Summary NERVOUS SYSTEM AND SPECIAL SENSES NOTES UPDATED

EMBRYONIC DEVELOPMENT OF THE NERVOUS SYSTEM  General Embryonic Development is Described as Either:  Trimesters (3x 3-Month Periods): o First: - Foundations of Major Organs o Second: - Development of Organs o Third: - Rapid Growth & Fully Functional Organs.  OR... Anatomical Stages: **(These are more relevant) o Pre-Embryonic Period: 0-2 Weeks  Fertilisation  Blastocyst Formation & Implantation  Gastrulation o Embryonic Period: 3-8 Weeks  Development & Differentiation of 3 Germ Layers into foundations of Organs. o Foetal Period: 9 Weeks → Birth.  Period of Growth, NOT Differentiation. Some Useful Terminology:  “Rostral” = Head  “Caudal” = Tail  “Dorsal” = Back  “Ventral” = Front  “Ganglia” = Groups of Nerve-Cell Bodies  “Gyrus” = Elevations (Crests) of the folds on the Cerebral Cortex.  “Sulcus” = Grooves / Furrows between the Gyri on the Cerebral Cortex.  Embryonic Development of the Nervous System:  Blastocyst: (Pre-Embryonic Period) o A fertilised egg reaches the Morula stage (Day 3), differentiates into a Blastocyst (Day 7) and thenimplants in the endometrium. o The implanted Blastocyst consists of an ‘Inner-Cell Mass’ surrounded by Trophoblasts. o This ‘Inner-Cell Mass’ differentiates to form the ‘Bilaminar Disc’ (2 layers of cells)  Epiblast Layer: The top layer of Columnar Cells.  Hypoblast Layer: The bottom layer of Cuboidal Cells.