The Everything Guide to the Human Brain

Journey Through the Parts of the Brain, Discover How It Works, and Improve Your Brain's Health

Rudolph C Hatfield

• Publisher: Everything
• Year: 2013
• ISBN:
  9781440559235
• Topic: Biological Sciences
• Subtopic: Neuroscience
• Index: Biological Sciences

An essential guide for understanding the inner workings of your brain! Do you really only use 10 percent of your brain? Can a bump to the head really restore memories? Does your brain ever lie to you? Why do you always forget where your glasses are, but never how to read?The brain makes you who you are. This fascinating organ creates your personality and controls your reactions and emotions. It's responsible for how you perceive the world around you--all while controlling hundreds of physical functions like breathing, moving, circulation, and digestion. The brain is simply amazing! The Everything Guide to the Human Brain will help you to unlock the mysteries of the brain. You'll learn how the brain communicates with each part of the body, how it affects your emotional life, why you dream, and how you remember things. And you'll also get in-depth descriptions of brain disorders and how science and medicine are working to heal or reverse them. Written in plain English, this ultimate user's guide will help you learn about the most influential part of your body!

CHAPTER 1

A Quick View

It is very difficult to begin a book on the brain without sounding like a cliché. The brain is certainly the most complex known entity in the universe. It is more complex than all of quantum physics (which was created by someone’s brain), all of the laws of the universe, and any other phenomenon that you can think of. This first chapter will look at some fundamental concepts that need to be addressed before discussing the brain in more detail. It will start with very basic information so that you can develop an overall understanding of how the brain functions.

The Two Different Nervous Systems

There are two major divisions of the nervous system: the central nervous system and the peripheral nervous system. The central nervous system (CNS) consists of the brain and the spinal cord. The peripheral nervous system (PNS) consists of nerves outside of the brain and the spinal cord. The peripheral nervous system is traditionally divided further into two divisions: the somatic nervous system (generally considered to be under voluntary control, such as the skeletal muscles) and the autonomic nervous system (generally considered not to be under voluntary control, such as digestion). The autonomic nervous system is further divided into the sympathetic nervous system (which functions to speed up your body’s organs) and the parasympathetic nervous system (which functions to slow down your body’s organs). This book will concentrate on the brain and its interaction with other nervous systems and the body.

The enteric nervous system is a third division of the autonomic nervous system not often mentioned in many texts on the brain. The enteric nervous system is a network of nerves that innervate the viscera, organs in the body cavities, especially in the abdominal cavity (e.g., the gastrointestinal tract, pancreas, gall bladder, etc.).

Brain Basics

The average human brain weighs about three pounds and is the consistency of Jell-O (the pickled brains you see in jars are actually hardened). However, there is quite a bit of variation in brain size just like there is variation in body size. A person with a bigger brain is not necessarily smarter than one with a smaller brain, all other things being equal. For instance, Albert Einstein’s brain, which he donated to science after his death, is reported to have weighed only 1,230 grams or about 2.71 pounds, which is slightly smaller than average.

A large number of brain cells are lost through attrition, programmed cell death, and other methods. However, claims that 5,000–10,000 or more brain cells are lost daily are unfounded. No one really knows how many brain cells there are and certainly no one knows how many get “lost.”

Many texts report that the human brain contains about 100 billion nerve cells (neurons) and trillions of support cells (e.g., glial cells). However, more recent estimates have suggested that this figure is somewhat overstated. Neurons are nerve cells that are specific to the CNS and are connected in a number of intricate pathways and networks. The actual number of these connections may exceed 100 trillion! It is the connections between the neurons (the nerve cells in the brain) that allow neurons to communicate with each other, and this activity is responsible for all of your actions.

How the Central Nervous System Works

For most of the voluntary actions that people make (and a good number of involuntary ones), these initial behaviors begin in the brain where they are formulated. The message is then sent down the spinal cord into the peripheral nervous system allowing one to take action. Your central nervous system operates as a type of body control center and complex communication system that is composed of a sophisticated network operating both chemically and electrically. Your brain also responds to information that is transmitted from your sense organs through your spinal cord and relayed to your brain.

Incoming information is transmitted via afferent (incoming) nerve cells in sense organs to afferent neurons on the underside of your spinal cord (the ventral, or belly, side). This information is sent through the spinal cord to your brain. Your brain then interprets this information and the appropriate action is decided on. This response is sent via outgoing (efferent) nerve cells or neurons back down your spinal cord to your muscles (or whatever part of the body that is appropriate) via the dorsal (back) side of your spinal cord.

So for instance, if you are touching a soft fur, the information about the feel of the fur is sent from your skin to your spinal cord (via afferents) to your brain. Suppose you decide that it is pleasing and that you want to stroke it further (this decision takes place in your brain). That information is sent from your brain (via efferent nerve cells) to your spinal cord and then to the muscles in your arm and hand that allow you to stroke it. Your nervous system integrates, detects, and processes countless bits of information at any given moment.

There are situations when the brain is not involved in movement. Certain reflexes like the patellar reflex, when the doctor strikes your knee with a rubber mallet and your knee extends, do not involve your brain. These occur via a loop from the receptors in your body to your spinal cord and back again. However, for the vast majority of actions, the brain is in control.

Mixing Chemicals and Electricity: The Neuron

The main architect of everything that happens in your brain is a very special nerve cell called the neuron. Neurons come in many different shapes and sizes and there will be more concerning them in subsequent chapters of this book. The first order of business is to take a look at a typical neuron, discuss its parts, and how it basically works. Figure 1-1 is a depiction of a typical neuron.

Neurons consist of several parts: At the top part of the neuron in Figure 1-1 there are several structures known as dendrites. Dendrites receive chemical messages from other neurons. Moving down the neuron is the soma or cell body. Here all the functions needed to maintain the health and integrity of the neuron occur, such as metabolic functions and so forth. Moving further down the neuron leads to the axon, which is the signaling part of the neuron. Most axons are covered with a fatty sheath known as the myelin sheath; however, the entire axon is not covered with myelin and there are small areas where the axon is uncovered. The myelin sheaths resemble elongated pillows running down the length of the axon (these spaces in between the myelinated areas are termed the nodes of Ranvier). At the end of the axon there is a bulb where the axon terminates (the terminal bulb) and a space called the synapse that separates the axon of one neuron (the sending part) from the dendrites of another neuron (the receiving part). The neuron depicted in Figure 1-1 is a prototype; there are several different types of neurons. In Appendix B you will find a link that allows you to view actual neurons.

Figure 1-1: A Typical Neuron

Excitatory neurons stimulate neuronal firing, whereas inhibitory neurons reduce the rate of neuronal firing. Motor neurons are involved in motor functioning, whereas sensory neurons are involved in detecting and interpreting sensory stimulation. An interneuron connects other neurons together and is neither sensory nor motor in its functioning.

How Neurons Communicate

The process of signaling between neurons is quite complicated and will be simplified for this discussion. Basically what happens is that stimulation from sensory systems or from your thoughts results in a neuron being “activated.” Typically this consists of chemical substances known as neurotransmitters attaching themselves to the dendrites of a neuron. If a sufficient amount of neurotransmitters attach themselves to the neuron, this will result in the activation of an electric charge (an actual signal) known as an action potential being sent down the axon of the neuron.

The process of the action potential in a neuron depends on its capacity to react to a stimulus with an electrical discharge. This process is quite complicated but it involves changes in the electrical charges of the ions within the neuron compared to the electrical charges of the ions outside o...

Table of contents

• Cover
• Title Page
• Dedication
• Contents
• The Top 10 Fascinating Facts About Your Brain
• Introduction
• Chapter 1: A Quick View
• Chapter 2: Dividing Up the Brain
• Chapter 3: Can You Believe Your Eyes? The Process of Vision
• Chapter 4: Hear No Evil, Speak No Evil: Language and Your Brain
• Chapter 5: Do You Feel Me? The Sense of Touch
• Chapter 6: Chemicals in Your Brain: Taste and Smell
• Chapter 7: You Move Me
• Chapter 8: Hot, Hungry, and Thirsty: Internal Body States
• Chapter 9: Sex
• Chapter 10: The Sleeping Brain
• Chapter 11: You Have to Grow Up Sometime: The Developing Brain
• Chapter 12: The Big Cheese: The Executive Brain
• Chapter 13: Say That Again? Attention and the Brain
• Chapter 14: Who Was the Fifth President? Learning and Memory
• Chapter 15: The Emotional Brain
• Chapter 16: Don’t Be So Smart: Intelligence and the Brain
• Chapter 17: Well, They Have a Great Personality
• Chapter 18: The Addicted Brain
• Chapter 19: Brain-Related Disorders
• Chapter 20: Some Brain Myths That You May Still Believe
• Appendix A: Glossary
• Appendix B: References
• Acknowledgments
• Copyright