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Ch 12 The Central Nervous System -Part 1

Ch 12 The Central Nervous System -Part 1 - Ch 12 The...

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1 Ch. 12: The Central Nervous System Shreya Buch Central Nervous System (CNS) CNS – composed of the brain and spinal cord Cephalization (during course of evolution) Elaboration of the anterior portion of the CNS Increase in number of neurons in the head Highest level is reached in the human brain The Brain Composed of wrinkled, pinkish gray tissue Surface anatomy includes cerebral hemispheres, cerebellum, and brain stem Average adult male brain has mass of about 1600g and of female 1450g Embryonic Development (fig.12.1) & (fig.12.2) During the first three weeks of embryonic development: Ectoderm thickens forming the neural plate The neural plate invaginates, forming the neural groove The neural groove fuses dorsally and forms the neural tube The brain forms anteriorly (rostrally) and the spinal cord develops from the caudal (posterior- towards tail) portion of the neural tube Neural Tube and Primary Brain Vesicles: (fig.12.2) Primary Brain Vesicles (fig.12.2.a&b) The anterior end of the neural tube expands and constricts to form the three primary brain vesicles Prosencephalon – the forebrain Mesencephalon – the midbrain Rhombencephalon – hindbrain Secondary Brain Vesicles (fig.12.2.c) In week 5 of embryonic development, secondary brain vesicles form Telencephalon and diencephalon arise from the forebrain Mesencephalon remains undivided Metencephalon and myelencephalon arise from the hindbrain Adult Brain Structures (fig.12.2 d) Fates of the secondary brain vesicles: Telencephalon – cerebrum: cortex, white matter, and basal nuclei
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2 Diencephalon – thalamus, hypothalamus, and epithalamus Mesencephalon – brain stem: midbrain Metencephalon – brain stem: pons Myelencephalon – brain stem: medulla oblongata Adult Neural Canal Regions (fig.12.2e) Adult structures derived from the neural canal Telencephalon – lateral ventricles Diencephalon – third ventricle Mesencephalon – cerebral aqueduct Metencephalon and myelencephalon – fourth ventricle Space Restriction and Brain Development (fig.12.3) Because brain grows faster than the membranous skull, two major flexures develop- the midbrain and cervical flexures (fig 12.3 a) Secondly cerebral hemispheres are forced to grow posteriorly and laterally (fig.12.3b &c) and completely envelop the diencephalon and midbrain By week 26, the continued growth of cerebral hemispheres cause their surface to crease and fold producing convolutions and increasing surface area (fig 12.3c &d) Basic Pattern of the Central Nervous System (fig.12.4) Basic pattern of CNS is of central cavity surrounded by gray matter core, and external to it is white matter (myelinated fibers). Spinal Cord
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Ch 12 The Central Nervous System -Part 1 - Ch 12 The...

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