Chapter 2
Brain Basics
Does Your Brain Know It's a Girl?
With modern parts atop old ones, the brain is like an iPod built around an eight-track cassette player.
Sharon Begley, journalist
If a woman has to choose between catching a fly ball and saving an infant's life, she will chose to save the infant's life without even considering if there are men on base.
Dave Barry, humorist
By the time my daughter was eight, she was pretty blasé when people mistook her for a boy, which was a fairly common occurrence. After all, my daughter usually wore a baseball (not softball) uniform or comfortable clothes from the boys’ department—not pink or purple clothes with short, useless sleeves and lace. Her hair was short, her style was brisk, and it was perfectly logical that sales clerks, strangers in the park, and even new parents at school would assume she was a boy.
Even though it wasn't easy for strangers to tell that my daughter was a girl, she knew she was one. And even though it's not easy to tell if a young brain (in a lab, without the body) belongs to a boy or girl, the brain knows what it is—at least as far as basic reproduction. Beyond that, there are plenty of questions and plenty of opinions about whether our actions are hardwired into the gender of the brain.
We'll look at the brain and sex in this chapter and the next, after we understand a little bit about the miracle everyone has inside their skull.
The Basic Brain
The brain is the most complex structure on earth.2 The physical brain—consisting of mostly water (about 78%), plus fats, proteins, and carbohydrates—can sense the outside and inner world, create thoughts and feelings, keep you breathing and pumping blood, and discover new ways to relate to the world. The brain is mind-boggling.
To understand the components of the awesome brain, let's create a model using your hands. Make two fists, touching the first knuckles together and keeping your thumbs parallel. Your combined fists are about the size of a brain.
Now, imagine that between your fists is a ball of bread dough about the size of a tennis ball; inside the dough are two shelled almonds and two shelled walnuts, one of each within the dough in either fist. This dough is your limbic system, the oldest part of your brain; it supports basic brain functions, including emotion, behavior, and long-term memory. The two almonds together are your amygdalae, which govern your emotions and fight-or-flight fear response. The two walnuts represent your thalamus, the center for sensory and motor functions.
Now bend your arms so your elbows point to the floor and your knuckles point to the sky. If someone put a pencil between your arms, that pencil would be your spinal cord, and your wrists would be your brain stem. The brain stem manages basic body functions, such as heart rate and consciousness (being awake or sleepy). Combine the limbic system and brain stem (the dough ball and your wrists), and you have a pretty functional brain system for animals.
But we're missing the cerebellum, which you can imagine as a big blob of dough squeezed out of the back, or pinky side, of your hand, by your wrist. The cerebellum is called a “little brain.” It's like a little computer that connects and coordinates motor control, cognitive functions such as attention and language, and probably some emotional responses such as fear and pleasure. The cerebellum connects to the more complex cerebral cortex on top of the brain.3
Your combined fists represent the two hemispheres of the cerebrum and their fissures (folds that increase the surface area of the brain). The thumb side is the front of the brain: the frontal lobes responsible for reasoning, motivation, and other higher brain functions that allow you to read, drive, and play Wii Fit. The middle fingers are the parietal lobes, which are responsible for touch, movement, and orientation. The backs of the hands (nearest the ears in a person, if the brain were in a head) are the temporal lobes, responsible for auditory stimuli, memory, and speech. Finally, the pinky fingers are the occipital lobes, responsible for visual processing.4
You've got the whole world in your hands. But beyond this basic view are many more ways to slice and analyze the brain.
A Universe of Neurons
The field of neuroscience is now being compared with astronomy, because they both deal with unknowns of similar magnitude. You know how you feel the infinite expanse of the universe when you see a thick carpet of stars in a dark sky? That magnitude is echoed in our brains, which hold hundreds of trillions of synapses—1,500 times the number of stars that fill the Milky Way galaxy.
Our brains have hundreds of trillions of synapses—1,500 times the number of stars in the Milky Way galaxy.
Information travels quickly in our brains—very quickly. The slowest speed that information is transferred between neurons is 260 mph. That's slightly faster than the speed of the original Bugatti EB, one of the fastest road-legal cars in the world, clocked at 253 mph.
Our brains are not only fast, but also busy. One human brain has an average of 70,000 thoughts per day and generates more electrical impulses than all the telephones in the world combined.
The most obvious magical marvels that do all this work are called neurons, the primary cells of our brain and nervous system. About 100 billion neurons live under your skull in your three-pound spongy ball of brilliance. Each neuron looks like a spindly tree drawn by Dr. Seuss and consists of three parts:
Dendrites, branches that receive input from other neurons,
Cell body, which sustains the life of the cell and contains its DNA,
Axon, a living cable that carries electrical impulses at very high speeds toward the dendrites of neighboring neurons.
A synapse is a junction between the axon of one neuron and the dendrite of another (or it can be between a neuron and a muscle). A synapse sends electrical or chemical (such as neurotransmitter) signals, which either excite or inhibit the chance for action. Each connection creates a weak electromagnetic field that can join together with the electromagnetic fields of other neural connections. Those combined connections increase the speed, empathy, and activity between neurons that are not in direct contact.5
The glia, or support cells for your neurons, are part of this electromagnetic “telepathy” of the brain. Glial cells are far more numerous than neurons, making up 90% of your brain's cells. They consume parts of dead neurons, manufacture myelin (a white neuron coating that protects the axon and increases axon impulses up to fifty times6), form an immune system,7 provide physical and nutritional support for neurons, and even communicate with other synapses.8
Science is learning more about glial cells, adding to knowledge about neurons. Half of glial cells are tiny granule cells, which hang out in the cerebellum. While the cerebellum (remember it's the “little brain”