<unk>  is a profound field that is devoted to the scientific study of the nervous system. Such studies span the structure, function, evolutionary history, development, genetics, biochemistry, physiology, pharmacology, informatics, computational<unk>  and pathology of the nervous system.  Traditionally it is seen as a branch of biological sciences.  However, recently there has been a surge in the convergence of interest from many allied disciplines, including cognitive and neuro-psychology, computer science, statistics, physics, and medicine.  The scope of<unk>  has now broadened to include any systematic scientific experimental and theoretical investigation of the central and peripheral nervous system of biological organisms.  The empirical methodologies employed by neuroscientists have been enormously expanded, from biochemical and genetic analysis of dynamics of individual nerve cells and their molecular constituents to imaging representations of perceptual and motor tasks in the brain. Many recent theoretical advances in<unk>  have been aided by the use of computational modeling.
The scientific study of the nervous systems underwent a significant increase in the second half of the twentieth century, principally due to revolutions in molecular biology, electrophysiology and computational<unk> .  It has become possible to understand, in much detail, the complex processes occurring within a single neuron. However, understanding of how networks of neurons produce intellectual behavior, cognition, emotion and physiological responses is still poorly understood.
The nervous system is composed of a network of neurons and other supportive cells (such as glial cells). Neurons form functional circuits, each responsible for specific tasks to the behaviors at the organism level.  Thus,<unk>  can be studied at many different levels, ranging from molecular level to cellular level to systems level to cognitive level.
At the molecular level, the basic questions addressed in molecular<unk>  include the mechanisms by which neurons express and respond to molecular signals and how axons form complex connectivity patterns.  At this level, tools from molecular biology and genetics are used to understand how neurons develop and die, and how genetic changes affect biological functions.  The morphology, molecular identity and physiological characteristics of neurons and how they relate to different types of behavior are also of considerable interest. (The ways in which neurons and their connections are modified by experience are addressed at the physiological and cognitive levels.)
At the cellular level, the fundamental questions addressed in cellular<unk>  are the mechanisms of how neurons process signals physiologically and electrochemically.  They address how signals are processed by the dendrites, somas and axons, and how neurotransmitters and electrical signals are used to process signals in a neuron.
At the systems level, the questions addressed in systems<unk>  include how the circuits are formed and used anatomically and physiologically to produce the physiological functions, such as reflexes, sensory integration, motor coordination, circadian rhythms, emotional responses, learning and memory, et cetera.  In other words, they address how these neural circuits function and the mechanisms through which behaviors are generated.  For example, systems level analysis addresses questions concerning specific sensory and motor modalities: how does vision work?  How do songbirds learn new songs and bats localize with ultrasound?  The related field of neuroethology, in particular, addresses the complex question of how neural substrates underlies specific animal behavior.
At the cognitive level, cognitive<unk>  addresses the questions of how psychological/cognitive functions are produced by the neural circuitry. The emergence of powerful new measurement techniques such as neuroimaging (e.g.,fMRI, PET, SPECT), electrophysiology and human genetic analysis combined with sophisticated experimental techniques from cognitive psychology allows neuroscientists and psychologists to address abstract questions such as how human cognition and emotion are mapped to specific neural circuitries.<unk>  is also beginning to become allied with social sciences, and burgeoning interdisciplinary fields of neuroeconomics, decision theory, social<unk>  are starting to address some of the most complex questions involving interactions of brain with environment.<unk>  generally includes all scientific studies involving the nervous system. Psychology, as the scientific study of mental processes, may be considered a sub-field of<unk> , although some mind/body theorists argue that the definition goes the other way — that psychology is a study of mental processes that can be modeled by many other abstract principles and theories, such as behaviorism and traditional cognitive psychology, that are independent of the underlying neural processes.  The term neurobiology is sometimes used interchangeably with<unk> , though the former refers to the biology of nervous system, whereas the latter refers to science of mental functions that form the foundation of the constituent neural circuitries. In Principles of Neural Science, nobel laureate Eric Kandel contends that cognitive psychology is one of the pillar disciplines for understanding the brain in<unk> .
Neurology and Psychiatry are medical specialties and are generally considered, in academic research, subfields of<unk>  that specifically address the diseases of the nervous system.  These terms also refer to clinical disciplines involving diagnosis and treatment of these diseases.  Neurology deals with diseases of the central and peripheral nervous systems such as amyotrophic lateral sclerosis (ALS) and stroke, while psychiatry focuses on mental illnesses.  The boundaries between the two have been blurring recently and physicians who specialize in either generally receive training in both.  Both neurology and psychiatry are heavily involved in and influenced by basic research in<unk> .
Neuroscience
Medicine
Obstetrics
Neuroeconomics
Otology
Coagulation
Sensory neuroscience
Oncology