Changes

==Neuronal Differentiation==

==Neuronal Differentiation==

===Embryonic Orientation===

===Embryonic Orientation===

An important element to the development of the CNS is the development and regulation of orientation within the embryo, i.e. which part is cranial, caudal, lateral etc. Within the neural tube this is controlled via '''HOX''' (Homeobox) transcription factors which ensure there is an orientation between rostral and caudal. Two HOX genes are expressed resulting in boundaries within the tissue that is expressing that particular gene. One HOX gene is expressed rostrally and the other along the length of the spinal cord. This ensures only appropriate neural development takes place for the given location and orientation.

An important element to the development of the CNS is the development and regulation of orientation within the embryo, i.e. which part is cranial, caudal, lateral etc. Within the neural tube this is controlled via '''HOX''' (Homeobox) transcription factors which ensure there is an orientation between rostral and caudal. Two HOX genes are expressed resulting in boundaries within the tissue that express that particular gene. One HOX gene is expressed rostrally and the other along the length of the spinal cord. This ensures only appropriate neural development takes place for the given location and orientation.

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The dorsal horn tissues eventually fuse allowing the formation of a 'median septum'. Ventral horn tissues expand more fully than the dorsal grey matter tissues and form a 'ventral fissure'.

The dorsal horn tissues eventually fuse allowing the formation of a 'median septum'. Ventral horn tissues expand more fully than the dorsal grey matter tissues and form a 'ventral fissure'.

===Neuronal Formation===

===Neuronal Formation===

Within the brain and the spinal cord the fundamental organisation of the neurons is into 'columns' or groupings of cells within both the sensory and motor regions of the brain and within the grey matter of the spinal cord. Groups of neurons with similar functions are able to form 'nuclei'. Cranial nerve nuclei can include both motor and sensory neurons and are able to undertake a wide variety of functions and tasks. Cranial nerves can also convey fibres from multiple cranial nerve nuclei. Within the spinal cord specific columns of neurones, or 'spinal tracts' convey specific information to high centres in the brain.

Within the brain and the spinal cord the fundamental organisation of the neurons is into 'columns' or groupings of cells within both the sensory and motor regions of the brain and within the grey matter of the spinal cord. Groups of neurons with similar functions are able to form 'nuclei'. Cranial nerve nuclei can include both motor and sensory neurons and are able to undertake a wide variety of functions and tasks. Cranial nerves can also convey fibres from multiple cranial nerve nuclei. Within the spinal cord specific columns of neurones, or 'spinal tracts' convey specific information to high centres in the brain.