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  3. The Human Brain The brain is the most complex organ in

The Human Brain The brain is the most complex organ in

游客2024-02-21  13
问题                      The Human Brain
    The brain is the most complex organ in human body. It produces our every thought, action, memory, feeling and experience of the world. This jelly-like mass of tissue, weighing in around 1.4 kilograms, contains a staggering one hundred billion nerve cells, or neurons (神经元). The complexity of the connectivity between these cells is mind-boggling (令人难以置信的). Each neuron can make contact with thousands or even tens of thousands of others, via tiny structures called synapses (突触). Our brains form a million new connections for every second of our lives. The pattern and strength of the connections is constantly changing and no two brains are alike. It is in these changing connections that memories are stored, habits learned and personalities shaped, by reinforcing certain patterns of brain activities, and losing others.
Grey Matter and White Matter
    While people often speak of their "grey matter", the brain also contains white matter. The grey matter is the cell bodies of the neurons, while the white matter is the branching network of threadlike tendrils — called dendrites and axons — that spread out from the cell bodies to connect to other neurons. But the brain also has another, even more numerous type of cell, called glial (神 经胶质的) cells. These outnumber neurons over ten times. Once thought to be support cells, they are now known to amplify neural signals and to be as important as neurons in mental calculations. There are many different types of neuron, only one of which is unique to humans and the other great apes, the so-called spindle cells.
    Brain structure is shaped partly by genes, but largely by experience. Only recently it was discovered that new brain cells are being born throughout our lives — a process called neurogenesis. The brain has bursts of growth and then periods of consolidation, when excess connections are removed. The most notable bursts are in the first two or three years of life, during puberty, and also a final burst in young adulthood. How a brain ages also depends on genes and lifestyle too. Exercising the brain and giving it the right diet can be just as important as it is for the rest of the body.
Chemical Messengers
    The neurons in our brains communicate in a variety of ways. Signals pass between them by the release and capture of neurotransmitter and neuromodulator chemicals, such as glutamate, dopamine, acetylcholine, noradrenalin, serotonin and endorphins. Some neurochemicals work in the synapse, passing specific messages from release sites to collection sites, called receptors. Others also spread their influence more widely, like a radio signal, making whole brain regions more or less sensitive. These neurochemicals are so important that deficiencies in them are linked to certain diseases. For example, a loss of dopamine in the basal ganglia (基底神经节), which controls movements, leads to Parkinson’s disease. It can also increase susceptibility to addiction because it mediates our sensations of reward and pleasure.
    Similarly, a deficiency in serotonin, used by regions involved in emotion, can be linked to depression or mood disorders, and the loss of acetylcholine in the cerebral cortex (大脑皮层) is characteristic of Alzheimer’s disease.
Brain Scanning
    Within individual neurons, signals are formed by electrochemical pulses. Collectively, this electrical activity can be detected outside the scalp by an electroencephalogram (EEG). These signals have wave-like patterns, which scientists classify from alpha (common while we are relaxing or sleeping), through to gamma (active thought). When this activity goes awry (错误 的), it is called a seizure. Some researchers think that synchronising the activity in different brain regions is important in perception. Other ways of imaging brain activity are indirect. Functional magnetic resonance imaging (fMRI) or positron emission tomography (PET) monitors blood flow. MRI scans, computed tomography (CT) scans and diffusion tensor images (DTI) use the magnetic signatures of different tissues, X-ray absorption, or the movement of water molecules in those tissues, to image the brain.
    These scanning techniques have revealed which parts of the brain are associated with which functions. Examples include activities related to sensations, movement, libido, choices, regrets, motivations and even racism. However, some experts argue that we put too much trust in these results and that they raise privacy issues. Before scanning techniques were common, researchers relied on patients with brain damage caused by strokes, head injuries or illnesses, to determine which brain areas are required for certain functions.
Some Structures in Mind
    The most obvious anatomical feature of our brains is the undulating surface of the cerebrum (大脑) — the deep clefts are known as sulci and its folds are gyri. The cerebrum is the largest part of our brain and is largely made up of the two cerebral hemispheres. It is the most evolutionarily recent brain structure, dealing with more complex cognitive brain activities. It is often said that the right hemisphere is more creative and emotional while the left deals with logic, but the reality is more complex. Nonetheless, the sides do have some specialization, with the left dealing with speech and language, the right with spatial and body awareness.
    Behind the ears and temples lie the temporal lobes (颞叶), dealing with sound and speech comprehension and some aspects of memory. And to the fore are the frontal and prefrontal lobes (额和额前叶), often considered the most highly developed and most "human" of regions, dealing with the most complex thought, decision making, planning, conceptualizing, attention control and working memory. They also deal with complex social emotions such as regret, morality and empathy. Another way to classify the regions is as sensory cortex and motor cortex, controlling incoming information, and outgoing behavior respectively.
    Below the cerebral hemispheres, but still referred to as part of the forebrain, is the cingulated (扣 带) cortex, which deals with directing behavior and pain. And beneath this lies the corpus callosum (胼胝体), which connects the two sides of the brain. Other important areas of the forebrain are the basal ganglia, responsible for movement, motivation and reward.
    The back of the brain has a highly convoluted and folded swelling called the cerebellum, which stores patterns of movement, habits and repeated tasks — things we can do without thinking about them. The most primitive parts, the midbrain and brain stem, control the bodily functions we have no conscious control of, such as breathing, heart rate, blood pressure, sleep patterns, and so on. They also control signals that pass between the brain and the rest of the body, through the spinal cord. [br] Neurogenesis occurs______.
选项 A、in our whole life
B、when excess connections are pruned
C、in three short periods
D、when the brain is exercised
答案 A
解析 该句中提到“直到最近人们才发现，在我们的一生中(throughout our lives)，新的脑细胞一直都有生成——这个过程称为神经形成(neurogen esis)”。[A]项中的in our whole life对应原文中的throughout ourlives。[B]对应的是大脑巩固期，[C]对应的是大脑快速生长期，[D]是防止脑细胞老化的措施。
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