Understanding the Brain: A Work in Progress

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brain

Side view of the brain showing its major structures. The large cerebrum is divided into two halves, …© Merriam-Webster Inc.Concentration of nerve tissue in the front or upper end of an animal's body. It handles sensory information, controls motion, is vital to instinctive acts, and in higher vertebrates is the centre of learning. Vertebrate brains consist of the hindbrain (rhombencephalon), midbrain (mesencephalon), and forebrain (prosencephalon). The hindbrain comprises the medulla oblongata and the pons, which connects the spinal cord with higher brain levels and transfers information from the cerebral cortex to the cerebellum. The midbrain, a major sensory integration centre in other vertebrates, serves primarily to link the hindbrain and forebrain in mammals. Large nerve bundles connect the cerebellum to the medulla, pons, and midbrain. In the forebrain the two cerebral hemispheres are connected by a thick bundle of nerve fibres (corpus callosum) and are divided by two deep grooves into four lobes (frontal, parietal, temporal, and occipital). The cerebrum, the largest part of the human brain, is involved with its more complex functions. Motor and sensory nerve fibres from each hemisphere cross over in the medulla to control the opposite side of the body.

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neurology

Medical specialty concerned with nervous system function and disorders. Clinical neurology began in the mid-19th century, when mapping of the functional areas of the brain first began and understanding of the causes of conditions such as epilepsy improved. The development of electroencephalography in the 1920s aided in the diagnosis of neurological disease, as did the development of computerized axial tomography in the 1970s and nuclear magnetic resonance imaging in the 1980s. In addition to dealing with physical disorders (e.g., tumours, trauma), neurology is unique among medical specialties in its intersection with psychiatry. Greater understanding of the brain chemistry of disorders such as schizophrenia and depression has led to a wide array of effective drugs that nevertheless work best in conjunction with psychotherapy. Side effects of drug or surgical therapy can be serious, and many nervous system disorders have no effective treatment.

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neuron

Structure of a neuron. Dendrites, usually branching fibres, receive and conduct impulses to the …© Merriam-Webster Inc.Any of the cells of the nervous system. Sensory neurons relay information from sense organs, motor neurons carry impulses to muscles and glands, and interneurons transmit impulses between sensory and motor neurons. A typical neuron consists of dendrites (fibres that receive stimuli and conduct them inward), a cell body (a nucleated body that receives input from dendrites), and an axon (a fibre that conducts the nerve impulse from the cell body outward to the axon terminals). Both axons and dendrites may be referred to as nerve fibres. Impulses are relayed by neurotransmitter chemicals released by the axon terminals across the synapses (junctions between neurons or between a neuron and an effector cell, such as a muscle cell) or, in some cases, pass directly from one neuron to the next. Large axons are insulated by a myelin sheath formed by fatty cells called Schwann cells. Bundles of fibres from neurons held together by connective tissue form nerves.

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