Inside the Brain
A tour of how the mind works
Three Pounds, Three Parts
Your brain is your most powerful organ, yet weighs only about three pounds. It has a texture similar to firm jelly.
The brain has three main parts:
![cerebrum]()
The cerebrum fills up most of your skull. It is involved in remembering, problem solving, thinking, and feeling. It also controls movement.
![cerebellum]()
The cerebellum sits at the back of your head, under the cerebrum. It controls coordination and balance.
![brain stem]()
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
Your brain is nourished by one of your body's richest networks of blood vessels. When you are thinking hard, your brain may use up to 50 percent of the fuel and oxygen.
![Brain Arteries]()
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.
![Brain Vessels]()
The whole vessel network includes veins and capillaries in addition to arteries.
The Cortex: "Thinking Wrinkles"
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.
View the specific regions of the cortex:
- Interpret Sensations From Your Body
- Processing Sights
- Processing Sounds
- Processing Smells
- Thoughts, Problem Solving & Planning
- Forming & Storing Memories
- Controlling Voluntary Movement
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. In most people, the language area is chiefly on the left.
The left half controls movement on the body's right side.
The right half controls the body's left side.
The Neuron Forest
Neurons are the chief type of cell destroyed by Alzheimer's disease.
![Neuron Cells]()
An adult brain contains about 100 billion nerve cells.
![Neuron Cells]()
Branches connect the nerve cells at more than 100 trillion points. Scientists call this dense, branching network a "neuron forest."
![Neuron Cells]()
Signals traveling through the neuron forest form the basis of memories, thoughts, and feelings.
Cell Signaling
The real work of your brain goes on in individual cells. 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.
![Cell Electrical Charge]()
1Signals that form memories and thoughts move through an individual nerve cell as a tiny electrical charge.
![Cell Synapses]()
2Nerve cells connect to one another at synapses.
![Cell Neurotransmitters]()
3When a charge reaches a synapse, it may trigger release of tiny bursts of chemicals called neurotransmitters.
Signal Coding
100 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:
- Reading Words
- Hearing Words
- Thinking About Words
- Saying Words