BI13_Ch12 Text Notes


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ANATOMY AND PHYSIOLOGY 1 TEXT NOTES Chapter 12 – The Central Nervous System 1. THE BRAIN a. Central Nervous System (CNS) – brain and spinal cord. b. Cephalization – an elaboration of the rostral, or anterior portion of the CNS, along with an increase in the number of neurons in the head. c. The average male brain has a mass of approximately 3.5 pounds; and female brain of approximately 3.2 pounds. d. Embryonic Development i. Starting in the 3-week-old embryo, the ectoderm (cell layer at the dorsal surface) thickens along the dorsal midline axis of the embryo to form the neural plate . ii. The neural plate invaginates, forming the neural groove , which is flaked by neural folds . iii. As the neural groove deepens, the superior edges of the neural folds fuse, forming the neural tube , which is formed by the 4 th week of pregnancy. iv. The neural tube differentiates into the CNS; The brain forms anteriorly (rostrally) and the spinal cord develops from the caudal (posterior) portion of the neural tube. v. Small groups of neural fold cells migrate laterally from between the surface ectoderm and the neural tube, forming the neural crest . Other terms not included e. Regions and Organization i. The basic pattern of the CNS consists of a central cavity surrounded by a gray matter core, external to which is white matter (myelinated fiber tracts). 1) Both the cerebral hemispheres and the cerebellum have an outer layer of gray matter consisting of neuron cell bodies called a cortex . f. Ventricles i. Brain ventricles arise from expansions of the lumen of the embryonic neural tube. 1) The hollow ventricular chambers are filled with CSF and lined with ependymal cells, a type of neuroglia. ii. The paired lateral ventricles lie close together, separated by a thin median membrane called the septum pellucidum . 1)
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