9 Quick Facts About the Brain

There are still many mysteries about the human brain, but researchers have uncovered a number of interesting facts about how it works. Here are nine quick facts to get you started on the path to a better understanding of the brain.


It's Heavier Than You Might Think

Female medical school professor with human brain model
Steve Debenport / Getty Images

The average adult human brain weighs approximately 3 pounds and tends to be larger in males than in females. It's also one of our body's biggest and fattiest organs.


It's Mostly Water

The human brain is composed of approximately 75 percent water, as well as fat and protein.


It Grows Tremendously From Infancy to Adulthood

The average weight of a newborn human infant brain is about 350 to 400 grams, or three-quarters of a pound. That means it grows to four times its original size from infancy to adulthood.


It's Made Up of Billions of Neurons

Recent estimates suggest that the average adult brain contains approximately 86 billion nerve cells, also called neurons. Neurons are the messengers in our brains, carrying information and communicating with our sensory organs, our muscles, and each other.


It's Also Made up of Billions of Glial Cells

Recent research has shown that the belief that there are 10 glial cells for every one neuron is false. The ratio is closer to 1:1. Glial cells make up approximately half of the brain and spinal cord, though this ratio can vary from one spot to the next.

Glial cells perform a range of functions, including acting as a glue to hold neurons together. They also perform housekeeping functions by cleaning up excess neurotransmitters and supporting synaptic growth.

There are several different types of glial cells: astrocytes, oligodendrocytes, microglia, ependymal cells, radial glial, satellite cells, and schwann cells.


It Can Form New Cells, Even in Adulthood

The brain continues to form new connections between neurons throughout our lives. Old beliefs suggested that the brain was fairly set in stone early in life, but neuroscientists now know that the brain never stops changing.


It Requires a Lot of Energy to Function

While it represents only about 2 percent of the body's total weight, the brain requires about 20 percent of the body's oxygen and 25 percent of the body's glucose.


Traumatic Brain Injuries Are Prevelant

Among children and adults between the ages of 1 and 44, traumatic brain injury is the leading cause of disability and death. The most common causes of these traumatic brain injury include falls, motor vehicles crashes, and assaults.


Our Brains Have Actually Been Getting Smaller

The average size of the human brain has decreased by about 9 cubic inches over the past 5,000 years. This may be due to the fact that our bodies have also gotten smaller over time.

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