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The central nervous system consists of the brain and spinal cord. The brain may be thought of as consisting of the cerebrum, cerebellum, thalamus, hypothalamus and the brainstem (figure 1).
The cerebrum is divided into left and right hemispheres, each of which is composed of frontal, parietal, temporal and occipital lobes (figure 2). The frontal lobe is responsible for voluntary movement, while the parietal lobe gives us our sense of touch. The occipital lobe is responsible for vision. Language is a complex function which requires many parts of the cerebrum to work together. An important center for hearing is within the temporal lobe. The locations of these various functions were discovered principally by looking at the symptoms of patients who had injuries to particular parts of their brains. The outer surface of the cerebrum, the cortex, is covered with raised convolutions, the gyri, which are separated by sulci. Deep within the cerebral hemispheres are the basal ganglia (figure 3), such as the caudate nucleus, which relay information traveling to and from the cortex. In particular, the basal ganglia help to provide fine control of movement. The thalamus, beneath the cerebrum, contains many distinct nuclei which are involved in functions such as regulation of body temperature, and responding to hunger and thirst. The hypothalamus is an important interface between nervous and hormonal function, regulating the secretions of the pituitary gland. The hypothalamus is also regarded as the controlling center of the autonomic nervous system.
The brainstem consists of three regions, the midbrain, the pons and the medulla oblongata (figure 4). Each of these regions contains important reflex centres which give rise to cranial nerves. The midbrain is involved in the control of eye movement, the pons relays information to and from the cerebellum, and the medulla oblongata contains centres which are involved in the regulation of respiration and cardiac function. The cerebellum (figure 5) is an important centre for the coordination of posture and movement. When the cerebellum is damaged, a person may have difficulty walking or standing up straight, especially when their eyes are closed.
Beneath the medulla oblongata, the spinal cord runs caudally through the neural canal of the vertebral column. In the infant, the spinal cord runs to about the level of the lumbosacral junction. In the adult, the spinal cord ends at about the level of the first or second lumbar vertebrae (figure 6). The spinal cord is divided into vertical tracts which convey sensory information towards the brain, and motor information towards the muscles and viscera (figure 7). Spinal nerves run from the spinal cord to the other organs of the body. Sensory nerves carry information into the spinal cord and brain. Motor nerves carry commands from the spinal cord and brain to the tissues of the body.
Both the brain and the spinal cord are enclosed in protective bone, the cranium and vertebral column. Within the cranium and vertebral column, protecting the brain and spinal cord, are three membranes or meninges (figure 8). These are the outer dura mater, the middle arachnoid mater, and the inner pia mater. Between the arachnoid and pia mater is a cushion of cerebrospinal fluid. The cerebrospinal fluid fills the ventricles of the brain (figure 9) and the central canal of the spinal cord. It is produced by the choroid plexi within the ventricles of the brain and circulates through the foramena of Magendie and Luschka to reach the subarachnoid space.
arachnoid mater: 脳くも膜 (noukumomaku); brain: 脳 (nou); brain stem: 脳幹 (noukan); central canal: 中心管 (chuushinkan); central nervous system: 中枢神経系統 (chuusuushinkeikeitou); cerebellum: 小脳 (shounou); cerebral hemisphere: 大脳半球 (dainouhankyuu); cerebrospinal fluid: 脳脊髄液 (nousekizuieki); cerebrum: 大脳 (dainou); cortex: 脳皮質 (nouhishitsu); cranial nerve: 脳神経 (noushinkei); dura mater: 脳硬膜 (noukoumaku); frontal lobe: 前頭葉 (zentouyou); hypothalamus: 視床下部 (shishoukabu); medulla oblongata: 延髄 (enzui); meninge: 脳膜 (noumaku); midbrain: 中脳 (chuunou); motor nerves: 運動神経 (undoushinkei); occipital lobe: 後頭葉 (koutouyou); parietal lobe: 頭頂葉 (touchouyou); pia mater: 脳軟膜 (nounanmaku); pons: 橋 (kyou); sensory nerves: 感覚神経 (kankakushinkei); spinal cord:脊髄 (sekizui); spinal nerve: 脊髄神経 (sekizuishinkei); temporal lobe: 側頭葉 (sokutouyou); thalamus: 視床(shishou); ventricle: 脳室(noushitsu)
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