Central Nervous System
Chapter 13
Introduction
Analogies; telephone switchboard; computer; miracle
A fantastically complex and flexible biological organ
Cephalization become more apparent in higher order species
Increase in the neurons at the rostral end of the CNS
Highest level of cephalization is found in humans
The Brain
The unimpressive appearance of the human brain give few hints of its abilities
It is about two handfuls of delicate pinkish gray tissue
Wrinkled surface
Consistency of cold oatmeal
Cerebral hemisphere
Brain |
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stem |
Cerebellum |
The Brain
Average adult male’s brain weighs about 1600 g (3.5 pounds)
Average adult female’s brain weighs about 1450 g
Brain size represents a proportional difference in body size
Brain size is not correlated to intelligence but is related to the complexity of the neural connections within the brain
Embryonic Development
Starting in the third week of pregnancy, the ectoderm thickens along the dorsal midline axis of the embryo to form a neural plate
The neural plate eventually gives rise to all neural tissues
Embryonic Development
The neural plate then invaginates, forming a groove flanked by neural folds
Development of Neural Tube
As the groove deepens the superior edges of the neural folds fuse, forming the neural tube
The tube then detaches from the surface ectoderm and assumes a deeper position in the embryo
Development of Neural Tube
The neural tube is formed by the fourth week of pregnancy and differentiates rapidly into the CNS
The brain forms anteriorly and the spinal cord posteriorly
Development of Neural Tube
Small groups of neural fold cells migrate laterally and locate between the surface ectoderm and the neural tube to forming the neural crest
The neural crest gives rise to sensory neurons and some autonomic neurons destined to reside in ganglia
Development of Neural Tube
As soon as the neural tube is formed, its anterior end begins to expand more rapidly than the remaining portion