Neuroscience For Dummies
Overview
A fascinating look at what’s rattling around in your skull
Neuroscience For Dummies introduces you to the mind-boggling study of the human brain. It tracks to the content of a typical introductory neuroscience class at the college level —and it’s perfect for anyone curious about what makes us tick. New technologies and an explosion of research have completely transformed our understanding of memory, depression, the mind-body connection, learning, and genetics. This updated edition—still in classic, beginner-friendly Dummies style—covers
the latest research advances and technologies in the field of neuroscience. Put some knowledge about the brain into your brain.
- Grasp the basic concepts and applications of neuroscience
- Understand the brain’s structure and function
- Explore how the brain impacts memory, learning, and emotions
- Discover how the brain is connected with other physical systems
For students and general readers alike, Neuroscience For Dummies is a great way to understand what’s going on inside our heads.
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About The Author
Frank Amthor is a professor of psychology at the University of Alabama at Birmingham, where he also holds secondary appointments in the UAB Medical School Department of Neurobiology, the School of Optometry, and the Department of Biomedical Engineering. His research is focused on retinal and central visual processing and neural prostheses.
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neuroscience for dummies
CHEAT SHEET
Why is Neuroscience important? The most complex structure in the world is the 3-pound mass of cells within your skull called the brain.The brain consists of about 100 billion neurons, which is about the same number as all the stars in our Milky Way galaxy and the number of galaxies in the known universe. It also contains about a trillion glial cells, which contribute to the proper function of neurons.
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The brain consists of many distinct functional areas. Some of these functional areas are anatomically distinct; other functions are spread out over many areas and not localized. In the cases where different brain areas are responsible for particular functions, destruction of those areas tends to lead to a severe loss of that function.
Neuroscience
This is an exciting time to be a neuroscientist. New tools for understanding the human brain and how it makes people what they are have become available. More tools are needed though, because the brain is the most complex structure in the known universe.
Most neuroscience research has two main goals:
Understanding the brain for its own sake in order to understand ourselves and use that understanding to make life better
Fixing broken brains — that is, diseases of the nervous system such as Alzheimer’s and Parkinson’s diseases, and mental illness such as depression, schizophrenia, and addiction
Understanding the brain is an immense challenge because of its complexity — nearly 100 billion neurons forming on the order of a quadrillion (10,000 billion) synapses.
Neuroscience
The neurotransmitter "juice" squirted from the presynaptic to the postsynaptic neuron consists of neurotransmitter molecules. A variety of different types of neurotransmitters exist, each varying in its type of effect and time course on the postsynaptic cell. Neurotransmitters are grouped into three major functional classes:
Fast, excitatory neurotransmitters: The most important neurotransmitters are the fast, excitatory neurotransmitters glutamate and acetylcholine.
Neurons are cells. As cells, they contain components common to all animal cells, such as the nucleus and Golgi apparatus. However, neurons have other features unique to neurons, or at least, not common in other cells. These unique features exist because neurons are specialized for processing and communicating information.
Researchers are at the brink of a revolution in treatment of brain diseases. Following are the current strategies (like deep brain stimulation) that show a lot of promise and cutting-edge technology (like neuroprostheses) that show a lot of potential.
Correcting developmental disorders through gene therapy
Genetic mutations, copying errors, unfortunate gene combinations, and environmental toxins can produce profound disorders that severely compromise human potential, even before birth.
The brain is amazing because of what it is (a switchboard of billions of neurons), and because of what it does (the memory and artistic skills of some savants almost defy belief). Here are seven attributes of the human brain that, when you think about it, are pretty amazing.
The brain has 100 billion cells and a quadrillion synapses
Your brain is built from an enormous number of neurons, on the order of 100 billion (plus possibly 1 trillion glial cells).
Revolutions in neuroscience that will have significant ramifications on humanity will occur within 20 years in these two areas: treatments and cures for dysfunctions and augmentation of the brain beyond its heretofore "normal" capabilities.
Treating dysfunction
Until the last quarter of the 20th century, attempts to treat brain problems were a lot like trying to fix a computer with a hammer and a hacksaw.
Neuroscience
Savants are people who have extraordinary skills, usually in a limited domain like music, mathematical calculation, or art. Many savants have autistic characteristics. The brains of most savants, to the extent determinable from imaging, are anatomically normal, but there are exceptions.The brain of Kim Peek, the model for the 1988 film Rain Man, was severely abnormal with, among other things, no corpus callosum.
The earliest brain recordings — electroencephalograms, or EEGs — used surface electrodes on the scalp to record ongoing brain potentials from large areas of the brain. Most of what researchers know about individual neuronal function (neurophysiology) began in about the middle of the 20th century with the invention and use of microelectrodes, which could sample the activity of single neurons, and oscilloscopes, which could display events lasting milliseconds or less.
Neuroscience
Does neuroscience contain the key to extraordinary evolution? For more than a century, comic books and science-fiction have postulated the sudden acquisition of superhuman abilities from events like lightning strikes and exposure to radiation. Many of these abilities consist of sensory enhancements, such as the ability to see non-visible wavelengths, or extraordinary calculating powers.
Can paralysis be cured using neuroscience? About 6 million people in the United States suffer from some serious form of paralysis. Major causes include stroke, spinal cord injury, and multiple sclerosis. Strokes damage the brain control centers for movement, while spinal cord injuries and multiple sclerosis damage neural axons that either control muscles directly or transmit signals from the brain to control muscles.
The effort to uncover principles of learning and memory used to be called the search for the engram, the memory trace in the brain that constituted a memory. Overwhelming evidence now shows that learning in the nervous system occurs because neurons modify the strength of the synapses between them. This synaptic modification allows small neural circuits to become highly selective for stimuli that have been learned.
Neuroscience
Although pain is a necessary function for preventing damage to the body, in some cases, pain itself becomes disabling. Chronic pain can occur in disease conditions such as cancer, in which case the normal function of pain that forces you to rest, protect, or not use some injured part of the body until it heals is simply inappropriate in a disease state in which destruction is occurring from the cancer all over the body that cannot be healed from rest.
Stem cells are cells that exist during development (and sometimes afterward) that are undifferentiated and retain the ability to turn into specialized cells such as neurons, kidney cells, blood vessel wall cells, and so on.Research suggests that injecting some types of stem cells into damaged tissues like the brain or heart causes the cells to differentiate according to the host environment into the appropriate tissues of that environment, sometimes repairing the damage.
Neuroscience
Depression, which affects nearly 15 percent of the population, is the most serious form of mental illness in terms of total cost. Some sources estimate the direct and indirect costs at over $50 billion yearly in the United States alone.Depression is poorly understood, but the term clearly designates many different syndromes and diseases, some of which may have a strong genetic basis, while others may not.
Neuroscience
Mental illness can clearly occur in a genetically normal brain which has suffered organic damage during development or later. It can also arise from trauma or stress that leads to indirect changes in the brain from factors like chronic stress or sleep deprivation.Well-known environmentally generated brain dysfunctions include the following:
Fetal alcohol syndrome: Fetal alcohol syndrome develops when the mother drinks excessive alcohol during pregnancy.
Neuroscience
Schizophrenia is a mental disorder in which thought is disordered and does not reflect reality. Schizophrenia is associated with significant social dysfunction and disability that, in severe cases, requires hospitalization.Symptoms of schizophrenia typically appear in young adulthood, and they fall into two general categories:
Positive symptoms mean active behaviors or processes such as hearing voices or trying to escape imagined people following the sufferer.
A weak but statistically significant correlation exists between brain size and intelligence in humans. In a nutshell, there is a general consensus that animals capable of what appears to be intelligent behavior, such as apes and dolphins, have larger brains than less intelligent animals, such as lizards.
Despite the correlation, however, variability in humans is enormous.
Learning is hard. Most people spend at least 7 hours a day for 12 years just to qualify for a high school diploma. If you have dyslexia, autism, or some other learning disability, your struggle to achieve this competence may be arduous.
Neuroscientists now understand much more about how the brain learns than even ten years ago, and what they know is that learning in some contexts at some rates is much easier than in others.
Neuroscience
Epilepsy is characterized by seizures in the brain. Seizures are incidents of hyper-synchronous neural activity during which normal, controlled brain function is severely compromised. Epilepsy has multiple causes, ranging from genetic to developmental abnormalities that may have environmental contributions. Treatments for epilepsy include
Pharmaceuticals: Drugs used to treat epilepsy are called anticonvulsants; currently, 20 are approved by the FDA.
Neuroscience
The autonomic nervous system. It has sensory, motor, and gland-stimulating components. The key components of the central nervous system are the brain and spinal cord. But when it comes to nervous systems, your body has more than just these two.The autonomic nervous system resides outside the central nervous system and controls not voluntary muscles as the peripheral nervous system does, but the heart, glands, and organs with smooth muscles (not under voluntary control) such as the intestines.
The skin is an organ, one of the largest organs in the body in terms of area, and it has a number of important functions. To perform all these functions, the skin has several layers with different properties.
The dermis and epidermis
The outermost layer of the skin is called the epidermis (epi means "on" or "above," and dermis means "skin").
Neuroscience
Research into mental illness has shown that many types of mental illness are associated with neurotransmitter abnormalities that have a genetic base or were caused by some life experience.Sequencing the human genome (and the genomes of many animals, particularly mice) has produced enormous advances in understanding how a number of brain dysfunction syndromes depend on particular genetic substitutions, deletions, or additions.
The nervous system consists of the central nervous system (the brain, retina, and spinal cord), the peripheral nervous system (the sensory and motor nerve axons that connect the central nervous system to the limbs and organs). The peripheral nervous system also includes the autonomic nervous system (which regulates body processes such as digestion and heart rate), and the enteric nervous system, which controls the gastrointestinal system.
You can detect more than just various kinds of pressure on your skin. Two other skin senses are temperature and pain. These receptors have similar structures, or, really, lack of structure. All the mechanoreceptors consist of an axon terminal with ion channel receptors embedded in some sort of structure, such as a corpuscle, disk, or myelin wrapping, that gives the receptor its particular responsiveness to different mechanical stimulation frequencies.
Somatosensory neurons, the tips of which form the mechanoreceptors, have an unusual morphology, or structure. This morphology is crucial to their function. Their morphological classification is called pseudounipolar. Although this rather unwieldy name isn't particularly illuminating about their function, understanding their structure explains some aspects about how these receptors work.
Neuroscience
The mapping of skin receptors to a specific area of neocortex illustrates one of the most fundamental principles of brain organization, cortical maps. The projection from the thalamus is orderly in the sense that receptors on nearby parts of the skin project to nearby cortical neurons. The figure shows a representation of the skin map on the somatosensory cortex.
Neurons originally evolved to coordinate muscle activity. Large, multi-celled animals can only move efficiently if muscles throughout the animal move in coordination. Coordinated muscle movement is achieved when neurons, embedded in a system that receives sensory input, can activate muscles in such a way as to produce specific muscle contraction sequences — which is precisely what the neuromuscular system does.
Neuroscience
You've certainly heard it: Humans use only 10 percent of their brains, but there is no scientific basis for this assertion. The origins of this myth are obscure. Some researchers have traced the idea to misattributions of the words of Albert Einstein, Dale Carnegie, or William James (a Harvard psychologist). Others use the following to bolster the idea:
The fact that some people who, through some developmental injury or anomaly, have brains 10 percent the size of the average adult human but appear normal.
Some neuroscientists have suggested that neurons actively seek to have variability in their responses over time. This may make for more robust neural circuits that can tolerate variation in their inputs, such as from noisy neural sensors. Neural noise analysis is a growing area in systems neuroscience.
Complete genetic coding outlining the entire structure of the nervous system is possible for an animal, like an invertebrate, that has a few hundreds or thousands of neurons.
A crucial aspect of neuronal function is their unique use of electricity. They use electricity both to secrete their neurotransmitters and for computation. Here's how.The membrane of the neuron contains a special kind of ion channel that is actually an active pump for ions. Ions are the charged atoms that are dissolved in fluids inside and outside the cell.
Why is Neuroscience important? The most complex structure in the world is the 3-pound mass of cells within your skull called the brain.The brain consists of about 100 billion neurons, which is about the same number as all the stars in our Milky Way galaxy and the number of galaxies in the known universe. It also contains about a trillion glial cells, which contribute to the proper function of neurons.
Neuroscience
The brain is composed of two nearly mirror-image lobes called the left and right hemispheres. The left hemisphere receives most inputs from and controls mostly the right side of the body. This hemisphere in humans is also specialized for language, rule-based reasoning, and analytic skills. The right hemisphere deals with the left side of the body, and it is better at visual pattern recognition and more holistic kinds of perception.
Neuroscience
The nervous system consists of the central nervous system (the brain and spinal cord), the peripheral nervous system (the sensory and motor neurons), and the autonomic nervous system (which regulates body processes such as digestion and heart rate).
All the divisions of the nervous system are based universally on the functions of neurons, specialized cells that process information.
Neuroscience
The neocortex plays an important role in neuroscience. When you look at a human brain from the top or sides, almost everything you see is neocortex. It’s called “neo” because it is a relatively recent invention of mammals. Prior to mammals, animals like reptiles and birds had relatively small brains with very specialized areas for processing sensory information and controlling behavior.
Most psychoactive drugs mimic the action of known neurotransmitters, but until a few decades ago, there was no known neurotransmitter that mediated the general effects of pain. Here's a mystery that puzzled researchers for a long time: Why does a substance produced by a poppy plant (morphine) relieve pain?This all changed with the discovery of endogenous opioids (that is, opioids that are developed naturally within the body).
Although the figure of 100 billion neurons in the brain is certainly impressive, within that same volume are at least ten times as many non-neuronal cells called glia. Glial cells fall into three major types — astrocytes, oligodendrocytes and Schwann cells, and microglia — each with a function, as the following sections explain.
As information processors, neurons receive information from other neurons, perform computations on that information, and send the output of those computations to other neurons.Neurons receive information via synapses. Most neurons have synapses on their cell bodies, and the first neurons probably were limited to such.
Neuroscience
The sense of pain can be reduced in several ways, including the body's own production of endorphins. Feeling pain is, well, painful. Wouldn't you be better off if you could just eliminate pain? The answer to the question of whether you would be better off without a sense of pain is a resounding no.This situation actually occurs in some people.
Neuroscience
Although not located in the skin, receptors mediating proprioception (position sense) and kinesthesis (movement sense), are either free nerve endings or structures similar to mechanoreceptors like Ruffini corpuscles (refer to the first figure below) and have similar layouts as the cell bodies in the dorsal root ganglia (refer to the second figure).
Inside the skin's dermis are four distinctive types of touch receptors, termed mechanoreceptors. The following figure shows the layers of the skin and some of its receptors. The layers of the skin and some of its receptors.
Merkel disks
Merkel disk receptors, as their name implies, are disk-shaped receptors located close to the border between the dermis and epidermis; sometimes they extend into the epidermis.
Skin receptors allow you to respond to things that contact your skin and to be aware of what those things are. The output of most somatosensory receptors participates in at least three different kinds of neural circuits:
Local reflexes are those that primarily involve contraction of a single muscle, such as a flexor like the biceps that contracts when, for example, you touch something hot.
On the physiological front, electroencephalographic (EEG) recordings in the early 20th century revealed that the brain was constantly producing electrical oscillations that could be recorded from the surface of the skull. These oscillations changed with external stimulation and when different thought patterns occurred inside the brain.
The axon is the device by which a neuron sends signals to muscles, glands, or other neurons. Axons are cablelike structures that have two functions: communicating action potentials from the cell body to the axon terminal and, at the axon terminal, releasing a neurotransmitter that binds to a membrane receptor on the postsynaptic cell and opens an excitatory or inhibitory ion channel.
Neuroscience
The spinal cord is a key part of the central nervous system. Specifically, within the spinal cord are the connections between the central nervous system (such as motor neurons from primary motor cortex) and the peripheral nervous system (skin, muscle, and tendon receptors going to the spinal cord, and alpha motor neurons relaying motor commands from the spinal cord to the actual muscles).
Nanotechnology is the assembling of devices with molecular components to achieve nanoscale structures. Current conceptions are for nanoscale devices to be autonomous, with the ability to sense, move, obtain, or store energy, and to accomplish some programmed function. A common name used for the (currently conceptual) devices is nanobots.
Neuroscience
The most effective drug treatments for schizophrenia are antipsychotic medications that reduce positive symptoms (few drugs alleviate negative symptoms). Antipsychotics typically suppress dopamine and sometimes serotonin receptor activity.
It was originally theorized that schizophrenia was caused by excessive activation of a particular type of dopamine receptor, the D2.
The loss of a major sense such as vision or hearing is one of the most disabling of all nervous system disorders. Most vision and hearing losses occur from damage to the peripheral receptors or receptor organs — the eye in the case of vision and the inner ear in the case of hearing.While many people are familiar with the use of mechanical prosthetics for limb loss, not many are aware of neuroprostheses, prosthetics designed to address nervous system disorders.
Neuroscience
Knowing the four lobes of the brain is important for neuroscience. The neocortex is divided into four major lobes: the frontal lobe, the parietal lobe, the temporal lobe, and occipital lobe. These lobes are further divided into different regions. The frontal lobes are involved with control of movement, from stimulation of individual muscles to abstract planning about what to do.
Neuroscience
Neuroscience tells us that the neocortex interacts with the rest of the brain primarily through a structure called the thalamus. The thalamus, which is underneath (and hierarchically below) the neocortex, functions like a command center that controls what information goes between different parts of the neocortex and the rest of the brain.
Few subjects generate more argument in neuroscience and philosophy than the nature of consciousness and its function. At one extreme, some philosophers and cognitive neuroscientists regard consciousness as an epiphenomenon — a kind of story people tell themselves after the fact of behavior to make some sense of what’s going on.
Neuroscience
Given the enormous complexity of the brain, it should not be surprising that sometimes it gets broken. Mental disorders range from those with a clear genetic basis, such as Down and Fragile X syndromes, to disorders with high but not complete heritability, such as schizophrenia and autism, to conditions that may be almost completely attributed to life events, like some types of depression.
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