Chapter 13

Chapter 13 - Chapter 13 The Central Nervous System Overview...

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Chapter 13 The Central Nervous System Overview of the Central Nervous System A. Major Landmarks 1. Two directional terms used to describe the human brain are rostral (closer to the forehead) and caudal (closer to the spinal cord.) 2. The brain can be divided into three major portions: the cerebrum, the cerebellum and the brainstem. 3. The cerebrum consists of two cerebral hemispheres, each marked by folds called gyri and grooves called sulci, with a few deeper grooves called fissures. a. The longitudinal fissure separates the left and right hemispheres, although they remain connected through the corpus callosum. b. The cerebrum constitutes 83% of brain volume. 4. The cerebellum also has gyri, sulci and fissures, but they are more delicate. a. The cerebellum lies inferior and posterior to the cerebrum. b. The cerebellum is the second largest brain region, constituting about 10% of the volume but more than 50% of its neurons. 5. The brainstem is at the base of the brain, and includes the thalamus, hypothalamus, midbrain, pons and medulla oblongata. B. Embryonic Development. 1. The nervous system forms from ectoderm. By the third week, the neuroectoderm appears along the length of the embryo and forms a neural plate. 2. The neural plate sinks into a neural groove, while cells along its margin form a neural fold that eventually fuses. 3. By four weeks, a neural tube is evident, the lumen of which forms the ventricles of the brain ad the central canal of the spinal cord.
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4. Some cells separate from the neural tube and form the neural crest, which gives rise to some sensory neurons and other cell types (Neuroglia and neurons). 5. At week four, the neural tube shows three primary vesicles, a forebrain, midbrain, and hindbrain: the forebrain then divided further in the telencephalon and diencephalon. The hindbrain divides into the metencephalon and myelencephalon. Meninges, Ventricles, Cerebrospinal Fluid and Blood Supply. A. Meninges 1. The meninges are three protective fibrous coverings that separate the brain and spinal cord for the skull and vertebrae. 2. The outermost meninx, the dura mater, consists of an outer periosteal layer and an inner meningeal layer. a. In certain places, these two layers are separated by dural sinuses where blood pools. b. In other places, the dura mater folds to separate major areas of the brain. These folds are the falx cerebri and tentorium cerebelli. 2. Within the vertebral canal, the periosteal layer of the dura is absent. The meningeal layer forms a dural sheath around the spinal cord; between the sheath and surrounding bone lies the epidural space. 3. The second meninx, the arachnoid mater, adheres to the dura and sends spider like extensions out to the pia mater. 4. The pia mater is highly vascular layer that closely follows the contours of the
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Chapter 13 - Chapter 13 The Central Nervous System Overview...

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