Brain Facts A PRIMER ON THE BR AIN AND NERVOUS SYSTEM THE SOCIET Y FOR NEUROSCIENCE Brain Facts A PRIMER ON THE BR AIN AND NERVOUS SYSTEM THE SOCIET Y FOR NEUROSCIENCE THE SOCIETY FOR NEUROSCIENCE The Society for Neuroscience is the world’s largest organization of sci- entists and physicians dedicated to understanding the brain, spinal cord and peripheral nervous system. Neuroscientists investigate the molecular and cellular levels of the nervous system; the neuronal systems responsible for sensory and motor function; and the basis of higher order processes, such as cog- nition and emotion. This research provides the basis for understand- ing the medical fields that are concerned with treating nervous system disorders. These medical specialties include neurology, neurosurgery, psychiatry and ophthalmology.
Founded in 1970, the Society has grown from 500 charter members to more than 29,000 members. Regular members are residents of Canada, Mexico and the United States—where more than 100 chapters organize local activities. The Society’s membership also includes many scientists from throughout the world, particularly Europe and Asia. The purposes of the Society are to: ∫ Advance the understanding of the nervous system by bringing together scientists from various backgrounds and by encouraging research in all aspects of neuroscience.
∫ Promote education in the neurosciences. ∫ Inform the public about the results and implications of new research. The exchange of scientific information occurs at an annual fall meeting that presents more than 14,000 reports of new scientific findings and includes more than 25,000 participants. This meeting, the largest of its kind in the world, is the arena for the presentation of new results in neuroscience.
The Society’s bimonthly journal, The Journal of Neuroscience, con- tains articles spanning the entire range of neuroscience research and has subscribers worldwide. A series of courses, workshops and sym- posia held at the annual meeting promote the education of Society members. The Neuroscience Newsletter informs members about Society activities. A major mission of the Society is to inform the public about the progress and benefits of neuroscience research.
The Society provides information about neuroscience to school teachers and encourages its members to speak to young people about the human brain and nervous system. Brain Facts INTRODUCTION. 4 Neurotransmitters ∫ Second Messengers BRAIN DEVELOPMENT. 8 Birth of Neurons and Brain Wiring ∫ Paring Back ∫ Critical Periods SENSATION AND PERCEPTION.
12 Vision ∫ Hearing ∫ Taste and Smell ∫ Touch and Pain LEARNING AND MEMORY. 22 The Stu∑ of Sleep ∫ Sleep Disorders ∫ How is Sleep Regulated? STRESS. 25 The Immediate Response ∫ Chronic Stress AGING. 28 Aging Neurons ∫ Intellectual Capacity ADVANCES.
30 Parkinson’s Disease ∫ Pain ∫ Epilepsy ∫ Major Depression Manic-Depressive Illness CHALLENGES. 33 Addiction ∫ Alzheimer’s Disease ∫ Learning Disorders Stroke ∫ Neurological Trauma ∫ Anxiety Disorders Schizophrenia ∫ Neurological AIDS ∫ Multiple Sclerosis Down Syndrome ∫ Huntington’s Disease ∫ Tourette Syndrome Brain Tumors ∫ Amyotrophic Lateral Sclerosis NEW DIAGNOSTIC METHODS. 43 Imaging Techniques ∫ Gene Diagnosis POTENTIAL THERAPIES. 46 New Drugs ∫ Trophic Factors ∫ Cell and Gene Therapy GLOSSARY.
53 Introduction I t sets humans apart from all other species by allowing us disease mechanisms and is beginning to suggest new treatments. to achieve the wonders of walking on the moon and com- With the mapping of the human genome, neuroscientists posing masterpieces of literature, art and music. Through- will be able to make more rapid progress in identifying genes that out recorded time, the human brain—a spongy, three- either contribute to human neurological disease or that directly pound mass of fatty tissue—has been compared to a cause disease. Mapping animal genomes will aid the search for telephone switchboard and a supercomputer.
genes that regulate and control many complex behaviors. But the brain is much more complicated than any of these ∫ Brain Plasticity. Scientists began to uncover the molecular devices, a fact scientists confirm almost daily with each new bases of neural plasticity, revealing how learning and memory discovery. The extent of the brain’s capabilities is unknown, but occur and how declines might be reversed.
It also is leading to it is the most complex living structure known in the universe. new approaches to the treatment of chronic pain. This single organ controls all body activities, ranging from ∫ New Drugs. Researchers gained new insights into the mech- heart rate and sexual function to emotion, learning and mem- anisms of molecular neuropharmacology, which provides a new ory.
The brain is even thought to influence the response to dis- understanding of the mechanisms of addiction. These advances ease of the immune system and to determine, in part, how well also have led to new treatments for depression and obsessive- people respond to medical treatments. Ultimately, it shapes our compulsive disorder. thoughts, hopes, dreams and imagination.
In short, the brain is ∫ Imaging. Revolutionary imaging techniques, including mag- what makes us human. netic resonance imaging and positron emission tomography, Neuroscientists have the daunting task of deciphering the now reveal brain systems underlying attention, memory and mystery of this most complex of all machines: how as many as emotions and indicate dynamic changes that occur in schizo- a trillion nerve cells are produced, grow and organize them- phrenia. selves into e∑ective, functionally active systems that ordinarily ∫ Cell Death.
The discovery of how and why neurons die, as remain in working order throughout a person’s lifetime. well as the discovery of stem cells, which divide and form new The motivation of researchers is twofold: to understand neurons, has many clinical applications. This has dramatically human behavior better—from how we learn to why people improved the outlook for reversing the e∑ects of injury both in have trouble getting along together—and to discover ways to the brain and spinal cord. The first e∑ective treatments for prevent or cure many devastating brain disorders.
stroke and spinal cord injury based on these advances have been The more than 1,000 disorders of the brain and nervous brought to clinical practice. system result in more hospitalizations than any other disease ∫ Brain Development. New principles and molecules respon- group, including heart disease and cancer. Neurological illnesses sible for guiding nervous system development now give scien- a∑ect more than 50 million Americans annually at costs exceed- tists a better understanding of certain disorders of childhood.
In addition, mental disorders, excluding drug Together with the discovery of stem cells, these advances are and alcohol problems, strike 44 million adults a year at a cost pointing to novel strategies for helping the brain or spinal cord of some $148 billion. regain functions lost to diseases. However, during the congressionally designated Decade of Federal neuroscience research funding of more than $4 bil- the Brain, which ended in 2000, neuroscience made significant lion annually and private support should vastly expand our discoveries in these areas: knowledge of the brain in the years ahead. Key disease genes were identified that underlie sev- This book only provides a glimpse of what is known about eral neurodegenerative disorders—including Alzheimer’s dis- the nervous system, the disorders of the brain and some of the ease, Huntington’s disease, Parkinson’s disease and amyotrophic exciting avenues of research that promise new therapies for lateral sclerosis.
This has provided new insights into underlying many neurological diseases. This part of the brain is divided into four sections: the Motor cortex Sensory cortex occipital lobe, the temporal lobe, the parietal lobe and the Frontal lobe frontal lobe. Functions, such as Parietal lobe vision, hearing and speech, are distributed in selected regions. Some regions are associated Occipital lobe with more than one function.
Major internal structures Temporal lobe (below). The (1) forebrain is credited with the highest intel- lectual functions—thinking, planning and problem-solving. The hippocampus is involved in memory. The thalamus serves as a relay station for almost all of Cerebrum the information coming into the Thalamus brain.
Neurons in the hypothala- Hypothalamus mus serve as relay stations for internal regulatory systems by monitoring information coming 1 Forebrain in from the autonomic nervous system and commanding the body through those nerves and Amygdala the pituitary gland. On the Hippocampus upper surface of the (2) mid- 2 Midbrain brain are two pairs of small Pons hills, colliculi, collections of Cerebellum 3 Hindbrain Spinal cord cells that relay specific sensory Medulla oblongata information from sense organs to the brain. The (3) hindbrain consists of the pons and medulla oblongata, which help control respiration and heart THE TOLL OF SELECTED BRAIN AND NERVOUS SYSTEM DISORDERS* rhythms, and the cerebellum, which helps control movement Condition Total Cases Costs Per Year as well as cognitive processes Hearing Loss 28 million $ 56 billion that require precise timing. All Depressive Disorders 18.8 million $ 44 billion Alzheimer’s Disease 4 million $ 100 billion Stroke 4 million $ 30 billion Schizophrenia 3 million $ 32.5 billion Parkinson’s Disease 1.5 million $ 15 billion Traumatic Head Injury 1 million $ 48.3 billion Multiple Sclerosis 350,000 $ 7 billion Spinal Cord Injury 250,000 $ 10 billion * Estimates provided by the National Institutes of Health and voluntary organizations.
3 The Neuron specialized cell designed to transmit infor- bind to receptors on the surface of the target neuron. A mation to other nerve cells, muscle or gland These receptors act as on and o∑ switches for the next cell. cells, the neuron is the basic working unit of Each receptor has a distinctly shaped part that exactly matches the brain. The brain is what it is because of a particular chemical messenger.
A neurotransmitter fits into the structural and functional properties of this region in much the same way as a key fits into an automo- neurons. The brain contains between one bil- bile ignition. And when it does, it alters the neuron’s outer lion and one trillion neurons. membrane and triggers a change, such as the contraction of a The neuron consists of a cell body containing the nucleus muscle or increased activity of an enzyme in the cell.
and an electricity-conducting fiber, the axon, which also gives Knowledge of neurotransmitters in the brain and the action rise to many smaller axon branches before ending at nerve ter- of drugs on these chemicals—gained largely through the study minals. Synapses, from the Greek words meaning to “clasp of animals—is one of the largest fields in neuroscience. Armed together,” are the contact points where one neuron communi- with this information, scientists hope to understand the circuits cates with another. Other cell processes, dendrites, Greek for responsible for disorders such as Alzheimer’s disease and Parkin- the branches of a tree, extend from the neuron cell body and son’s disease.
Sorting out the various chemical circuits is vital receive messages from other neurons. The dendrites and cell to understanding how the brain stores memories, why sex is such body are covered with synapses formed by the ends of axons of a powerful motivation and what is the biological basis of men- other neurons. Neurons signal by transmitting electrical impulses along their axons that can range in length from a tiny fraction of an Neurotransmitters inch to three or more feet. Many axons are covered with a lay- Acetylcholine The first neurotransmitter to be identified 70 ered insulating myelin sheath, made of specialized cells, that years ago, was acetylcholine (ACh).
This chemical is released speeds the transmission of electrical signals along the axon. by neurons connected to voluntary muscles (causing them to Nerve impulses involve the opening and closing of ion chan- contract) and by neurons that control the heartbeat. ACh also nels, water-filled molecular tunnels that pass through the cell serves as a transmitter in many regions of the brain. membrane and allow ions—electrically charged atoms—or ACh is formed at the axon terminals.
When an action small molecules to enter or leave the cell. The flow of these ions potential arrives at the terminal, the electrically charged cal- creates an electrical current that produces tiny voltage changes cium ion rushes in, and ACh is released into the synapse and across the membrane.