and controls automatic functions such as breathing, digestion, heart rate and blood pressure.

Supply lines

blood_vessels

Your brain is nourished by one of your body’s richest networks of blood vessels.

With each heartbeat, arteries carry about 20 to 25 percent of your blood to your brain, where billions of cells use about 20 percent of the oxygen and fuel your blood carries.

When you are thinking hard, your brain may use up to 50 percent of the fuel and oxygen.

The whole vessel network includes veins and capillaries in addition to arteries.

The cortex: “Thinking wrinkles”

03a

Your brain’s wrinkled surface is a specialized outer layer of the cerebrum called the cortex. Scientists have “mapped” the cortex by identifying areas strongly linked to certain functions.

Specific regions of the cortex:

Left brain/right brain

Your brain is divided into right and left halves. Experts are not certain how the “left brain” and “right brain” may differ in function, except:

The neuron forest

neuron_forest

The real work of your brain goes on in individual cells. An adult brain contains about 100 billion nerve cells, or neurons, with branches that connect at more than 100 trillion points. Scientists call this dense, branching network a “neuron forest.”

Signals traveling through the neuron forest form the basis of memories, thoughts, and feelings.

Neurons are the chief type of cell destroyed by Alzheimer’s disease.

Cell signaling

synapses_neurotransmitters

Signals that form memories and thoughts move through an individual nerve cell as a tiny electrical charge.

Nerve cells connect to one another at synapses. When a charge reaches a synapse, it may trigger release of tiny bursts of chemicals called neurotransmitters. The neurotransmitters travel across the synapse, carrying signals to other cells. Scientists have identified dozens of neurotransmitters.

Alzheimer’s disease disrupts both the way electrical charges travel within cells and the activity of neurotransmitters.

Signal coding

brain_activity

00 billion nerve cells. 100 trillion synapses. dozens of neurotransmitters. This “strength in numbers” provides your brain’s raw material. Over time, our experiences create patterns in signal type and strength. These patterns of activity explain how, at the cellular level, our brains code our thoughts, memories, skills and sense of who we are.

The positron emission tomography (PET) scan on the left shows typical patterns of brain activity associated with:

Activity is highest in red areas and then decreases through the other colors of the rainbow from yellow to blue-violet.

Specific activity patterns change throughout life as we meet new people, have new experiences and acquire new skills. The patterns also change when Alzheimer’s disease or a related disorder disrupts nerve cells and their connections to one another.

Alzheimer’s Disease and the Brain

brain_changes

Alzheimer’s disease leads to nerve cell death and tissue loss throughout the brain. Over time, the brain shrinks dramatically, affecting nearly all its functions.

These images show:

More brain changes

alzheimer_brain

Here is another view of how massive cell loss changes the whole brain in advanced Alzheimer’s disease. This slide shows a crosswise “slice” through the middle of the brain between the ears.

In the Alzheimer’s brain:

  • The cortex shrivels up, damaging areas involved in thinking, planning and remembering.
  • Shrinkage is especially severe in the hippocampus, an area of the cortex that plays a key role in formation of new memories.
  • Ventricles (fluid-filled spaces within the brain) grow larger.

Under the microscope

plaques_tangles

Scientists can also see the terrible effects of Alzheimer’s disease when they look at brain tissue under the microscope:

  • Alzheimer’s tissue has many fewer nerve cells and synapses than a healthy brain.
  • Plaques, abnormal clusters of protein fragments, build up between nerve cells.
  • Dead and dying nerve cells contain tangles, which are made up of twisted strands of another protein.

Scientists are not absolutely sure what causes cell death and tissue loss in the Alzheimer’s brain, but plaques and tangles are prime suspects

More about plaques

plaques

Plaques form when protein pieces called beta-amyloid (BAY-tuh AM-uh-loyd) clump together. Beta-amyloid comes from a larger protein found in the fatty membrane surrounding nerve cells.

Beta-amyloid is chemically “sticky” and gradually builds up into plaques.

The most damaging form of beta-amyloid may be groups of a few pieces rather than the plaques themselves. The small clumps may block cell-to-cell signaling at synapses. They may also activate immune system cells that trigger inflammation and devour disabled cells.

More about tangles

12a_2

Tangles destroy a vital cell transport system made of proteins. This electron microscope picture shows a cell with some healthy areas and other areas where tangles are forming.

In healthy areas:

  • The transport system is organized in orderly parallel strands somewhat like railroad tracks. Food molecules, cell parts and other key materials travel along the “tracks.”
  • A protein called tau (rhymes with wow) helps the tracks stay straight.

In areas where tangles are forming:

Progression through the brain

alzheimers_progression

Plaques and tangles (shown in the blue-shaded areas) tend to spread through the cortex in a predictable pattern as Alzheimer’s disease progresses.

The rate of progression varies greatly. People with Alzheimer’s live an average of eight years, but some people may survive up to 20 years. The course of the disease depends in part on age at diagnosis and whether a person has other health conditions.

Earliest Alzheimer’s stages

early_stage

In the earliest stages, before symptoms can be detected with current tests, plaques and tangles begin to form in brain areas involved in:

Mild to moderate Alzheimer’s

mild_moderate_stage

In mild to moderate stages, brain regions important in memory and thinking and planning develop more plaques and tangles than were present in early stages. As a result, individuals develop problems with memory or thinking serious enough to interfere with work or social life. They may also get confused and have trouble handling money, expressing themselves and organizing their thoughts. Many people with Alzheimer’s are first diagnosed in these stages.

Plaques and tangles also spread to areas involved in:

As Alzheimer’s progresses, individuals may experience changes in personality and behavior and have trouble recognizing friends and family members.

Severe Alzheimer’s disease

severe_stage

In advanced Alzheimer’s disease, most of the cortex is seriously damaged. The brain shrinks dramatically due to widespread cell death. Individuals lose their ability to communicate, to recognize family and loved ones and to care for themselves.

English: Diagram of how microtubules desintegr...

Diagram of how microtubules desintegrate with Alzheimer’s disease

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